Overview of the Rectum

The rectum as measured by rigid proctoscopy extends approximately 12–15 cm in length from the anal verge. It occupies the pelvis and angulates at the level of the coccyx to pass through the levator muscles. In a female, the rectum is posterior to the uterus, cervix, and posterior vaginal wall; in a male, it is posterior to the bladder, vas deferens, seminal vesicles, and prostate (Figure 1 and Figure 2).[1]

The proximal limit of the rectum can be defined in various ways. The National Comprehensive Cancer Network® (NCCN^®) defines the rectum by the intestine that lies below the line that can be drawn between the sacral promontory and the upper edge of the pubic symphysis. Both these structures can be seen easily on magnetic resonance imaging (MRI; Figure 3).[2]

Figure 1. Fascial Relationships of the Rectum

Figure 2. Perianal and Perirectal Spaces (Lateral View)

Carmichael JC and Mills S. Male Anatomy and Embryology of the Colon, Rectum, and Anus. In: Steele SR, Hull TL, Hyman N, Makel JA, Read TE, Whitlow CB, eds. The ASCRS Textbook of Colon and Rectal Surgery, Fourth Edition. Springer, 2022:3–28.

Figure 3. Rectum Lies Below the Yellow Line

Referenced with permission from the NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®) for Guideline Name V.4.2025. © National Comprehensive Cancer Network, Inc. 2025. All rights reserved. Accessed February 11, 2026. To view the most recent and complete version of the guideline, go online to NCCN.org.
NCCN makes no warranties of any kind whatsoever regarding their content, use or application and disclaims any responsibility for their application or use in any way.

Other definitions describe the proximal aspect located where the outer longitudinal muscles form the tenia coli from a cephalad angle, as shown in Figure 4.[1] Intraoperatively, most surgeons would note this point on the bowel where the taenia coli of the sigmoid splay to denote the upper margin of the rectum (again, see the diagram in Figure 4), especially during a diverticulitis surgery.[3]

Figure 4. Colon Displaying the Teniae Changes at the Rectosigmoid Junction

2025. Used with permission of Elsevier. All rights reserved.

Endoscopically, rectal anatomic landmarks are classically described as three convex curves created by submucosal folds in the lumen known as the valves of Houston. The first is located, on average, 7.8 cm from the anal verge, with the second at 9.4 cm and the third at 11.3 cm. In actuality, the three valves were present in fewer than 50% of patients based on endoscopic evaluation of 400 participants.[4] The middle valve (Kohlrausch’s plica) can correspond to the anterior peritoneal reflection.[5] Therefore, the middle valve and or the peritoneal reflection can be used to estimate intraperitoneal versus extraperitoneal location of a rectal cancer.[6] Below the peritoneal reflection, the rectum is entirely extraperitoneal and loses its serosal surface.[7][8]