Pheochromocytomas: Tumors originating from chromophores in the adrenal medulla that synthesize, store, and catabolize catecholamines and cause symptoms due to the release of the latter. Paragangliomas: Tumors originating from chromophores outside the adrenal glands, including those originating from sympathetic (abdomen, pelvis, chest) and parasympathetic (head and neck) nerves. The former tend to have functional catecholamine hormone activity, while the latter rarely produce excess catecholamines. In 2004, the WHO classification of endocrine tumors defined pheochromocytomas as tumors of catecholamine-producing chromophores originating from the adrenal medulla, i.e., intra-adrenal paragangliomas; and those of sympathetic and parasympathetic ganglion origin as extra-adrenal paragangliomas. The current more uniform view is that pheochromocytoma refers specifically to adrenal pheochromocytoma, while the traditional concept of extra-adrenal or ectopic pheochromocytoma is collectively referred to as paraganglioma.