What is the anatomy of the rectum in relation to rectal cancer?

Updated: Apr 06, 2021
  • Author: Burt Cagir, MD, FACS; Chief Editor: N Joseph Espat, MD, MS, FACS  more...
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The surgical definition of the rectum differs from the anatomical definition; surgeons define the rectum as starting at the level of the sacral promontory, while anatomists define the rectum as starting at the level of the 3rd sacral vertebra. Therefore, the measured length of the rectum varies from 12 cm to 15 cm. The rectum differs from the rest of the colon in that the outer layer consists of longitudinal muscle. The rectum contains three folds, namely the valves of Houston. The superior (at 10 cm to 12 cm) and inferior (at 4 cm to 7 cm) folds are located on the left side and the middle fold (at 8 cm to 10 cm) is located at the right side.

National Comprehensive Cancer Network guidelines define rectal cancer as cancer located within 12 cm of the anal verge by rigid proctoscopy. [1] This definition was developed by the Dutch Colorectal Cancer Group study, which found that the risk of recurrence of rectal cancer depends on the location of the cancer. Univariate sub-group analyses showed that the treatment effect for surgery alone vs preoperative radiotherapy plus surgery was not significant in patients whose cancer (TNM stage I to IV) was located between 10.1 cm and 15 cm from the anal verge. [5]

Computed tomography or magnetic resonance imaging is the most common modality to define the anatomic rectum. The variations in the definition of anatomic rectum result in variations in the treatment options, most importantly determining whether neoadjuvant chemoradiotherapy is indicated.  Neoadjuvant therapy has significant consequences in the functional and oncologic outcomes of patients. 

The following features are used to define the rectum apart from the sigmoid colon [6] :

  • The sacral promontory
  • The third valve of Houston
  • The coalescence of tenia of sigmoid
  • The transition from sigmoid mesocolon to mesorectum
  • Loss of appendiceal epiploicae
  • Anterior peritoneal reflection 

In order to standardize treatment of colorectal cancer, an international group of colorectal experts established a consensus definition of the anatomic rectum, using the Delphi technique. This consensus meeting came up with new terminology, the sigmoid takeoff, which defines the junction of sigmoid colon and rectum and the junction of sigmoid mesocolon and mesorectum radiographically. [6]  Although there are many publications on this topic in the literature, all rectal surgeons should familiarize themselves with the Delphi consensus article, as well as "The 'Holy Plane' of rectal surgery", which defines an optimal dissection plane around rectal tumors in terms of the pelvic fascia. [6, 7]

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