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Body Surface

The primary surface landmarks of the anterior and lateral neck are associated with the mandible (angle and inferior margin), temporal bone (mastoid process), sternocleidomastoid, trapezius (anterior border), larynx (hyoid, thyroid prominence and cricoid arch), clavicle, and sternum (sternal notch). Branches of the great auricular, lesser occipital, transverse cervical and supraclavicular nerves innervate (sensory and postganglionic sympathetic) the skin overlying the anterior and lateral neck.

Skeleton and Joints

The bones associated with the anterior and lateral neck are the temporal, mandible, hyoid, clavicle, sterum and cervical vertebrae. The cervical spine is supported by the anterior longitudinal, posterior longitudinal, ligamenta flava, intertransverse, interspinous and supraspinous ligaments. There are facet (zygapophyseal) joints between adjacent superior and inferior articular processes, and symphases (intervertebral discs) between the adjacent vertebral bodies. The cervical spine moves in flexion, extension, lateral flexion and rotation. The sternoclavicular joint (a sellar joint) moves during elevation and depression, protraction and retraction, and rotation of the scapula.

Organization

The superficial fascia of the neck is a thin layer coverying the platysma muscle. There are three layers (investing, pretracheal and prevertebral) of deep cervical fascia. The investing fascia covers the anterior and posterior cervical triangles (described below) extending from the ligamentum nuchae to the midline and splitting around the trapezius and sternocleidomastoid muscles. The pretracheal fascia surrounds the thyroid gland, trachea, esophagus, larynx and lower pharynx, and blends laterally with the carotid sheath and investing fascia. The prevertebral fascia is thick and prominent where it covers the anterior vertebral muscles and is thin and non-distinct deep to the trapezius. It covers the cervical ventral rami and is continuous with the axillary sheath. The carotid sheath is a fascial tube surrounding the common and internal carotid arteries, the internal jugular vein, the vagus nerve and portions of the ansa cervicalis. It is positioned anterior to the prevertebral muscles and deep to the sternocleidomastoid. There are two important spaces associated with the deep fascial layers of the neck. The pretracheal space surrounds the trachea bounded by the anterior wall of the espohagus, the pretracheal fascia and infrahyoid muscles. The retrovisceral space is positioned between the prevertebral fascia and the posterior wall of the esophagus, and is continuous with the retropharyngeal space (between the prevertebral fascia and pharyngeal constrictors).

For descriptive purposes the neck is organized into a series of triangles. The two major triangles are the anterior and posterior triangles.

The anterior cervical triangle is bounded by the inferior margin of the mandible, midline of the neck and anterior border of the sternocleidomastoid. It is further subdivided into four triangles:

• The submandibular triangle is bounded by the base of the mandible, and the anterior and posterior bellies of the digastric muscle. The mylohyoid and hyoglossus muscles form its floor, and it contains the submandibular glands and lymph nodes.
• The submental triangle is bounded by the two anterior digastric muscles and the body of the hyoid. The mylohyoid muscle forms its floor and it contains the submental lymph nodes.
• The muscular triangle is bounded by the midline of the neck, anterior border of the sternocleidomastoid and superior belly of the omohyoid muscle. The muscular triangle contains the infrahyoid muscles and thyroid gland.
• The carotid triangle is bounded by the anterior border of the sternocleidomastoid, superior belly of the omohyoid and the posterior belly of the digastric. The floor is formed by portions of the thyrohyoid, hyoglossus, and inferior and middle constrictors, and contains the upper portion of the carotid artery and its bifurcation. Portions of the hypoglossal and superior laryngeal nerves and ansa cervicalis may also traverse the carotid triangle.

The posterior cervical triangle is bounded by the posterior border of the sternocleidomastoid, the superior surface of the middle clavicle and anterior margin of the trapezius. It is further subdivided into supraclavicluar and occipital triangles:

• The supraclavicular triangle is bounded by the clavicle, inferior belly of the omohyoid and posterior border of the sternocleidomastoid muscle. Its floor is formed by the 1st rib, middle scalene and upper serratus anterior muscles, and it contains a portion of the subclavian artery and trunks of the brachial plexus.
• The occipital triangle is bounded by the posterior border of the sternocleidomastoid, anterior border of the trapezius and inferior belly of the omohyoid. The splenius capitis, levator scapulae, scalene and semispinalis capitis muscles contribute to its floor, and it contains the accessory nerve and lymph nodes.

Muscles

The anterolateral muscles of the neck may be subdivided into three subgroups, suprahyoid, infrahyoid and prevertebral. The suprahyoid muscles (anterior and posterior digastric, geniohyoid, mylohyoid, stylohyoid and thyrohyoid) function to elevate the hyoid (and larynx) or depress the mandible. The infrahyoid muscles (omohyoid, sternohyoid and sternothyroid) function to depress the hyoid (and larynx). The prevertebral muscles (longus capitis, longus colli, rectus capitis anterior and lateralis, and scalenus anterior, middle and posterior) function to flex, laterally flex and rotate the head and neck. The sternocleidomastoid muscle does not fit in with the other muscles and functions during flexion and contralateral rotation of the head and neck.

Innervation

Branches of the facial and mandibular nerves, and ventral rami of cervical spinal nerves innervate (motor, sensory and postganglionic sympathetic) the suprahyoid muscles. Branches of the ansa cervicalis innervate (motor, sensory and postganglionic sympathetic) the infrahyoid muscles. Branches of the ventral rami of cervical spinal nerves innervate (motor, sensory and postganglionic sympathetic) the prevertebral muscles. The accessory nerve (cranial nerve XI) (motor and postganglionic sympathetic) and branches of the cervical plexus (sensory and postganglionic sympathetic) innervate the sternocleidomastoid muscle.

Blood Supply

Branches of the superior thyroid and vertebral arteries, and thyrocervical trunk supply the structures of the anterior and lateral neck. Tributaries of the external jugular, internal jugular, vertebral and left brachiocephalic vein drain the anterior and lateral neck.

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