Level I - Submental and Submandibular

Level Ia - Submental

• Single midline zone within the submental triangle (between the two anterior bellies of digastric and the hyoid bone)
• Contains the submental lymph nodes
• Drains: anterior floor of mouth, lower lip, ventral tongue

Level Ib - Submandibular

• Located within the submandibular triangle
• Contains the submandibular lymph nodes, closely related to the facial vessels
• Drains: lateral oral cavity - lateral tongue, floor of mouth, buccal cavity

Level II - Upper Jugular Chain

• Uppermost nodes of the jugular chain, from the skull base to the inferior border of the hyoid bone
• First echelon nodes for the oropharynx; also drain oral cavity, nasopharynx, hypopharynx, larynx, and parotid gland
• Divided into IIa and IIb by the spinal accessory nerve

Level IIa

• Caudal to the spinal accessory nerve
• Most clinically significant subzone - presence of IIa disease mandates dissection of IIb

Level IIb (Suárez's Triangle)

• Cranial to the spinal accessory nerve
• Triangular area with apex at the junction of the posterior SCM border and the posterior belly of digastric

Level III - Middle Jugular Chain

• From the inferior border of the hyoid to the inferior border of the cricoid cartilage
• Drains: lower oropharynx, hypopharynx, and larynx

Level IV - Lower Jugular Chain

• From the inferior border of the cricoid to the clavicle
• Omohyoid muscle crosses the superior aspect of this level
• Drains: hypopharynx and larynx
• Clinically important: Virchow's node (supraclavicular metastasis from upper GI malignancy) is in level IV on the left side; infraclavicular primaries (bronchus, breast) can also metastasize here

Level V - Posterior Triangle

• Large area from the junction of trapezius and SCM (apex) down to the clavicle
• Anterior limit: posterior border of SCM; posterior limit: anterior border of trapezius
• Spinal accessory nerve runs across the roof; transverse cervical artery in the inferolateral aspect
• Subdivided at the level of the inferior border of the cricoid cartilage

Level Va

• Above the subdivision line
• Contains nodes related to the spinal accessory nerve
• Commonly involved in nasopharyngeal and cutaneous scalp primaries

Level Vb

• Below the subdivision line
• Contains nodes related to the transverse cervical artery and supraclavicular nodes

Level VI - Anterior/Central Compartment

• Single midline zone between the common carotid arteries laterally
• Superior border: inferior aspect of the hyoid
• Inferior border: innominate artery (right) / corresponding level (left)
• Contains: paratracheal, perithyroid, and precricoid (Delphian) nodes
• Drains: thyroid, glottis, subglottis, apex of piriform fossa, cervical oesophagus
• Note: dissection risks inadvertent parathyroid removal - leading to postoperative hypocalcaemia

Level VII - Superior Mediastinal

• Lymph nodes of the superior mediastinum, accessed via the neck or sternotomy
• May harbour metastasis from thyroid, subglottic, tracheal, or cervical oesophageal malignancies
• The thymic remnant is also found here

Quick Summary Table

• There are approximately 100 lymph nodes on either side of the neck, ranging from 3 mm to 3 cm (mean 1 cm)
• Lymph flows from superficial to deep, then cephalic to caudal
• This level system is the basis for selective neck dissection in head and neck oncology