Anal Fistulas and Fissures
- Author: Bruce M Lo, MD, CPE, RDMS, FACEP, FAAEM, FACHE; Chief Editor: Robert E O'Connor, MD, MPH more...
An anal fissure is a superficial linear tear in the anoderm that is distal to the dentate line. Anal fissures are often associated with the passage of hard stools or anal trauma, but the exact etiology often remains unclear. 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. The 4 categories of fistulas, based on the relationship of fistula to sphincter muscles, are intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric.
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.
Pathophysiology and Etiology
In anal fissures, the anus distal to the dentate line is involved. About 90% of anal fissures occur in the posterior midline, where skeletal muscle fibers that circle the anus are weakest. Ten percent are found in the anterior midline, while about 1% are found off a midline position.
An anal fissure is shown in the image below.
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, leukemia, inflammatory bowel disease such as Crohn disease, previous anal surgery, HIV disease, anal cancer, and other conditions or diseases. 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.
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.[4, 5, 6]
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. 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, radiation exposure, and HIV disease. Approximately 30% of patients with HIV disease develop anorectal abscesses and fistulas.
Anal fistulas are classified into the following 4 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%). 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. and approximately 80% of anal fistulas arise from anorectal infection.
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, with recurrence rates around 7-21% depending on the complexity and location of the fistula.[9, 10] Use of fibrin glue or fistula plug has variable success rates.
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