Superior lateral flexure of rectum

The superior lateral flexure of rectum is the uppermost of the three permanent lateral curvatures of the rectum. It is located in the upper part of the rectum near the rectosigmoid junction, approximately opposite the third sacral vertebra (S3). The flexure is typically convex to the right and corresponds to the level of the superior transverse rectal fold (superior valve of Houston), which projects into the rectal lumen from the left lateral wall.

The superior lateral flexure contributes to the characteristic zigzag course of the rectal lumen. The associated superior transverse rectal fold is formed by the mucosa, submucosa, and a thickening of the circular muscle layer, and helps support the weight of faecal contents within the rectum. Together, the rectal flexures and transverse folds slow the direct descent of faeces into the anal canal, thereby facilitating temporary storage and contributing to the maintenance of continence.

Clinical Correlation

The superior lateral flexure and its associated transverse rectal fold are important anatomical landmarks during sigmoidoscopy and colonoscopy. Awareness of these normal curvatures helps facilitates safe advancement of instruments through the rectum.