Pheochromocytoma with normal urinary and plasma catecholamines but elevated plasma free metanephrines in a patient with adrenal incidentaloma

We present an asymptomatic 75-year-old patient (normal renal function, no h ypertension) with adrenal incidentaloma (5 cm) who repetitively had had neg ative screening tests for pheochromocytoma by determination of urinary and plasma catecholamines. The attempt then to exclude malignant disease by fin e needle aspiration biopsy caused the patient's one and only hypertensive c risis. A high performance liquid chromatography (HPLC) method for measureme nt of plasma metanephrines, however, showed raised levels consistent with t he diagnosis of pheochromocytoma, later confirmed by histology. Finally, op en transperitoneal surgery caused the tumor to release large quantities of the parent amines norepinephrine and epinephrine in addition to normetaneph rine and metanephrine. This case is to demonstrate the difficulties and possible serious consequen ces often encountered in the diagnostic work-up of pheochromocytoma. In add ition, it suggests that the measurement of plasma metanephrines by means of the presented HPLC method may contribute to the diagnosis of this conditio n to minimize interventional risks and to raise diagnostic sensitivity. Int ratumor metabolism of catecholamines to metanephrines is well known, especi ally in large tumors, leading to complete absence of symptoms. As in this p atient, however, there are certain clinical situations (such as fine-needle biopsy of the lesion or abdominal surgery) that have to be kept in mind fo r their ability to dramatically raise plasma catecholamines even in "catech olamine-negative" pheochromocytomas.