How is the rectum mobilized during total mesorectal excision (TME)?

Updated: Feb 16, 2021
  • Author: Nanda Kishore Maroju, MRCS, MS, MBBS, DNB; Chief Editor: Kurt E Roberts, MD  more...
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Answer

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 as follows:

  • Posterior dissection
  • Lateral (right and left) dissection
  • 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.

Anterior dissection

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 the 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 used 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. [3]

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 for identifying 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 the stapler is released. (See the image below.)

Total mesorectal excision: Mobilization of the rec Total mesorectal excision: Mobilization of the rectum and division.

Injury to autonomic nerves during TME is very likely. The four areas described as most vulnerable to operative injury are as follows [4] :

  • Origin of the inferior mesenteric artery
  • Area anterior to the sacral promontory
  • Lateral walls of the pelvis
  • Posterolateral corners of the prostate

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