endocrine and metabolic disorders
Pheochromocytoma
Introduction
A pheochromocytoma is a catecholamine-secreting tumor of chromaffin cells typically located in the adrenals. It causes persistent or paroxysmal hypertension. Diagnosis is by measuring catecholamine products in blood or urine. Imaging tests, especially CT or MRI, help localize tumors. Treatment involves removal of the tumor when possible. Drug therapy for control of blood pressure includes alpha-blockade, usually combined with beta-blockade. (See also Overview of Adrenal Function .) The catecholamines secreted includenorepinephrine,epinephrine,dopamine, and dopa in varying proportions. Most pheochromocytomas are in the Adrenal medulla (about 90%) Pheochromocytomas may also be located in other tissues derived from neural crest cells. Possible sites include the following: Paraganglia of the sympathetic chain Retroperitoneally along the course of the aorta Carotid body Organ of Zuckerkandl (at the aortic bifurcation) Genitourinary system Brain Pericardial sac Dermoid cysts Pheochromocytomas in the adrenal medulla occur equally in both sexes, are bilateral in 10% of cases (20% in children), and are malignant in<10%. Of extra-adrenal tumors, known as paragangliomas, 30% are malignant. Although pheochromocytomas occur at any age, peak incidence is between the 20s and 40s. Nearly 50% are thought to be due to germline mutations. Pheochromocytomas vary in size but average 5 to 6 cm in diameter. They weigh 50 to 200 g, but tumors weighing several kilograms have been reported. Rarely, they are large enough to be palpated or cause symptoms due to pressure or obstruction. Regardless of the histologic appearance, the tumor is considered benign if it has not invaded the capsule and no metastases are found, although exceptions occur. In general, larger tumors are more likely to be malignant. Pheochromocytomas may be part of the syndrome of familial Overview of Multiple Endocrine Neoplasias (MEN) (MEN) types 2A and 2B, in which other endocrine tumors (parathyroid or medullary carcinoma of the thyroid) coexist or develop subsequently. Pheochromocytoma develops in 1% of patients with 