Paraganglioma pathophysiology

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Overview
A paraganglioma is a rare neoplasm that can be found in the abdomen, thorax, and in the head and neck region. 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.

Pathophysiology
The paragangliomas appear grossly as sharply circumscribed polypoid masses and they have a firm to rubbery consistency. They are highly vascular tumors and may have a deep red color.

On microscopic inspection, the tumor cells are readily recognized. Individual tumor cells are polygonal to oval and are arranged in distinctive cell balls, called Zellballen. These cell balls are separated by fibrovascular stroma and surrounded by sustentacular cells.

By light microscopy, the differential diagnosis includes related neuroendocrine tumors, such as carcinoid tumor, neuroendocrine carcinoma, and medullary carcinoma of the thyroid; middle ear adenoma; and meningioma.

With immunohistochemistry, the chief cells located in the cell balls are positive for chromogranin, synaptophysin, neuron specific enolase, serotonin and neurofilament; they are S-100 protein negative. The sustentacular cells are S-100 positive and focally positive for glial fibrillary acid protein. By histochemistry, the paraganglioma cells are argyrophilic, periodic acid Schiff negative, mucicarmine negative, and argentaffin negative.