Coloanal anastomosis in surgery for rectal cancer.

The definition of coloanal anastomosis should be based on anatomy of the anal canal. The anal canal is terminal portion of the digestive tract and comprises muscle tube of approximately 3 cm long with a lumen coated with several types of mucosa or epithelium. Muscle tube of the anal canal consists of two layers, inner sphincter muscle and external sphincter muscle. The former is a continuation of rectal muscle layer and the latter extends to the levator ani muscle. Colo-anal anastomosis (CACA): whole of the rectum is excised with a separation line placed just above the anal canal. An anastomosis is made between colonic cut end and upper limit of the anal canal. Colo-anus anastomosis in a narrow sense (CAA): rectum is excised with a bit of upper part of the anal canal. Then an anastomosis is made inside the anal canal.