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Chemodectoma
A paraganglioma is a rare neoplasm that can be found in the head and neck region and other less common areas. They are usually considered benign and complete surgical removal results in cure. However, in about 3% of cases they are malignant and have the ability to metastasize. Paragangliomas are still sometimes called glomus tumors (not to be confused with glomus tumors of the skin) and chemodectomas, but paraganglioma is the currently accepted and preferred term.
Paragangliomas arise from the glomus cells, which are special chemoreceptors located along blood vessels that have a role in regulating blood pressure and blood flow. The main concentration of glomus cells are found are in the carotid body, located in the upper neck at the branching of the common carotid artery, and the aortic bodies, located near the aortic arch. The glomus cells are a part of the paraganglion system composed of the extra-adrenal paraganglia of the autonomic nervous system, derived from the embryonic neural crest. Thus, paragangliomas are a type of neuroendocrine tumor, and are closely related to pheochromocytomas. Although all paragangliomas contain neurosecretory granules, only about 1-3% have clinical evidence of oversecretion.
Paragangliomas are found predominantly in the abdomen (85%) and the thorax (12%), and only 3% are found in the head and neck region. Most occur as single tumors. When they occur in multiple sites they are usually found as a part of a heritable syndrome such as multiple endocrine neoplasia types II-A and II-B and Carney's complex.
Familial paragangliomas are found in 10-50% of cases, are often multiple and bilateral, and occur at an earlier age. The genes SDHD (previously known as PGL1), PGL2, and SDHC (previously PGL3) have been identified as the genes which can cause familial paragangliomas when mutated.
According to the World Health Organization classification of neuroendocrine tumors, paragangliomas are classified as having a neural cell line of origin. In the categorization proposed by Wick, the paragangliomas belong to Group II.
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