Anatomy of the Rectum

Rectum Anatomy

• The proximal border of the anal sphincter complex is located at the level of the levator ani, approximately 2 cm above the dentate line.
• The rectum is approximately 15-20 cm in length and is divided into thirds based on its peritoneal relationships.

Rectum Structure

• The upper third of the rectum is covered by peritoneum anteriorly and laterally, extending to approximately 10 cm above the dentate line.
• The middle third is covered by peritoneum only anteriorly, extending from 5 to 10 cm above the dentate line.
• The lower third of the rectum is totally extraperitoneal, extending from 1 to 5 cm above the dentate line.
• The rectum has three lateral curves or valves of Houston, with the proximal and distal valves folding to the right and the middle to the left.
• The valves of Houston are lost after full surgical mobilization of the rectum, providing approximately 5 cm of additional length for anastomosis.

Rectal Relationships

• The anterior peritoneal reflection between the rectum and anterior structures is located 7-9 cm from the anal verge in males and 5-7.5 cm in females.
• The anterior peritoneal reflection is the lowest dependent part of the peritoneal cavity and is a common location for fluid and pus accumulation and peritoneal metastases from visceral tumors.

Mesorectum and Surgical Importance

• The mesorectum refers to the visceral mesentery of the rectum.
• Recognition of mesorectal planes during rectal surgery is crucial for bloodless dissection and excision of relevant lymphatic tissues.
• Total mesorectal excision (TME) has been shown to reduce local recurrence of rectal cancer and preserve urinary and sexual function.

Adjacent Anatomic Structures

• In males, the rectum is adjacent anteriorly and extraperitoneally to the urinary bladder, ureters, vas deferens, seminal vesicles, and prostate.
• In females, the rectum is adjacent to the urinary bladder and uterus intraperitoneally.

This quiz covers the anatomical landmarks of the rectum, such as the proximal border of the anal sphincter complex and the division of the rectum into thirds based on its peritoneal relationships. Test your knowledge on the lengths and peritoneal coverings of different sections of the rectum.