What causes anal fissures?

Updated: Nov 09, 2018
  • Author: Bruce M Lo, MD, MBA, CPE, RDMS, FACEP, FAAEM, FACHE; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Answer

In anal fissures, the anus distal to the dentate line is involved. About 90% of anal fissures occur in the posterior midline. Ten percent are found in the anterior midline, more commonly in women. Only 1% occur off midline.

While the exact etiology is often unknown, passage of hard stools and anal trauma are often associated with anal fissures. Other causes of anal fissures can be observed in patients with chronic diarrhea, during childbirth, and those with a habitual use of cathartics. When an anal fissure occurs in an atypical location, it may be associated with syphilis and other sexually transmitted diseases, tuberculosis, [3] leukemia, [4] inflammatory bowel disease such as Crohn disease, previous anal surgery, HIV disease, and anal cancer. Once a fissure is formed, ongoing pain can cause the internal analsphincter to spasm (hypertonicity), which causes the wound edges of the fissure to pull apart, impairing healing. Local ischemia is also thought to contribute to anal fistulas, especially in the posterior quadrant where blood flow is significantly less than other quadrants. As the anal sphincter continues to spasm, increased pressures are thought to further impede blood flow. [5, 1]


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