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 5 4 years old. Both patients presented with macroscopic hematuria and flank p ain. Computed tomographic (CT) scan and ureterocystoscopy revealed in case 1 a mass in the left renal pelvis and the calyces. In case 2, urography sho wed a lacuna of the renal pelvis, and CT scan showed an irregular thickenin g of the renal pelvis. in both cases, the preoperative clinical diagnosis w as urothelial carcinoma, and both patients underwent nephrectomy. Microscop ic examination revealed in case 1 a tumor of the renal pelvis composed of s pindle cells with eosinophilic cytoplasm in a myxoid and vascular stroma wi th abundant inflammatory infiltrate. In case 2, the tumor was composed of d ensely basophilic spindle tells in a fascicular pattern intermingled with l ymphocytes and plasma cells and involving the lamina propria of the renal p elvis. The spindle cells reacted strongly with antibody to vimentin and foc ally with antibodies to smooth muscle actin and muscle-specific actin. In t he urogenital tract inflammatory pseudotumor involves preferentially the ur inary bladder. Rare cases have been reported in the kidney. The 2 cases pre sented here are unusual due to the location in the renal pelvis, mimicking urothelial carcinoma.