Cavernous hemangioma mimicking a cystic renal cell carcinoma.

A 69-year-old man was hospitalized for treatment of a left renal tumor. The tumor had originally been demonstrated as a simple renal cyst 4 years before. However, the size of the tumor decreased, and at the time of hospitalization, the tumor showed a solid, papillary component that was enhanced by contrast medium on computed tomography (CT) and had high signal intensity on T2-weighted magnetic resonance imaging (MRI). We diagnosed this tumor as a cystic renal cell carcinoma of the left kidney, cT1aN0M0, arising from the epithelium of a renal cyst, and performed a left partial nephrectomy. The pathological diagnosis was cavernous hemangioma of the left kidney. Generally, it is difficult to diagnose a cavernous hemangioma of the kidney preoperatively. This case is unusual because the configuration of this tumor changed within a few years. When we find a renal cyst with a solid component, renal cavernous hemangioma arising from the cyst wall should be considered in the differential diagnosis, and a conservative surgical approach should be considered.