A rare, usually benign tumor that develops from cells of the paraganglia. Paraganglia are a collection of cells that came from embryonic nervous tissue, and are found near the adrenal glands and some blood vessels and nerves. Paragangliomas that develop in the adrenal gland are called pheochromocytomas. Those that develop outside of the adrenal glands near blood vessels or nerves are called glomus tumors or chemodectomas.