What is the length of the rectum?

Length of the Rectum

The rectum is defined as the distal segment of the gastrointestinal tract extending 15 cm from the anal margin, as measured by rigid sigmoidoscopy. 1

Anatomical Definition and Landmarks

The rectum is classified into three distinct segments based on distance from the anal margin:

• Low rectum: Up to 5 cm from the anal margin
• Middle rectum: >5 cm to 10 cm from the anal margin
• High rectum: >10 cm to 15 cm from the anal margin 1

This anatomical classification is clinically important for several reasons:

• Determines surgical approach (sphincter-preserving vs. non-preserving)
• Guides radiotherapy planning
• Influences risk stratification for local recurrence
• Affects functional outcomes after treatment

Peritoneal Reflection and Other Landmarks

The peritoneal reflection varies in its relationship to the rectum:

• Anterior peritoneal reflection: Approximately 8.8 cm (males) and 8.1 cm (females) from the anal verge 2
• Lateral peritoneal reflection: Approximately 10.8-11.4 cm from the anal verge 2
• Posterior peritoneal reflection: Approximately 13.8-14.0 cm from the anal verge 2

The sacral promontory, which marks the transition from sigmoid colon to rectum, is located approximately 16.1-16.5 cm from the anal verge 2.

Individual Variability

It's important to note that significant individual variability exists in rectal anatomy. A study by Wasserman et al. demonstrated that the location of common pelvic landmarks is highly variable among individuals 3. Factors affecting these measurements include:

• Gender: Men generally have longer distances to the dentate line, puborectalis muscle, and anterior peritoneal reflection compared to women 3
• Body habitus: Patient weight correlates with distances to most anatomical landmarks 3
• Height: Correlates with the length to the sacral promontory 2

Clinical Implications

The precise definition of the rectum is critical for:

1. Cancer staging and treatment planning: Tumors with distal extension to 15 cm or less from the anal margin are classified as rectal, while more proximal tumors are considered colonic 1

2. Surgical approach selection:

   • Upper third cancers and usually middle third cancers can be treated with sphincter preservation (anterior resection or colo-anal anastomosis)
   • Lower third cancers typically require radical resection (abdomino-perineal resection) 1

3. Radiotherapy planning: Preoperative radiotherapy is indicated for T3 and T4 tumors of the rectum and may be indicated for T2 tumors 1

4. Endoscopic procedures: For local treatment of early rectal cancers, precise localization is essential 1

Measurement Methods

The most accurate method for measuring rectal length is rigid sigmoidoscopy 1. This is preferred over flexible endoscopy for precise measurements because flexible scopes can loop and provide inaccurate distance measurements.

The use of predefined absolute measurements from the anal verge without accounting for individual patient factors may lead to inaccurate localization of rectal pathology 3.