I. Anatomical basis The rectum above the peritoneal fold is covered by peritoneum, while the rectum below the fold is not covered by peritoneum, but by pelvic fascia. The pelvic fascia is divided into a dirty layer and a wall layer. The dirty layer of the pelvic fascia is formed by the subperitoneal fascia entering below the peritoneal fold and its superficial lobe wrapping around the internal organs of the pelvic cavity, such as the bladder, uterus and rectum, etc. The wall layer of the pelvic fascia corresponds to the dirty layer and is formed by the deep lobe of the subperitoneal fascia entering the pelvic cavity and covering the surrounding pelvic wall. In front of the S4 cone the dirty layer and the wall layer fascia converge to form a dense fibrous fasciculus, the rectosacral fascia (or ligament). The perirectal fat surrounded by the visceral fascia is the mesorectum, which is rich in lymphatic and vascular tissues, and the primary rectal tumor invades and metastasizes to this area first. Between the two layers of fascia is filled with avascular loose connective tissue (COTON-CANDY, marshmallow-like). The pelvic genital ducts, internal iliac vessels, pelvic autonomic nerves and muscles of the lateral pelvic wall are covered by the mural fascia.
Theoretical basis Since TME was proposed by heald in 1982, it has been proved to be a better radical surgical operation for lower and middle rectal cancer after nearly 20 years of clinical practice, which can effectively reduce the local recurrence rate to 3-7% and improve the long-term survival rate. It is now becoming a standard radical surgical procedure for rectal cancer accepted by more and more clinicians. The theoretical basis is based on the theory that there is a surgical plane between the visceral and mural layers of the pelvis, which sets the resection range for complete resection of rectal cancer and rectal cancer infiltration is usually confined to this range.
TME is mainly applicable to stage T1-3 rectal cancer in the middle and lower part of the rectum without distant metastasis, and the cancer does not invade the visceral layer of the fascia, and most patients suitable for low anterior resection are basically suitable for TME; for patients whose cancer invades the fascia of the wall or surrounding organs or sacrum, TME has lost its original meaning. For rectal cancer at the junction of upper rectum and recto-b, the rectum itself is covered by peritoneal reflex, and part of the distal rectal mesentery can be preserved, so complete rectal mesorectal resection is not necessary.
The principles of surgery: (1) sharp separation in the anterior sacral space under direct vision; (2) keep the pelvic fascia intact and unbroken; (3) resection of the distal rectal mesentery of the tumor should not be less than 5 cm. During the operation, the sigmoid colon is firstly freed from the left side, the submesenteric vein is dissected out, and the submesenteric artery is ligated at 1 cm from the aorta and splenic vein respectively to complete lymph node dissection. Subsequently, the visceral fascia, malignant tumor and perirectal mesentery of the left and right inferior abdominal nerves were completely freed along the pelvic visceral and mural fascia with scissors or electric knife under direct vision until the plane of the anal raphe, keeping the integrity of the visceral fascia. This can avoid damage to the pelvic fascia and protect the autonomic plexus. If the level of separation is correct, there are no large vessels other than the rectal side vessels, which will not lead to serious bleeding.
It is very different from the traditional surgical method. First of all, the separation of rectal mesentery is performed with scissors or electric knife along the non-vascular area between the pelvic fascia of the dirty wall layer around the rectal mesentery until all the rectal mesentery and rectum are free. Traditional surgery usually separates the rectum bluntly with unclear anatomical levels, which can easily tear the mesentery or tumor leading to residual rectal mesentery and tumor dissemination. This is the biggest difference between TME and traditional surgery. Secondly, it is emphasized that the rectal mesentery, including the rectum and tumor, should be detached around the rectum, and the distal rectal mesentery of the tumor should be removed up to 5 cm or all of the rectal mesentery, which is different from the traditional surgery that only focuses on the distance of the cutting edge from the tumor.