A male case of primary retroperitoneal mucinous cystadenoma: a diagnostic dilemma.

We report a male case of primary retroperitoneal mucinous cystadenoma (PRMC) that was at initially misdiagnosed as a complicated renal cyst. On ultrasonography, a 71-year-old man was found to have an abdominal mass suspicious for right renal cyst. The initial computed tomography scan showed an unenhanced, low-density mass that deformed the edge of the right kidney into a beak shape. Four years later, the mass had increased in size. Magnetic resonance imaging revealed a cystic lesion. Its intracystic content showed relatively high intensity on a T1-weighted image, and the coronal gadolinium-enhanced T1-weighted image with fat suppression clearly showed a multilocular cystic mass without enhancing mural nodules. The final diagnosis of PRMC was obtained pathologically after surgery. Because PRMC has malignant potential, this rare entity should be considered when a retroperitoneal cystic tumor is evaluated, even in a male patient.