Surgical Anatomy

This section describes, in an orderly fashion, the anatomical structures found by the surgeon in the course of functional and selective neck dissection.

The Skin

The vascular supply of the skin of the neck is provided by descending branches of the facial, submental, and occipital arteries and by ascending branches of the transverse cervical and suprascapular arteries.

The surgeon must take into consideration the blood supply of the skin when planning the incision. Access to the primary tumor and incisions for lymph node dissection should be designed to avoid skin complications. Every effort should be made to design a skin incision that crosses the carotid artery only once on each side, with the crossing point located as far as possible from the carotid artery bifurcation. Whenever possible, incision trifurcations should be avoided.

Platysma Muscle

The platysma is a wide, thin sheet of muscle located in the anterolateral aspect of the neck, immediately below the skin and over the superficial layer of the deep fascia (Fig. 2-11). It runs obliquely from the skin and fascia of the pectoralis and deltoid muscle to the lower border of the mandible and skin of the lower face. The platysma muscle is innervated by the cervical branch of

Platysma Muscle Flap
Figure 2-10 Topographic distribution of the posterior triangle of the neck. oc, occipital triangle; om, omoclavicular triangle.

the facial nerve; thus, preservation of this nerve should be attempted to prevent the skin from falling away in slack folds.

Raising the skin flap between the platysma muscle and the superficial layer of the deep cervical fascia, on which it rests, allows the identification of the following anatomical structures: external and anterior jugular vein, great auricular nerve, and marginal branch of the facial nerve.

External Jugular Vein

The external jugular vein begins near the angle of the mandible, within the parotid gland, by the union of the posterior division of the retromandibular vein (posterior facial vein) with the posterior auricular vein (Fig. 2-12). It then runs obliquely across the sternocleidomastoid muscle, in the superficial layer of the cervical fascia, accompanied by the great auricular nerve in its upper half. The vein pierces the deep fascial layer at the posterior border of the muscle, about 5 cm above the clavicle. It usually terminates in the subclavian vein, but it may also end in the internal jugular vein. It may be double or have a bifid termination. Sometimes the external jugular vein is very small and may even be absent. In these cases the anterior jugular vein, the internal jugular vein, or both, are usually enlarged. Tributaries and communicating branches to the external jugular vein include the posterior auricular, occipital, posterior external jugular, transverse cervical, suprascapular, and anterior jugular veins.

Anterior Jugular Vein

The anterior jugular vein begins below the chin and communicates with the submental, mental, inferior labial, and hyoid veins (Fig. 2-13). It descends near the midline, within the superficial fascia. Just above the clavicle it turns laterally, piercing the superficial layer, where it passes deep to

Strap Muscles

the sternocleidomastoid muscle and opens into the external jugular vein just before its junction with the subclavian vein. As it turns laterally, the anterior jugular vein sends a branch across the midline to join the anterior jugular vein of the opposite side, forming the jugular venous arch.

Strap Muscles

The strap muscles, also known as infrahyoid muscles, lie beneath the superficial layer of the cervical fascia (Fig. 2-14). Their function is primarily related to the stability of the hyoid bone and

Goat External Jugular Vein
Figure 2-12 External jugular vein. rm, retromandibular or posterior facial vein; pa, posterior auricular vein; f, facial vein; EJ, external jugular vein.

Figure 2-13 Superficial venous system of the neck. AJ, anterior jugular vein; ej, external jugular vein; va, jugular venous arch; kv, communicating vein (Kocher's vein).

Figure 2-13 Superficial venous system of the neck. AJ, anterior jugular vein; ej, external jugular vein; va, jugular venous arch; kv, communicating vein (Kocher's vein).

Vein KocherSternohyoid Muscles
Figure 2-14 Strap muscles. sh, sternohyoid muscle; oh, omohyoid muscle; st, sternothyroid muscle; th, thyrohyoid muscle.

larynx during swallowing and speaking. They are innervated by cervical nerve fibers that join the hypoglossal nerve to reach the muscles by means of the ansa cervicalis.

The sternohyoid muscle is the most superficial and medial of the strap muscles. It originates in the body of the hyoid bone and attaches inferiorly to the manubrium of the sternum and medial end of the clavicle.

The omohyoid muscle extends between the hyoid bone and the superior margin of the scapula, near the transverse ligament of the scapula. It has two bellies united by an intermediate tendon located beneath the sternocleidomastoid muscle. This tendon is held in place by a strong portion of the pretracheal layer of the cervical fascia, which binds it to the posterior surface of the clavicle. The inferior belly of the omohyoid muscle is partly covered by the trapezius and crosses the scalene muscles, brachial plexus, internal jugular vein, carotid artery, sternothyroid, and thyrohyoid muscles. The superior belly of the omohyoid ascends posterolateral to the sternohyoid muscle, running parallel to it in the last part.

The sternothyroid muscle takes its origin from the dorsal surface of the manubrium and inserts by short tendinous fibers into the oblique line on the lamina of the thyroid cartilage. It lies superficial to the brachiocephalic vein, the trachea, and the thyroid gland.

The thyrohyoid muscle continues the sternothyroid muscle superiorly. It is largely covered by the omohyoid and sternohyoid muscles. It takes its origin from the oblique line on the lamina of the thyroid cartilage and inserts into the inferior margin of the lateral third of the body of the hyoid bone.

Cervical Plexus: Superficial Branches

The cervical plexus is a neural network formed by the communications between the ventral rami of the superior four cervical nerves, which form loops with one another. It has both deep and superficial branches.

The superficial cutaneous branches of the cervical plexus emerge around the midportion of the posterior border of the sternocleidomastoid muscle (Erb's point) to supply the skin of the neck and scalp between the auricle and the external occipital protuberance (Fig. 2-15). These superficial branches diverge into ascending, descending, and transverse ramifications.

Cervical Plexus
Figure 2-15 Superficial branches of the cervical plexus. lo, lesser occipital nerve; ga, great auricular nerve; tc, transverse cervical nerve; sc, supraclavicular nerve; ac, Superior root of the ansa cervicalis (descendens hypoglossi); Erb's point.

The ascending branches include the lesser occipital nerve (C1, C3) and the great auricular nerve (C2, C3). The lesser occipital nerve ascends along the posterior margin of the sternocleidomastoid muscle to the mastoid process. It divides into auricular, mastoid, and occipital terminal branches, to provide sensory innervation to these areas. The great auricular nerve crosses at a point superficial to the sternocleidomastoid muscle and passes toward the angle of the mandible, dividing into mastoid, auricular, and facial terminal branches.

The transverse cervical nerve (C2, C3) passes transversely across the sternocleidomastoid muscle and divides into superior and inferior terminal twigs for the skin of the neck.

The supraclavicular nerve (C3, C4) constitutes the main descending branch of the cervical plexus. It arises as a single trunk and divides into medial, intermediate, and lateral branches, supplying the skin over the anterior aspect of the chest and shoulder. The medial and lateral supraclavicular nerves also supply the sternoclavicular and acromioclavicular joints, respectively.

The ansa cervicalis is part of the cervical plexus. It is formed by the union of the descendens hypoglossi, also known as superior ramus of the cervical loop, and the inferior ramus of the cervical loop. The superior ramus of the cervical loop is formed by the union of the ventral rami of the first and second cervical nerves. This nerve travels for some time in the sheath of the hypoglossal nerve. This is the reason why it was called the descendens hypoglossi, but none of the fibers are derived from the hypoglossal nucleus. It arises as the hypoglossal nerve crosses the internal carotid artery and runs inferiorly to join the inferior ramus of the cervical loop. The inferior ramus comes from the loop of the ventral rami of the second and third cranial nerves. The superior and inferior rami interlace to form the ansa cervicalis. The ansa cervicalis may be found between the sternocleidomastoid muscle and the common carotid artery, superficial to the internal jugular vein.

Marginal Mandibular Branch of the Facial Nerve

This thin branch of the facial nerve provides motion to the lower lip and chin. A precise knowledge of its location is fundamental during functional and selective neck dissection because it runs parallel to the superior border of the surgical field. The nerve courses deep to the superficial layer of the cervical fascia, but superficial to the adventitia of the anterior facial vein (Fig. 2-16). This is an important key to help preservation of the nerve at surgery.

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