Figure 2

A. Level I : (Figure 2)
Requisite Anatomy

The Level I lymph nodes include all nodes above located below the mylohyoid muscle, above the hyoid bone and anterior to a transverse line drawn connecting posterior edge of the sub-mandibular gland. The Level I nodes are subclassified into Levels IA and IB(22, 23)

Level IA:	Represents Level I nodes that lie between the medial margins of the anterior bellies of the digastric muscles, ("submental nodes")(22, 23)
Level IB:	Represents Level I nodes that are lateral to the anterior belly of the digastric muscles. ("submandibular" nodes)(22, 23)

Figure 3

B. Level II: (Figure 3)
Requisite Anatomy:

The Level II lymph nodes extend from the skull base, at the lower level of the bony margin of the jugular fossa, to the lower margin of the body of the hyoid bone. Level II nodes are located anterior to a transverse line connecting the posterior edge of the sternocleidomastoid muscles and posterior to a transverse line connecting the posterior edge of the submandibular glands(22, 23).

Level IIA:	These are Level II lymph nodes that are located anterior, medial or lateral to the internal jugular vein. These also define Level II lymph nodes that are posterior to the internal jugular vein but directly abut the vein(22, 23).
Level IIB:	These nodes are posterior to the internal jugular vein and have an identifiable fat plane between the lymph node and the vein(22, 23).

Figure 4

C. Level III: (Figure 4)
Requisite Anatomy:

Level III nodes lie between the level of the lower body of the hyoid bone and the level of the lower margin of the cricoid cartilage arch and are anterior to a line connecting the posterior margins of the sternocleidomastoid muscle. These nodes are lateral to the medial margin of either the common carotid artery or the internal carotid artery(22, 23).

Figure 5

D. Level IV: (Figure 5)
Requisite Anatomy:

Level IV lymph nodes are located between the lower margin of the cricoid cartilage and the level of the clavicle and are lateral to the medial margin of the common carotid artery. These nodes are anterior and medial to an oblique line drawn connecting the posterior edge of the sternocleidomastoid muscle and the posterolateral edge of the anterior scalene muscle(22, 23).

Figure 6

E. Level V: (Figure 6)
Requisite Anatomy:

Level V nodes are located between the skull base and the clavicle. However, unlike other Levels, these nodes are behind the sternocleidomastoid muscle and anterior to the trapezius muscle(22, 23).

Level VA:	These nodes lie between the skull base and the level of the lower margin of the cricoid cartilage arch and are behind the posterior edge of the sternocleidomastoid muscle(22, 23).
Level VB:	These lymph nodes are situated between the lower margin of the cricoid cartilage and the clavicle. They are behind an oblique line connecting the posterior edge of the sternocleidomastoid muscle and the posterolateral edge of the anterior scalene muscle(22, 23).

Figure 7

F. Level VI: (Figure 7)
Requisite Anatomy:

Level VI nodes lie inferior to the lower body of the hyoid bone and superior to the top of the manubrium. These nodes are located between the medial margins of the left and right common or internal carotid arteries(22, 23).

Figure 8

G. Supraclavicular Nodes (Figure 8)
Requisite Anatomy:

The supraclavicular nodes are located at or caudal to the level of the clavicle and lateral to the carotid arteries on each side of the neck(22, 23).

Figure 9

H. Level VII: (Figure 9)
Requisite Anatomy:

Level VII nodes lie caudal to the top of the manubrium in the superior mediastinum, between the medial margins of the left and right common carotid arteries. These superior mediastinal nodes extend caudally to the level of the innominate vein(22, 23).