Anal Fistulas and Fissures

Updated: May 27, 2022
  • Author: Bruce M Lo, MD, MBA, CPE, RDMS, FACEP, FAAEM, FACHE; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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An anal fissure is a superficial linear tear in the anoderm that is distal to the dentate line. Anal fissures are often associated with local trauma such as the passage of hard stools or anal trauma, but can also be due to secondary causes such as inflammatory bowel disease. Anal fissures are among the most common anorectal disorders in the pediatric population. Adults are also affected, although it is thought to be underreported in the adult population.

Fissures are defined as acute if present for less than 8 weeks, and they are defined as chronic if present for more than at 8-12 weeks and feature edema and fibrosis. [1, 2] Chronic anal fissures persist as nonhealing ulcers by anal sphincter spasm and result in ischemia. [2]

An anal fistula is an inflammatory tract between the anal canal and the skin. The four categories of fistulas, based on the relationship of fistula to sphincter muscles, are intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric. [3]

An anal fistula can be categorized as either simple or complex. A simple anal fistula includes low transsphincteric and intersphincteric fistulas that cross 30% of the external sphincter. Fistulas are complex if the primary track includes high transsphincteric fistulas with or without a high blind tract, suprasphincteric and extrasphincteric fistulas, horseshoe fistulas, multiple tracks, anteriorly lying track in a female patient, and those associated with inflammatory bowel disease, radiation, malignancy, preexisting incontinence, or chronic diarrhea. Note the image below.

Anal Fistulas and Fissures. This patient reported Anal Fistulas and Fissures. This patient reported constipation.

Pathophysiology and Etiology

Anal fissure

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, [4] leukemia, [5] 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 anal sphincter 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. [1, 6]

Evidence suggests that blood flow to the anal canal and internal anal sphincter tone play a role in the development and healing of anal fissures. Decreased blood flow has been described in chronic, nonhealing fissures. Hypertonicity of the internal sphincter may also cause decreased blood flow in the area of a fissure. [7, 8, 9]

Anal fistula

Most anal fistulas originate in anal crypts, which become infected, with ensuing abscess formation. When the abscess is opened or when it ruptures, a fistula is formed. An anal fistula can have multiple accessory tracts complicating its anatomy.

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. [10] 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 can also be associated with diverticulitis, foreign-body reactions, actinomycosis, chlamydia, lymphogranuloma venereum (LGV), syphilis, tuberculosis, [4] radiation exposure, and HIV disease. Approximately 30% of patients with HIV disease develop anorectal abscesses and fistulas.

Anal fistulas are classified into the following four general types:

  • Intersphincteric: Through the dentate line to the anal verge, tracking along the intersphincteric plane, ending in the perianal skin

  • Transsphincteric: Through the external sphincter into the ischiorectal fossa, encompassing a portion of the internal and external sphincter, ending in the skin overlying buttocks

  • Suprasphincteric: Through the anal crypt and encircling the entire sphincter, ending in the ischiorectal fossa

  • Extrasphincteric: Starting high in the anal canal, encompassing the entire sphincter and ending in the skin overlying the buttocks



Anal fissures affect males and females equally; however, an anterior fissure is more likely to develop in women (25%) than in men (8%). [6] 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. Anal fissures in children may indicate sexual abuse.

Anal fistulas are a complication of anorectal abscesses, which are more common in women than in men. For reasons of intrinsic anatomy, rectovaginal fistulas are found only in women. Approximately 30-50% of patients with an anorectal abscess form an anal fistula, [11] and approximately 80% of anal fistulas arise from anorectal infection. [12]



Approximately half of uncomplicated fissures resolve in 2-4 weeks with supportive care. [1] Fissures that heal with conservative treatment can recur, depending on the type of treatment the patient has undergone (ranging from 16% to more than 50%). [6] Chronic anal fissures frequently require surgical treatment.

Surgical treatment of anal fissures is associated with some degree of incontinence in approximately 14% of patients. [13]

Prognosis for fistulas is excellent after surgery, with recurrence rates around 7-21% depending on the complexity and location of the fistula. [12, 14] Use of fibrin glue or fistula plug has variable success rates.


Constipation or fecal impaction may occur. The pain from an anal fissure can be so overwhelming that it discourages people from defecating. Acute fissures can become chronic, and sentinel pile can result. A permanent skin tag can result, and fistulas may form.

The following complications may occur with surgical intervention [3, 15] :

  • Urinary retention

  • Bleeding

  • Abscess formation

  • Flatus, liquid, and stool incontinence

  • Recurrence of fissures

Carcinoma has been reported in cases of chronic untreated anorectal fistulas.