Pitfalls in the diagnosis of pheochromocytoma.

Two patients were diagnosed as having pheochromocytoma based upon clinical findings, abnormal biochemical assays, and the presence of an adrenal mass. However, adrenalectomy in both cases revealed nonfunctioning cortical adenomas. Although both patients had some evidence of catecholamine excess, the early finding of an adrenal mass in each case appeared to confirm the diagnosis. In addition, selective venous assays resulted in false positive results in these patients. Interestingly, the selected venous assays falsely localized the catecholamine excess to the same side as the lesions found on CT. These cases demonstrate that localization studies should not be obtained prior to documentation of an unequivocal biochemical diagnosis of pheochromocytoma. If this principle is violated, an incidental cortical adenoma found on CT may be mistaken for a pheochromocytoma. Since there are multiple sources of error during selective venous sampling, it should not be used routinely in the initial evaluation of patients with pheochromocytoma.