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. The system was revised in 2002 and 2008. These systems employ the American Joint Committee on Cancer staging system and traditionally established node levels. 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. 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).
This system is not inclusive of several important groups, however, such as the supraclavicular, parotid and retropharyngeal space nodes.
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
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.
Nb: any nodes that lie medial to the internal carotid artery are retropharyngeal and not level II
Lymph node from level III (middle jugular nodes) extend from the level of the bottom of the body of the hyoid bone to the level of the bottom of the cricoid arch. They are located around the middle third of the internal jugular vein.
The anterior (medial) boundary is the lateral border of the sternohyoid muscle and the posterior (lateral) boundary is the posterior border of the sternocleidomastoid muscle (they also lie lateral to the medial margin of either the common carotid artery or the internal carotid artery, separating them from the level VI that is medial).
The level IV (Lower jugular nodes) extends from the level of the bottom of the cricoid arch to the level of the clavicle.
Nodes lie anterior to a line connecting the back of the sternocleidomastoid muscle and the posterolateral margin of the anterior scalene muscle and are also lateral to the medial margin of carotid arteries.
The nodes from level V (posterior cervical nodes) lie posterior to the back of the sternocleidomastoid muscle from the skull base to the level of the bottom of the cricoid arch and posterior to a line connecting the back of the sternocleidomastoid muscle and the posterolateral margin of the anterior scalene muscle from the level of the bottom of the cricoid arch to the level of the clavicle. They also lie anterior to the anterior edge of the trapezius muscle.
The lymph nodes from level VI (anterior cervical node; superior visceral nodes; prelaryngeal; pretracheal; Delphian node) lie between the carotid arteries from the level of the bottom of the body of the hyoid bone to the level of the manubrium (or innominate vein). They are anterior to visceral space and anterior to levels III and IV
If the term level VII is to be used, it should refer to the extension of the chain of paratracheal nodes below the suprasternal notch (the dividing line between levels VI and VII) to the level of the innominate artery only. Alternatively, these nodes might be defined as the superior mediastinal lymph nodes above the level of the innominate artery.