Diagnosis and localization of pheochromocytoma.

This Hypertension Grand Rounds shows how applying new clinical laboratory techniques helped to diagnose pheochromocytoma in a difficult case. In the setting of long-standing, sustained hypertension, the patient had a hypertensive paroxysm during anesthesia induction for surgery, leading to suspicion of a pheochromocytoma. Conventional testing, including CT scanning and fractionated urinary metanephrine test, was not diagnostic. The patient had another hypertensive paroxysm during subsequent anesthesia induction, requiring intensive care. Consistently elevated plasma levels of free normetanephrine provided the first and only biochemical evidence for a pheochromocytoma in this case. 6-[18F]Fluorodopamine positron emission tomography and 123I-metaiodobenzylguanidine scintigraphy subsequently agreed on the existence of a small left adrenal mass, which when removed surgically proved to be a pheochromocytoma. Postoperatively, plasma levels of normetanephrine normalized, and there were no further hypertensive paroxysms, although the patient remained hypertensive. This case illustrates the superiority of plasma levels of free (unconjugated) metanephrines, compared with other biochemical tests, to detect pheochromocytoma. It also confirms that functional imaging by 6-[18F]fluorodopamine or 123I-metaiodobenzylguanidine scanning can localize pheochromocytoma in difficult cases in which other imaging tests are not diagnostic.