Level I: Submental and Submandibular Groups
This consists of the submental group of lymph nodes within the triangle bounded by the ante rior belly of digastric and hyoid bone, and the submandibular group of nodes bounded by the posterior belly of digastric and body of the mandible.
Level II: Upper Jugular Group
This consists of the lymph nodes located around the upper third of the internal jugular vein and adjacent spinal accessory nodes extending from the skull base down to the level of the carotid bifurcation where the digastric muscle crosses the internal jugular vein. This point relates to level of the hyoid bone on a computed tomographic (CT) scan. It contains the junc-tional and sometimes the jugulodigastric nodes. Level II is further subdivided into level IIA, which is in front of the accessory nerve, and level IIB, which is behind. This is known as Suarez's triangle and contains Suarez's fat pad .
Level III: Middle Jugular Group
This consists of lymph nodes located around the middle third of the internal jugular vein extending from the carotid bifurcation superiorly (bottom of level II) down to the upper part of the cricoid cartilage (seen on a CT scan) and represents the level where the omohyoid muscle crosses the internal jugular vein. It usually contains the jugulo-omohyoid nodes and may contain the jugulodigastric node.
Level IV: Lower Jugular Group
This consists of lymph nodes located around the lower third of the internal jugular vein extending from the cricoid cartilage down to the clavicle inferiorly. It may contain some jugulo-omohyoid nodes.
Level V: Posterior Triangle Group
These nodes are located along the lower half of the spinal accessory nerve and the transverse cervical artery. Supraclavicular nodes are also included in this group. The posterior limit is the anterior border of the trapezius and the anterior border is the anterior border of ster-nomastoid. Level V is further subdivided into level VA above the omohyoid muscle and level VB below.
Level VI: Anterior Compartment Group (Visceral Group)
This consists of lymph nodes surrounding the midline visceral structures of the neck extending from the hyoid bone superiorly to the suprasternal notch inferiorly. The lateral border on each side is the medial border of the ster-nomastoid muscle. It contains the parathyroids, the paratracheal and pretracheal, and the peri-laryngeal and precricoid lymph nodes.
This contains the lymph nodes in the upper anterior mediastinum as well as the thymus gland. The lymph node levels are shown in Figure 13.2.
The above drainage patterns apply only to the non-violated neck. Once the natural history of the disease is altered, lymph node metastases can occur anywhere. This explains why the operation of selective neck dissection is only applicable in the previously untreated neck. An incision in the neck for a nodal biopsy can alter patterns of lymphatic drainage for up to 1 year following surgery. Further shunting of lymph with opening up of abnormal channels occurs when more extensive surgery and radiotherapy are undertaken, and once a malignant lymph node is palpable, there may be shunting of cells to the contralateral neck. All of these factors play a part in the management of neck disease and need to be borne in mind when assessing anatomical images following previous surgery.
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