Total Mesorectal Excision
- Author: Nanda Kishore Maroju, MBBS, MS, DNB, MRCS; Chief Editor: Kurt E Roberts, MD more...
Total mesorectal excision (TME) is a common procedure used in the treatment of colorectal cancer in which a significant length of the bowel around the tumor is removed. TME addresses earlier treatment concerns regarding adequate local control of rectal cancer when an anterior resection is performed.
The term total mesorectal excision strictly applies in the performance of a low anterior resection for tumors of the middle and the lower rectum, wherein it is essential to remove the rectum along with the mesorectum up to the level of the levators. The principles of TME (sharp mesorectal excision) are also applied during an abdominoperineal excision of the rectum and for tumors of the upper rectum, though these are considered distinct from standard TME. In an abdominoperineal excision of the rectum where the tumor exists below the level of the levators, the lateral margins of the tumor are inferior to the mesorectum, and the benefits of TME do not apply.
Anterior resections involving the upper rectum may be completed with mobilization of the rectum to beyond 5 cm of the lower margin of the tumor, and which is often above the level of the levator and is sometimes referred to as partial mesorectal excision.
The treatment of rectal cancers is multimodal with adjuvant radiotherapy and chemotherapy having benefits in some settings. In addition, accurate preoperative staging is dependent on good radiological support. It is therefore necessary to subject all rectal cancers to multidepartment conference and to design individualized treatment plans based on a well-defined protocol. This serves the dual purposes of maintaining a consistent evidence-based approach and creating a dataset for prospective analysis and feedback.
TME is indicated as a part of low anterior resection for patients with adenocarcinoma of the middle and lower rectum. It is now considered the gold standard for tumors of the middle and the lower rectum.
The circumferential resection margin positivity rate is about 5% or less for low anterior resections with TME, whereas it is between 10% and 25% for abdominoperineal excision of the rectum. There is, understandably, a higher local recurrence rate following abdominoperineal excision of the rectum. The 5-year survival and disease-free survival rates are significantly lower with TME.
Evidence suggests that a circumferential resection margin of 1 mm or less adversely affects cancer-specific survival, local recurrence, and distant metastasis.
Patient education and consent
The advantages of total mesorectal excision (TME) are better clearance of the tumor and hence lower rates of recurrence and better 5-year survival rates. However, in patients who undergo TME as a part of anterior resection, there is a higher rate of anastomotic dehiscence. In practice, this has lowered the threshold for considering a covering ileostomy. It may be a safer option to consider an ileostomy than to risk an anastomotic leak.
Patients may also experience urgency and incontinence to a higher degree than they would if TME were not performed. However, these issues usually decrease with time. The choice of a colonic pouch may reduce the urgency and incontinence in the early postoperative period. An indwelling catheter may be retained for a week for the bladder to regain its tone, especially in men.
The process of consenting should ensure that the patient has a chance to speak to a stoma nurse, a colorectal specialist nurse, or both. This is important not only for helping the patient understand the implications of a stoma but also for ensuring that the patient has access to specialist nursing care and support in the postoperative period.
Bowel preparation and stoma-site marking are performed on the day before the procedure. Polyethylene glycol or sodium picosulphate solution is usually chosen for preparation. Adequate care to ensure hydration of the patient during preparation is important. Marking of the site for stoma formation is done by a stoma nurse, which gives an opportunity for the patient to discuss stoma issues. Patients are scored for the risk of DVT and receive appropriate prophylaxis. Prophylactic antibiotics are administered as per protocol at anesthetic induction.
Equipment for TME includes the following:
Standard laparotomy tray
Stapling devices (linear staplers, heavy-wire linear stapler with articulating head, circular end-to-end anastomosis stapler)
Ultrasonic scalpel (optional)
Vessel-sealing system (optional)
Patients are administered general anesthesia, with or without epidural analgesia. Specific measures that an anesthetist should be aware of is the need for a Trendelenburg position during pelvic dissection. The options for postoperative analgesia include continuous epidural infusions, patient-controlled analgesia, wound catheters with local anesthetic, and conventional parenteral/enteral analgesia.
The standard position for TME is an extended Lloyd-Davies position. A right-handed surgeon would have a good view into the pelvis and be able to operate comfortably while standing on the left of the patient. The first assistant stands on the right and a second assistant, if available, is positioned between the patient’s legs.
The main steps of performing an anterior resection include the following:
Laparotomy and exploration for confirming the stage of the disease and assessing operability on the table
Mobilization of the left colon and the splenic flexure
Mobilization of the rectum
Resection of the rectal tumor along with sigmoid colon
Although each step of the procedure has its own significance towards a successful outcome of the procedure, mobilization of the rectum is of primary importance in terms of cancer control; it also has a bearing on nerve preservation and reduced intraoperative bleeding. Total mesorectal excision (TME) essentially describes the recommended technique of mobilizing the rectum; of the various techniques, it has the lowest incidence of positive margins and local recurrence.
The principles of TME are derived from a better understanding of the pelvic anatomy and include precise sharp dissection using scissors or diathermy, as well as delicate handling of tissues of the rectum-mesorectum and pelvic walls. In most cases, the proof of a properly performed TME is the gross appearance of the specimen itself. The gross inspection of the specimen is being increasingly recognized as a reliable predictor of an adequate rectal cancer operation.
The rectum does not have a true mesentery, and only its anterior and anterolateral parts are covered by peritoneum. However, there does exist a clear visceral envelope that encloses the mesorectum laterally and posteriorly. This visceral layer is separated from the lateral pelvic fascia by a distinct layer of areolar tissue. In the posterior midline, the pelvic fascia, visceral envelope, and areolar tissue aggregate to form a dense anchoring fascia of the rectum, referred to as the rectosacral fascia. As the rectosacral fascia is sharply divided, the rest of the areolar tissue submits beautifully and almost effortlessly to sharp dissection, allowing mobilization without breaching the mesorectum or the rectum.
The anterior relations of the rectum vary in men and women. In men, the correct plane for dissection is between the rectum and prostate and extends through the Denonvilliers fascia, posterior to the seminal vesicles. In women, the plane for dissection is through the rectovaginal septum, a breach of which may injure the thin vaginal wall and result in a rectovaginal fistula. Adherence to these planes has benefits besides the obvious oncologic ones. Pelvic sympathetic and parasympathetic nerves lie on the lateral pelvic fascia and are less likely to be damaged during rectal mobilization if the correct approach is followed.
Laparotomy and exploration
A midline incision provides the best access to the the peritoneal cavity. Though the primary organ of interest is pelvic in location, the incision must be taken well into the upper abdomen in order to enable proper mobilization of the splenic flexure. This is an early step in the procedure, and a surgeon will not want to waste energy or time in trying to get the flexure down through a smaller and lower incision.
Exploration involves inspection of the liver, viscera, and peritoneum, as well as precise locoregional evaluation of the disease. At this stage, the surgeon will also prepare the field for the subsequent operation by placing self-retaining retractors to provide a good view of the pelvic and peritoneal cavity. The small bowel must be moved to yield a clear view of the left side of the peritoneal cavity and the pelvis. This can be achieved either by packing the bowel into the right and upper part of the peritoneum or by delivering it over the right hypochondrium and holding in a laparotomy pad. (See the image below.)
Mobilization and division of colon
This step involves mobilizing the sigmoid colon, left colon, and the splenic flexure. At the end of a properly performed mobilization, the colon from the sigmoid to the transverse colon can be lifted freely towards the right side, up to the midline. The purpose of this step is to ensure a tension-free anastomosis between the colon and the rectum during reconstruction.
Conventionally, the sigmoid colon is mobilized first from the left. Adhesions between the sigmoid and the lateral abdominal wall must be divided before the line of peritoneal reflection can be identified and divided. Once the sigmoid is stood up to its full length at the apex, the peritoneal reflection is incised just behind the white line.
The surgeon and assistant work in tandem in applying traction and countertraction to demonstrate the correct surgical planes. The left ureter and hypogastric nerves can be demonstrated overlying the bifurcation of the common iliac artery at the base of the sigmoid mesentery (the apex of the V formed by the sigmoid mesocolon). These are swept laterally and dissection proceeds inferiorly, towards the sacral promontory in a plane anterior to the nerves.
The surgeon, in creating this plane, will push down the nerves onto the pelvic fascia. The appearance of a loose areolar tissue below the level of the promontory confirms the correct plane between the visceral peritoneum and the pelvic fascia. Further rectal mobilization is deferred until later in the operation.
The division of the peritoneal reflection is now taken superiorly to mobilize the left colon. While mobilizing the left colon, an inexperienced surgeon may lose the plane and enter the Gerota fascia. This can be avoided by ensuring a more medial dissection after division of the peritoneal reflection, while keeping the colon lifted anteriorly. The left colon is mobilized until the splenic flexure.
The splenic flexure can be easily brought down by entering the lesser sac after separating the greater omentum from the transverse mesocolon. Often, a difficult splenic flexure mobilization is due to an inadequate incision and therefore inadequate exposure of the flexure.
High ligation of the inferior mesenteric artery, which was earlier considered to be a part of proper oncologic surgery, does not have any proven survival benefit. However, it serves a different but important function in ensuring successful anastomosis. Ligation of the artery at its origin and ligation of the inferior mesenteric vein at the inferior margin of the pancreas increase the mobility of the colon and therefore reduce tension. This technique also serves to preserve the arterial arcade along the colon and again contributes to the survival of the anastomosis.
The surgeon starts from the base of the sigmoid mesocolon again, but on the right side. The peritoneum is divided anterior to the plane of the hypogastric nerves, and the division is taken superiorly in a plane just anterior to the aorta. The inferior mesenteric artery is identified as it takes off from the aorta. It is good technique to dissect out the artery before ligation to avoid injury to the hypogastric nerves. Superior dissection after division of the artery allows identification and division of the inferior mesenteric vein just below the pancreas.
The colon must be divided before one proceeds with rectal mobilization. The level of division is conventionally at the junction of the descending colon and the sigmoid colon. If vascularity is good, division at the midpoint or apex of the sigmoid colon is acceptable as well. It is important to recognize that this step also prepares the proximal component of the anastomosis, and the division of the mesocolon should ensure that the arterial arcade to the colon at the level of division is preserved.
The technique used in dividing the colon is determined by the choice of reconstruction. Stapled division is ideal when a short colonic pouch–rectum anastomosis is considered. For a straight colorectal anastomosis, the proximal and distal divided ends may be tied with purse-string sutures and clamped, respectively, to save on staplers. (See the image below.)
Mobilization and division of rectum
The task is to free the rectum with an intact mesorectum all around up to the level of the levators. It is easier to break up this task into three parts: posterior dissection, lateral (right and left) dissection, and anterior dissection. The posterior and lateral dissection is a brisk process up to the midsacral level because of the presence of the loose areolar tissue as the cleavable plane; beyond that level, dissection involves identification and division of a few fascial fibers, vessels, and nerves.
The anterior dissection requires careful identification of the seminal vesicles in men and the vagina in women. The length dissected anteriorly is quite short, but meticulous technique is required to remain in the correct plane. The keys to success in this step are maintaining good visibility of the pelvic structures (facilitated by a good headlight) and providing strong countertraction away from the plane of dissection. A St Mark's retractor is an invaluable friend to a rectal surgeon.
Initial posterior and lateral dissection
Strong anterior traction on the rectum will allow sharp dissection in the rectosacral plane. The key is to keep the hypogastric nerves always in sight and proceed inferiorly in a plane just anterior to the nerves. The same plane can be developed laterally to the right and left, one side at a time. Lateral dissection again is facilitated by retracting the rectum to the opposite side with a St Mark's retractor. Posterior dissection can proceed as far as the surgeon can go down comfortably at this point in time. Further posterior and lateral mobilization is easier once the anterior dissection is completed.
For obvious anatomic reasons, anterior dissection is different in men and women. In women, the dissection starts with identification of the peritoneum over the pouch of Douglas. This is best achieved by retracting the uterus anteriorly and rectum posteriorly while maintaining an upward pull on both. Meticulous dissection is required to prevent any damage to the thin-walled vagina as the rectum is separated from the vagina along most of its length. Diathermy or sharp scissors can be sued to carry out this part of the dissection.
In men, the line of division of the peritoneum can be identified by retracting the bladder anteriorly and the rectum posteriorly. It is safer to enter the plane by dividing the peritoneum just anterior to the fold to avoid entering the rectal wall. After division of the peritoneum, the seminal vesicles are identified, and dissection proceeds slowly in a plane just posterior to the seminal vesicles. Advancing the retractor over the seminal vesicles and maintaining anterior traction will help one remain in the correct plane.
Intraoperative neuromonitoring is an emerging technique. Early reports suggested that the use of neuromonitoring during TME is associated with significantly lower rates of urinary and anorectal dysfunction.
Completion of lateral and posterior dissection
At the midsacral level, the fascia in the posterior midline tends to get slightly denser. Division of these rectosacral fascial fibers will lead to the levators. The inferior margin of the piriformis is a useful site to identify the emerging sacral nerves. As the nerves reach seminal vesicles anterolaterally, their dissection becomes difficult. Care should be taken to only divide those branches of the nerves entering the rectal wall. Lateral pedicles are not searched for or clamped because of the high incidence of injury to these nerves. Diathermy and clips may be handy in achieving adequate hemostasis during this dissection.
Division of rectum
The rectum is divided at the level of the levators. At this level, there is no further mesorectum, and the rectum is largely seen as a muscular tube. A 30-mm heavy-wire linear stapler delivering two rows of staples is fired at this level. An occlusion clamp is applied proximal to the stapler, and the rectum is divided on the stapler with a knife before releasing the stapler. (See the image below.)
Injury to autonomic nerves during TME is very likely. The four areas described as most vulnerable to operative injury are as follows :
Origin of the inferior mesenteric artery
Anterior to the sacral promontory
Lateral walls of the pelvis
Posterolateral corners of the prostate
Anastomosis using stapling devices is the current standard for low anterior resection. Although a sutured anastomosis is technically feasible, a stapled anastomosis is more consistent and ergonomically superior, as well as being easier to teach and learn. Stapling is a skill, and adherence to the correct technique is essential to avoiding a catastrophic loss of joinable rectum inferiorly.
The colon is anastomosed to the rectum either as a straight colorectal anastomosis or as a colonic pouch–rectum anastomosis. The pouch is actually a short J pouch with a 6- to 8-cm limb; it owes its popularity to reports suggesting lesser stool frequency in the first year after surgery. The pouch can be constructed with a 80-mm linear cutter.
The pouch-rectum anastomosis is constructed with a circular stapler that can fire two rows of staples while dividing tissue centrally. The anvil of the circular stapler is secured at the apex of the colonic pouch with a purse-string suture. The stapler is introduced by an assistant through the anus. The surgeon, with an eye and a hand on the rectal stump, guides the assistant in positioning the stapler safely and securely within the rectal stump. A dependable way of proiding verbal guidance is to instruct the assistant to either drop his or her hands or pick them up so as to move the stapler accordingly.
At this point, the assistant advances the central spike to emerge either through the staple line of the rectum or close to it. The anvil is engaged onto the spike and the stapler is closed to approximate the two components of the anastomosis. Before the stapler is fired, every care must be taken to ensure that no other structure—especially the vaginal wall—does not get caught in between. After firing, the stapler is disengaged carefully, and only after it has been opened by 1.5 turns. The presence of two complete donuts confirms a complete anastomosis.
The anastomosis is evaluated by performing an air leak test after filling the pelvis with saline. Repair or a complete takedown and reanastomosis is indicated only in very large leaks. A small leak is taken care of with a proximal diversion. In the absence of a leak, the choice of diversion is trickier. Centers with a high volume of low anterior resections are more selective in the use of proximal diversion. Most other surgeons routinely perform a proximal diversion by a loop ileostomy. The loop ileostomy is closed after 6-8 weeks after the integrity of the anastomosis has been confirmed by means of a water-soluble contrast study. (See the image below.)
Nerve-oriented mesorectal excision (NOME) is described as a newer technique wherein autonomic pelvic nerves serve as landmarks for a standardized navigation along fascial planes. Proponents of this technique claim that it achieves high-quality mesorectal specimens and a high rate of preservation of autonomic nerve function.
TME can also be performed laparoscopically. A 2014 Cochrane review suggests that survival and recurrence rates are similar to those for the equivalent open procedure, though the evidence is not yet sufficiently precise to rule out the possibility that one approach may be superior to the other.
Transanal approaches to TME have also been the subject of considerable interest. So far, such approaches appear to be safe and feasible in the treatment of rectal cancer.[6, 7]
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