Presentation of the Male Semilunar Folds from a Lateral Standpoint

Description

Seen from a lateral standpoint in the male pelvis, the rectal wall is opened to emphasize the transverse rectal folds (plicae transversae recti, Houston’s valves) projecting into the lumen as semilunar ridges. Superiorly, these folds relate to the sigmoid colon and rectosigmoid junction; inferiorly, they step toward the anorectal junction where the rectum angles posteriorly into the anal canal. Their shelf-like margins span partially across the lumen, creating alternating recesses on the opposite wall and a subtly spiraling course in profile. Endoscopic navigation and operative planning both benefit from a clear lateral appreciation of Houston’s valves, because these folds can be mistaken for obstructing pathology or, conversely, can hide a lesion on the contralateral wall during flexible sigmoidoscopy. They also explain why the rectum is not a straight tube: the folds correspond to the rectal curvatures and support the fecal column, a relationship that matters during transanal instrumentation and during assessment of low rectal tumors where distance to the anorectal ring and relation to the peritoneal reflection influence staging and approach. Small anatomy, big consequences. Misidentifying a normal fold as a stricture can derail the exam. Use this asset in colorectal surgery teaching decks, GI endoscopy orientation materials, and anatomy curricula covering the distal large bowel, pelvic viscera, and continence mechanisms in the adult male. It also suits atlas plates and review articles discussing rectal anatomy landmarks for TME planning, low anterior resection, and accurate localization of bleeding or polyps during colonoscopy reporting. Anatomical accuracy verified by SciePro's Medical Advisory Board.