Transverse rectal folds

The transverse rectal folds (a.k.a. the valves of Houston), are permanent semilunar folds of the rectal wall that project into the lumen of the rectum. Unlike temporary mucosal folds that disappear when the bowel is distended, these transverse folds persist because they are formed by the mucosa, submucosa, and thickened circular smooth muscle layer of the rectal wall. They play an important role in supporting the weight of faecal contents, helping to prevent the sudden passage of faeces into the anal canal and thereby contributing to continence.

Typically, there are three transverse rectal folds.

• The superior fold arises from the left lateral wall of the upper rectum,

• The middle fold (Kohlrauschs fold) arises from the right lateral wall of the middle rectum, and

• The inferior fold arises from the left lateral wall of the lower rectum.

These folds correspond approximately to the three lateral flexures of the rectum and contribute to its characteristic curved course. The superior and inferior folds are associated with rectal convexities to the right (superior and inferior), whereas the middle fold corresponds to a convexity to the left.

The middle transverse rectal fold (Kohlrauschs fold) is the largest and most constant of the three folds and is situated approximately 6-8 cm from the anal verge. It is an important anatomical landmark during digital rectal examination, sigmoidoscopy, colonoscopy, and rectal surgery. Clinically, it lies near the level of the rectovesical pouch in males and the rectouterine pouch (pouch of Douglas) in females.