A Case of Perianal Mucinous Adenocarcinoma Arising from an Anorectal Fistula Successfully Resected after Preoperative Radiotherapy
A 60-year-old man with a 45-year history of perianal fistula who had recently been suffering from mucinous discharge, pain and perianal induration was referred to hospital for treatment. Two years before, he had undergone surgery at another institution for incision and drainage of recurrent perianal abscess. Physical examination revealed an indurated, ulcerative lesion 7 cm in diameter with an external anal fistula opening (fig. ). The internal opening of the fistula was indicated at the right side of dentate line. There was no tumor in the rectum on digital examination. Histological examination of a biopsy specimen taken from the induration revealed mucinous adenocarcinoma. Magnetic resonance imaging (MRI) demonstrated a large demarcated tumor at the level of the anorectal junction with extension to the right side of the ischiorectal fossa and presacral space (fig. ). No enlarged pelvic lymph node was observed, nor was there evidence of distant metastasis. Neither colonoscopy nor barium enema showed any evidence of mucosal lesion in the colon or rectum. Laboratory data showed renal dysfunction caused by pyelonephritis, and the carcinoembryonic antigen serum level was extremely elevated to 40.8 ng/ml (normal <5 ng/ml).\nTo increase resectability and decrease the rate of local recurrence, preoperative radiotherapy was proposed without chemotherapy because of the renal dysfunction. Preoperative radiotherapy was given with 40 Gy in 25 fractions for 5 weeks through posterior and bilateral portals. After radiotherapy the tumor was markedly shrunk (fig. ) and carcinoembryonic antigen serum level gradually decreased to 13.0 ng/ml.\n8 weeks after radiotherapy the patient underwent radical resection. An APR with lymph node dissection was performed. The skin surrounding the tumor was excised with adequate tumor-free margin. The resected specimen revealed that the tumor had developed in the ischiorectal fossa, but there was no evidence of cancer extension to the mucosal surface of the anal canal and rectum (fig. ). Histological examination of the excised specimen showed foci of mucinous adenocarcinoma involving the lower internal and external anal sphincter muscles, and the resected margins did not show any residual tumor (fig. ). According to the UICC TNM staging criteria, the treatment outcome with preoperative radiotherapy revealed minimal response (grade 2). Metastases to the lymph node were not detected. After the operation, the patient died due to renal failure.