Incidental Pheochromocytoma Mimicking Adrenal Adenoma Because of Rapid Contrast Enhancement Loss
John K. Yoon ; Erick M. Remer ; Brian R. Herts

1 Department of Radiology, Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195. Received March 20, 2005; accepted after revision April 26, 2005.

The characterization of adrenal masses using noninvasive imaging has been the focus of much interest, with the goal of easily differentiating between benign and malignant lesions. A large body of literature exists on the subject of characterizing adrenal lesions found during the staging of patients with known extraadrenal primary malignancy. Signal loss on opposed-phase gradient-echo MR images compared with in-phase images and mean attenuation values of less than 10 H on unenhanced CT are both specific for differentiating adenomas from nonadenomas. Each method exploits the abundance of intracytoplasmic fat typically present in adenomas. Another well-studied characteristic of adenomas is their relatively rapid enhancement and washout on delayed contrast-enhanced images when compared with nonadenomas [1-3]. A recent study [4] suggests that the enhancement loss in pheochromocytomas and adrenocortical carcinomas is similar to that seen in adrenal metastases but is significantly less than that seen in adrenal adenomas, so an absolute washout 10 minutes after contrast medium injection of greater than 50% is highly specific for adenomas. We present a pathologically proven case of an incidental adrenal pheochromocytoma with an absolute contrast medium washout of 72%.