Trusted medical expertise in seconds.

Access 1,000+ clinical and preclinical articles. Find answers fast with the high-powered search feature and clinical tools.

Try free for 5 days
Evidence-based content, created and peer-reviewed by physicians. Read the disclaimer.

Anal abscess and fistula

Last updated: August 13, 2021

Summarytoggle arrow icon

Anal abscesses are the acute manifestation of a purulent infection in the perirectal area, while anal fistulas are the chronic manifestation of such infections. An anal abscess is a pus-filled cavity that most commonly develops from an infected anal crypt gland following obstruction and bacterial overgrowth. Less common causes for the formation of anorectal abscesses are inflammatory bowel disease, acute gastrointestinal infections (e.g., appendicitis), radiation-induced proctitis, or malignancy. An anorectal abscess may heal spontaneously following drainage into the anal canal. In about 30–60% of cases, anal abscesses progress into fistulas, which are ductal connections between the abscess and the anal canal or the perianal skin. Complications of abscesses and fistulas involve chronic tissue damage, fecal incontinence, and sepsis. Patients with an anal abscess present with anorectal pain, a palpable tender mass on digital rectal examination, and fever in more advanced cases. Patients with anal fistulas may present with a visible perianal site draining pus and discomfort during defecation. Imaging studies such as CT, MRI, or anal ultrasonography are only needed for extended abscesses or complex fistulas. Definitive management of an anal abscess and fistula involves surgical treatment. Abscesses are incised and drained, followed by open wound healing. The standard treatment option for anal fistulas is fistulotomy.

Epidemiological data refers to the US, unless otherwise specified.

Anal abscesses and fistulae may be classified according to their variations in anatomical position and distribution.


Fistulas (Park's classification)

  • Typical development
  • Rare forms of development
    • Pathophysiology and localization depend on the specific comorbidities (e.g., Crohn's disease)
    • See “Less common causes” under etiology above.

Invasive examinations are painful and can only be tolerated by the patient while under anesthesia or with adequate pain relief.


Fistulae [2]

  1. Abscess and Fistula Expanded Information. Updated: January 1, 2021. Accessed: August 12, 2021.
  2. Treatments for an anal fistula. Updated: June 8, 2016. Accessed: February 14, 2017.