Embryology and anatomy of the anorectum. Basis of surgery.

The rectum is a pelvic organ, complex in its morphology and its topographic relationships. Its double embryologic origin explains the two types of tumors that develop in the rectum: (1) lieberkühnian adenocarcinoma in the pelvic rectum and (2) squamous epithelioma in the anal canal. Its venous and lymphatic supply, intensively developed, realizes early pathway of tumoral dissemination. The pelvic relationships of the rectum and anus explain the technical difficulty of rectal surgery, especially when subperitoneal resection and anastomosis are concerned. Imaging of this area permits an early diagnosis of rectal tumors and allows a less invasive surgery with a carcinologic precision.

Cloacogenic tumors of the anorectal junction.

The cloacogenic zone of the anal canal is a vestigial remnant of the cloacal membrane. This region corresponds to the columnae anales and anal glands. The epithelial lining of the anal glands and of the cloacogenic zone is of the transitional variety. The anal glands are well known to the surgeon because of their role in the pathogenesis of perianal abscesses and fistula in ano. Tumors arising from the cloacogenic zone of the anal canal are rare. In most instants these carcinomas have characteristic clinicopathological features. These lesions are named transitional cloacogenic carcinoma. The therapy of choice is an abdominal-perineal rectum amputation with wide excision of the perineal soft tissue. Inguinal node dissection is indicated if the nodes appear clinically involved. No conclusions have been reached to determine the radiosensitivity of cloacogenic carcinomas. Five cases of cloacogenic carcinoma are reported and the clinicopathological and therapeutic aspects discussed.