Secondly, suppurative nodes frequently show central areas of low attenuation indicating the formation of pus. The location of the low attenuation focus is of help as necrosis is generally situated centrally while fat is usually deposited around the hilum. Density measurements are of limited value in small lesions because of partial volume averaging. Firstly, fat deposition may produce a low attenuation focus in the suspected node on computed tomography (CT). Nodal necrosis may be confused in two conditions. The detection of nodal necrosis is therefore most useful if the necrotic nodes are less than 10 mm and there are no other abnormal nodes. In general, the frequency of nodal necrosis increases with nodal size. These nodes are already by size criterion considered as nodes affected by metastasis ( Fig. This is because most nodes with nodal necrosis are larger than 10 mm. Although this sign is highly specific for metastatic disease it is of limited usefulness in clinical practice. The presence of nodal necrosis, irrespective of size, indicates metastatic involvement. On the other hand, 23% of nodes that show extracapsular spread measure less than 10 mm. However, 20% of nodes that exceed 10 mm harbour no metastatic deposits and histologically show only hyperplasia. Nodes larger than 10 mm are conventionally considered abnormal. Group VI nodes are anteriorly located: between the hyoid bone superiorly, the suprasternal notch inferiorly and between the carotid sheaths laterally ( Fig. Group V nodes can be identified on axial images posterior to the posterior margin of the sternocleidomastoid muscle. Group V nodes are found in the posterior triangle ( Fig. 4), and Group IV nodes are located below the cricoid cartilage ( Fig. 3), Group III nodes are found between the hyoid bone and cricoid cartilage ( Fig.
Hence, Group II nodes are located above the hyoid cartilage ( Fig. Groups II, III and IV are internal jugular (deep cervical) nodes and they are divided into these three groups by two landmarks: the hyoid bone and the inferior border of the cricoid cartilage. Group IB (submandibular) nodes are found in the submandibular space, around the submandibular gland ( Fig. These levels are Ia, Ib, II, III, IV, V, VI, VII, VIII, IX, X.In practical terms, the Group IA (submental) nodes are located in the submental space, between the anterior bellies of the digastric muscles ( Fig. The lymph nodes of the neck are further classified by level. These include the nasopharynx, pharyngeal wall, base of the tongue, soft palate, and larynx. Conversely, most structures drain ipsilaterally, except in the case of structures situated at the anatomic midlines. On the right side, they flow directly into the lymphatic duct. On the left side, they drain either directly into the vasculature via the jugulo-subclavian venous confluence or directly into the thoracic duct. From there it moves into the spinal accessory chain adjacent to the spinal accessory nerve, or cranial nerve XI, and then meets the supraclavicular chain. This lymphatic drainage originates at the base of the skull, then proceeds to the jugular chain adjacent to the internal jugular vein. These lymphatic chains are strongly lateralized and typically do not directly communicate between left and right in the absence of a pathologic process. Aponeuroses bind them together with the muscles, nerves, and vessels of the head and neck. The head and neck contains a rich and elaborate lymphatic network of more than 300 nodes and their intermediate channels. A detailed understanding of the principle lymphatic nodal levels of the neck is required, including their anatomical configuration and boundaries, patterns of drainage, and risk of metastatic involvement in the context of malignancy. This knowledge is especially crucial in guiding the approach to proper locoregional therapy, whether by surgery or irradiation. As such, intimate knowledge of the anatomic relationships of the lymphatic nodal levels and the structures they drain is critical in the delivery of appropriate therapy in many patients with cancers of the head and neck. The involvement of specific nodal groups is an indicator of pathologically-affected organs and tissues, especially in the context of malignancy. Lymphadenopathy is a significant clinical finding associated with acute infection, granulomatous disease, autoimmune disease, and malignancy. It is inclusive of osseous, nervous, arterial, venous, muscular, and lymphatic structures. The head and neck, as a general anatomic region, is characterized by a large number of critical structures situated in a relatively small geographic area.