Perianal and Ischiorectal Abscesses

Localized collections of pus resulting from infections of the pararectal spaces.

Abscesses may cause substantial tissue destruction. Perianal abscesses, the more common type, usually result from inflammation of anorectal crypts or of glands located between the sphincters. These abscesses are located close to the anus and are relatively superficial. Pus tends to track internally into the lower rectum just above the anal canal and externally, forming a tender swelling. The swelling is usually posterior to the midline of the anus but may be anywhere within several centimeters of the anal verge.

Ischiorectal abscesses are located above the anorectal line. They are more difficult to diagnose, are usually larger, and are accompanied by marked systemic symptoms (eg, severe pain, fever). They usually result from a break between the extraperitoneal rectum and the fatty tissue in the fossa; however, the source of infection may lie within the peritoneal cavity. In elderly patients, diverticulitis is the most likely cause.

The cardinal symptom of an ischiorectal abscess is pain. If surgery is delayed, signs of sepsis (eg, chills, fever), local swelling, induration, and tenderness develop, as may life-threatening necrotizing soft tissue infections. Superficial abscesses may rupture spontaneously, but this possibility should not delay surgery. Aerobic and anaerobic organisms similar to those in feces can be cultured from the pus.

Treatment

Surgical drainage should be performed as soon as the abscess is discovered. Antibiotics are given but do not substitute for drainage. Because nearly all abscesses result from a break in the rectal mucous membrane, 25 to 35% of patients may have a persistent fistula after simple incision and drainage. Therefore, a fistula should be sought and repaired during the original operation.