High Grade Transitional Cell Carcinoma of the Renal Pelvis with Diver- gent Differentiation Mimicking a Renal Abscess

We describe an unusual case of high-grade transitional cell carcinoma of the renal pelvis with sarcomatoid and squamous differentiation that presented as a left renal abscess. The patient had originally been treated for minimally invasive transitional cell carcinoma of the urinary bladder and ureteral orifices five years prior. Computerized tomography scan findings were consistent with an abscess of the left kidney. Percutaneous nephrostomy with drainage afforded no clinical improvement. Nephrectomy was performed and tissue was removed piecemeal because of the diagnosis of an abscess. Macroscopically the tissue was fragmented and necrotic with patches of gray-tan abscess. Microscopic sections revealed a biphasic neoplasm with squamous and sarcomatous elements that were co-existent with evident morphologic transition. There was also evidence of residual papillary transitional cell carcinoma in the renal pelvis. The sarcomatoid component was immunoreactive for cytokeratin, and vimentin. A malignant process must always be considered as an underlying cause when patients present with an abscess especially when there is a prior history of malignancy.