Evaluation of the cervical lymphoid tissue and lymph nodes is an important topic but is also the source of a lot of confusion. Large lymph nodes can be reactive whereas small ones can harbor metastases. They can be measured in short or long axis. The range of normal lymph node size varies by location. Measurements in the axial plane differ from those in the coronal or sagittal plane as they may be elongated in the cranio-caudal axis. There are cervical lymph node 'levels' but some important cervical lymph nodes don't belong to any level at all. The size of lymph nodes and lymphoid tissue can vary by age.

Waldeyer's ring is a ring of MALT in the oropharynx and nasopharynx predominantly comprised of the nasopharyngeal tonsil (adenoid), paired palatine tonsils, and lingual tonsil. This tissue is important as it can be affected by important malignancies such as oropharyngeal squamous cell carcinoma, lymphoma, and nasopharyngeal carcinoma and infections. Viral infections may produce diffuse enlargement. Bacterial infection can be a source of tonsillitis and pyogenic abscess.

Several important features of the cervical lymph nodes merit attention including: size, morphology, shape, margins, location, and-importantly-clinical context. Knowledge of normal drainage routes and results of metabolic imaging (typically FDG PET) are useful.

What is a normal sized cervical lymph node? When is a cervical lymph node suspicious for malignancy? It depends. If the clinical setting is inflammatory such as cellulitis, retropharyngeal abscess, parotitis, etc. enlarged lymph nodes are likely reactive. In the setting of malignancy, small lymph nodes may be pathologic, especially if there are other abnormal features.

While lymph nodes in most areas are measured in short axis, cervical lymph nodes can be measured in either short axis or long axis depending on preference. Various cut-offs of 'normal' have been studied and various ones can be used, trading off sensitivity for specificity. An understanding of your institutional customs and the limitations of measurements in addition to specifying the method of measurement in radiology reports are vital.

At our institution, most neuroradiologists use 1cm long axis on axial images as a cut-off of normal size in most locations when malignancy is suspected. But, jugulodigastric lymph nodes (just posterior to the submandibular gland) can normally measure up to about 1.5cm long axis. Retropharyngeal lymph nodes are smaller, especially in adults.

Key abnormal morphologic features to assess for include loss of a normal fatty hilum, cystic change/necrosis, calcifications, and contrast enhancement. A round configuration rather than the typical ‘bean’ or oval shape can also signify pathology. Irregular margins and infiltration of adjacent fat can indicate extracapsular tumor spread. Spread and invasion of other structures, especially blood vessels, are important to assess. Carotid artery invasion can be difficult to ascertain, but the greater degree of circumferential involvement with loss of intervening fat plane (typically at least 180 degrees), the more likely invasion is.

Key locations include the ‘levels’ I-VII and other areas without a ‘level’ designation including facial, parotid, post-auricular, and occipital lymph nodes. A typical neck exam may also include supraclavicular, upper mediastinal, axillary, and subpectoral lymph nodes.

Most head and neck cancers employ the same N stage grading system. The key elements of lymph node staging can be recalled by the acronym ‘SNL’ standing for Size, Number, and Laterality. The ‘obvious’ abnormal lymph node isn’t necessarily the most important one to characterize other than its size (0-3cm, 3-6cm, > 6cm); it is a second ipsilateral abnormal lymph node (number) and a contralateral abnormal lymph node (laterality) that are key.

Reference

Hoang JK et al. Evaluation of cervical lymph nodes in head and neck cancer with CT and MRI: tips, traps, and a systematic approach. AJR 2013;200:W17-W25

Hellings P et al. The Waldeyer's ring. Acta Otorhinolaryngol Belg 2000;54(3):237-41

Necrotic found in certain pathology, such as HPV + oropharyngeal carcinoma metastases.