Giant cystic pheochromocytoma located in the renal hilus.

A malignant tumor in the past medical history of a patient often makes the differential diagnosis of a second tumor more difficult, especially if one of the tumors does not show its characteristic features. The authors report a case of a 55-year-old male who presented with a malignant melanoma on his left shoulder. A retroperitoneal giant cystic mass, 200 mm in diameter, was found incidentally. Adrenal origin was ruled out by imaging techniques. The absence of typical clinical symptoms made a correct preoperative diagnosis unlikely, and severe cardiovascular complications set in during surgery. Considering the characteristics of the cutaneous malignant melanoma, the metastatic origin of the giant retroperitoneal tumor was not likely either. During surgery the left kidney, with a cystic tumor located in the hilus, was removed. The postoperative pathologic diagnosis was pheochromocytoma located in the hilus of the left kidney.