An anal fissure is a cut or tear occurring in the anus. Fissures are a fairly common condition and responsible for six to 15 percent of the visits to a colorectal specialist.
They affect men and women equally – both the young and the old. Fissures usually cause pain, often severe, during bowel movements and is the most common cause of rectal bleeding in infants.
Where Do Anal Fissure Occur?
Anal fissures occur in the anoderm – the specialized tissue that lines the anus and anal canal. At a line, just inside the anus, referred to as the anal verge or intersphincteric groove, the skin of the inner buttocks changes to anoderm.
Unlike skin, anoderm has no hairs, sweat glands, or sebaceous glands and contains a larger number of somatic sensory nerves that sense light touch and pain. The abundance of nerves in this region is the reason why anal fissures are so painful. The hairless, gland-less, extremely sensitive anoderm continues for the entire length of the anal canal until it meets the demarcating line for the rectum, called the dentate line.
What Causes Anal Fissures?
Anal fissures are caused by trauma to the anus and anal canal. Typically, fissure is caused by a hard stool or repeated episodes of diarrhea. Childbirth is also a common cause of anal fissures. Though extremely rare, the insertion of a rectal thermometer, enema tip, endoscope, or ultrasound probe can result in sufficient trauma to produce a fissure.
The most common location for an anal fissure in both men and women (ninety percent of all fissures) is the midline posteriorly in the anal canal, the part of the anus nearest the spine. Fissures are more common posteriorly because of the configuration of the muscle that surrounds the anus. This muscle complex, referred to as the external and internal anal sphincters, underlies and supports the anal canal.
The sphincters are oval-shaped and are best supported at their sides and weakest posteriorly. When tears occur in the anoderm, therefore, they are more likely to be posterior. In women, there also is weak support for the anterior anal canal due to the presence of the vagina anterior to the anus. For this reason, ten percent of fissures in women are anterior, while only one percent are anterior in men. At the lower end of fissures a tag of skin may form, called a sentinal pile.
When fissures occur in locations other than the midline posteriorly or anteriorly, they should raise the suspicion that a problem other than trauma is the cause. Other causes of fissures are anal cancer, Crohn’s disease, leukemia as well as many infectious diseases including tuberculosis, viral infections (cytomegalovirus or herpes), syphilis, gonorrhea, chlamydia , chancroid (Hemophilus ducreyi), and human immunodeficiency virus (HIV).
Among patients with Crohn’s disease, four percent will have an anal fissure as the first manifestation of their Crohn’s disease, and half of all patients with Crohn’s disease eventually will develop an anal ulceration that may look like a fissure.