Anal stenosis is a narrowing of the anal canal. Long-term inflammation in the rectum sometimes causes scarring. Repeated ulceration and healing can also result in scar tissue, as can surgical procedures for hemorrhoids, skin tags, anal dilation, and sphincterectomy. Scar tissue is not as flexible as healthy tissue, and the gradual build-up can narrow and constrict the rectal or anal canal, resulting in a rectal or anal narrowing, or stricture (also called stenosis).
For most people, rectal strictures are caused by one or a combination of these factors: constipation or straining to have a bowel movement, anal or rectal fissures (tears), trauma, weak blood vessels, irritation from constant diarrhea, inflammatory bowel disease, or rectal infection.