Muconephrosis.

We report a case of a mucus-filled kidney (muconephrosis) encountered during laparoscopic nephrectomy for presumed xanthogranulomatous pyelonephritis. Conversion to open nephrectomy and en-bloc right hemicolectomy were necessary because of severe perinephric fibrosis and suspected renal-enteral fistula. Pathologic examination revealed a renal pelvic villous adenoma and diffuse intestinal metaplasia of the urothelium; no enteral communication or gastrointestinal pathologic features were found. Urothelial villous adenoma is extremely rare, and one should consider neoplastic etiologies, including appendiceal mucinous cystadenocarcinoma and mucus-secreting adenocarcinoma of the renal pelvis, in directing the appropriate management of muconephrosis.