A radical neck dissection includes the removal of level I to level V nodes, en bloc with the sternocleidomastoid muscle, internal jugular vein, and spinal accessory nerve. It is performed in patients with large, palpable cervical nodes contiguous with these structures. A modified radical neck dissection (also called a functional neck dissection) is usually possible despite the presence of palpable nodes: a thorough dissection of the nodes is performed, and clean planes are used to skeletonize and preserve one or more of these three anatomical structures. In selective node dissection, one or more nodal groups are omitted from the procedure of a radical or modified radical neck dissection on the perception that the omitted nodal groups are out of the direction of spread of the particular primary lesion in the head and neck area, or they are too far from palpably involved nodal groups. The dissection of a whole nodal group that contains normal-appearing nodes may indicate that the dissection is complete, as it is uncommon for tumor cells to bypass a whole nodal group in the line of spread and metastasize to the next group. A supra-omohyoid dissection is limited to the removal of level I to level III nodes; a lateral dissection includes the dissection of level II to level V nodes.

The theoretical basis of the sentinel node biopsy has been attributed to the orderly, sequential progression of the lymph flow through the regional nodes by tumor cells, but it is known that often the spread of a tumor within a nodal basin is not anatomically orderly, in the sense of involving successively all anatomically contiguous nodes. It is now considered a fact that cutaneous lymphatic vessels from a certain area of skin, as they approach the nodal basin, come together to form fewer, stouter lymphatic channels (usually one channel, or less often two or three), with each channel entering one lymph node—the sentinel node. By definition, then, a sentinel node is the first lymph node encountered by lymphatic channels draining a certain skin area, and therefore the first node to subject the lymphatic drainage from this particular area of skin to the filtering, clearing function of a lymph node—which includes the trapping of malignant cells. Lymph nodes are inefficient in destroying trapped malignant cells, however, often allowing their local growth and later passage into higher echelons of nodes and, at the base of the neck, into the bloodstream, although entry into the venous side of the bloodstream by tumor cells is also known to occur at the primary site. Removal of the sentinel node and careful pathologic examination should detect any focus of metastatic tumor if metastatic cells have lodged successfully in the regional nodal basin. Multiple sections through the sentinel node and the use of routine staining, immunohistochemistry, and the exquisitely sensitive method of reverse transcriptase polymerase chain reaction (RT-PCR) (though its clinical significance is disputed) should help to detect the presence of any tumor focus. In a large series dealing with all nodal basins, 72 % of patients had one sentinel node, 20 % had two sentinel nodes, and 8 % had three or more [1].