Inflammatory pseudotumor of the renal pelvis. A report of 2 cases with clinicopathologic and immunohistochemical study.

We describe 2 cases of inflammatory pseudotumor of the renal pelvis. Case 1, the male patient, was 37 years old, and case 2, the female patient, was 54 years old. Both patients presented with macroscopic hematuria and flank pain. Computed tomographic (CT) scan and ureterocystoscopy revealed in case 1 a mass in the left renal pelvis and the calyces. In case 2, urography showed a lacuna of the renal pelvis, and CT scan showed an irregular thickening of the renal pelvis. In both cases, the preoperative clinical diagnosis was urothelial carcinoma, and both patients underwent nephrectomy. Microscopic examination revealed in case 1 a tumor of the renal pelvis composed of spindle cells with eosinophilic cytoplasm in a myxoid and vascular stroma with abundant inflammatory infiltrate. In case 2, the tumor was composed of densely basophilic spindle cells in a fascicular pattern intermingled with lymphocytes and plasma cells and involving the lamina propria of the renal pelvis. The spindle cells reacted strongly with antibody to vimentin and focally with antibodies to smooth muscle actin and muscle-specific actin. In the urogenital tract inflammatory pseudotumor involves preferentially the urinary bladder. Rare cases have been reported in the kidney. The 2 cases presented here are unusual due to the location in the renal pelvis, mimicking urothelial carcinoma.