Chad A. Zender, Evan McBeath and Pierre Lavertu

Introduction

Neck dissection has been a standard method of removing at-risk or involved cancerous lymph nodes in the head and neck for more than 100 years. Crile first described the radical neck dissection in the early 1900s, but modifications by Bocca and others helped reduce the morbidity associated with lymph node removal, allowing for nerve and structure preservation when oncologically sound. This chapter discusses one of these modifications in detail, the selective or supraomohyoid neck dissection. A selective neck dissection, including levels I through III, is typically used for malignancies of the oral cavity in patients with N0 disease. When a larger nodal burden is present, an extended (levels I-IV) selective neck dissection or a modified radical neck dissection (levels I-V) is indicated. Lesions in the oral cavity that approach or cross the midline require treatment of both sides of the neck.

Neck Anatomy for Surgical Planning

Understanding the regional lymphatic drainage pathways is critical when planning which type of neck dissection will be employed (Fig. 1-1). A supraomohyoid neck dissection is performed when treating patients who are at risk for micrometastasis in levels I, II, and III. The boundaries of levels I (submental and submandibular), II (upper jugular nodal chain), and III (midjugular nodal chain) are defined as follows:

Incision Planning and Patient Positioning for Neck Dissection

Positioning for a neck dissection includes extending the neck and turning the patient’s head away from the surgeon. This usually entails placing a shoulder roll under the patient to facilitate adequate extension.

Various types of incisions may be employed. The authors typically use a “hockey stick” incision that extends from the mastoid tip down the middle of the SCM and then across the neck in a crease, which is usually over the lowest level that will be surgically treated. The incision can be brought across the midline to the contralateral neck in the same manner, creating an “apron” incision, which will allow access to both sides of the neck when indicated to treat bilateral neck disease.

Level Ia-Ib Neck Dissection

After flap elevation, expose the anterior belly of the digastric muscle by making a midline incision from below the mentum to the hyoid bone. It is important to include all the fibrofatty contents from the contralateral medial edge of the digastric muscle. The elevation continues to the medial aspect of the submandibular gland to complete the level Ia dissection (Fig. 1-3).

The marginal mandibular branch of the facial nerve can be located approximately 1 cm inferior to angle of the mandible. Incisions brought across the neck are always two fingerbreadths below the angle to prevent inadvertent injury to this nerve. The marginal mandibular branch of the facial nerve lies between the superficial layer of the deep cervical fascia and the adventitia investing the anterior facial vein. The superficial layer of the deep cervical fascia is incised at the inferior border of the submandibular gland. It must be elevated and may be tacked to the platysma muscle to aid in elevation.

Care must be taken to preserve the marginal mandibular branch of the facial nerve and reflect it superiorly, along with the superficial layer of the deep cervical fascia, and to remove any submandibular retrovascular (perifacial) lymph nodes in the area. This is accomplished by developing a plane between the vein and superficial layer of the deep cervical fascia, keeping the fat pad that contains the facial nodes down in the specimen, along with the submandibular gland, and elevating and protecting the nerve.

At this point the anterior belly of the digastric muscle is isolated, and the gland and fibrofatty contents of level Ia are brought posteriorly across the mylohyoid muscle.

Retract the mylohyoid muscle; identify and preserve the lingual and hypoglossal nerves; then identify, ligate, and divide the submandibular duct, submandibular ganglion, and corresponding vasculature. Level I is released and left pedicled by the inferior fibrofatty attachments to levels II and III (Fig. 1-3).

Level II-III Neck Dissection

Identify the posterior belly of the digastric muscle, creating the digastric tunnel back to the mastoid tip under the SCM (Fig. 1-4).

Incise the investing fascial layer along the anterior border of the SCM, ligating and dividing the external jugular vein in the process. An attempt should be made to preserve the greater auricular nerve, if not involved with disease.

Unwrap the SCM from its investing fascia. This is accomplished along a broad, superior-to-inferior plane, from the digastric muscle superiorly to the omohyoid muscle inferiorly.

Identify the spinal accessory nerve at its entrance into the SCM, and trace it under the posterior belly of the digastric muscle. The spinal accessory nerve typically passes lateral to the internal jugular vein just before diving under the posterior belly of the digastric muscle. The nerve will occasionally bisect or run deep to the jugular vein.

The spinal accessory nerve is released from the surrounding soft tissue, and then level IIb is released from the skull base, the back of the jugular vein, the SCM, and the deep cervical fascia. Level IIb is left attached to IIa and brought under the spinal accessory nerve.

Once the investing fascial layer is elevated off the SCM down to the level of the deep cervical rootlets, the dissection is taken medially across the rootlets from the omohyoid muscle to the spinal accessory nerve superiorly. Care must be taken to avoid injuring the spinal accessory nerve in this area as it exits the SCM posteriorly (Fig. 1-5).

Dissect levels II and III medially in a plane lateral to the cervical rootlets and the carotid sheath, which invests the carotid artery, internal jugular vein, and vagus nerve.

Once the elevation reaches the jugular vein, the fascia from the internal jugular vein is unwrapped. Branches of the vein may be ligated and divided as the specimen is brought medially. The ansa cervicalis will be transected during the inferior dissection as the specimen is brought across the jugular vein to the lateral aspect of the strap muscles. Superiorly, the hypoglossal nerve, which runs lateral to the carotid artery and medial to the jugular vein, must be protected under the digastric muscle. The ansa hypoglossi will likely need to be transected as the specimen is brought medially to the hyoid bone and strap musculature.

The specimen is then dissected away from the hypoglossal nerve and posterior belly of the digastric muscle until it can be easily removed. The anterior dissection will meet with the posterior dissection as the specimen is brought across the strap muscles, carotid artery, and jugular vein (Fig. 1-5).

Suggested Readings