Laparoscopic nephron-sparing surgery for a tumor near the isthmus of a horseshoe kidney with a complicated blood supply.

A horseshoe kidney is a congenital kidney malformation commonly associated with complications such as hydronephrosis, renal calculi, and infections of the renal pelvis. Renal cell carcinoma is extremely rare in a horseshoe kidney; once it occurs, however, it is intractable because of vascular abnormalities. This is especially true in laparoscopic nephron-sparing surgery, even for tumors of <4 cm in diameter. We herein report a case involving an asymptomatic 65-year-old man with an incidental finding of a 4-cm solid mass near the isthmus of a horseshoe kidney on B-mode ultrasonography. Preoperative computed tomography of the renal artery revealed six arterial vessels supplying the affected kidney. Laparoscopic partial nephrectomy was performed. The outcome of this case suggests that laparoscopic nephron-sparing surgery might be a successful treatment method for a horseshoe kidney but that preoperative vessel evaluation and experienced laparoscopic skills are needed.