Kevin E Snyder, M.D.

November 05, 2002

Discussion

Paroxysmal hypertension is the most common presenting complaint in patients with pheochromocytoma. The diagnosis of pheochromocytoma is generally made during the 4th or 5th decades of life. 10% of the lesions are found in children, predominantly in males. I-131 mIBG is utilized to image the adrenal medulla. Prior to the exam, patients are treated with Lugol's iodine for thyroid protection. Imaging is generally performed at the 48 hour time interval with whole body images obtained in the anterior and posterior projections. In some cases, imaging may be required out to 72 hours for greater confidence. The normal adrenal medulla is uncommonly identified on the exam (approx 20%), and even then is only faintly seen. Most pheochromocytomas are localized to the adrenal gland. In the 10% of cases where more than one tumor is present, mIBG may be utilized to identify these lesions anywhere in the body. MIBG is of particular value in these cases, as many of these lesions are not identifiable by computed tomography either due to their small size or their close relationship to other structures. Extra-adrenal pheochromocytomas may be found anywhere from the skull through the pelvis. Blood plasma levels of chromogranin A may be used to evaluate patients for pheochromocytoma. Chromogranin A is a protein found in the same chromaffin granule core as the catecholamines. Elevation of chromogranin A is 83% sensitive and 96% specific for the diagnosis of pheochromocytoma. While its level is unaffected by drugs used to treat pheochromocytoma, chromogranin A may be released into the bloodsteam by other neuroendocrine tumors.

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