What is the anatomy of the pelvis relevant to performing 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 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 specimen's appearance on gross inspection 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 dissection 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.


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