[Extravasation into a renal sinus cyst due to ureteral calculus: a case report].

A 71-year-old man who had been treated conservatively for advanced prostate cancer with hormonal therapy presented with complaint of left flank pain. Intravenous urography demonstrated obstruction caused by a left upper ureteral calculus and leakage of contrast medium outside the renal pelvis and calyces. Left percutaneous nephrostomy was performed, and subsequent nephrostography showed extravasation into a parapelvic renal sinus cyst previously recognized on follow-up computed tomography (CT). The left ureteral calculus was treated with extracorporeal shock wave lithotripsy (ESWL), after which obstruction and extravasation disappeared. One month later, abdominal CT demonstrated no left renal nor ureteral calculi, as well as a reduction in the left renal sinus cyst. Urinary extravasation sometimes occurs as a complication of acute urinary obstruction. However, extravasation into a cyst is very rare. We have found only one case reported in the literature, so far.