A nonsecreting pheochromocytoma presenting as an incidental adrenal mass. Report on a case.

A 25 year old women presented an incidental adrenal mass which was diagnosed to be a pheochromocytoma before surgery by means of a positive 131-I-MIBG scintigraphy. Urinary vanilmandelic acid resulted repeatedly normal as well as basal plasma norepinephrine (NE), epinephrine (E) and dopamine (DA). Urinary homovannilic acid resulted in the normal range. Stimulation tests with iv glucagone, tyramine and metoclopramide evoked normal NE and E responses while a slight increase in plasma DA was observed after metoclopramide. Oral clonidine suppressed plasma catecholamines (CA) normally. Histologic and immunohistochemical studies confirmed that the tumor was a pheochromocytoma showing positivity for tyrosine hydroxylase but not for dopamine-beta-hydroxylase activity. This case is the first report on a completely asymptomatic pheochromocytoma presenting as an incidental adrenal mass which was investigated with repeated biochemical tests before surgery and demonstrates that, among the extremely variable functional attitudes of pheochromocytomas, a defect in CA synthesis and secretion is also to be included.