Pheochromocytoma is a catecholamine-producing tumor - Catecholamine producing tumors arising from chromaffin tissues - Rare disorders with an annual detection rate of 2 to 5 per million. - Hypertension is the most common symptom of Pheochromocytoma - Other symptoms include palpitation, diaphoresis - Most pheochromocytoma are benign with only 15% of adrenal tumors and 35% of extra-adrenal tumors being malignant - Approximately 30% to 40% are hereditary. Mutation of the genes encoding succinate dehydrogenase, MYC associated factor X are some of the identified susceptibility genes. Biochemical Basis - Mechanisms of excessive production of catecholamines in the patients with pheochromocytoma is unclear - the presence of tumors leads to a relatively large increase in the production of O-methylated metabolites. - Multiple Endocrine Neoplasia syndromes (MEN) mainly MEN2A and MEN 2B manifest as pheochromocytoma in addition to thyroid carcinoma and others. - MEN 2A (...