Renal cell carcinoma with hemorrhagic cyst formation in a 4-year-old boy.

We report on a case of renal cell carcinoma (RCC) with hemorrhagic cyst formation in a 4-year-old boy. The patient presented with asymptomatic macrohematuria. Abdominal ultrasound, computed tomography and magnetic resonance imaging demonstrated a left renal complicated cyst, 18 mm in diameter. Renal malignancy was suspected, and left radical nephrectomy was performed. Pathological diagnosis was a complicated cyst filled with bloody clots, with a wall composed of RCC. No metastases to the regional lymph nodes or other organs were found. This is an extremely rare occurrence of such a small RCC that developed a hemorrhagic cyst in a boy of this young age. The boy is being followed-up without any additional treatment.