Principles for circumferential dissection
The dissection must be performed as a TME (total mesorectal excision) as described by Heald. A sharp, visually controlled, dissection is performed in the plane between the visceral (Told) and parietal mesocolic/mesorectal fascia.
This plane is identified at open operation by primarily freeing the sigmoid from the lateral abdominal wall continuing medially for the whole mesosigmoid till the central part of the posterior abdominal wall. The autonomic nerves and ureter will be left unharmed on the posterior abdominal wall. Continue in the same plane at the pelvic entrance.
Thereafter the dissection is continued medially. Vessels and lymph nodes are divided at the proper level, the bowel is divided and can be pulled forward. Sharp, visually led dissection is continued in the mesorectal (“holy”) plane on the outside of the mesorectal fascia into the pelvis. The plane is usually easy to identify posteriorly and in front – at the back of the vesicles and prostate in men, the vagina in women. The proper plane should first be identified and followed posteriorly far into the pelvis, thereafter briefly at the front. The plane is more difficult to define laterally, especially at 10 and 2 o’clock. The dissection here should only be performed after the initial posterior and anterior dissection. Functionally important autonomic nerves are located just on the outside of the proper plane and will be injured by an improper dissection. Dissection on the inside of the proper plane will increase the risk for local recurrence.
The quality of the resection can be visualized by inspection of the specimen. This should have an intact, even and smooth mesorectal fascia covering the mesorectal fat. In scientific studies it is customary to grade the appearance of the specimen and this also ought to be performed in clinical routine and described in the surgical record:
- Grade A: Intact mesorectal fascia on the whole specimen
- Grade B: Cuts in the mesorectal fascia, none onto the outside of the bowel
- Grade C: Cuts in the mesorectal fascia onto the rectal wall
The quality of the dissection can further be estimated by the integrity of the parietal fascia on the posterior abdominal/ pelvic wall. This should be intact and cover aorta and nerves.
Principles for circumferential dissection when a low anterior resection may be performed while anastomosis is considered too risky.
A standard TME is performed to the pelvic floor. When an anastomosis is no option the alternatives are:
- Low Hartmann’s procedure. Rectum is divided distally.
- Intersfincteric amputation.
Standard TME is performed till the anal canal. A minimal skin incision is performed from below followed by an intersfincteric dissection. This way a large defect in the pelvic floor and skin is avoided and there are few healing problems. A short rectal stump, as in the Hartmann’s procedure, is avoided which can give rise to leakage and pelvic infection.
Principles for regional lymph node dissection
- For cancer in the rectosigmoid flexure the vessels/lymph nodes should be resected as in sigmoid cancer, which means at the origin of the inferior mesenteric artery at the aorta.
- For cancer in the upper rectum it is probably adequate to resect the inferior mesenteric artery just distal to the origin of the left colic artery with removal of the local lymph nodes. Fat and lymph nodes in the apical station may be removed even if the artery is resected distal to the left colic artery.
- For cancer in the middle/lower rectum the vessels/lymph nodes are resected just distal to the origin of the left colic artery.
Principles for division of the rectum and mesorectum during low anterior resection.
Orally the bowel is resected between the sigmoid and descending colon. The blood circulation of the oral bowel end must be inspected. If this seems inadequate the resection should be performed more orally. The left flexure must frequently be mobilized to obtain adequate length of the oral bowel to obtain a tension free anastomosis. This can be facilitated by dividing the inferior mesenteric vein just below the pancreas.
Microscopic tumor does not spread more than 1 cm beyond the macroscopic tumor border. In contrast discontinuous tumor spread in the mesorectum can go as far as 5 cm anal to the lower tumor border, even though it rarely is found further than 3 cm. This is the reason for the following procedures:
- Tumor in the rectosigmoid flexure or upper rectum (above 12 cm): The rectum and mesorectum are divided 5 cm anal to the tumor. Avoid coning from the mesorectal fascia to the bowel (the total mesorectum must be resected in all 5 cm). A small remnant of the mesorectum will then remain. In Norway this is called PME (partial mesorectal excision), but this term is not applied internationally and may be misunderstood.
- Tumor at level 8(9) -12 cm: Bowel and mesorectum is resected 5 cm below the tumor which means TME for all practical purposes.
- Tumor at 5 to 8-9 cm, planned low anterior resection: Resect all mesorectum to the pelvic floor. Adequate distance on the bowel wall < 1 cm.
Reconstruction of the bowel tube after low anterior resection for rectal cancer.
Anastomosis is performed between the descending colon/upper sigmoid and the remaining part of the rectum, if necessary down at the dentate line of the anal canal. A staple instrument is customary applied. An anastomosis at the dentate line can be sutured manually from below.
Types of anastomoses:
- End-end colorectal anastomosis, also called straight anastomosis.
- Side-end colorectal anastomosis without reservoir.
- Side-end anastomosis with reservoir and a blind loop around 5 cm long. The functional result of this is somewhat better for the first 1-2 years, but the final result is similar to the straight anastomosis. Some consider there is a slightly lower frequency of leakage after a side-end anastomosis, but this has not been clarified. The latter carries the possibility of leakage from the staplers closing the blind loop.
- End-end coloanal anastomosis, colon is sutured to the dentate line.
Temporary defunctioning stoma after low anterior resection
When the anastomosis is 6 cm or below from the anal verge is recommended a temporary defunctioning stoma for 2-3 months until healing of the anastomosis. A defunctioning stoma may also be constructed for anastomoses higher than 6 cm in cases with surgical-technical problems or when a leakage is feared for other reasons in.
While it is possible that the frequency of leakage is reduced by a temporary stoma, this will at any rate reduce the consequences of a leakage. The pelvic infection is usually milder and a reoperation is unnecessary after a temporary stoma. The leakage problem can often be solved by the application of an “EndoSponge” in the perirectal cavity.