Anorectal Diseases Anal Fissure Fistula

Infection can cause a perirectal abscess, which can in turn cause a rectal or anal fistula. A perirectal abscess is a collection of pus, often in a blocked anal gland. Anal fistulas are abnormal anal tracts, starting in the anal canal and usually terminating in the perianal skinthe skin surrounding the anus.

Perirectal Abscess Risks

Crohn’s disease, an inflammatory bowel disease, is often the root of both anal fistulae and perirectal abscesses. An anal or rectal abscess can also result from diabetes, immunosuppression, pregnancy and ulcerative colitis.

Whatever the trigger for perirectal abscesses, the end result is infection. Infection usually occurs in the anal glands, which produce mucus that drains into the anal crypts, small recesses in the anal canal. If an anal gland is blocked, bacteria become trapped and begin to proliferate rapidly.

Bacterial infections associated with an anal or rectal abscess usually originate from bacteria on the skin or in the bowels. In rare cases, vaginal bacteria cause anal abscess or infections. A perirectal abscess is often caused by more than one type of bacterial infection, including:

  • Escherichia coli (E. coli)
  • Proteus vulgaris
  • Bacteroides
  • Staphylococci
  • Streptococci.

Anal Fistula Risk Factors

Like a perirectal abscess, an anal fistula may be due to Crohn’s disease. Other risk factors include physical injury, diverticulitis and cancer. An anal fistula may also develop after a perirectal abscess is drained. Anal or rectal abscesses and anal fistulas often occur together.

Rectovaginal fistulas, where the fistula connects the anal tract to the vagina, are less common than anal fistulas. When rectovaginal fistulas do occur, they are usually caused by complications of Crohn’s disease, trauma, radiation therapy or chemotherapy.

An anal fistula can also occur spontaneously, with no apparent cause. Anal fistulas due to congenital conditions are very common in babies. Male infants are more susceptible to anal fistulas than female infants.

Anal or Rectal Abscess Symptoms

A perirectal abscess can occur subcutaneously (just below the perirectal skin), or deeper within the anal tract. An anal or rectal abscess close to the skin’s surface causes localized pain, tenderness, swelling and redness.

A deep perirectal abscess can also cause pain, but usually of lesser severity than a subcutaneous abscess. Pain from a deep anal or rectal abscess tends to be dull, persistent and achy.

Pain from all perirectal abscesses worsens when sitting, coughing or sneezing. Perirectal abscess pain also worsens just prior to a bowel movement and eases after defecation.

If a perirectal abscess infection spreads to other areas of the body, sepsis may result. Sepsis is a serious systemic infection that can cause organ damage and even death.

Other symptoms associated with a perirectal abscess include:

  • anorexia (in up to fifteen percent of cases)
  • chills
  • constipation
  • fever
  • lower abdominal pain.

Anal Fistula Symptoms

Like a perirectal abscess, an anal fistula can cause pain and swelling. In general, however, an anal fistula causes surprisingly few symptoms. If infection is a factor, some drainage may be apparent where the fistula connects to the skin. Irritation of the skin surrounding the fistulae can also occur.

Diagnosing Fistulae and Perirectal Abscesses

A diagnosis of either perirectal abscess or anal fistula begins with a history of symptoms and a thorough physical examination. From there, more specific diagnostic tools may be required.

Anal Fistula Diagnosis

A history of perirectal abscess increases the risk of anal fistulas. Physical examination may expose a perirectal skin opening and possibly discharge, if infection is an issue. Physical palpitation of the fistula may reveal the presence of the fistula tract.

An anoscopea thin tube containing a fiberoptic cameramay be used to examine the anal fistula tract. Anoscopy can determine the depth of the anal fistula and the location of the fistula’s primary opening in the anal tract.

Perirectal Abscess Diagnosis

A physical examination reveals an anal or rectal abscess 95 percent of the time. When palpitated, a subcutaneous perirectal abscess presents as a tender, slightly moveable mass just beneath the perirectal skin. A digital rectal exam can reveal deeper abscesses. Coupled with reported symptoms, physical examination findings are usually sufficient for a perirectal abscess diagnosis.

Ruling Out Crohn’s Disease

If a perirectal abscess is detected with or without an accompanying anal fistula, the presence of Crohn’s disease must be considered. Blood tests, x-rays and a colonoscopy can be used to rule out or confirm Crohn’s disease.

Treating Perirectal Abscesses

Perirectal abscess treatment should begin promptly after diagnosis to prevent the infection from becoming systemic and developing into sepsis.

Drainage is the treatment of choice for anal or rectal abscesses. A surgical incision is made in the perirectal abscess, and the abscess is drained of the infected pus.

Drainage is performed on an outpatient basis in most cases. Hospitalization is required only if the rectal abscess is especially deep, or if treatment is complicated by diabetes or other health conditions.

Antibiotics can be prescribed to prevent the spread of infection, but antibiotics alone cannot replace drainage as a perirectal treatment. Antibiotics travel through the blood stream and cannot reach the self-contained infected pus of the perirectal abscess.

The most common post-surgical complication of perirectal abscess drainage is the development of an anal fistula.

Anal Fistula Treatment

Surgery is required to treat most anal fistulae. During a fistulotomy the anal fistula is drained, then the fistula tract is rerouted so the two openings come together. This turns the anal fistula into a self-contained loop, and the fistula heals from the inside.

Most fistula surgery requires an incision in the anal sphincter muscles. Although not common, fecal incontinence can occur following anal fistula surgery.

Anal fistula surgery is contraindicated in Crohn’s disease. Instead, fistulas associated with Crohn’s disease are treated with b-mercaptopurine, infliximab or metronidazole. These medications effectively treat eighty percent of Crohn’s-related anal fistulas.


Beers, M.H.