Villous adenoma of urinary tract: a common tumor in an uncommon location.

The presence of colonic-type epithelium in the urinary tract is not an uncommon occurrence, but tumors derived from it are rare. Tumors arising from colonic-type epithelium, including villous adenoma and adenocarcinoma, have been reported in the renal pelvis, ureter, urinary bladder, and urethra. Villous adenomas of the urinary tract are rare, being most common in the urinary bladder, followed by the urethra. Morphologic features of these tumors are similar to those of the colonic adenomas. The largest published series of villous adenomas of the urinary tract was a study of 23 patients. This study is reviewed and other reports on villous adenomas of the urinary tract are discussed.