Squamous cell carcinoma in the renal pelvis of a horseshoe kidney

We report a rare case of squamous cell carcinoma in the renal pelvis of a horseshoe kidney. An 80-year-old woman was referred to the National Nagano Hospital for the examination of occult blood in her urine. Microscopic hematuria was found, but pyuria was not seen. Computed tomography and magnetic resonance imaging showed a mass in the left renal pelvis of the horseshoe kidney. No renal stone or hydronephrosis was found. Cytopathological examination in the voided urine specimen was positive. Left nephroureterectomy with the splitting of the isthmus of the horseshoe kidney was performed without renal pedicle clamping using a microwave tissue coagulator. No bleeding was encountered after separating the isthmus. A final pathological diagnosis of squamous cell carcinoma with a tumor thrombus was made. Lymph node metastasis had developed and rapidly progressed and the patient died of disseminated malignancy 4 months after the operation. We reviewed 24 cases of renal pelvic tumor in horseshoe kidneys previously reported in Japan. Seven cases (30%) included components of squamous cell carcinoma. The incidence is higher than that of renal pelvic tumors in the general population.