Anal Fissure

An anal fissure is an unnatural crack or tear in the anus skin. As a fissure, these tiny tears may show as bright red rectal bleeding and cause severe periodic pain after defecation. The tear usually extends from the anal opening and located posteriorly in the midline. This location is probably because of the relatively unsupported nature of the anal wall in that location.
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Anal fissure n. A crack or slit in the mucous membrane of the anus. Anal fissure An ulcer on the margin of the anus. Mentioned in: Anoscopy [more]Anal fissure - Community and Resources

Common tear in the anal canal. One of the common causes of red blood in the stool.