What is the basic normal anatomy and Ultrasound imaging appearance of cervical lymph nodes?
The American Joint Committee on Cancer (AJCC) classification system of nodal location is recommended when reporting nodal location on imaging exams because it more accurately corresponds with surgical and pathology reporting.
This classification system divides the neck into three compartments, the central compartment and the paired lateral compartments, each having multiple nodal levels.
The distinction of the lateral and central compartments is very important for surgical planning, because abnormal nodes in the lateral neck cannot be accessed from the central compartment and vice versa.
The lateral compartment nodes (levels I through V) are found in the submental region (level I), along the jugulocarotid vascular bundle (levels II through IV) and posterior to the sternocleidomastoid muscle (V).
The jugulocarotid or anterior cervical nodes are further classified as follows: level II lymph nodes are located above the level of the hyoid bone to the base of the skull; level III nodes are between the levels of the hyoid bone and the cricoid cartilage; and level IV nodes are below the level of the cricoid cartilage extending to the clavicle.
Level V nodes are in the posterior neck, posterior to the lateral border of the sternocleidomastoid muscle. The central compartment contains the thyroid and parathyroid glands, is bordered laterally by the carotid sheaths, and extends superiorly to the hyoid bone and inferiorly into the upper mediastinum.
The central compartment level VI nodes are located anterior to the thyroid gland (prelaryngeal nodes), posterior and inferior to the thyroid gland, and adjacent to the trachea (paratracheal nodes). Central compartment nodes that are below the level of the suprasternal notch are level VII nodes.
Normal lymph node morphology is characterized by a hypoechoic outer cortex with densely packed lymphocytes and a central hyperechoic hilum containing lymphatic sinuses and vessels.
The size of normal lymph nodes may vary depending on the neck region, with submandibular or level II lymph nodes tending to be larger, perhaps due to reactive hyperplasia from repeated oral cavity inflammation, with a long axis up to 2 cm. The short axis diameter varies less and is typically less than 8 mm in level II and less than 5 mm in the other cervical regions