A Case of Metastatic Carcinoma at an Anal Fistula

Since 1995, a 69-year-old man had noted pus discharge and bleeding from the perianal region, where a soybeen sized tumor appeared in May 1999. He was admitted to our hospital in May 2000 because the perianal tumor enlarged gradually and bleeding and pus discharge from the tumor became frequent. Biopsy of the ul- cerated 38×27mm tumor showed moderately differentiated adenocarcinoma. Colonoscopy revealed an ulcer-ated tumor 20cm from the anus. Biopsy showed moderately differentiated adenocarcinoma. Because the his- tologic features of the perianal tumor closely resembled those of the sigmoid colon tumor, we considered exfo- liate cells from the sigmoid colon carcinoma had implanted and made the metastatic tumor in an anal fistula. The patient underwent abdominosacral excision of the sigmoid colon and rectum with an uneventful postop-erative course. Anal fistula is common, but our case emphasizes that the whole colon should be examined if carcinoma is found in an anal fistula. Anal fistula in a patient who has been operated on for colon cancer should be closely checked at follow-up.