The inflammatory process that leads to abscess may begin with an abrasion or tear in the lining of the anal canal, rectum, or perianal skin and subsequent infection with Escherichia coli, staphylococci, or streptococci. Such trauma may result from abrasive contact with certain objects, such as enema tips, ingested eggshells, fish bones, or very hard stools. An abscess may also develop after infection of submucosal hematomas, sclerosed hemorrhoids, or anal fissures.

Other causes include obstruction of glands in the anal area, extension of cryptitis, infection in the apocrine glands, or folliculitis in the perianal region. Certain systemic illnesses also may lead to abscess formation, including ulcerative colitis and Crohn’s disease and immunosuppressive conditions such as acquired immunodeficiency syndrome.

Anorectal abscess may lead to anorectal fistula. Either disorder can cause perineal cellulitis, scar tissue formation, and anal stricture. Hemorrhage is a potential complication in the postoperative period. Rarely, peritonitis develops from internal abscess rupture.

Signs and symptoms depend on the severity of the infection and whether or not the abscess is a chronic condition. Assessment findings also vary according to the type of abscess.

Usually, the first symptom the patient reports is rectal pain, which he usually describes as throbbing. Occasionally, diarrhea precedes the onset of rectal pain. The patient may also state that he can’t sit comfortably because of the development of a hard, painful lump on one side. With a perianal abscess, the patient may report that sitting or coughing increases his pain. A submucosal or high intermuscular abscess may cause a dull, aching pain in the rectum, whereas a pelvirectal abscess typically causes no pain.