Inflammatory myofibroblastic tumor of kidney with heterotopic bone formation: An unusual case mimicking a renal malignancy
A 32-year-old male patient came with complaints of pain in the lower abdomen and urinary tract symptoms since 1 year. The patient had a history of renal lithiasis 8 years back. Laboratory investigations including complete blood count, serum biochemistry and urine analysis were within the normal limits. Computed tomography (CT) scan revealed a heterogeneously enhancing mass lesion measuring 4.5 cm × 4.4 cm arising from the lower pole of the right kidney with an exophytic component. Calcific areas were also noted in the mass. It was confined to the cortex with no evidence of extension into renal calyces. Right renal vein was patent and there was no evidence of renal vein thrombosis. The contralateral kidney was normal. Radiological and clinical features strongly suggested a renal cell carcinoma (RCC) for which the patient underwent a right radical nephrectomy. Macroscopically, a well-circumscribed hard grey white tumor was noted in the lower pole of nephrectomy specimen with exophytic component also. The tumor was hard and had a gritty sensation on cutting through it. Histological examination revealed a tumor composed of cellular and hypocellular hyalinized areas. The cellular foci were composed of spindle cells in short fascicles and prominent storiform pattern. Spindle cells showed mild atypia and mitotic activity ranged from 4 to 7/10 high power field (HPF). There were lymphoid aggregates with germinal center formation and plasma cells interspersed amongst these spindle cells. Extravasated red blood cells were also seen prominently at many foci. Within the hypocellular hyalinized zones, the spindle cells were arranged in an unusual perivascular whorled pattern resembling meningeal whorls. In addition, heterotopic bone formation was seen bordered by osteoblastic cells []. Mitotic rate up to 3-6/10 HPF was appreciated focally in the cellular areas. However, no atypical mitosis was appreciated. No areas of conventional RCC were demonstrable even after studying additional sections from the tumor. On immunohistochemistry, the spindle cells were strongly positive for smooth muscle antibody [] and were negative for CD 34, ALK-1, CK7, CD 23, CD21 and h-caldesmon. p53 was positive in few of the spindle cells. The remaining renal parenchyma was unremakable. Surgical margins of excision were clear with no evidence of extension into the renal vein or renal pelvis. The patient is asymptomatic 18 months after his surgery.