Anal Fistulas and Fissures 

An anal fissure is a superficial linear tear in the anoderm that is most commonly caused by passage of a large, hard stool. This tear is distal to the dentate line. Anal fissures are among the most common anorectal disorders in the pediatric population; however, adults are also affected.

Fissures are defined as acute if present for less than 6 weeks, and they are defined as chronic if present for more than 6 weeks.

An anal fistula is an inflammatory tract between the anal canal and the skin, as shown in the image below. The 4 categories of fistulas, based on the relationship of fistula to sphincter muscles, are intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric.^[1]

In anal fissures, anus distal to dentate line is involved. About 90% of anal fissures occur in the posterior midline, where skeletal muscle fibers that circle the anus are weakest. The remaining 10% are found in the anterior midline.

An anal fissure is shown in the image below.

Anal fissures can be observed in patients with syphilis and other sexually transmitted diseases, tuberculosis, leukemia,^[2] inflammatory bowel disease such as Crohn disease, previous anal surgery, HIV, and other conditions or diseases.

The incidence of anal fissures in patients with leukemia is approximately 24%.

Most anal fistulas originate in anal crypts, which become infected with abscess formation. When the abscess is opened or ruptures, a fistula is formed.

Other causes of anal fistulas include opened perianal or ischiorectal abscesses, which drain spontaneously through these fistulous tracts. Fistulas are also found in patients with inflammatory bowel disease, particularly Crohn disease.^[3] The incidence of fissures in Crohn disease is 30-50%. Perianal activity often parallels abdominal disease activity, but it may occasionally be the primary site of active disease.

Anal fistulas also are associated with diverticulitis, foreign-body reactions, actinomycosis, chlamydia, lymphogranuloma venereum (LGV), syphilis, tuberculosis, radiation exposure, and HIV. Approximately 30% of patients with HIV develop anorectal abscesses and fistulas.

Additional causes include the following:

• Passage of hard stool
• Chronic diarrhea
• Childbirth (accounts for 10% of chronic anal fissures)
• Habitual use of cathartics
• Anal trauma (can occur with anal intercourse or a rectal examination using a speculum or digit)

Anal fissures affect males and females equally; however, an anterior fissure is more likely to develop in women (25%) than in men (8%). Although anal fissures are the most common cause of rectal bleeding in infants, they are primarily seen in young adults. Eighty-seven percent of people with a chronic anal fissure are between the ages of 20 and 60 years old. Anal fissures in children may indicate sexual abuse.

Only 8% of anal fissures are anterior in men; 75-90% of fissures in women are posteriorly located.

Anal fistulas are a complication of anorectal abscesses, which are more common in men than in women (male-to-female ratio of 2:1 to 3:1). For reasons of intrinsic anatomy, rectovaginal fistulas are found only in women.

Most uncomplicated fissures resolve in 2-4 weeks with supportive care. Fissures that heal with conservative treatment have a recurrence rate of up to 27%. Chronic anal fissures frequently require surgical treatment.

Surgical treatment of anal fissures is associated with some degree of incontinence in 30% of patients. Prognosis for fistulas is excellent after surgery.