Etiology and management of low anterior resection syndrome based on the normal defecation mechanism.

Low anterior resection syndrome (LARS) commonly develops after an anal sphincter-preserving operation (SPO). The etiology of LARS is not well understood, as the anatomical components and physiological function of normal defecation, which may be damaged during the SPO, are not well established. SPOs may damage components of the anal canal (such as the internal anal sphincter, longitudinal conjoint muscle, or hiatal ligament), either mechanically or via injury to the nerves that supply these organs. The function of the rectum is substantially impaired by resection of the rectum, division of the rectococcygeus muscle, and/or injury of the nervous supply. When the remnant rectum is small and does not function properly, an important functional role may be played by the neorectum, which is usually constructed from the left side of the colon. Hypermotility of the remnant colon may affect the manifestation of urge fecal incontinence. To develop an SPO that minimizes the risk of LARS, the anatomy and physiology of the structures involved in normal defecation need to be understood better. LARS is managed similarly to fecal incontinence. In particular, management should focus on reducing colonic motility when urge fecal incontinence is the dominant symptom.