Perianal Abscess

A perianal abscess is (simply) a collection of pus, outside the anus. Infection of an anal fissure, sexually transmitted infections, and blocked perianal glands are all thought to be inciting factors. The abscess usually begins when bacteria enters through a tear in the lining of the rectum or anus. Most often, this occurs between the internal and external sphincters (intersphincteric abscess), where the perianal glands are located. As the abscess increases in size, most will follow the plane of least resistance and spread towards the surface, creating a perianal abscess. Occasionally, the infection can spread into the ishiorectal fossa or above the level of the levator muscles, creating ischiorectal and/or supralevator abscesses, respectively. Although supralevator abscesses are difficult to diagnose, perianal and ischiorectal abscesses still seem to account for the majority of the ones encountered.

In terms of risk, those individuals with diabetes, immunocompromised states, those with inflammatory bowel disease, or who engage in receptive anal sex, appear to be at higher risk for developing an abscess, than those without these risk factors.

Clinical Presentation

Pain and swelling in the perianal area is the most common presenting complaint of perianal abscesses. Discharge of pus may be apparent, but is not necessary for diagnosis. The cardinal signs of infection (pain, fever, redness, swelling, and loss of function) are typically present, as would be in most types of abscess or infectious processes. A good rectal exam may confirm the presence of an anorectal abscess, and/or proctosigmoidoscopy can be used to exclude other or associated diseases. In addition, a good history is always warranted, as deep rectal abscesses may be caused by intestinal disorders such as diverticulitis or Crohn's disease.


As for virtually any abscess, the primary treatment is prompt incision and drainage of the abscess. Depending on its location, the procedure may take place in an outpatient setting. Deeper abscesses may require surgery with appropriate anesthesia. Secondary treatment would include the use of antibiotics (however, their use as primary therapy alone is unwarranted). Their adjunct use is especially important for those with increased risk factors, as mentioned above.

The expectations following treatment is very good, particularly with prompt treatment. Complications include systemic infection, anal fistula formation (see Fistula-in-Ano below), recurrence, and scarring.

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