The Neck

Chapter 7 The Neck



I. Triangles of Neck (Figure 7-1)

• Anterior and posterior triangles separated by sternocleidomastoid muscle

A. Anterior Cervical Triangle

1. Submandibular triangle

a. Floor formed by mylohyoid and hyoglossus muscles

b. Contains submandibular salivary gland (superficial part) and lymph nodes, facial vein and artery, nerve to the mylohyoid, and submental artery

image

7-1 Triangles of neck viewed from right side.


(From Norton, N S: Netter’s Head and Neck Anatomy for Dentistry. Philadelphia, Saunders 2007, p 113.)



Enlarged submandibular lymph nodes may be confused with an enlarged gland.



Enlarged lymph nodes in the submandibular triangle (e.g., from tongue cancer or infection) can be mistaken for an enlarged submandibular gland. Correct identification of the nodes can often be made by bimanual palpation with one finger on the floor of the oral cavity. During excision of the submandibular gland for a tumor, the cervical and mandibular branches of the facial nerve are at risk. Cutting the mandibular branch causes facial deformity because the lower lip and chin muscles are paralyzed.



Damage to the mandibular branch of VII during submandibular gland surgery causes lower facial paralysis.


2. Submental triangle

a. Floor formed by mylohyoid muscles meeting in median fibrous raphe

b. Unpaired median triangle above hyoid bone between anterior bellies of digastric muscles

c. Contains submental lymph nodes, which receive lymph from apex of tongue and middle of lower lip


Cancer from the tip of the tongue and the lower lip metastasizes to submental lymph nodes.


3. Carotid triangle


The carotid triangle is used for a surgical approach to the carotid arteries, internal jugular vein, and hypoglossal and vagus nerves.


• Contains common, internal, and external carotid arteries, internal jugular vein, and vagus and hypoglossal nerves

4. Muscular triangle

a. Floor formed by sternohyoid and sternothyroid (infrahyoid) muscles

b. Anterior jugular vein descends in fascia superficial to triangle

B. Posterior Cervical Triangle

1. Overview

a. Floor formed by prevertebral fascia overlying splenius capitis, levator scapulae, posterior and middle scalene muscles

b. Subdivided by inferior belly of omohyoid muscle into superior occipital and inferior subclavian (omoclavicular) triangles

2. Contents

a. Spinal accessory nerve

b. Roots and trunks of brachial plexus

c. Subclavian artery crossing rib 1


Subclavian artery compression against the first rib helps to control axillary and upper-extremity bleeding.


d. Supraclavicular nerves (C3,4) descending in fascial roof of triangle


Pain carried by the phrenic nerve from the diaphragmatic pleura or peritoneum or from the pericardium may be referred to the shoulder via the supraclavicular nerves.


e. Suprascapular, dorsal scapular, and long thoracic nerves

f. Transverse cervical and suprascapular arteries from thyrocervical trunk

II. Cervical Fasciae (Figure 7-2)

A. Superficial Cervical Fascia

• Subcutaneous connective tissue containing platysma muscle, superficial veins, cutaneous nerves, and variable amount of fat

image

7-2 Horizontal section of neck at the level of the C7 vertebra showing cervical fasciae. Note the “danger space” between the anterior (alar) and posterior layers of prevertebral fascia and the retropharyngeal space between the alar fascia and buccopharyngeal fascia. These spaces are two pathways for the spread of infection into the mediastinum.


(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 35.)



Laceration that penetrates platysma suggests a serious neck wound and requires further evaluation.


B. Deep Cervical Fascia

• Forms series of cylindrical compartments descending through neck


Cervical fasciae form cleavage planes that direct the spread of infection.


1. Investing layer of deep cervical fascia

a. Cylindrical layer deep to superficial fascia forming roof of anterior and posterior triangles and splitting to invest sternocleidomastoid and trapezius muscles

b. Attached superiorly to cranium and mandible and inferiorly to shoulder girdle and manubrium

2. Pretracheal fascia

a. Lies deep to infrahyoid muscles anterior to larynx, thyroid gland, and trachea

b. Splits to enclose thyroid gland and fuses on each side with carotid sheath

c. Attaches superiorly to thyroid cartilage and inferiorly blends with connective tissue of anterior mediastinum


Swelling from pretracheal space infection may cause dyspnea, dysphagia, and hoarseness.



Infection can spread from the neck into the mediastinum through the potential pretracheal space between the pretracheal fascia and the trachea, causing fatal mediastinitis. Swelling from the infection may compress the trachea and esophagus, causing hoarseness and difficulty breathing (dyspnea) and swallowing (dysphagia).


3. Carotid sheath

• Encloses common and internal carotid arteries, internal jugular vein, and vagus nerve from base of skull to root of neck

4. Buccopharyngeal fascia

a. Covers pharyngeal constrictor and buccinator muscles

b. Sometimes described as posterior part of pretracheal fascia

5. Pharyngobasilar fascia

• Well-developed fascia in pharyngeal wall between mucosa and pharyngeal constrictor muscles


Pharyngeal mucosa is tightly bound to the underlying pharyngobasilar fascia, and inflammation of the pharyngeal wall with fluid accumulation is painful because swelling stretches the mucosa. Gargling with hypertonic saline solution removes excess fluid from the wall, relieving discomfort. Group A streptococcal pharyngitis has the potential to cause acute rheumatic fever with damage to heart valves, glomerulonephritis, and toxic shock syndrome.



Streptococcal pharyngitis may cause rheumatic fever with mitral valve damage.


6. Prevertebral fascia

a. Cylindrical layer enclosing vertebral column and covering prevertebral, scalene, and intrinsic back muscles

b. Over front of cervical vertebrae divides into anterior and posterior layers


The space between the anterior (alar) and posterior layers of prevertebral fascia has been called the “danger space” because it provides a route for the spread of infection from the base of the skull all the way to the respiratory diaphragm.


7. Retropharyngeal space


Retropharyngeal space is located between the buccopharyngeal and prevertebral fascia.


• Between prevertebral fascia posteriorly and buccopharyngeal fascia anteriorly, extending from base of skull into mediastinum at T3 or T4 vertebra


Retropharyngeal infection may spread into the mediastinum, causing fatal mediastinitis.



Infection can spread from the neck into the mediastinum through the retropharyngeal space. A retropharyngeal abscess may arise from the pharynx, from vertebral bodies, or from infected deep cervical lymph nodes. The abscess, if untreated, may cause dyspnea and dysphagia or rupture into the pharyngeal cavity, causing aspiration pneumonia. Alternatively, it may erode into the carotid artery to produce a fatal hemorrhage or cause internal jugular venous thrombosis.



A retropharyngeal abscess may cause dyspnea, dysphagia, aspiration pneumonia, carotid hemorrhage, or jugular thrombosis.


8. Suprapleural membrane


• Thickening of endothoracic fascia that covers cupola and apex of lung and separates thoracic cavity from neck


The cervical pleura and apex of the lung may be injured in wounds to the base of the neck.



The cervical pleura (cupola) and apex of the lung are vulnerable in a penetrating injury to the posterior triangle or when inserting a subclavian venous catheter. Pneumothorax or hemothorax is possible in these instances.


III. Muscles of Neck

A. Sternocleidomastoid

1. Laterally flexes head to same side and rotates face toward opposite side and acts as accessory muscle of respiration

2. Innervated by spinal accessory nerve (CN XI) with proprioceptive fibers from C3-4


Torticollis (wryneck) is muscle shortening that reproduces the position of a strongly contracting sternocleidomastoid. It may be congenital (usually from a birth injury) or spasmodic (usually psychogenic).



Congenital or spasmodic torticollis mimics spasming sternocleidomastoid.


B. Scalene Muscles

1. Anterior, middle, and posterior scalenes descend from transverse processes of cervical vertebrae to rib 1 or 2.

2. Stabilize neck and act as accessory muscles of respiration


A cervical rib or hypertrophied anterior scalene muscle causes thoracic outlet syndrome.



Roots of the brachial plexus and the subclavian artery pass into the posterior triangle between the anterior and middle scalenes. An elongated transverse process on vertebra C7 (cervical rib, Figure 7-3) or hypertrophy of the scalene muscles may stretch or compress the subclavian artery and/or lower trunk of the brachial plexus (C8, T1) to produce thoracic outlet syndrome. It is characterized by pain, numbness, and muscular weakness of the upper extremity, most commonly in the distribution of the ulnar nerve.


image

7-3 Cervical rib may stretch or compress lower trunk of brachial plexus or subclavian artery in thoracic outlet syndrome.


(From Netter, F H: Netter’s Atlas of Human Anatomy, 3rd ed. Icon Learning Systems, 2003, Plate 181.)



Collateral circulation between the subclavian and external carotid arteries occurs via their costocervical and occipital branches.


IV. Arteries of Neck

A. Subclavian Artery (Figure 7-4; Table 7-1)

1. On right side arises from brachiocephalic trunk and on left side arises from arch of aorta

2. Arches laterally over cervical pleura and apex of lung and grooves rib 1 between anterior and middle scalene muscles

3. Becomes axillary artery at lateral border of rib 1

4. Divided into three parts in relation to anterior scalene

image

7-4 Arteries of the neck and head, lateral view. Ramus of mandible has been removed to expose maxillary artery in infratemporal fossa of deep face.


(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 69.)


TABLE 7-1 Branches of Subclavian Artery



























































  Supplies Comments
First Part   Medial to anterior scalene muscle
Vertebral artery Spinal nerve roots, spinal cord, brainstem Ascends transverse foramina of C1-C6, crosses posterior arch of atlas to enter foramen magnum; medullary branches reinforce blood flow to spinal arteries
Thyrocervical trunk   Three main branches
Inferior thyroid Thyroid, parathyroid gland, larynx, esophagus Main supply to parathyroid glands; forms collateral circulation with external carotid via anastomosis with superior thyroid artery
Transverse cervical Trapezius, levator scapulae, and rhomboid muscles Superficial branch on deep surface of trapezius; deep branch deep to rhomboids
Suprascapular Supraspinatus and infraspinatus muscles Crosses posterior triangle behind clavicle to pass above superior transverse scapular ligament
Internal thoracic See Chapter 2  
Second Part   Posterior to anterior scalene muscle
Costocervical trunk   Runs posteriorly over cervical pleura dividing into deep cervical and superior intercostal branches
Deep cervical Posterior neck muscles Forms collateral circulation between subclavian and external carotid via anastomosis with occipital artery
Superior intercostal First two intercostal spaces Gives first two posterior intercostal arteries
Third Part   Between lateral borders of anterior scalene and rib 1
Dorsal scapular Levator scapulae and rhomboid muscles Variably present; replaces deep branch of transverse cervical when present


The axillary artery is vulnerable to traumatic injury in the posterior triangle. Compressing the third part of the subclavian artery against rib 1 may control hemorrhage in the axilla or upper extremity. Aneurysms of the subclavian artery usually involve the third part and may compress the lower trunk of the brachial plexus. The distal subclavian artery often can be ligated without adversely affecting the upper extremity because of extensive anastomoses around the scapula between subclavian and axillary artery branches.



The distal subclavian artery often can be safely ligated due to collateral circulation around the scapula.


The carotid pulse can be felt in the angle between the sternocleidomastoid and thyroid cartilage.


B. Common Carotid Artery (see Figures 7-4 and 7-5)

1. Overview

a. Arises from brachiocephalic trunk on right and from arch of aorta on left

b. Divides into internal and external carotid arteries at superior border of thyroid cartilage (level of C4)

image

7-5 Axial MRI at level of larynx. Vocal fold = 1; rima glottidis = 2; arytenoid cartilage = 3; common carotid artery = 4; internal jugular vein = 5; sternocleidomastoid muscle = 6; external jugular vein = 7; vertebral body = 8; vertebral artery = 9; spinal cord = 10; trapezius muscle = 11; semispinalis muscle = 12; levator scapulae muscle = 13.


(From Weir, J, Abrahams, P: Imaging Atlas of Human Anatomy, 3rd ed. London, Mosby Ltd., 2003, p 23, f.)



The common carotid artery divides at the superior border of the thyroid cartilage.



Ligation of the common carotid artery may be possible because of excellent collateral circulation between the external carotid branches of the two sides to the face and scalp; between the superior and inferior thyroid arteries and the occipital and deep cervical arteries connecting the external carotid and subclavian arteries; and from vertebral artery contributions to the cerebral arterial circle.


Extracranial carotid aneurysms are uncommon and may present as asymptomatic, pulsatile swellings or cause symptoms such as dyspnea, dysphagia, hoarseness, tongue weakness, and Horner syndrome.


2. Internal carotid artery

• Normally has no branches in neck


The internal carotid artery has no branches in the neck.



Partial occlusion of the internal carotid artery through atherosclerosis may reduce flow through the middle cerebral artery, with impaired sensory and motor function on the opposite side of the body. The central artery of the retina may also be affected, causing ipsilateral visual symptoms. A carotid endarterectomy may be performed to remove plaque, usually from the internal carotid artery at its origin.



A carotid endarterectomy removes internal carotid plaque to reduce stroke risk.


3. External carotid artery (Table 7-2)

a. Gives eight branches, four or five of which arise in carotid triangle

b. Ends within parotid gland by dividing into maxillary and superficial temporal arteries

TABLE 7-2 Branches of External Carotid Artery







































Artery Supplies Comments
Superior thyroid Larynx, infrahyoid muscles, and thyroid gland Travels with external laryngeal nerve
Lingual Tongue, palatine tonsil, sublingual gland, and floor of mouth Passes deep to hyoglossus muscle
Facial Face, soft palate, palatine tonsil, and submandibular muscles May arise in common with lingual artery
Ascending pharyngeal Pharynx, palatine tonsil, and meninges  
Occipital Posterior scalp, sternomastoid, and meninges Parallels greater occipital nerve in scalp
Posterior auricular Scalp, auricle, and facial nerve  
Maxillary Muscles of mastication, temporomandibular joint, meninges, nasal cavity, palate, mandibular and maxillary teeth, and face Terminal branch described with infratemporal and pterygopalatine fossae
Superficial temporal Parotid gland, face, and scalp Terminal branch described with face; ascends with auriculotemporal nerve


To control bleeding from an inaccessible branch such as the middle meningeal, sphenopalatine, or lingual artery, the external carotid artery can be ligated. Collateral circulation occurs across the midline between external carotid branches and occurs also with branches of the internal carotid that originate intracranially.


4. Carotid sinus and carotid body

• Innervated mainly by carotid sinus branch of glossopharyngeal nerve (IX)

a. Carotid sinus

(1) Dilated terminal portion of common carotid artery and/or first part of internal carotid

(2) Functions as baroreceptor for arterial blood pressure


Some individuals develop hypersensitivity to external pressure on the carotid sinus, which may cause fainting (carotid sinus syncope). Care should be exercised, especially with cardiac patients, when taking the carotid pulse near the superior border of the thyroid cartilage.



External pressure on carotid sinus slows heartbeat and lowers blood pressure, causing some individuals to faint.


b. Carotid body

(1) Small structure deep to carotid bifurcation

(2) Functions as chemoreceptor for blood gases reflexly changing heart rate, blood pressure, and respiration


Carotid sinus: blood pressure receptor. Carotid body: blood gases receptor


V. Veins of Neck and Superficial Head (Figure 7-6)

A. Retromandibular Vein

1. Formed in parotid gland by union of maxillary and superficial temporal veins

2. Splits into anterior division and posterior division

B. Facial Vein

1. Begins at medial angle of eye as angular vein and descends on face with facial artery

2. Below mandible joins anterior division of retromandibular vein to form common facial vein, which ends in internal jugular vein

C. External Jugular Vein (see Figure 7-6)

1. Formed by union of posterior auricular vein and posterior division of retromandibular vein

2. Descends obliquely across sternocleidomastoid to empty into subclavian vein

image

7-6 Veins of the neck and head, lateral view. Ramus of mandible has been removed to expose pterygoid plexus and maxillary veins in infratemporal fossa. Most of sternocleidomastoid muscle and overlying external jugular vein have been removed.


(From Netter, F H: Atlas of Human Anatomy, 4th ed. Philadelphia, Saunders, 2006, Plate 70.)



A venous air embolism from a cut external jugular vein may obstruct blood flow through the right heart.



The external jugular vein can be easily cannulated. In the recumbent patient, the vein is normally distended and can usually be made more prominent by increasing intrathoracic pressure (e.g., holding one’s breath). If the vein is lacerated where it penetrates the investing layer of deep cervical fascia, the fascial attachment prevents its collapse so that air sucked into the vein travels to the right side of the heart and may obstruct blood flow (venous air embolism).


D. Anterior Jugular Vein

1. Begins in submental region, descends near anterior midline, and drains into external jugular vein

2. Just above jugular notch may be connected to opposite vein by jugular venous arch


The jugular venous arch is in danger during a tracheostomy.


E. Internal Jugular Vein (see

Related posts:

  1. The Upper Extremity
  2. The Lower Extremity
  3. The Pelvis and the Perineum
  4. The Head

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Jun 16, 2016 | Posted by in ANATOMY | Comments Off on The Neck

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