Tumors of the Adrenal Medulla and Extra-adrenal Paraganglia

Abstract

According to World Health Organization definitions updated in 2004, pheochromocytomas (PCC) are tumors derived from chromaffin cells in the adrenal medulla. Closely related tumors arising outside the adrenal medulla are called extra-adrenal sympathetic paragangliomas (PGL). The latter can occur anywhere in the vicinity of sympathetic ganglia or visceral branches of sympathetic nerves and, like PCC, are often associated with signs and symptoms of catecholamine overproduction. A pheochromocytoma is an intra-adrenal sympathetic PGL. The arbitrary separation between PCC and other sympathetic PGL emphasizes distinctive properties of adrenal tumors, including frequent production of epinephrine rather than norepinephrine, relatively low rate of malignancy, and tendency to occur in particular hereditary syndromes. A third group of related tumors consists of parasympathetic PGL in the head and neck. Those tumors are usually not clinically functional.