A supernumerary kidney discovered incidentally on occasion of annual health checkups

Supernumerary kidney is one of the rarest anomalies of urinary system. We experienced a 51-year-old female with a left supernumerary kidney complaining microhematuria found by annual health checkups. Intravenous pyelography (IVP) revealed completely duplicated kidneys and ureters on the left side, confirmed by abdominal computed tomography (CT), demonstrating a supernumerary kidney at the caudal and abdominal portion of the left normal kidney. On the cystoscopy, there were normal ureteral orifice on both sides and one extra orifice near left urethral meatus. The supernumerary kidney was not atrophic nor hydronephrotic, and was almost as normal as the major kidney. She is under observation at our clinic. This seems one of the rarest case reported in japan for the past 20 years, since most of the supernumerary kidneys reported in the past were atrophic, hydronephrotic or non functioning.