Anatomic considerations in the treatment of cancers of the head and neck must include a thorough understanding of the neural, vascular, and (especially) lymphatic structures of the neck. Detailed anatomic studies have described the organization of the lymphatic drainage of the UADT. Specific regions of the head and neck and the tumors that arise there have lymphatic drainage that is consistent and predictable. There are 12 major groups of lymph nodes (six each bilaterally) in the head and neck (

Figure 90-1) although only levels I to V play a major role in SCCHN. Primary and secondary echelons of lymph node drainage have been derived for each major region of the head and neck mucosa. A standard rule of thumb is that the lymphatic drainage for any particular region is predicted by the arterial supply of that region. The lip, cheek, and anterior gingiva drain to submandibular and submental lymph node groups.

In addition, the cheek and upper lip also drain to inferior parotid nodes, while the posterior gingiva and palate drain to the internal jugular chain and lateral retropharyngeal groups. Lymphatic drainage for the tongue drains to the internal jugular, subdigastric, omohyoid, submandibular, and submental nodal groups. Midline lesions can drain bilaterally. Although metastases to the lower neck nodes are infrequent from the oral cavity, generally the more anterior the tumor location in the tongue, the more likely it is that metastases also will spread to lower jugular nodes. The floor-of-mouth drainage is similar to that of the tongue. The upper portion of the pharynx drains directly to the upper cervical lymph nodes along the internal jugular chain. The oropharynx and tonsil drain through the peripharyngeal space to the midjugular region, particularly to the jugulodigastric nodes. The regions of the hypopharynx and larynx drain primarily along the routes of their vascular supply to either the deep cervical nodes along the midjugular (upper pharynx, larynx) or the deep nodes along the lower jugular and peritracheal region (lower pharynx, larynx).

For the purposes of local treatment, the various lymph node groups of the neck have been divided into levels (

Figure 90-2).

Level I includes the submental group of nodes (IA), located within the triangle bounded by the anterior belly of the digastric muscles and the hyoid bone, and the submandibular group (IB), bounded by both bellies of the digastric muscle and the body of the mandible. Level II nodes consist of the upper jugular lymph nodes located in proximity to the upper third of the internal jugular vein and extending from the skull base to the level of the bifurcation of the carotid artery. The anterior and posterior boundaries are the lateral border of the sternohyoid muscle and the posterior border of the sternocleidomastoid muscle, respectively.

Level II is further divided into those lymph nodes located anteroinferior to the vertical plane of the spinal accessory nerve (IIA) and those lymph nodes posterosuperior to the nerve (IIB). Level III nodes include those nodes located adjacent to the middle third of the internal jugular vein from the carotid bifurcation to the omohyoid muscle (level of the cricothyroid notch). Anterior and posterior boundaries are the same as level II. Level IV nodes include the lower jugular group extending from omohyoid muscle to the clavicle below. Level V nodes are those located along the lower half of the spinal accessory nerve and transverse cervical artery. This level is bounded by the anterior border of the trapezius muscle, the posterior border of the sternocleidomastoid muscle, and the clavicle below. This level, too, is further divided into VA and VB nodes, with VA nodes being those nodes located above the plane along the inferior edge of the cricoid and iincluding the chain of nodes along the spinal accessory nerve posterior to the sternocleidomastoid muscle. VB nodes are the nodes below the cricoid plane and include the nodes along the transverse cervical artery and all of the supraclavicular fossa.