Anal fissure

What it is

An anal fissure is a tear at the anus, usually caused by a hyperactive, contracted, stiff anal sphincter. One that is only days old is an acute anal fissure. A chronic anal fissure shows three signs: a hypertrophied anal papilla, a fissure with heaped up scarred edges, and a sentinel skin tag.

An anal fissure is a tear of the anal canal below the dentate line, in the very sensitive squamous epithelium. 90% lie in the posterior midline and 10% in the anterior midline. One that lies off the midline should raise other possible causes such as IBD, STIs, TB, leukemia or anal carcinoma.

It arises from forceful dilation of the anal canal by large, hard stools and irritant diarrheal stools, and from tightening of the anal canal secondary to nervousness or pain, which leads to further tearing. The acute fissure gives very painful bright red bleeding, especially after a bowel movement, with sphincter spasm on limited DRE. After 6 weeks it is a chronic anal fissure.