Cancer du rectum : anatomie chirurgicale, préparation à l'intervention, installation du patient

Abstract

The rectum is the terminal portion of the digestive tube. It includes 1) the pelvic rectum of 12-15 cm length, derived from the primary intestine and with, therefore, an anterior meso (the mesorectum), and 2) the perineal rectum or anal canal, of 3-4 cm length, which corresponds to the sphincters, easily localizable by rectal examination, derived from the ectoderm, thus without meso. The peritoneum covers the anterior face and the lateral faces of the upper half of the rectum; this upper half is commonly – and wrongly – called the intra-peritoneal part as opposed to the lower half which is localized under the Douglas’ pouch, and which is totally sub-peritoneal. The pelvic rectum is therefore surrounded either by the peritoneum, or by the visceral lamina of the pelvic fascia (also called fascia propria, or fascia recti). The parietal lamina is sometimes called pre-sacrum fascia (Waldeyer fascia) despite the fact that it covers the whole surface of the pelvis cavity walls and not only the sacrum. The pelvic rectum is vascularized (blood and lymph) in the mesorectum which is localized between the fascia recti and the pelvis rectum. One of the current proctectomy techniques is the complete resection of the mesorectum, an ambiguous formulation that refers both to the extrafascial exeresis – performed outside the fascia recti, and which is always indicated – and the mesorectum amputation which is indicated only for the tumours of the lower rectum. The visceral and parietal laminas of the pelvic fascia merge at the front and at the back level, so as total exeresis of the mesorectum induces frontal displacement of Denonvilliers aponeurosis, and retro displacement of the sacro-rectal ligament. Pelvic sympathetic and parasympathetic nerves are always covered by the parietal fascia, at the back and outside, then at the front and outside the rectum. These nerves remain preserved by extrafascial exeresis, but they are very close to the operated area on the lower anterior-lateral faces where nerves enter the fascia recti to innerve the terminal rectum. The perineal rectum has no fascias, non-systematic vascularization at the skin level and ischio-rectal cavities, partly through anal elevator muscles. In terms of surgery, localization of the anal margin is not useful in case of a tumour of the pelvic rectum, due to wide position-induced variability, adiposity, and length of the canal. The upper side of the elevator muscles is much more easy to localize and the type of resection will depend on it. Distances from the anal margin may be distorted depending on whether the anterior face is measured, very short with the Douglas’ pouch at 5.5 cm of the margin (but sometimes at 4 cm, in women), or the posterior side, very long and inducing, in terms of colonoscopy, a colorectal junction at 18 cm and sometimes 19 cm from the anal margin. Localization from the anal margin of very low tumours is important but it should be confirmed by rectoscopy or proctoscopy. In clinical terms, the rectum may be subdivided into 1) the high rectum or higher half of the rectum, roughly localized above the Douglas’ pouch, the length of which range from 6-8 cm to 15-19 cm from the anal margin depending on measurement conditions; 2) the lower rectum or the lower half of the pelvic rectum, which ends at the upper side of the elevator muscles and corresponds to the sub-peritoneal rectum; 3) the anal canal, at 0 to 3-4 cm from the anal margin, which is also the site of epidermoid carcinomas of integument origin, which will not be included in this chapter.