What is the normal length of the rectum?

Normal Length of the Rectum

The normal rectum is approximately 12-15 cm in length, with tumors having distal extension to 15 cm or less from the anal margin classified as rectal cancer. 1

Anatomical Classification of the Rectum

• The rectum extends from the anal verge to approximately 15 cm proximally, as measured by rigid sigmoidoscopy or proctoscopy 1
• The rectum is further categorized into three segments based on distance from the anal verge 1:
  • Low rectum: up to 5 cm from anal verge
  • Middle rectum: >5 to 10 cm from anal verge
  • High rectum: >10 to 15 cm from anal verge

Peritoneal Reflection and Rectum Measurements

• The peritoneal reflection varies in its relationship to the rectum 2:

  • Anterior peritoneal reflection: approximately 8-9 cm from anal verge
  • Lateral peritoneal reflection: approximately 11 cm from anal verge
  • Posterior peritoneal reflection: approximately 14 cm from anal verge

• These measurements show no statistically significant differences between males and females 2

Clinical Significance of Rectal Length

• Understanding rectal length is crucial for:
  • Proper classification of rectal tumors (vs. colonic tumors) 1
  • Selection of appropriate surgical techniques 3
  • Planning for neoadjuvant therapy in rectal cancer 3

Variations in Rectal Dimensions

• The median diameter of the rectum is approximately 39 mm (range: 22-67 mm) 4
• Women tend to have larger rectal cross-sectional areas compared to men, which may reflect the higher prevalence of constipation in females 4
• Age does not significantly affect rectal diameter or cross-sectional area 4

Measurement Techniques

• Rigid sigmoidoscopy is the standard method for measuring rectal length in clinical practice 1
• Other measurement techniques include:
  • Digital rectal examination (limited to distal rectum) 5
  • Magnetic resonance imaging (MRI) 1
  • Endorectal ultrasound 1
  • Computed tomography (CT) scans 4

Clinical Implications

• Proper measurement of rectal length is essential for:

  • Determining treatment approaches for rectal cancer 1, 3
  • High rectal cancers (10-15 cm) generally require wide mesorectal excision rather than total mesorectal excision 3
  • Low and middle rectal cancers may require different surgical and neoadjuvant approaches compared to high rectal cancers 3

• Misclassification of rectal tumors based on incorrect length measurements can lead to inappropriate treatment selection, including unnecessary preoperative chemoradiotherapy for high rectal cancers 3

Pediatric Considerations

• In children, the rectum comprises approximately 9-12% of the total large bowel length 6
• The rectum increases in length with age, from early childhood through adolescence 6