Anatomical Basis of Transverse Colon Cross-Sectional Shape
The transverse colon appears triangular in cross-section on imaging due to the presence of three longitudinal bands of smooth muscle called taeniae coli that run along its length, causing the colon wall to pucker between them and creating a characteristic triangular configuration.
Anatomical Structure
The triangular appearance is a normal anatomical feature that results from:
- Three taeniae coli that are evenly spaced around the circumference of the colon, creating three distinct "corners" when viewed in cross-section
- The colonic wall between these muscular bands forms the three "sides" of the triangle
- This configuration is most prominent in the transverse colon due to its intraperitoneal position and mobility
Clinical Relevance
Understanding this normal triangular morphology is important for several clinical scenarios:
- Surgical planning: The transverse mesocolon has complex embryologic anatomy due to fusion with the frontal surface of the duodenum and pancreas during development, and knowledge of normal anatomy is essential for complete mesocolic excision 1
- Imaging interpretation: Recognition of the normal triangular shape prevents misinterpretation as pathology on CT scans, where anatomic variations of the colon are relatively common 2
- Procedural safety: The transverse colon's mobility and anatomical relationships make it susceptible to injury during percutaneous interventions if its position is not properly identified 2
Distinguishing from Pathology
The triangular shape should be:
- Symmetric with smooth contours between the taeniae
- Consistent along the length of the transverse colon
- Without wall thickening or mass effect
This differs from the triangular-shaped bare area described posteriorly in the rectum, which represents the nonperitonealized margin extending superiorly in continuity with the sigmoid mesentery—an entirely different anatomical structure relevant for rectal cancer staging 3.