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The sternocleidomastoid muscle (SCM) divides each side of the neck into two major triangles, anterior and posterior. The anterior triangle is delineated by the anterior border of the SCM laterally, the midline medially, and the lower border of the mandible superiorly. The borders of the posterior triangles are the posterior border of the SCM anteriorly, the clavicle inferiorly, and the anterior border of the trapezius muscle posteriorly.1

 

In the midline, from above downward, the following landmarks are noted:

 

– The most prominent midline feature and the most readily palpated is the thyroid cartilage, the "Adam's apple," which is especially prominent in post-pubertal males. It is located between the third and fifth cervical vertebrae. The bifurcation of the common carotid artery is located on the horizontal plane at this level. Variations in the site of division of the carotid artery will always be located above this point.

– The body of the hyoid bone can be palpated at about 1.5 cm above the thyroid cartilage at the level of the third cervical vertebra. (Note: At the midpoint of a line between the mastoid process and the thyroid prominence, the greater horn of the hyoid bone can be palpated laterally.)

– The arch of the cricoid cartilage is palpable just inferior to the thyroid cartilage. The cricoid cartilage forms the only complete cartilaginous ring around the airway, something that is not observed with the other cartilages of the respiratory system.

– The cricoid cartilage is located at the level of the sixth cervical vertebra.

A horizontal plane approximately at the junction of the sixth and seventh cervical vertebrae can be associated with the following anatomic entities (Figs. 1-4, 1-5, 1-6, and 1-7):

 

– pharyngoesophageal junction

– laryngotracheal junction

– inferior thyroid artery (which is ventral to the middle cervical ganglion), and then (in order), the carotid sheath, and the omohyoid muscle

– entrance of the inferior laryngeal nerve (recurrent nerve) into the larynx

– entrance of the vertebral artery into the transverse foramen of the sixth cervical vertebra and, slightly more inferiorly, the stellate ganglion

– thyroid isthmus and the greatest height of the thoracic duct, which are located at the level of the seventh cervical vertebra

Surface Anatomy - NeckThe third cervical vertebra is at the level of the hyoid bone; the fourth and fifth cervical vertebrae are at the level of the thyroid cartilage.

 

Neck 2

Neck 3Seventh cervical vertebra.

Neck 4Diagrammatic cross section through the neck below the hyoid bone showing the layers of the deep cervical fascia and the structures that they envelop.

 

References

1. ttp://www.med.umich.edu/lrc/coursepages/M1/anatomy/html/surface/index.html#headneck

 

It is convenient to use the level system to describe the location of lymph node disease in the neck. Level I contains the submental and submandibular nodes. Levels II through IV contain lymph nodes along the jugular vein (upper, middle and lower). Level V contains the lymph nodes located along the lower half of the spinal accessory nerve and the transverse cervical artery, posterior to the SCM. The supraclavicular nodes are included in the posterior triangle group. The pre- and paratracheal nodes, precricoid (Delphian) node, and perithyroidal nodes are found within level VI. Lymph nodes are located throughout the head and neck region and are the most common sites of neck masses.1

 

 


Reference

1. http://www.redorbit.com/news/health/98241/evaluation_of_the_neck_mass/#XjFqu7aWpmmRmg1x.99

 

 

 

Laterally, it is bounded by the anterior belly of the digastric muscle, and the mylohyoid muscle forms the floor. The body of the hyoid bone lies opposite the third cervical vertebra. The area between the hyoid bone and the thyroid cartilage is the thyrohyoid membrane, while the notched upper border of the thyroid cartilage is at the level of the fourth cervical vertebra. The cricothyroid ligament or membrane occupies the space between the thyroid cartilage and the cricoid cartilage, which lies at the level of the sixth cervical vertebra and the junction of the pharynx with the esophagus. The interval between the cricoid cartilage and the first tracheal ring is filled by the cricotracheal ligament. Moving inferiorly, the isthmus of the thyroid gland is at the level of the second, third, and fourth tracheal rings. The suprasternal notch can be palpated between the clavicular heads and lies opposite the lower border of the body of the second thoracic vertebra. The sternocleidomastoid muscles, which divide the sides of the neck into anterior and posterior triangles, can be palpated from sternum and clavicle to the mastoid process. The borders of the posterior triangle are the body of the mandible, the sternocleidomastoid muscle anteriorly, and the border of the trapezius muscle posteriorly, along with the clavicle inferiorly.

Posteriorly, the structures of the neck that can be palpated in the midline are the external occipital protuberance, the nuchal groove, and the spinous process of the seventh cervical vertebra (cervical spines 1–6 are covered by the ligamentum nuchae).

The platysma, a thin muscular sheet, is enclosed by the superficial fascia. Its origin is from the deep fascia that covers the upper part of the pectoralis major and deltoid muscles, and it inserts into the lower margin of the body of the mandible. It is the anatomic landmark that is often cited when determining whether a penetrating wound of the neck is superficial or deep. The potential for injury to a vital structure exists when this structure is penetrated.

Beneath the superficial sternocleidomastoid, strap, and trapezius muscles that envelop much of the neck, there are eight body systems that lie within or pass through the neck. Included among these are the following: (1) skeletal system (seventh cervical vertebra, hyoid bone); (2) nervous system (spinal cord and the glossopharyngeal [IX], vagus [X], spinal accessory [XI], and hypoglossal [XII] cranial nerves); (3) respiratory system (oropharynx, larynx, cervical trachea); (4) gastrointestinal system (oropharynx, cervical esophagus); (5) vascular system (common, internal, and external carotid arteries, vertebral arteries, internal and external jugular veins); (6) lymphatic system (thoracic duct); (7) endocrine system (thyroid and parathyroid glands); and (8) immune system (cervical extensions of the thymus).

 

 

 

The sternocleidomastoid muscle separates the anterior part of the neck (anterior triangle) from the posterior part of the neck (posterior triangle).

The muscle attaches to the superior aspect of the manubrium sternum by a tendinous head and from the medial third of the clavicle by a muscular head. It passes superiorly in a lateral, and then posterior, direction. Its superior attachment is to the mastoid process, and the lateral end of the superior nuchal line. Unilateral contraction of the muscle approximates the ear to the ipsilateral shoulder, while rotating the chin to the contralateral side. Bilateral contraction of the muscle can result in either flexion or extension of the head. If the head is slightly flexed, bilateral contraction will result in increased flexion. If the head is slightly extended, bilateral contraction will result in increased extension. The pulsation of the carotid artery is palpable, anterior to the edge of the muscle.

The lateral portion of the trapezius muscle produces much of the fullness of the gentle curve that joins the lateral posterior part of the neck with the shoulder region.

The anterior tuberosity of the transverse process of the sixth cervical vertebra is located at the medial border of the sternocleidomastoid and at the level of the cricoid cartilage. Pressure at this point will compress the common carotid artery.

In the midline, from above downward, the following landmarks are noted:

 

– The most prominent midline feature and the most readily palpated is the thyroid cartilage, the "Adam's apple," which is especially prominent in post-pubertal males. It is located between the third and fifth cervical vertebrae. The bifurcation of the common carotid artery is located on the horizontal plane at this level. Variations in the site of division of the carotid artery will always be located above this point.

– The body of the hyoid bone can be palpated at about 1.5 cm above the thyroid cartilage at the level of the third cervical vertebra. (Note: At the midpoint of a line between the mastoid process and the thyroid prominence, the greater horn of the hyoid bone can be palpated laterally.)

– The arch of the cricoid cartilage is palpable just inferior to the thyroid cartilage. The cricoid cartilage forms the only complete cartilaginous ring around the airway, something that is not observed with the other cartilages of the respiratory system.

– The cricoid cartilage is located at the level of the sixth cervical vertebra.

A horizontal plane approximately at the junction of the sixth and seventh cervical vertebrae can be associated with the following anatomic entities (Figs. 1-4, 1-5, 1-6, and 1-7):

 

– pharyngoesophageal junction

– laryngotracheal junction

– inferior thyroid artery (which is ventral to the middle cervical ganglion), and then (in order), the carotid sheath, and the omohyoid muscle

– entrance of the inferior laryngeal nerve (recurrent nerve) into the larynx

– entrance of the vertebral artery into the transverse foramen of the sixth cervical vertebra and, slightly more inferiorly, the stellate ganglion

– thyroid isthmus and the greatest height of the thoracic duct, which are located at the level of the seventh cervical vertebra

Surface Anatomy - NeckThe third cervical vertebra is at the level of the hyoid bone; the fourth and fifth cervical vertebrae are at the level of the thyroid cartilage.

 

Neck 2

Neck 3Seventh cervical vertebra.

Neck 4Diagrammatic cross section through the neck below the hyoid bone showing the layers of the deep cervical fascia and the structures that they envelop.

 

References

1. ttp://www.med.umich.edu/lrc/coursepages/M1/anatomy/html/surface/index.html#headneck

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  • Trapezius muscle that has a very broad origin from the medial portion of the superior nuchal line, external occipital protuberance, ligamentum nuchae, spinous processes, and the supraspinous ligaments of the thoracic vertebrae. The muscle fibers converge and insert on the lateral third of the clavicle and the acromion process of the scapula. Because of the extensive origin of the muscle, differential contraction will create different movements. Contraction of the upper fibers will cause elevation of the scapula. Depression of the scapula is created by contraction of the inferior fibers. The middle fibers will cause the medial edge of the scapula to approach the midline. The external branch of the accessory nerve provides innervation to the trapezius and sternocleidomastoid muscles. Branches from the second and third cervical nerves provide added innervation.
  • Mastoid process.
  • Ramus of mandible.
  • Hyoid bone, palpable in the midline of the neck when the mandible is slightly depressed. It is located at the level of the third cervical vertebra. The greater horn of the hyoid bone can be traced to its lateral termination. This is the approximate level of origin of the lingual branch of the external carotid artery. The superior thyroid branch arises just inferior to this point, and the facial branch begins just superior to the same palpable landmark.
  • Fused laminae of the thyroid cartilage. The upper edge of this palpable structure is situated at the level of the fourth cervical vertebra. It represents the site of bifurcation of the common carotid artery.
  • Arch of the cricoid cartilage, palpable below the inferior end of the thyroid laminae. A small defect separates them. The cricoid cartilage represents an “anatomical bonanza” because it is a landmark for many anatomical occurrences. It may be referred to as the “cricoid plane.”
    • The larynx ends, and the trachea begins.
    • The pharynx ends, and the esophagus begins.
    • The cricoid cartilage is at the level of the sixth cervical vertebra.
    • The intermediate tendon of the omohyoid muscle is found anterior to the carotid sheath.
    • The inferior thyroid artery passes posterior to the carotid sheath on its way to the lateral lobe of the thyroid gland.
    • The middle cervical sympathetic ganglion lies on the transverse mass of the sixth cervical vertebra.
    • The recurrent laryngeal nerve enters the larynx.
    • The ansa cervicalis is found anterior to the carotid sheath.
    • The vertebral artery enters a foramen in the transverse mass of the sixth cervical vertebra. This occurs at the apex of a muscular triangle formed by the anterior scalene and longus coli muscles. The base of the triangle is the first portion of the subclavian artery.
    • TThe superior pair of parathyroid glands is often found at this level.
  • Upper tracheal rings that are palpable between the cricoid cartilage and the superior edge of the manubrium sternum.
  • Superior edge of the manubrium of the sternum. It is at the level of the second thoracic vertebra.
Structure of the Neck
Skeletal Background
The cervical portion of the vertebral column creates the skeletal background. It is composed of seven cervical vertebrae, with a characteristic anterior convex curvature. Vertebrae C3 through C6 are considered to be typical cervical vertebrae. Vertebrae C1, C2, and C7 are atypical cervical vertebrae. C1 (atlas) has no body. C2 (axis) has incorporated the body of C1 in its structure. The combination of the two bodies results in a tooth-like projection called the odontoid process, or dens epistrophe.
This provides an axis of rotation for the skull on the atlas. C7 has a large transverse mass with a primitive foramen and a prominent spinous process (vertebra prominens). The typical cervical vertebrae have a bifid spinous process and a distinct foramen in the transverse mass. There are anterior and posterior tubercles related to the transverse mass. The first rib must be included in the skeletal background. Many of the neck structures are attached to, or pass over, the first rib. The superior surface of the first rib is flattened. This will avoid trauma to the neurovascular structures that travel over it. Midway between the vertebral and the sternal ends of this rib is the scalene tubercle, point of insertion of the anterior scalene muscle. A vascular sulcus is found on both sides of the scalene tubercle. The anterior sulcus provides passage for the subclavian vein. The subclavian artery passes over the posterior sulcus. The anterior scalene muscle attaches to the first rib between the subclavian vessels. The middle scalene muscle attaches to the first rib posterior to the groove for the subclavian artery. Therefore, the subclavian artery passes through the scalene triangle that is created by the anterior and middle scalene muscles. This area is referred to as the root of the neck. It will be described in more detail later in this chapter.
Ligamentous Background
The ligamentous background includes supporting structures for the atlanto-occipital and atlantoaxial joints. The anterior longitudinal ligament is found on the anterior aspect of the vertebral bodies. It extends
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from the atlas down to the upper sacral segment. It is attached to the intervertebral disc and that portion of the vertebral body lying just superior and inferior to the disc. The nuchal ligament covers the spinous processes of all the cervical vertebrae.
Muscular Background
The muscular background includes muscles that are attached to the anterior aspect of the vertebra (anterior vertebral) and muscles that are attached to the lateral mass of the vertebra (lateral vertebral). Both of these groups are combined and are referred to as prevertebral muscles. The longus coli and longus capitis muscles are anterior to the vertebral column. The longus coli is a complex muscle that is attached inferiorly to the upper thoracic portion of the anterior longitudinal ligament. These lower fibers pass superolaterally and attach to the transverse masses of the typical cervical vertebrae. Fibers of this same muscle then pass superomedially and attach to the anterior portion of the arch of the atlas. There are vertical fibers of this same muscle that lie between the two oblique portions laterally and the anterior longitudinal ligament medially.
The longus capitis muscle lies anterior to the superomedial fibers of the longus coli muscle. It passes from the base of the skull to the tubercles of the typical cervical vertebrae. The muscles that are lateral vertebral in position are the levator scapula, middle, and anterior scalene muscles. The levator scapula muscle is the most posterior of this lateral group. It arises from the posterior tubercles of the transverse masses of the first four cervical vertebrae, descends, and attaches to the superior portion of the vertebral border of the scapula. The middle scalene muscle is on a more anterior plane (Fig. 1).
The middle scalene muscle may be attached to the posterior tubercles of all cervical vertebrae. It descends and affixes to the superior flattened surface of the first rib, posterior to the groove for the subclavian artery. A few muscle fibers extend down to the second rib and create the posterior scalene muscle. The most anterior of the lateral vertebral muscles is the anterior scalene (Fig. 1). It arises from the anterior tubercles of the transverse masses of the typical cervical vertebrae and attaches below to the scalene tubercle of the first rib. It is in the same frontal plane as the longus capitis muscle. The anterior vertebral muscles will flex the cervical spine. The lateral vertebral muscles will cause lateral bending of the same area. Motor innervation is provided by ventral rami of cervical nerves.
Fig. 1. Structures of the Neck-1. Scalene muscles of the neck.
Nerve Background
The nerve layer should now be inserted. The nerves and the muscles are intimately related, so that the term “neuromuscular layer” is appropriate. The cervical and brachial plexuses and the cervical sympathetic chains are now encountered as we continue the reconstruction of the neck.
The cervical sympathetic chain consists of three ganglia with connecting branches. The superior ganglion is the largest, and it is found on the transverse mass of the second and third cervical vertebrae. It is >1 in. long and lies on the longus capitis muscle, posterior to the carotid sheath. The middle cervical ganglion is the smallest and lies on the transverse mass of the sixth cervical vertebra. The inferior cervical ganglion is related to the vertebral end of the first rib and the transverse mass of the seventh cervical vertebra. It frequently joins with the first thoracic ganglion to form a dumbbell-shaped structure called the cervicothoracic, or stellate, ganglion. Stellate refers to the star-like appearance created by the multiple branches that are emitted. It is posterior to the vertebral artery. At times, branches from the middle cervical ganglion will form a loop around the subclavian artery before entering the inferior ganglion. This is referred to as the ansa subclavia.
The cervical plexus is formed by the ventral rami of the first four cervical nerves. These nerves connect to each other by forming loops that lie in the interval between the levator scapula, or the middle scalene, muscle posteriorly, and the longus capitis or its inferior continuation, the anterior scalene muscle, anteriorly (Fig. 2).
Each of the first four cervical ventral rami receives a branch from the superior cervical ganglion. The cervical nerves lie within the prevertebral fascia. The cervical plexus provides muscular and cutaneous innervation. There are cutaneous branches from a superficial cervical plexus and muscular branches from a deep cervical plexus. The cutaneous branches will be described with the posterior triangle. Muscular branches innervate the prevertebral muscles. In addition, a branch from C1 travels with the hypoglossal nerve and gives rise to the superior limb (descending hypoglossal nerve) of the ansa cervicalis. Branches from C2 and C3 will form the inferior limb (descending cervical nerve). The two limbs unite and form the ansa cervicalis. This nerve loop is on the anterior aspect of the carotid sheath, in the cricoid plane. Branches arise from the ansa cervicalis that provide motor innervation to the strap muscles in the muscular triangle. Other branches of C1,
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traveling with the hypoglossal nerve, provide motor innervation to the thyrohyoid and geniohyoid muscles. A branch from C4 descends on the anterior surface of the anterior scalene muscle, within the prevertebral fascia. It is the phrenic nerve and it may receive branches from C3 and C5. It is, at first, seen on the lateral aspect of the anterior scalene muscle, but as it descends it passes obliquely across the anterior surface of the muscle and reaches its medial edge in the root of the neck. It then passes anterior to the subclavian artery and courses medial to the internal mammary artery before entering the thorax. It provides sensory and motor innervation to the respiratory diaphragm (Fig. 2). There are some proprioceptive branches arising from the cervical plexus that pass to the sternocleidomastoid and trapezius muscles.
Fig. 2. Structures of the Neck-2. Ganglia and cervical plexus structures.
As we pass inferiorly in the cervical region, the nerves now encountered will consist of the roots and trunks of the brachial plexus. The brachial plexus is created by the ventral rami of C5 through T1. These roots will form three trunks. C5 and C6 join to form the upper trunk. The C7 root will become the middle trunk, and roots C8 and T1 will merge and form the lower trunk. These roots and trunks pass between the middle and the anterior scalene muscles. The lower trunk is draped over the first rib immediately posterior to the subclavian artery (Fig. 2).
The subclavian vein, unlike the accompanying artery, does not pass between the scalene muscles. It passes anterior to the anterior scalene muscle. Enclosing the skeletal background and the neuromuscular layer is the prevertebral portion of the deep cervical fascia. The neurovascular structures will pierce the deep cervical fascia and drag a portion of it along with them, creating the axillary, or cervicoaxillary, sheath.
Fascia of the Neck
The cervical fascia is composed of superficial and deep layers. The superficial fascia is not well developed and not easy to find. It consists of fat and some connective tissue. The platysma muscle is in the superficial fascia. It arises inferiorly from the fascia of the pectoralis major muscle and its fibers converge as they ascend to their insertion in the inferior part of the mandibular region. Some of the muscle fibers ascend and mix with the intrinsic depressor muscles of the lips. The cutaneous nerves and the superficial veins course below this muscle of facial expression. The cervical branch of the facial nerve innervates this muscle.
The deep cervical fascia consists of several layers. The superficial, or investing, layer of the deep cervical fascia splits to invest the trapezius and sternocleidomastoid muscles and the submandibular and parotid glands. It creates a complete tube that surrounds the neck. The deep layer of the deep cervical fascia, or prevertebral fascia, encloses the vertebral column and the attached erector spinae and prevertebral muscles and proximal portions of the cervical and brachial plexuses. It creates a complete tube.
The pretracheal fascia creates a tube that encircles the pharynx and esophagus, larynx and trachea, and the thyroid and parathyroid glands. The buccopharyngeal fascia is the posterior extension of the pretracheal fascia that covers the constrictor muscles of the pharynx. It is in contact with the anterior, or prevertebral, portion of the prevertebral fascia. This potential space between the prevertebral and the buccopharyngeal fascia layers extends from the neck down to the mediastinum. This retropharyngeal space can serve as a pathway for the spread of an infection from the neck to the thorax. The middle cervical fascia extends from the hyoid bone to the sternum. It encompasses all the strap muscles. This fascia layer extends laterally to the omohyoid muscle and therefore is only related to the muscular and subclavian triangles.
The carotid sheath is a protective, tubular fascial sheath found between the base of the skull and the root of the neck. It receives tissue contributions from all layers of the deep cervical fascia and encloses the common carotid and internal jugular vascular conduits and vagus nerve. After the bifurcation of the common carotid artery, the internal carotid branch will assume its position in the sheath. The vein is anterolateral to the artery, except at the base of the skull, where the vein lies posterior to the artery. The vagus nerve is between, and slightly posterior to, the blood vessels. The ansa cervicalis is on the anterior surface of the sheath in the cricoid plane. The sympathetic chain is in contact with the posterior surface of the sheath.
Root of the Neck
The root of the neck is the anatomical intersection between the thorax, neck, and axilla. The superior thoracic aperture, or thoracic inlet, and axillary (or cervicoaxillary) sheath create a pathway for the neurovascular
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structures found in this area. Neck structures also contribute to the complexity of the anatomy in this important region. Passing between the clavicle and the first rib are nerves, arteries, and veins of the upper extremity. Narrowing of this costoclavicular canal can cause compression of these neurovascular structures. The thoracic inlet is created by the upper end of the manubrium anteriorly, the first rib and its costal cartilage laterally, and the first thoracic vertebra posteriorly. Structures passing through this area are medial or lateral in position. The esophagus and the trachea are medial as they enter the mediastinum. The thoracic duct lies just to the left of, and posterior to, the esophagus. In the root of the neck, at the level of C7, the duct passes laterally. It courses anterior to the left vertebral and left inferior thyroid arteries and posterior to the carotid sheath. It then travels anterior to the anterior scalene muscle. It is superficial to the prevertebral layer of the deep cervical fascia. The duct then descends anterior to the left subclavian artery and terminates at the lateral edge of the junction between the left internal jugular and the left subclavian veins (see Fig. 5).
Fig. 3. The apex of the lung ascends out of the thorax into the root of the neck.
The equivalent of the thoracic duct on the right side of the root of the neck is called the right lymphatic duct. It is much smaller and may be represented by several small ducts. It receives lymph from the right hemithorax, right upper extremity, and right side of the head and the neck. Lymph from all other parts of the body is transported by the thoracic duct. The sympathetic chains are in contact with the head of the rib at this level. The recurrent laryngeal nerves, branches of the vagus (X) nerve, are also medial. The right recurrent laryngeal nerve arises in the root of the neck, loops around the right subclavian artery, and passes superomedially as it courses toward the tracheoesophageal groove. Its counterpart on the left arises in the mediastinum, loops around the aortic arch, and then ascends into the neck by way of the left tracheoesophageal groove. The right recurrent nerve, in the root of the neck, travels toward the right tracheoesophageal groove, but it may not yet have reached this protected position and is therefore more exposed to injury.
The apex of the cervical parietal pleura ascends to the neck of the first rib. The anterior end of the rib is lower than the posterior end; therefore, the apex of the lung can ascend out of the thorax into the root of the neck (Fig. 3). This ascension is most marked during deep inspiration and occupies the lateral portion of the superior thoracic inlet. This portion of the cervical pleura may extend above the superior edge of the clavicle. A tent-like thickening of the prevertebral fascia extends from the transverse mass of C7 to the first rib. It is called Sibson, or vertebropleural, fascia and provides some protection to the pleura when incisions are made in this area.
Lateral structures include the subclavian artery and subclavian vein and their branches, and nerve branches from the cervical and brachial plexuses. The cervical or apical area of the lung is also found in the lateral portion of the root of the neck. The first rib and the scalene muscles have important spatial relationships with the anatomy in this area.
The brachiocephalic trunk is the first branch of the arch of the aorta (Fig. 4). It passes superolaterally and bifurcates at the level of the right sternoclavicular joint into the right common carotid and right subclavian arteries. The common carotid artery will pass superiorly on the right side of the neck in the carotid sheath. It will be discussed in more detail later in this chapter. The next branch of the arch of the aorta is the left common carotid artery. The last branch of the aortic arch is the left subclavian artery (Fig. 4). The anterior scalene muscle divides the subclavian artery into three segments. The first portion extends from the origin of the vessel to the medial edge of the anterior scalene muscle. The second part lies behind the muscle, and the third segment extends from the lateral edge of the muscle to the lower edge of the first rib. Most of the branches of the subclavian artery arise from the first portion. The first and largest branch is the vertebral artery. It arises from the superior edge of the parent vessel, ascends vertically, and enters a foramen in the transverse mass of the sixth cervical vertebra. The accompanying vein covers it.
The foramen is situated at the apex of a muscular triangle created by the longus coli muscle medially and the anterior scalene muscle laterally. This is referred to as the triangle of the vertebral artery. The second branch is the thyrocervical trunk, which also arises from the superior surface and has a short course before it divides into the following branches. The inferior thyroid artery passes superiorly, anterior to the anterior scalene muscle. The phrenic nerve is within the prevertebral fascia as it passes inferiorly on the anterior surface of this muscle. The inferior thyroid artery is superficial to the prevertebral fascia. At about the level of the apex of the triangle of the vertebral artery the inferior thyroid artery passes medially, coursing posterior to the carotid sheath but anterior to the vertebral artery, and enters the substance of the lateral lobe of the
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thyroid gland. The transverse cervical and the suprascapular arteries are branches of the thyrocervical trunk that run transversely as they head for the lateral aspect of the neck. They cross the anterior scalene muscle and the phrenic nerve, but are superficial to the prevertebral fascia. The transverse cervical artery will divide into an ascending and descending branch when it reaches the margin of the trapezius muscle. The suprascapular artery will dip down below the clavicle after entering the posterior triangle, pass inferiorly, and contribute to the periscapular vasculature.
Fig. 4. Structures of the Neck-3. Branch of the aortic arch.
The next branch originating from the superior aspect of the subclavian artery is the costocervical trunk (Fig. 4). It may arise from the second portion of the subclavian, and is therefore less at risk during surgical procedures. It arches over the cervical pleura and, when it reaches the neck of the first rib, divides into the deep cervical artery that passes up and supplies the muscles in the back of the neck and the supreme intercostal artery that creates the first and second posterior intercostal arteries. The first posterior intercostal vein that will enter the ipsilateral brachiocephalic vein, accompanies it.
The last branch of the subclavian artery is the internal thoracic or internal mammary artery. It arises from the inferior aspect of the subclavian artery across from the thyrocervical trunk. It passes inferomedially, courses posterior to the subclavian vein, and initially is in contact with the cervical pleura as it heads for the first costal cartilage. It then assumes its characteristic location parallel to the lateral edge of the sternum. The subclavian vein begins at the outer end of the first rib and then passes anterior to the anterior scalene muscle (Fig. 5). It receives the external jugular vein before reaching the medial edge of this muscle.
When the vein is medial to this muscle, it is joined by the internal jugular vein, forming the brachiocephalic vein. The left brachiocephalic vein will pass to the right, just inferior to the superior edge of the manubrium sternum, and join with its right counterpart behind the right first costal cartilage to create the superior vena cava. Each brachiocephalic vein will receive the corresponding vertebral vein. Each vagus nerve passes anterior to the related subclavian artery. The left nerve then passes posterior to the left brachiocephalic vein. The right nerve is posterolateral to the related brachiocephalic vein.
Fig. 5. Structures of the Neck-4. Subclavian vein origin.
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Anterior to this anatomical jungle is the thymus gland. It is largest during the childhood years, and then starts to regress with the onset of sexual maturation. The gland may extend from the thyroid cartilage above, to the pericardial sac below. Therefore, its superior portion is part of the medial, or anterior, aspect of the root of the neck. The gland is composed of two separate, asymmetrical lobes. The gland is contiguous with the large veins previously described. This explains why venous invasion is frequently seen with malignant disease of the gland.
The roots of the brachial plexus, C5 through T1, will create three trunks: an upper trunk (C5, C6), middle trunk (C7), and lower trunk (C8, T1) (Fig. 4). They will pass between the anterior and the middle scalene muscles on their way to the axilla. It is the lower trunk that is in direct contact with the upper surface of the first rib. It lies immediately posterior to the subclavian artery. The trunks pass through the posterior triangle. Each trunk will divide into an anterior and posterior division. These divisions, along with the accompanying subclavian vessels, will then pass through the costoclavicular space. The subclavian vein is the most medial of the structures passing through this space (Fig. 5). This vein is anteroinferior to the accompanying subclavian artery and can, therefore, be approached after the pulsations of the accompanying artery are palpated. The roots and trunks of the brachial plexus are within the prevertebral layer of the deep cervical fascia. As they head for the axilla, accompanied by the subclavian vessels, they drag some of this deep fascia along with them and create a protective tubular sheath for these neurovascular items called the cervicoaxillary, or axillary, sheath. These nerves and blood vessels, on their way to the axilla, pass under the insertion of the pectoralis minor muscle to the coracoid process of the scapula.
The Anatomy of the Root of the Neck Compression Syndromes
The root of the neck compression syndromes include the following:
  • Costoclavicular compression syndrome
  • Cervical rib syndrome
  • Anterior scalene compression syndrome
  • Pectoralis minor syndrome
If the space between the first rib and the clavicle should be decreased, there could be compression of the neurovascular structures traversing this area (Fig. 5). The subclavian vein is the most medial of the neurovascular structures passing through the costoclavicular space. The vein is in the narrowest portion of this space, and if additional narrowing occurs, venous outflow from the upper extremity may be impaired.
A cervical rib may present itself in several ways. It is frequently bilateral. It is an extension of the transverse mass of the seventh cervical vertebra and it may be a complete rib that articulates with the sternum. At times, it may fuse with the first rib or present as a fibrous band that attaches to the first rib. In some patients, it may have an anterior end that is free. The subclavian vessels and the brachial plexus, especially the lower trunk, will be affected adversely when they try to pass over this additional obstacle.
The anterior scalene compression syndrome results from spasm, or hypertrophy, of the anterior scalene muscle, with resultant constriction of the neurovascular elements as they pass through the scalene triangle. If the clinician treats this condition by transecting the anterior scalene muscle near its insertion, the position of the phrenic nerve and the subclavian vein, passing anterior to the muscle, must be remembered.
The term “thoracic outlet compression syndrome” is frequently used when defining some clinical conditions encountered in the root of the neck. Thoracic outlet is a misnomer when used to identify the clinical problems in this area. The true anatomical thoracic outlet is the area related to the respiratory diaphragm. Correct terms for these conditions would include superior thoracic aperture compression syndrome or cervicoaxillary compression syndrome.
All of these compression syndromes can result in neurologic deficits and/or arterial and venous circulatory problems in the upper extremity.
Clinical Anatomical Applications
  • Cervical incisions should be made parallel to the skin lines (lines of Langer) for good cosmesis. The neurovascular structures lie deep to the platysma muscle. The muscle must be carefully repaired for the best cosmetic result.
  • The middle cervical ganglion block: this sympathetic ganglion is found anterior to the transverse mass of the sixth cervical vertebra. At the level of the cricoid cartilage, retract the carotid sheath laterally and inject the medication after the needle strikes the lateral mass of the vertebra.
  • Control of bleeding may be possible if the common carotid artery is compressed against the transverse mass of the sixth cervical vertebra. This is the cricoid plane.
  • Carotid angiography: the common carotid artery is palpable in the carotid triangle. It is partially covered by the sternocleidomastoid muscle. Lateral retraction of the muscle will facilitate insertion of a catheter into the palpable artery.
  • Internal jugular vein catheterization: the internal jugular vein accompanies the common and internal carotid vessels. They all lie within the carotid sheath. The vein is anterolateral to the palpable artery.
  • The right internal jugular and right brachiocephalic veins, along with the superior vena cava, create a straight conduit to the right atrium and the inferior vena cava.
  • The subclavian vessels can be approached while passing through the costoclavicular space. The artery is palpable and the vein is situated anterior and medial to the artery. The vein is the most medial structure passing through the costoclavicular interval. A supraclavicular, or infraclavicular, technique can be used for catheterization.
  • The brachial plexus block approaches the nerves as they pass through the costoclavicular space. The subclavian artery is anterior to the branches of the plexus.
  • In cricothyroidotomy, the interior of the larynx is entered through the cricothyroid interval. The cricothyroid artery, a branch of the superior thyroid, pierces the cricothyroid ligament near the middle of the interval between the cricoid and the thyroid cartilages. A transverse incision, made close to the upper border of the cricoid arch, will avoid injury to this artery. The vocal ligaments are spared because they are superior to the point of entry.
  • For drainage of the retropharyngeal space, an incision is made at the level of the cricoid cartilage. The sternocleidomastoid muscle and carotid sheath are retracted posteriorly, and the lateral lobe of the thyroid gland is retracted anteriorly.
  • Using the external jugular vein as a conduit for central venous access, the external jugular vein is readily accessible because of its superficial position. It empties into the subclavian vein in the posterior triangle, but it may be difficult to negotiate the angle at the termination when attempting to introduce a device into the central portion of the circulatory system. Direct approach to the larger veins, right internal jugular or right subclavian, would eliminate this technical problem.
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Triangles of the Neck
The layer-by-layer recreation of the neck anatomy now requires the addition of the carotid sheath with the vascular contents and their branches, the last four cranial nerves, and the viscera of the neck, which includes the thyroid and parathyroid glands, pharynx, and larynx. The superficial cervical plexus will also be outlined. The cervical lymphatic pathways will then be described, and finally the superficial venous circulation will be examined. This information is presented with a discussion of the triangles of the neck.
Anterior and Posterior Triangles
The sternocleidomastoid and trapezius muscles divide the neck into anterior and posterior triangles (Fig. 6; also see Fig. 13). The boundaries of the posterior triangle are the trapezius muscle posteriorly and the sternocleidomastoid muscle anteriorly. The middle third of the clavicle creates the inferior limit, and the apex of the triangle extends to the superior nuchal line. The triangle is spiral in shape. The inferior portion is anterior in the neck, but the apex is posterior. The anterior triangle includes the area between the anterior edges of the sternocleidomastoid muscles. The superior limit is the mandible and a line drawn from the angle of the mandible to the tip of the mastoid process. Two double-bellied muscles, omohyoid and digastric, subdivide the triangles. The inferior belly of the omohyoid muscle attaches to the superior transverse scapular ligament and a portion of the adjacent superior edge of the scapula. It passes superior to the clavicle and enters the lower portion of the posterior triangle. The intermediate tendon is in the cricoid plane, anterior to the carotid sheath, and is angulated by a fascial sling attached to the clavicle and the manubrium. The superior belly ascends to the hyoid bone.
The posterior triangle now consists of the large occipital and the smaller subclavian triangles. The digastric is the other double-bellied muscle that creates subdivisions of the anterior triangle. The posterior belly attaches just medial to the mastoid process. The intermediate tendon is tethered to the hyoid bone by a fold of deep cervical fascia. The stylohyoid muscle arises from the styloid process of the temporal bone and is in intimate contact with the anterior surface of the posterior belly of the digastric muscle. The tendon of insertion of the stylohyoid muscle to the hyoid bone is split and allows for passage of the intermediate tendon of the digastric muscle. The anterior triangle includes the submandibular and carotid triangles. They are separated from each other by median submental and muscular triangles.
Fig. 6. Boundaries of the triangles of the neck (see also Fig. 14).
The hyoid bone is a central structure in the neck. It is directly or indirectly attached to most of the muscular and membranous entities in the anterior triangle and in the floor of the mouth. If one considers the hyoid bone and the attached posterior belly of the digastric muscle, it is possible to divide the anterior triangle into suprahyoid and infrahyoid portions. The submandibular, or digastric triangles, and the submental triangle, are suprahyoid entities and are related to the floor of the mouth. They have been discussed in another chapter. The carotid and the muscular triangles are found in the infrahyoid portion of the anterior triangle.
Carotid Triangle
The muscular boundaries of the carotid triangle are the sternocleidomastoid muscle posteriorly, the posterior belly of the digastric muscle anterosuperiorly, and the superior belly of the omohyoid muscle anteroinferiorly (Fig. 7). The greater horn of the hyoid bone is part of the anterior and superior segment of the floor of this triangle. The hyoglossus and thyrohyoid muscles are attached to this portion of the hyoid bone, and are part of the anterior portion of the muscular floor. A small portion of the thyrohyoid membrane is found just behind the thyrohyoid muscle and makes up a small area of the floor. The middle and inferior pharyngeal constrictor muscles create the posterior section of the muscular floor of the carotid triangle. The longus capitis, a prevertebral muscle, also contributes to the posterior portion of the muscular floor of this triangle. The pretracheal layer of the deep cervical fascia creates the fascial carpet. The investing layer of the deep fascia creates a fascial roof.
The contents of the triangle will be described beginning with the deepest structures (Fig. 8). The superior laryngeal nerve is a branch of the vagus nerve that is given off at the base of the skull. It travels inferiorly, in contact with the superior constrictor, courses deep to the internal and external carotid arteries, passes under the posterior belly of the digastric muscle, and is now in the carotid triangle. When it reaches the middle constrictor muscle, it creates an internal and external branch. The internal branch enters the larynx after
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piercing the thyrohyoid membrane. It provides sensory innervation to the interior of the larynx above the vocal ligaments. The external branch passes inferiorly, in contact with the inferior constrictor, and gives some branches to this muscle. It also provides motor innervation to the cricothyroid, one of the intrinsic muscles of the larynx. This nerve, for a portion of its course just superior to the thyroid gland, is very close to the medial side of the superior thyroid vascular bundle. It should be located and swept medially in order to avoid its injury when ligating and dividing these blood vessels. In the superior part of this triangle, the spinal accessory nerve is seen as it passes inferolaterally, deep to the sternocleidomastoid muscle, and enters the posterior triangle.
Fig. 7. Muscular boundaries and muscular floor of the carotid triangle.
Fig. 8. The deepest structures of the carotid triangle.
The ascending pharyngeal artery, a branch of the proximal portion of the external carotid artery, ascends on the constrictor muscles as it heads for the base of the skull. The remaining contents of this triangle include the common carotid artery and its branches, the internal jugular vein and its branches, the cranial nerves X, XI, XII, and the ansa cervicalis of the deep cervical plexus.
The common carotid artery begins in the root of the neck and passes cephalad in the carotid sheath (Fig. 9). It is medial to the accompanying internal jugular vein. The vagus nerve (X) is between, but slightly posterior to, the blood vessels. At about the level of the superior aspect of the thyroid cartilage, the common carotid artery bifurcates and gives rise to the internal and external carotid vessels. The internal carotid artery, at its origin, has a small area of dilatation, the carotid sinus. It contains specialized nerve cells, which regulate blood pressure. This area receives autonomic, glossopharyngeal, and vagus nerve branches (Fig. 10). There is also an area of thickening in the arterial wall at the site of bifurcation of the common carotid artery. This is the carotid body, which contains chemoreceptor cells receiving branches from the glossopharyngeal nerve. The common and internal carotid arteries do not provide any branches in the neck.
The external carotid artery leaves the carotid sheath and, at first, is anteromedial to the internal carotid artery. It will become anterolateral in position at a higher level, after passing superficial to the carotid sheath. It is the external carotid artery that provides vascular flow to the cervical structures. The branches are medial and posterior. The medial branches are the superior thyroid, lingual, and facial (external maxillary) arteries. The posterior branches include the ascending pharyngeal, occipital,
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and posterior auricular arteries. The occipital branch runs along the inferior edge of the posterior belly of the digastric muscle. The posterior auricular branch follows a similar course on the superior aspect of this important muscle. The external carotid artery continues superiorly to the parotid region. At the neck of the condylar process of the mandible, the end branches arise. They are the superficial temporal and internal maxillary arteries.
Fig. 9. Common carotid artery and branches.
Fig. 10. External carotid artery.
The internal jugular vein begins at the base of the skull (Fig. 11). At this point, it is posterior to the internal carotid artery. The last four cranial nerves pass between these vessels and then head for their specific destinations. The vein passes inferiorly, quickly assuming a more anterolateral position to the internal and common carotid arteries, while in the carotid sheath. It receives the following branches: common facial vein, lingual vein, superior thyroid vein, branches from the pharyngeal venous plexus, and the middle thyroid vein. At its termination, it will receive the thoracic duct (left) and the right lymphatic duct (right). The vagus nerve (X) is found with the vascular structures in the carotid sheath. It lies between, and slightly posterior to, the artery and the vein. In the root of the neck, it will pass posterior to the large veins and enter the thorax. The spinal accessory nerve (XI) will pass obliquely across the superior part of the carotid triangle, continue under the sternocleidomastoid muscle, travel across the posterior triangle, and disappear under the trapezius muscle (Fig. 12). It provides motor innervation to both of those muscles. The hypoglossal nerve (XII) passes between the internal jugular vein and the internal carotid artery, and then descends below the posterior belly of the digastric muscle to enter the carotid triangle. It frequently hooks around a branch of the occipital artery, passes superficial to internal and external carotid arteries, and then leaves the carotid triangle by passing back under the posterior belly to reenter the submandibular triangle. The glossopharyngeal nerve (IX) is also found between the internal jugular vein and the internal carotid artery near the base of the skull. It passes inferiorly, travels between the internal and the external carotid arteries, and then enters the interval between superior and middle pharyngeal constrictors. The stylopharyngeus muscle accompanies this nerve. After penetrating the wall of the pharynx, the muscle attaches to the posterior free end of the thyroid cartilage lamina and is now part of the muscular wall of the pharynx. The cervical sympathetic chain lies on the prevertebral fascia. It is posterior to the carotid sheath.
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Fig. 11. Internal jugular vein.
Fig. 12. Carotid triangle with the sternocleidomastoid muscle removed.
The posterior belly of the digastric muscle plays an important role in this area. It is superficial to all of these neurovascular structures. It presses them against the pharyngeal wall. Incisions can be made on the posterior belly without risk of injury to nerves or arteries in this area. There may be some superficial veins and, occasionally, a low-lying cervical branch of the facial nerve found in the area superficial to this relatively safe landmark.
Muscular Triangle
The boundaries of the muscular triangle are the superior bellies of the omohyoid muscles superolaterally and the inferior part of the sternocleidomastoid muscles inferolaterally (Fig. 13). The hyoid bone is superior, and the upper edge of the manubrium sternum creates the inferior limit. The triangle contains the thyroid and parathyroid glands, larynx and trachea, and pharynx and esophagus. These cervical viscera are found below the muscular floor. The muscles are paired and referred to as the strap muscles. They are all infrahyoid in location and present in two layers. The superficial layer is composed of two long muscles. The omohyoid muscle is lateral and is composed of two muscle bundles that are separated by an intermediate tendon. The intermediate tendon is in the cricoid plane. The inferior belly is attached to the superior surface of the scapula. It subdivides the posterior triangle and then passes anterior to the carotid sheath. The intermediate tendon is tethered to the clavicle. The superior belly passes up to the hyoid bone. Medial to this is the sternohyoid muscle, which passes from the sternum to the hyoid bone. The deeper layer is composed of shorter structures. The sternohyoid muscle is attached inferiorly to the manubrium of the sternum, and extends up to the oblique line of the thyroid cartilage. This upper attachment is just superior to the lateral lobe of the thyroid gland, and prevents enlargement of the lobe from extending in a superior direction The thyrohyoid muscle seems to be its superior continuation that passes from the oblique line to the hyoid bone. The inferior pharyngeal constrictor is also attached to the oblique line of the thyroid cartilage. The middle layer of the deep cervical fascia surrounds the strap muscles. It is not only found in the muscular triangle, but also extends laterally to the inferior belly of the omohyoid muscle. This belly creates the lateral boundary of the subclavian subdivision of the posterior triangle.
All the strap muscles are depressors of the larynx. The nerve supply comes from
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the deep cervical plexus (C1, C2, and C3) by way of the ansa cervicalis. The nerves enter the inferior portion of the muscle. A branch of C1, which travels with the hypoglossal nerve, innervates the thyrohyoid muscle.
Fig. 13. The boundaries of the muscular triangle of the neck.
Clinical Anatomical Aids
  • Transection of strap muscles should be done closer to the superior end to preserve nervous innervation, which enters the muscle near its inferior end.
  • Proper entrance into the cleavage plane between the sternothyroid muscle and the thyroid gland provides excellent exposure of, and facilitates surgical approach to, the gland.
Posterior Triangle
The boundaries of the posterior triangle are the anterior border of the trapezius muscle and the posterior edge of the sternocleidomastoid muscle, and the middle third of the clavicle is the base. The apex of this triangle is the superior nuchal line. This triangle, therefore, presents as a spiral as the base is anterior and the apex is posterior. The triangle is subdivided by the inferior belly of the omohyoid muscle into smaller entities that are named for the blood vessels found in them. There now is a larger, superior, occipital triangle, and the smaller, inferior, subclavian triangle. The muscular floor of the entire posterior triangle is composed mainly of three muscles whose fibers run inferolaterally. They are, from above down, the splenius capitis, the levator scapula, and the middle scalene muscles (Fig. 14). The anterior scalene muscle is not seen in the posterior triangle because the sternocleidomastoid muscle covers it. In the apex are seen a few vertically oriented fibers of the semispinalis capitis muscle. It is, along with the splenius capitis, classified as a back muscle.
Fig. 14. Muscular floor of the posterior triangle.
The muscles of the floor are covered by prevertebral fascia, which creates a fascial carpet. There is also a fascial roof, generated by the investing layer of the deep cervical fascia. The contents of the triangle will be described layer by layer, beginning with the deeper contents found below the fascial carpet in contact with the muscular floor (Fig. 15). They include: (a) the occipital artery, which frequently exits the posterior triangle at its apex; (b) branches of the deep cervical plexus passing inferolaterally on the surface of the levator scapula muscle, destined to provide innervation to the inferior portion of the trapezius muscle; and (c) portions of the brachial plexus. The roots of the plexus combine deep to the
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sternocleidomastoid. The C5 and C6 roots combine to create the upper trunk, C7 becomes the middle trunk, and C8 and T1 create the lower trunk. The trunks are seen in the posterior triangle. There are branches arising from these roots and trunks that are seen in the posterior triangle. The dorsoscapular nerve (C5) pierces the middle scalene muscle and passes laterally toward the rhomboid and levator scapula muscles, which it innervates. The long thoracic nerve (C5, C6, and C7) courses inferiorly, passes deep to the other portions of the brachial plexus, and then passes over the first rib to reach the superficial surface of the serratus ventralis, where it innervates. Arising from the upper trunk of the plexus is the suprascapular nerve, which is seen just above the upper trunk, passes across the posterior triangle to the scapula, and innervates the supraspinatus and infraspinatus muscles. The subclavius nerve is also seen in the posterior triangle. It arises from the upper trunk, passes inferiorly, and crosses the main portion of the brachial plexus superficially. It innervates the subclavius muscle.
Fig. 15. Structures below fascia floor of the posterior triangle.
The trunks create anterior and posterior divisions that will pass under the clavicle, and when reaching the axilla, create other combinations called cords. The cords will give rise to the named nerves of the upper extremity and the third portion of the subclavian artery is also related to the fascial floor of the posterior triangle. It can be palpated as it passes under the midportion of the clavicle and over the first rib. The subclavian artery and the brachial plexus branches, after passing between the scalene muscles, will drag a portion of the prevertebral fascia along with them and create the cervicoaxillary sheath (Figs. 16 and 17).
Fig. 16. Fascial floor of the posterior triangle.
Structures that pass between the fascial floor and the fascial roof include the transverse cervical and suprascapular (transverse scapular) branches of the thyrocervical trunk, originating from the first portion of the subclavian artery. They pass transversely across the anterior aspect of the anterior scalene muscle and are separated from the phrenic nerve by the prevertebral fascia. After entering the posterior triangle, the suprascapular artery will pass below the clavicle and participate in important collateral vascular channels that exist in the scapular region. The spinal accessory nerve (XI) as it traverses the posterior triangle. It is found on the anterior surface of, and runs with, the levator scapula muscle. It will disappear under the trapezius muscle about 2 in. superior to the clavicle. There are some motor branches from the deep cervical plexus that
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travel with this cranial nerve. These nerves, and the spinal accessory nerve, are the only motor branches that are superficial to the prevertebral layer of the deep cervical fascia in the posterior triangle.
Fig. 17. Structures superficial to fascial floor of the posterior triangle.
The external jugular vein, which passes obliquely across the sternocleidomastoid muscle, pierces the deep cervical fascial layers of the subclavian triangle, and ends in the subclavian vein. The transverse cervical, suprascapular, and anterior jugular veins are tributaries of the external jugular vein. The inferior belly of the omohyoid muscle creates the lateral boundary of the subclavian triangle. It is attached inferiorly to the superior surface of the scapula, courses anterosuperiorly, and passes deep to the sternocleidomastoid muscle, where its intermediate tendon is angulated by attachments of deep cervical fascia to the clavicle. The superior belly continues to the hyoid bone. The superficial cervical plexus is created by the ventral rami of C2, C3, and C4. It includes the lesser occipital nerve (C2), which appears at the posterior edge of the sternocleidomastoid muscle just inferior to the spinal accessory nerve. It ascends near the posterior edge of the muscle and will provide sensory innervation to the external ear and the adjacent skin. The superficial cervical plexus also includes the great auricular nerve (C2, C3), which emerges from the cover of the sternocleidomastoid muscle just inferior to the lesser occipital nerve, hooks around the posterior edge of the muscle, and now lies on its superficial surface (Figs. 17 and 18). It then passes superiorly toward the parotid region and provides sensory innervation to the overlying skin and a portion of the ear. This nerve can frequently be found just posterior to the external jugular vein as it passes obliquely across the muscle. The transverse cervical nerve (C2, C3) also appears at the posterior edge of the sternocleidomastoid muscle in the vicinity of the other nerves of this plexus. It wraps itself around the posterior edge of the muscle and passes transversely across its external surface to reach the anterior triangle. It will then divide into ascending and descending branches that will provide cutaneous sensory innervation to the anterior triangle.
Fig. 18. Superficial structures of the posterior triangle.
The supraclavicular nerves (C3, C4) first appear in the same area, just below the site of emergence of the other nerves, and then divide into medial, intermediate, and lateral branches. They provide cutaneous sensory innervation to the anterior aspect of the thorax down to the level of the second rib. All branches of the superficial cervical
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plexus, and the spinal accessory nerve, are quite close to each other as they first appear in the posterior triangle at the edge of the sternocleidomastoid muscle. If one divides the posterior edge of this muscle into thirds, at the junction of the middle and superior third is the site where all these nerves can be found gathered in a small localized area. This is referred to as the nerve point. They will then diverge as they head toward their specific destinations. As the nerves pass through the posterior triangle, it will be seen that the spinal accessory nerve is the most superior of all the nerves that are in the triangle. Therefore, incisions that are made superior to the spinal accessory nerve are not likely to encounter any important nerves. This area has been referred to as the carefree area; whereas, an incision made below this nerve can injure major structures and is called the careful area.
Clinical Anatomical Aids
  • Superficial cervical plexus nerve block. The nerve point is located and the local anesthetic is injected in that region of the posterior edge of the sternocleidomastoid muscle. It can provide adequate anesthesia to the anterior triangle if bilateral nerve point injection is performed.
  • Catheterization of the subclavian artery or vein. The third portion of the artery is palpable as it passes between the midportion of the clavicle and the first rib. The accompanying vein is anteroinferior to the artery and is the most medial of the neurovascular structures that pass through the costoclavicular space.
  • Dissection can be performed safely in the posterior triangle in the area superior to the spinal accessory nerve (XI).
  • There are one or two motor branches for the trapezius muscle that originate from the deep cervical plexus. They run with, but are slightly inferior to, the spinal accessory nerve in the posterior triangle. In this area, these cervical nerves and the spinal accessory nerve are the only motor nerves that lie external to the prevertebral layer of the deep cervical fascia.
  • When veins pass through layers of fascia, the wall of the vein is adherent to the margins of the opening in the tissue being breached. If a vein is transected at the level of fascia penetration, bleeding may be prolonged because the attachments to the vessel wall may prevent it from going into spasm. Spasm of the cut end of a blood vessel assists in achieving hemostasis.
Viscera of the Neck
Thyroid Gland
The development of the thyroid gland begins with the appearance of the foramen caecum (Fig. 19). This is a pit or depression that appears at the junction of the anterior two-thirds with the posterior third of the tongue. It continues inferiorly and creates the thyroglossal duct, which continues caudad and becomes the thyroid gland. The duct is a midline structure down to the thyroid cartilage and then usually deviates to the left. The pyramidal lobe of the gland represents the distal portion of this embryologic structure. The duct has a tortuous U-shaped course around the body of the hyoid bone. Portions of this duct may remain patent and create thyroglossal duct cysts. These will be median in position, but closer to the gland they can deviate from the midline. Cysts found below the hyoid bone require excision of the central portion of this bone in order to include the tortuous portion of this persistently patent remnant of the thyroglossal duct. Accessory thyroid tissue may be found anywhere along the pathway of this developmental entity. The most frequent site is the posterior portion of the tongue near the foramen caecum.
Fig. 19. Thyroid gland anatomy.
The thyroid gland is composed of two pyramidal-shaped lateral lobes, connected by a transverse bridge of glandular tissue, that crosses anterior to the second, third, and fourth tracheal rings. This connection across the midline is the isthmus. There may be a superior extension of glandular tissue originating from the left portion of the isthmus. This is the pyramidal lobe, and it may be connected to the hyoid bone by a fibrous band. If there are muscle fibers in this band, it is called the levator glandulae thyroidea. The lateral lobe extends from the oblique line of the thyroid cartilage down to the sixth tracheal ring. The gland possesses a true capsule, created by condensation of the normal stroma, and is enveloped by the pretracheal layer of the deep cervical fascia, creating the false or surgical capsule. The pretracheal fascia surrounding the isthmus is adherent to the trachea. This deep cervical fascia also attaches the posteromedial aspect of the lateral lobe to the first and second tracheal rings. This is the ligament of Berry, which usually contains some small blood vessels. These attachments are responsible for superior and inferior movement of the thyroid gland during the act of swallowing. Medial relations of the lateral lobe include thyroid and cricoid cartilages, trachea,
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esophagus, cricothyroid and inferior constrictor muscles, external branch of the superior laryngeal, and the recurrent laryngeal nerves. The carotid sheath and inferior thyroid artery are posterior. The superior thyroid vessels and the external laryngeal branch of the superior laryngeal nerve approach the lobe from above. The sternohyoid, omohyoid, and sternothyroid muscles are anterior relations. The left lateral lobe is related to the thoracic duct as it travels superiorly, just to the left of the esophagus. It maintains this position until C7, where it arches laterally.
Fig. 20. Vascular supply to thyroid gland.
The superior and inferior thyroid arteries provide the vascular supply (Fig. 20). In 8% to 10% of the individuals, a thyroid ima artery is present. It may be a direct branch of the arch of the aorta, appearing between the brachiocephalic and the left common carotid vessels. Occasionally, it may arise from the brachiocephalic trunk or the right common carotid artery. The superior thyroid artery is the first of the anteromedial branches of the external carotid artery. It creates a superior laryngeal vessel that enters the larynx, after piercing the thyrohyoid membrane, along with the superior laryngeal vein and the internal branch of the superior laryngeal nerve. This nerve provides sensory innervation to the interior of the larynx above the vocal ligaments. The superior thyroid artery then passes vertically downward, accompanied by the superior thyroid vein, as it heads for the superior pole of the lateral lobe. Accompanying these blood vessels is the external branch of the superior laryngeal nerve. It is medial, and very close to the vessels. The nerve will turn medially, just superior to the upper pole of the lateral lobe, and head for the larynx. It provides motor innervation to the inferior part of the inferior constrictor of the pharynx and the cricothyroid muscle of the larynx.
Fig. 21. Posterior view of thyroid gland.
The inferior thyroid artery arises from the thyrocervical trunk, a branch of the first portion of the subclavian artery (Fig. 21). It will ascend to the cricoid plane, passes posterior to the carotid sheath, and then passes inferomedially to reach the posterior surface of the lateral lobe. In this area, the artery is intimately related to the recurrent laryngeal nerve, a branch of the vagus (X), providing motor innervation to all the intrinsic muscles of the larynx except the cricothyroid.
The superior thyroid artery will provide an anterior and posterior branch (Fig. 22). The anterior branch will communicate with its contralateral counterpart through branches
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that cross the midline by way of the isthmus. The posterior branch of the superior thyroid artery communicates with branches of the inferior thyroid artery. The venous drainage is via the superior thyroid vein into the internal jugular or common facial vein, the short middle thyroid vein into the internal jugular vein, and the inferior thyroid veins into the brachiocephalic vein.
Fig. 22. Right lateral view of thyroid gland.
The lymphatic drainage of the thyroid gland can be divided into superior or ascending, and inferior or descending pathways. They can be further subdivided into lateral and medial components. The superomedial pathway leads to the prelaryngeal or Delphian node found anterior to the cricothyroid membrane. The superolateral channels pass, with the superior thyroid artery, to nodes situated at the bifurcation of the common carotid artery, or to the omohyoid nodes of the internal jugular chain. The inferomedial lymph vessels are related to nodes found anterior, and adjacent, to the trachea. The inferolateral lymph flow is to the supraclavicular nodes.
Parathyroid Gland
The parathyroid glands are found on the posterior surface of the thyroid gland between the surgical and the true capsule (see Fig. 21). They may also be situated outside the surgical capsule, or within the true capsule (intraglandular). There are usually four glands, and each one measures only 5 to 6 mm in diameter. The upper pair is found at the level of the cricoid cartilage and is frequently adjacent to a descending branch of the superior thyroid artery that anastomoses with an ascending branch of the inferior thyroid artery. They are yellowish brown and, therefore, distinguishable from normal thyroid tissue, which is reddish pink. The inferior pair of glands is found superior or inferior to the inferior thyroid artery, as this vessel passes transversely across the posterior aspect of the lower pole of the lateral thyroid lobe. They receive their blood supply from the superior and inferior thyroid arteries. Aberrant glandular tissue is not uncommon.
Clinical Anatomical Aids
  • A parathyroid gland may resemble a small lymph node, but the glandular tissue is softer when palpated, compared with the firmer feel of the node.
  • Superior enlargement of the thyroid lobe is prevented by the insertion of the sternothyroid muscle into the oblique line of the thyroid cartilage. Lateral expansion can occur.
  • Occasionally, there may be extralaryngeal branching of the recurrent nerve, resulting in loss of a single main trunk. This will usually occur superior to the inferior thyroid artery. Therefore, it is better to look for the main trunk of the nerve inferior to the artery.
  • The inferior thyroid artery will usually divide into two or three branches before entering the parenchyma of the thyroid gland. The recurrent nerve usually passes between these branches.
  • If the inferior thyroid artery is divided laterally, just after passing posterior to the carotid sheath, nerve injury is unlikely.
  • Anteromedial retraction of the lateral lobe of the thyroid gland will displace the recurrent laryngeal nerve from its expected position in the tracheoesophageal groove, toward the posterolateral aspect of the trachea.
  • There may not be a recurrent laryngeal nerve found in the tracheoesophageal groove if there is a high origin of the nerve. This is referred to as a nonrecurring nerve.
  • A cricothyroidotomy provides access to the infraglottic space. This area of the larynx is below the vocal ligaments.
Pharynx
The pharynx is a muscular tube, approximately 5 in. long, that extends from the base of the skull to the cricoid cartilage, where it is continuous with the esophagus (Fig. 23). An anterior wall is lacking where it faces the nasal and oral cavities and the larynx. This creates nasopharynx, oropharynx, and laryngopharynx subdivisions. The nasopharynx is between the soft palate and the base of the skull. The soft palate is attached to the posterior end of the hard palate. It is a soft tissue shelf, approximately 2 in. long. A small grape-like swelling, the uvula, is attached to its free end. It contains the small, paired, uvular muscles. There are four additional paired muscles in the soft palate area: palatoglossus, palatopharyngeus, levator, and tensor palati. They narrow the oropharyngeal junction, tense the soft palate, and elevate the uvula in order for the oropharynx to be separated from the nasopharynx and oral cavity during deglutition. The posterior and lateral walls are immobile; therefore, the nasopharynx is always patent. In the lateral wall, at the level of the inferior nasal concha, is the opening of the auditory tube (eustachian). There is a bulge at the posterior end of the tube created by the
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cartilage in its wall. Passing inferiorly from this elevation is the salpingopharyngeal fold, created by the salpingopharyngeus muscle. Posterior to the bulge and the fold is the pharyngeal recess. On the posterior wall, there may be collections of lymphatic tissue referred to as pharyngeal tonsils, or adenoids. An anterior wall is created by the nasal cavity.
Fig. 23. Posterior view of pharynx with right portion of constrictor muscle retracted laterally.
The oropharynx faces the oral cavity and the posterior surface of the tongue (Fig. 24). The palatoglossal arch is located at the junction between the mouth and the oropharynx. Posterior, and slightly lateral to this arch, is the palatopharyngeal arch. The arches are named for the muscles they enclose. Between the arches is the palatine or tonsillar fossa, a space for the palatine tonsil. The fauces is considered as the area between the oral cavity and the pharynx. The posterior third of the tongue contains lymphatic tissue called lingual tonsil. Behind the tongue is the upper free edge of the epiglottis. Its anterior surface and lateral edges are attached to the tongue by mucosal folds named glossoepiglottic folds. Shallow depressions between the folds are the valleculae. The buccopharyngeal fascia covering the posterior aspect of the pharyngeal wall is in contact with the prevertebral fascia lying anterior to the upper cervical vertebrae.
Fig. 24. Interior view of pharynx.
The laryngopharynx receives, in its upper portion, products of the digestive and respiratory systems. Its lower segment is related only to the digestive system. The anterior wall is created by the entrance into the vestibule of the larynx, bounded laterally by the aryepiglottic fold, the arytenoid cartilages, and the lamina of the cricoid cartilage. The posterior wall is in contact with the prevertebral fascia situated anterior to the lower cervical vertebrae. The anterior and posterior walls of the distal segment of pharynx are in contact but are separated by the passage of food. The lateral wall is supported by the posterior free edge of the thyroid lamina. A small piriform recess is found between the thyroid lamina laterally and the aryepiglottic fold medially. This space receives sensory innervation from the internal laryngeal nerve, and if a foreign body, or a morsel of food, is trapped in this area, it will cause severe and persistent coughing.
Ligamentous Background
  • Stylohyoid ligament is found between the tip of the styloid process of the skull and the lesser horn of the hyoid bone (Fig. 25). It supports the hyoid, and through the
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    thyrohyoid membrane is also responsible for suspension of the larynx.
  • Pharyngeal raphe is a fibrous seam, which represents the posterior site of attachment for the left and right constrictor muscles. It is attached superiorly to the pharyngeal tubercle found on the basal portion of the occipital bone, 1/2 in. anterior to the foramen magnum. Inferiorly, it merges with the esophageal wall.
  • Pterygomandibular raphe is a fibrous structure between the pterygoid hamulus and the mandible. It provides attachment for the superior constrictor and the buccinator muscles.
Fig. 25. Skeletal framework of pharynx.
Muscular Background
There are five paired voluntary muscles contributing to the pharyngeal wall. The superior, middle, and inferior constrictors create an external circular muscle layer (Fig. 26). The stylopharyngeus and the palatopharyngeus create an inner longitudinal muscle layer. Each constrictor muscle partially overlaps, externally, the inferior edge of the muscle above. The superior constrictor arises from the posterior edge of the lower part of the medial pterygoid plate, pterygoid hamulus, pterygomandibular raphe, side of the tongue, and the mylohyoid line of the mandible. The middle constrictor arises from the inferior end of the stylohyoid ligament and the lesser and greater horns of the hyoid bone. The inferior constrictor arises from the oblique line of the thyroid cartilage, the lateral aspect of the arch of the cricoid, and from the fascia overlying the cricothyroid muscle of the larynx. These muscles widen as they pass laterally and then posteriorly, where they insert into the posterior midline pharyngeal raphe. The lowest fibers of the inferior constrictor that arise from the cricoid cartilage create the cricopharyngeus muscle (Fig. 27). This is the superior esophageal sphincter, which can regulate flow into the esophagus. The upper fibers of the muscle pass superomedially and attach to the pharyngeal raphe, but the lower fibers pass transversely. There is a slight muscular defect between the transverse and the oblique portions of the cricopharyngeus muscle. This is Zenker area, a weak point, where pulsion diverticula may develop, and is a potential site for endoscopic perforation.
Fig. 26. Constrictor muscles of pharynx.
The stylopharyngeus and palatopharyngeus muscles create the internal longitu-dinal muscle layer. The stylopharyngeus muscle receives motor innervation from the glossopharyngeal nerve. The remainder of the muscular wall is supplied by the vagus and glossopharyngeal nerves via the
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pharyngeal plexus. The superior laryngeal nerve arises from the vagus at the base of the skull. It creates the external laryngeal nerve, which innervates the lower portion of the inferior constrictor, and the cricothyroid muscle of the larynx.
Fig. 27. Posterior view of pharynx.
Completion of the Wall of the Pharynx
There are defects in the pharyngeal wall superior and inferior to the narrow origins of the constrictor muscles. There are structures that pass through these areas of muscular deficiency. Two layers of fascia close these openings: (a) buccopharyngeal fascia, which also creates an external covering of the constrictors, and (b) pharyngobasilar fascia, which is submucosal in position, and internal to the muscular wall.
The pharyngeal nervous plexus and the pharyngeal venous plexus are found between the constrictor muscles and the buccopharyngeal fascia. In addition, there are submucosal venous plexuses. The uppermost opening, between the base of the skull and the superior constrictor, provides passage for the cartilaginous portion of the auditory tube, levator palatine muscle, and small palatine vessels. The stylopharyngeus muscle and the glossopharyngeal nerve pass between the superior and the middle constrictor muscles (Fig. 28). The third gap, between the middle and the inferior constrictors, includes the area between the greater horn of the hyoid and the thyroid cartilage. The thyrohyoid membrane is found here and is penetrated by the superior laryngeal artery arising from the superior thyroid, the internal branch of the superior laryngeal nerve providing sensory innervation to the laryngeal mucosa above the vocal folds, and the superior laryngeal vein. Passing between the inferior constrictor and the esophagus are the continuation of the recurrent laryngeal nerve and the inferior laryngeal artery and vein (Fig. 24).
Fig. 28. Cartilages of the larynx.
Innervation of the Pharynx
The pharyngeal plexus, created by the vagus (X) and glossopharyngeal (IX) nerves, supplies motor innervation to the pharyngeal
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muscles. The stylopharyngeus muscle receives motor innervation from the glossopharyngeal nerve. The superior laryngeal nerve arises from the vagus at the base of the skull. It creates the external laryngeal nerve that innervates the lower portion of the inferior constrictor and the cricothyroid muscle of the larynx. The remainder of the muscular wall receives motor innervation from the pharyngeal plexus. Sensory innervation is provided by the glossopharyngeal nerve via the pharyngeal plexus.
Larynx
The larynx is responsible for vocalization. The superior opening faces the laryngopharynx. The inferior end is at the cricoid cartilage, where it becomes continuous with the trachea. It is anterior to vertebral bodies C3 through C6. The anterior wall of the larynx is related to cervical fascia and skin. The strap muscles are anterolateral. The thyroid gland and the carotid sheath are lateral. The laryngopharynx separates the larynx from the vertebral column. It has some degree of rigidity and is composed of bone and cartilage that are held together by membranes, ligaments, and synovial joints. The hyoid bone is part of the anatomy of the floor of the mouth, but as it provides important support for the larynx, it will be discussed in this section.
Skeleton of Larynx
The hyoid bone is a U-shaped structure with a central body, measuring 1 in. wide and 1/2 in. high. It is continuous, on each side, with the greater horn that passes posterolaterally for approximately 1½ in. The free end of the greater horn is directly inferior to the angle of the mandible. The lesser horns are small, superior protrusions found at the junction of the body and greater horns. The stylohyoid ligament, which suspends the hyoid bone from the base of the skull, is attached here.
Laryngeal Cartilages
There are three unpaired and three paired cartilages (Fig. 28). The larger unpaired cartilages are the thyroid, cricoid, and epiglottis. The paired cartilages are the arytenoid, corniculate, and cuneiform.
The hyoid bone and the thyroid and cricoid cartilages provide the principal support of the larynx. The thyroid cartilage is palpable 1/2 in. below the body of the hyoid bone. It is composed of hyaline cartilage and formed by two laminae that fuse anteriorly. The anterosuperior point of fusion is incomplete, leaving a palpable V-shaped notch called the laryngeal, or thyroid, prominence. It is also referred to as Adam's apple, and is a more prominent structure in males. The posterior border of each lamina is free and creates projections called the superior and inferior horns. The superior horn extends up approximately 1/2 in. toward, and is vertically inferior to, the tip of the greater horn of the hyoid. The inferior horn is only 1/4 in. long, and extends down from the free edge of the thyroid lamina toward the posterior end of the arch of the cricoid cartilage. There is a ridge beginning at the root of the superior horn that extends inferomedially toward the lower edge of the fused thyroid laminae. This is the oblique line, and it represents the point of attachment of three muscles: sternothyroid, thyrohyoid, and the inferior constrictor of the pharynx.
The cricoid cartilage creates a complete ring. It is the only complete cartilaginous ring in the respiratory system. The anterior and lateral portion of the ring is narrow and creates the arch. The posterior part widens and creates the lamina. It does resemble a signet ring. The arch has been identified as the cricoid plane. This is the level that was referred to as an anatomical bonanza earlier in this chapter. The cricoid participates in two synovial joints: cricoarytenoid and cricothyroid. The epiglottis is the third of the unpaired cartilages. It is composed of elastic cartilage, which allows this racket-shaped structure to help seal off the entrance into the larynx during deglutition. Its lower pointed end is attached to the thyroid cartilage just inferior to the laryngeal prominence by the thyroepiglottic ligament. The superior edge extends above the body of the hyoid bone. The hyoepiglottic ligament attaches to the posterior aspect of the body of the hyoid. The anterior aspect is connected to the dorsum of the tongue by left, right, and median glossoepiglottic folds. Between the folds are depressions referred to as vallecula epiglottica. The superior edge of the epiglottis may be visible during oral examination if the dorsum of the tongue is depressed. The posterior surface of this cartilage is part of the anterior wall of the laryngeal vestibule.
The arytenoids are the largest of the paired cartilages. They lie on the superior border of the lamina of the cricoid cartilage and participate in the cricoarytenoid joint. They are pyramidal in shape and measure 1/2 to 3/4 in. in height. The base is on the superior surface of the lamina of the cricoid. The medial end of the base is prolonged anteriorly to create the vocal process. The posterolateral angle of the base is enlarged and forms the muscular process. The medial surface faces its partner. The anterolateral surface provides attachment for muscles inferiorly and the quadrangular membrane superiorly. The arytenoid is composed of hyaline cartilage, but the apex is created by elastic cartilage. The corniculate and cuneiform are small bars of elastic cartilage that lie within the aryepiglottic fold, just above the apex of the arytenoid.
Membranes and Ligaments
The thyroid cartilage is suspended from the body and greater horn of the hyoid bone by the thyrohyoid membrane. This membrane is thickened in the midline and at each edge, creating the median and lateral thyrohyoid ligaments. The median cricothyroid ligament is a midline thickening between the anterior aspect of the cricoid arch below, and the inferior end of the thyroid cartilage above (Fig. 28). Other strong fibers arise from the remainder of the arch of the cricoid and pass superomedially. The anterior fibers pass to the internal aspect of the thyroid cartilage below the thyroid notch (Fig. 29). The posterior fibers attach to the vocal process and the base of the arytenoids. The fibers between these anterior and posterior attachments are free and are called the vocal ligaments. The vocal ligaments are the superior free edge of the cone-shaped structure that attaches below to the arch of the cricoid cartilage. It is called the conus elasticus and encloses the infraglottic space of the larynx (Fig. 30). The cricotracheal ligament attaches the cricoid to the first tracheal cartilage. Above the level of the vocal ligaments is a thinner membrane, which passes from the anterolateral surface of the arytenoid cartilage to the lateral edge of the epiglottis, below its superior edge, and to the thyroepiglottic ligament. This is the quadrangular membrane. The lower edge, between the arytenoids and the thyroepiglottic ligament, is free, and forms the vestibular ligaments, or false vocal cords. The distance between the vocal ligaments and the more superiorly located vestibular ligaments separates the conus elasticus and the quadrangular membrane from each other inferiorly. The two structures create the fibroelastic membrane of the larynx. Both are cone-shaped and are aligned so that they resemble an hourglass.
Interior of the Larynx
The membranes and ligaments previously described are lined by mucosa. The larynx is divided into three portions (Fig. 29). The vestibule is superior and the infraglottic space is inferior. Separating these two areas is the ventricle. The vestibule is bounded anteriorly by the epiglottis. The quadrangular membrane is the lateral limit, and posteroinferiorly are the arytenoids and the
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interarytenoid fold. The mucosa covering the superior edge of the quadrangular membrane forms the aryepiglottic fold. The space between the aryepiglottic folds is the entrance into the vestibule. It is the laryngeal aditus. The mucosa covering the vestibular ligament creates the vestibular fold, which is the inferior end of the vestibule. The space between the vestibular folds is the rima vestibuli. Below the vestibular folds are the vocal folds. The mucosa covering the vocal ligaments creates the vocal folds. It is very adherent and has a white coloration. The mucosa of this fold is stratified squamous. The remainder of the laryngeal mucosa is pseudostratified ciliated columnar. The space between the vocal folds is the rima glottidis. It is found 1/4 in. below the rima vestibuli and is easily visualized by endoscopic examination through the wider rima vestibuli.
Fig. 29. Membranes of the interior of the larynx.
The middle portion of the larynx is the ventricle. It separates the vestibule superiorly from the infraglottic space inferiorly. It is found between the rima vestibuli and the rima glottidis. The mucosa extends laterally between the vestibular and the vocal folds and creates the sinus. A small outpouching from this area ascends for a short distance, lateral to the vestibular fold, and creates the saccule. Numerous mucous-secreting glands are found here. The infraglottic space is internal to the conus elasticus and the cricoid cartilage. The rima glottidis is the upper limit, and inferiorly it is continuous with the lumen of the trachea.
Fig. 30. Superior view of the vocal ligaments.
Joints and Intrinsic Muscles of the Larynx
The cricothyroid and cricoarytenoid joints are synovial and created by hyaline cartilaginous structures. The cricothyroid joint allows a pivoting movement, which elevates the arch of the cricoid cartilage while depressing the lamina and the arytenoid cartilages found on its superior surface (Fig. 30). This results in tensing of the vocal ligaments, which creates high-pitched sounds. The axis of rotation is transverse, through both cricothyroid joints. The cricoarytenoid joint permits two types of movements of the arytenoid cartilage. Rotation around a vertical axis passing through the arytenoids will result in adduction or abduction of the vocal ligaments. In addition, a gliding movement can occur, which allows the arytenoids to move toward, or away from, each other. The rima glottidis is triangular, and the base is the interval between the vocal processes. The transverse gliding movement, or the rotation of the arytenoids around a vertical axis, can result in either widening or narrowing of the rima glottidis. There are nine intrinsic muscles of the larynx, eight are paired and one is unpaired. Six of the paired and the unpaired act
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directly on the arytenoids, with resultant effect on the vestibular and vocal ligaments. The muscles can be divided into three functional groups. The first provides protection by sphincter-like activities. They are in the aryepiglottic fold. The aryepiglottic muscle passes from the posterior surface of the arytenoids to the lateral aspect of the epiglottis (Fig. 31). The thyroepiglottic muscle extends from the internal aspect of the thyroid lamina to the lateral aspect of the epiglottis. These muscles help close the laryngeal aditus. The second group of muscles tenses, relaxes, or adducts the vocal ligaments. The cricothyroid muscle, found between the arch of the cricoid and the internal aspect of the fused thyroid lamina, causes elevation of the arch of the cricoid and depression of the lamina. This results in tensing of the vocal ligaments. The thyroarytenoid muscle, which is found between the thyroid cartilage anteriorly, and the arytenoids oppose this action posteriorly. It pulls the vocal processes anteriorly and relaxes the vocal ligaments. Fibers from the medial aspect of this muscle attach directly to the vocal ligaments and can cause differential contraction and relaxation of portions of the vocal ligament. These specialized fibers are named the vocalis muscle. The lateral cricoarytenoid muscle, between the posterior portion of the arch of the cricoid and the muscular process of the arytenoids, is the main adductor of the vocal ligaments. The transverse arytenoid is the only unpaired muscle of the larynx; it passes between the arytenoids and causes narrowing of the rima glottidis and the rima vestibuli. The third group of muscles is responsible for widening of the rima glottidis. The posterior cricoarytenoid muscle passes obliquely between the posterior surface of the cricoid lamina and the muscular process of the arytenoid. It widens the rima glottidis by abducting the vocal process of the arytenoid cartilage.
Fig. 31. Interior of the larynx after removal of the right portion of hyoid and thyroid cartilages.
Blood Supply and Nervous Innervation of the Larynx
The superior laryngeal branch of the superior thyroid artery provides vascular flow. It enters the larynx through the thyrohyoid membrane, along with the internal laryngeal nerve and superior laryngeal veins. Vascular inflow also occurs via the inferior laryngeal artery, a branch of the inferior thyroid that enters the larynx below the lower edge of the inferior constrictor muscle, along with the inferior laryngeal nerve. This nerve is the intralaryngeal continuation of the recurrent laryngeal nerve.
Vagus nerve branches provide all sensory and motor innervation. Sensory innervation, above the vocal folds, comes from the internal branch of the superior laryngeal nerve. The inferior laryngeal nerve supplies sensory innervation to the infraglottic space and trachea. The external branch of the superior laryngeal nerve innervates the cricothyroid muscle. The inferior laryngeal nerve supplies all the other intrinsic laryngeal muscles.
Laryngeal nerve injury may occasionally occur during thyroid surgery. Knowledge of anatomy will allow the surgeon to perform any procedure, anywhere in the body, expeditiously and safely.
Division of the superior laryngeal nerve will cause loss of sensory innervation of the larynx above the vocal folds (internal laryngeal branch). The cough reflex will be lost. In addition, there will be loss of motor innervation of the cricothyroid muscle. The voice will become husky and unable to reach high tones.
Unilateral division of the recurrent laryngeal nerve will result in the vocal ligament being midway between adduction and abduction. This is the cadaveric position. The uninjured cord can cross the midline and approach its partner so that the voice changes may be minimal. If both recurrent nerves are cut, the vocal ligaments become lax, resulting in voice changes but no respiratory problems. Within several months, the voice will begin to reappear as a result of fibrotic changes and tightening of the vocal ligaments. This will also result in narrowing of the rima glottidis and the appearance of respiratory problems. If there is bilateral injury, created by crushing, stretching, or incorporation in a ligature, without transection, then a different set of symptoms may occur. Respiratory problems appear early. This may be explained by Semon's law, which states that in progressive disease of motor laryngeal nerves, the abductors are occasionally the only muscles affected. In addition, the unopposed action of the cricothyroid muscles, and narrowing of the rima glottidis and respiratory difficulties are to be expected.
Superficial Venous System
These veins and the other superficial neurovascular structures are deep to the platysma muscle.
  • Common facial vein is formed by the union of the anterior facial vein with the anterior division of the retromandibular (posterior facial) vein. It passes over the submandibular triangle and the posterior belly of the digastric muscle, and empties into the internal jugular vein in the superior portion of the carotid triangle.
  • External jugular vein is created by the union of the posterior auricular vein with the posterior division of the retromandibular vein. The vein passes inferolaterally, runs obliquely across the superficial aspect of the sternocleidomastoid muscle, pierces the deep cervical fascia in the subclavian division of the posterior triangle, and empties into the subclavian vein. The great auricular nerve (C2, C3) is posterior to this superficial vein in the upper part of the neck.
  • Anterior jugular vein begins in the suprahyoid portion of the neck and descends vertically, close to the midline, down to the clavicle. It then pierces the investing layer of the deep cervical fascia, passes deep to the sternocleidomastoid, and ends in the ipsilateral external jugular vein. It frequently gives a branch in the suprasternal area that crosses the midline and joins with the contralateral anterior jugular vein. This transverse communicating branch is referred to as the jugular venous arch.
  • Vein of Kocher arises in the submandibular area as a branch of the anterior facial vein, descends on the anterior edge of the sternocleidomastoid muscle, and terminates in the jugular venous arch, or the internal jugular vein.
Lymphatic Pathways of the Neck
The lymphatic pathways of the neck (Fig. 32) can be divided into a superior horizontal group found at the junction of the head and the neck. It includes the submental, submandibular, parotid (preauricular), mastoid
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(postauricular), and occipital nodes. It creates a ring of lymph nodes in this area.
Fig. 32. Deep lymphatic drainage.
Fig. 33. Lymphatic drainage.
  • A vertical group that receives the lymphatic drainage from the superior horizontal components (Fig. 33). There are three pathways possible in this grouping. (a) The posterior cervical group consists of superficial nodes traveling with the external jugular vein and a deep group of nodes that journey with the spinal accessory nerve (XI). They are in the posterior triangle. (b) The jugular group is intermediate in position and is frequently referred to as the deep cervical group. This pathway is the most important. It consists of nodes at several levels, as this vertical channel descends with the internal jugular vein. There is a juguloparotid node located near the angle of the mandible, a jugulodigastric node where the posterior belly of the digastric muscle crosses the internal jugular vein, a jugulocarotid node near the bifurcation of the common carotid artery, and a jugulo-omohyoid node where the omohyoid muscle crosses the internal jugular vein. The jugulodigastric node receives drainage from the tonsil. The jugulo-omohyoid node receives drainage from the tongue. (c) The visceral chain is the most anterior of the vertical pathways and drains all the cervical viscera. The individual components of this nodal chain are parapharyngeal, paralaryngeal, prelaryngeal or Delphian, paratracheal, and pretracheal. The Delphian node is a constant finding and receives lymphatic drainage from the larynx and the thyroid gland.
  • An inferior horizontal group, called supraclavicular nodes, is found in the subclavian triangle. They receive lymphatic flow from the vertical cervical channels and the upper extremity, axilla, and the thoracic wall. They communicate, by way of efferent channels, with internal jugular and subclavian conduits. Some of these supraclavicular nodes lying anterior to the anterior scalene muscle are referred to as scalene nodes. They receive bronchomediastinal channels from the thorax and may be enlarged as a result of spread from an intrathoracic disease process.
  • The thoracic duct receives inflow from all lymphatics below the respiratory diaphragm, the left hemithorax by way of the left bronchomediastinal trunk, the left side of head and neck via the left vertical cervical trunks, and from the left
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    upper extremity through the left subclavian trunk. It empties into the venous system on the lateral aspect of the junction between the left internal jugular and the left subclavian veins. The trunks may enter separately into the venous circulation. On the right side, it is unusual for the bronchomediastinal, subclavian, and vertical cervical trunks to combine before entering the venous circulation. They frequently empty, as separate entities, into the vascular compartment.
Suggested Readings
Arnold M. Reconstructive Anatomy: A Method for the Study of Human Structure. Philadelphia: WB Saunders; 1968.
Healey JE, Hodge J. Surgical Anatomy, 2nd ed. Philadelphia: BC Decker; 1990.
Leeson CR, Leeson TS. Human Structure: A Companion to Anatomical Studies. Philadelphia: WB Saunders; 1972.
Thorek P. Anatomy in Surgery. Philadelphia: JB Lippincott; 1951.
Editor's Comment
There is little attention paid nowadays to the neck. It is almost as if general surgeons are abrogating their responsibility and interest in the neck except in cases of diseases of the thyroid and parathyroid, and even in those circumstances, interest may be waning, or at least the interest of others such as otorhinolaryngologists seems to have increased. The reason for this is difficult to know.
  • Otorhinolaryngologists were liberated from the destructive surgery, for example, in mastoids and with otitis media, with the advent of effective antibiotics. In addition, pharyngeal neck abscesses from various colds and infections also vanished from the scene with effective antibiotics. Thus, they tried to reinvent themselves in the same area in which they were trained, but in which much of the destructive surgery based on infectious disease was not cared for with antibiotics. In those cases, they turned, as well as others, from destructive surgery to constructive surgery.
  • The rise of oral surgery. Oral surgery emerged as differentiated from dentistry some time in the early 1940s and gradually developed in the 1950s and 1960s. Carcinoma of the tongue, carcinoma of the tonsil, and pharyngeal maxillary cancer to a certain extent. This was also when submandibular cancer became part of the repertoire of the oral surgeon in some geographical areas.
  • General surgeons were held in sway by some leaders who didn't believe in the resection of nodes for thyroid cancer. A papillary carcinoma, of course, has a low mortality, and so it is difficult for some surgeons to believe that general surgeons, especially those taking care of thyroid cancer, should pursue the adenopathy, since mortality is so low. Others believed that carcinoma of the thyroid could be treated with psychiatry. In any event, this tide has turned, and at this point in time, most surgeons dealing with thyroid cancer have gotten much more aggressive at attacking the adenopathy with node dissections.
  • Other specialties began to concentrate on parathyroid surgery, which previously was the field of general surgery and endocrine services. In other chapters of this book, it does appear that the rates of success between ENT surgeons and general surgeons differ. In some of the well-recognized centers for parathyroid surgery, a success rate of 99% is expected. For those in the ENT field, it does appear as if perhaps a 95% or 96% rate of success in “curing” hypoparathyroidism is the norm.
In addition, medical schools stopped teaching anatomy. As medical schools became more research oriented, bragging rights was not about how well the students were taught but was about the NIH grants and the total number of NIH dollars appropriated to that school. In addition, in schools that have not given up anatomy, there were inappropriate instructors who were utilized to [make] up the funds that were [not] appropriated in their NIH grants. A classic example of this is to have acute abdomen taught by internists who were not called to the emergency room to see patients with acute abdomen. In many schools, surgeons are no longer asked to teach the acute abdomen. It is also now thought that medical students can learn in a truncated general surgery rotation, which is now increasingly shared with other surgical specialties, such as ophthalmology, in the time frame which in the past was solely utilized by general surgery. I am not criticizing ophthalmology in this statement, but I am just pointing out that those surgical specialties have now lost their own space to surgery time.
One appreciable thing about this chapter is that Professor Ruhalter is very well aware of clinical correlation and anatomic correlation. I just list these because I think they are of interest and have some clinical relevancy.
Anatomic goodies:
  • The cricoid bone is an anatomic bonanza, as is detailed in this chapter.
  • The superior surfaces of the first rib are flattened, so that neurovascular structures can travel over it without compression. This, of course, is true of thoracic outlet syndrome, in which the vasculature and sometimes the nerves are compressed.
  • The subclavian artery passes over the posterior sulcus of the scalene tubercle. The anterior scalene muscle attaches to the first rib between the subclavian vessels and, therefore, is in a position to compress the subclavian artery, giving rise to the thoracic outlet syndrome.
  • The cervical sympathetic chain has as its apex a “dumbbell-shaped structure, called the cervicothoracic, or stellate, ganglion.” The reason for it being called stellate ganglion is that it is star-like and gives out the multiple branches. The stellate ganglion, when invaded by a tumor at the apex of the lung on one side or the other, gives rise to the Horner's syndrome and is often the first symptom or sign of the presence of that tumor.
  • The brachial plexus is formed by the ventral rami of C5 through T1. These nerve roots will form three trunks—C5 and C6 form the upper trunk, C7 root forms the middle trunk, and C8 and T1 form the lower trunk. These pass between the middle and anterior scalene muscles.
  • The lower trunk of the brachial plexus is draped over the first rib immediately posterior to the subclavian artery.
  • The fascia of the neck: The superficial fascia, which is often is not well developed, forms the platysma, which may or may not be very robust; the cervical branch of the facial nerve enervates the platysma, which contributes to facial expression.
  • The cutaneous branches and the superficial veins are below the muscles of facial expression, which are the platysma.
  • Deep cervical fascia: The superficial or investing layer of the deep cervical fascia splits to surround the trapezius and the sternocleidomastoid muscle and the submandibular and parotid glands.
  • The carotid sheath, which is part of the deep cervical fascia, surrounds the common carotid, the internal jugular, and the vagus nerve. The vagus nerve is between the common carotid and the internal jugular, which is somewhat posterior to the common carotid.
  • When the common carotid artery divides the internal carotid, it immediately goes anterior to the carotid, except at the base of the skull; the vein is anterolateral to the artery.
  • The sympathetic chain is in contact with the posterior sheath.
  • The thoracic duct is to the left of, and posterior to, the esophagus. It enters at the junction of the internal jugular vein and the subclavian vein.
  • The right lymphatic duct, which is the counterpart of the left thoracic duct, is not large as the thoracic duct and consists of several smaller lymphatics. It drains the right upper extremity and the upper right hemithorax.
  • The right recurrent laryngeal nerve loops around the right subclavian. The left recurrent nerve loops the aortic arch on the left. The right recurrent nerve is less well protected, as it comes up lateral to the tracheoesophageal groove, but, to get to the tracheoesophageal groove on the right, it is more superficial and more widely exposed.
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  • Sibson's fascia is at the apex of the lung and runs between C7 and the first rib. It is somewhat protective of the apex of the lung.
  • The inferior thyroid artery is superficial to the prevertebral fascia. It courses posterior to the carotid sheath and anterior to the vertebral artery.
  • The last branch given off by the subclavian artery, as it goes from medial to lateral, is the internal mammary, which then travels behind the sternum and attaches to the sternum medial to the ribs.
  • The anatomy of the root-of-the-neck compression syndromes includes the following:
    • Costoclavicular compression syndrome.
    • Cervical-rib compression syndrome.
    • Anterior scalene compression syndrome (thoracic-outlet syndrome).
    • Pectoralis minor syndrome.
    The following are the clinical anatomic applications which are practical in the surgery of this area.
  • Cervical incisions should be made parallel to the skin lines for good cosmesis.
  • Control of bleeding may be possible, if the common carotid artery is compressed against the transverse mass of the sixth cervical vertebra, which is the cricoid plane.
  • The hyoid bone is the central structure of the neck. Most of the structures of the neck—muscular and membranous—attach to the hyoid bone. If one considers the hyoid bone and the attached posterior belly of the digastic muscle, it is possible to divide the anterior triangle into suprahyoid and infrahyoid portions.
  • The vagus nerve is behind and slightly posterior to the carotid and internal jugular vessels.
  • The posterior belly of the digastic muscle is superficial to the neurovascular structures and presses them against the pharyngeal wall. Therefore, owing to this structure, incisions can be made without the risk of injuring the nerves or arteries.
  • The intermediate tendon of the omohyoid between the two bellies is in the cricoid plane with a number of other venous and tendinous structures.
  • The transection of the strap muscles closer to the superior end will preserve the nervous innervation, since the nerve enters the muscle near the inferior end. Most individuals who divide the strap muscles to get at the thyroid do so at the interior end. Personally, I have never been taught that one divides the strap muscles at the superior end because the nerve enters inferiorly, but it is something good to remember, because one of the cosmetic difficulties following thyroid surgery is the denervation of the strap muscles, at times with a bulge in the lower neck.
  • When one enters the cleavage between the sternothyroid muscle and the thyroid gland, this provides excellent exposure of and facilitates surgical approach to the gland, which is avascular.
  • The long thoracic nerve originates from C5, C6, and C7 and courses inferiorly, passing to the other portions of the brachial plexus, and then passing over the first rib to reach the superficial surface of the serratus ventralis, which it innervates.
  • Dissection on the posterior triangle is safe in the area superior to the spinal accessory nerve.
  • A good landmark for the upper thyroid glands is that they are usually at the level of the thyroid cartilage.
  • If there is a high origin of the recurrent laryngeal nerve, it may not be in the tracheoesophageal groove and it is called a nonrecurring nerve. Obviously, if there is a high origin, it is more exposed and not protected by not being in the tracheoesophageal groove.