An anal fissure is a tear in the lining of the anus. The tear typically extends into a circular ring of muscle called the internal anal sphincter. The fissure is described as acute if it has been present for less than six weeks or chronic if present for more than six weeks. Once a fissure develops, the internal anal sphincter typically goes into spasm, causing further separation of the tear, constricting blood flow to the area, impairing healing, and causing pain.
Usually, an anal fissure may be diagnosed by visual inspection of the anus or by gentle exam with the tip of the finger.