Cervical lymph nodes
Cervical lymph nodes are lymph nodes found in the neck. Of the 800 lymph nodes in the human body, 300 are in the neck. Cervical lymph nodes are subject to a number of different pathological conditions including tumours, infection and inflammation. Classification. There are approximately 300 lymph nodes in the neck, and they can be classified in a number of different ways. History. The classification of the cervical lymph nodes is generally attributed to Henri Rouvière in his 1932 publication "Anatomie des Lymphatiques de l'Homme" Rouviere described the cervical lymph nodes as a collar which surrounded the  upper aerodigestive tract, consisting of submental, facial, submandibular, parotid, mastoid, occipital and retropharyngeal nodes, together with two chains that run in the long axis of the neck, the anterior cervical and postero-lateral cervical groups. However, this system was based upon anatomical landmarks found in dissection, making it imperfectly suited to the needs of clinicians, which led to new terminology for the lymph nodes that could be palpated. The most commonly used system is one based on a classification of the lymph nodes into numbered groupings, devised at the Memorial Sloan Kettering Cancer Center in the 1930s. This has been  variously modified since. In 1991, the American Academy of Otolaryngology published a standardised version of thisto provide a uniform approach to neck dissection that was updated in 2002, including the addition of sub-levels, e.g. IIA and IIB. Modern systems. More recently, classification systems have been proposed organized around what can be observed via diagnostic imaging. In addition to the American Academy of Otolaryngology, systems have been devised by the American Joint Committee on Cancer (AJCC). The AJCC system from the 7th edition of the Staging Manual (2009) remains unchanged in the 8th edition of 2018. Lymph node levels. The  American Academy of Otolaryngology system (2002) divides the nodes as follows: The American Joint Committee on Cancer (AJCC) system differs from the above by including Level VII, but the American Academy considered these to be anatomically mediastinal rather than cervical nodes, and therefore should not be included in the classification of neck nodes. However it is based on the 2002 American Academy system, although the boundaries are defined slightly differently. The boundaries are defined as (Superior, Inferior, Antero-medial, Postero-lateral) While an imaging based system was proposed in 1999, these concepts were integrated into the 2002 revision of the  American Academy system. In addition to needing a standardised approach to classification of lymph nodes for the purposes of neck dissection, the application of radiation therapy also requires such an approach and has resulted in an international consensus guideline (2013). Clinical significance. Infectious mononucleosis "(glandular fever)" affects the cervical lymph nodes which become swollen. The characterization of cancerous lymph nodes on CT scan, MRI or ultrasound is difficult, and usually requires confirmation by other nuclear imaging techniques such as PET scans. Tissue diagnosis by fine needle aspiration (which has a high rate of accuracy), may also be required. Involvement of  the cervical lymph nodes with metastatic cancer is the single most important prognostic factor in head and neck squamous cell carcinoma and may be associated with a halving of survival. Where the cancer has penetrated the capsule of the lymph gland (extracapsular extension) survival may be decreased by a further 50%. Other important factors are the level, the number of nodes and their size, which are also correlated with the risk of distant metastases. Cervical lymph node metastasis is also a common feature of papillary thyroid carcinoma.