level IIa: anterior, lateral, or medial to the vein or posterior to the internal jugular vein and inseparable from it.Lymph nodes from level II (upper jugular nodes, deep cervical chain) extend from the skull base to the level of the bottom of the body of the hyoid bone. They are posterior to the back of the submandibular gland and anterior to the back of the sternocleidomastoid muscle. IB (Submandibular nodes) lie on each side lateral to the level IA nodes and anterior to the back of each submandibular gland.IA (Submental nodes) lie between the medial margins of the anterior bellies of the digastric muscles.Level I nodes lie above the hyoid bone, below the mylohyoid muscle, and anterior to a transverse line drawn on each axial image tangent to the posterior surface of the submandibular gland on each side of the neck This system is not inclusive of several important groups, however, such as the supraclavicular, parotid and retropharyngeal space nodes. It has been adapted to radiological imaging for some boundaries (ex: boundary that separates sublevel IB from sublevel IIA was defined as the border of the stylohyoid muscle and adapted as the vertical plane defined by the posterior edge of the submandibular gland). The neck dissections are grouped into four broad categories of radical neck dissection, modified radical neck dissection, selective neck dissection (this group is subclassified according to which node levels are removed) and extended neck dissection.
These systems employ the American Joint Committee on Cancer staging system and traditionally established node levels. The lymph node levels of the neck (Robbins) is the most often employed and was published in 1991 by the American Head and Neck Society and the American Academy of Otolaryngology-Head and Neck Surgery.
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