An anorectal abscess is a localized collection of pus in the perirectal spaces. Abscesses usually originate in an anal crypt. Symptoms are pain and swelling. Diagnosis is primarily by examination and CT or pelvic MRI for deeper abscesses. Treatment is surgical drainage.
(See also Evaluation of Anorectal Disorders.)
An abscess may be located in various spaces surrounding the rectum and may be superficial or deep.
A perianal abscess is superficial and points to the skin.
An ischiorectal abscess is deeper, extending across the sphincter into the ischiorectal space below the levator ani; it may penetrate to the contralateral side, forming a “horseshoe” abscess. An abscess above the levator ani (ie, supralevator abscess) is quite deep and may extend to the peritoneum or abdominal organs; this abscess often results from diverticulitis or pelvic inflammatory disease.
Crohn disease (especially of the colon) sometimes causes anorectal abscess.
Most anorectal abscesses are mixed infections, with Escherichia coli, Proteus vulgaris, Bacteroides, streptococci, and staphylococci predominating.
Symptoms and Signs of Anorectal Abscess
Superficial abscesses can be very painful; perianal swelling, redness, and tenderness are characteristic. Fever is rare.
Deeper abscesses may be less painful but cause toxic symptoms (eg, fever, chills, malaise). There may be no perianal findings, but digital rectal examination may reveal a tender, fluctuant swelling of the rectal wall. High pelvirectal abscesses may cause lower abdominal pain and fever without rectal symptoms. Sometimes fever is the only symptom.
Diagnosis of Anorectal Abscess
Clinical evaluation
Sometimes examination under anesthesia or rarely CT
Patients who have a pointing cutaneous abscess, a normal digital rectal examination, and no signs of systemic illness do not require imaging.
CT scan is useful when a deep abscess or Crohn disease are suspected. Higher (supralevator) abscesses require CT to determine the intra-abdominal source of the infection. Pelvic MRI and endoscopic ultrasonography are alternative imaging studies.
Patients with any findings suggestive of a deeper abscess or complex perianal Crohn disease should have an examination under anesthesia at the time of drainage.
Treatment of Anorectal Abscess
Incision and drainage
Antibiotics for high-risk patients
(See also the American Society of Colon and Rectal Surgeons' 2016 clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula.)
Prompt incision and adequate drainage are required and should not wait until the abscess points. Many abscesses can be drained as an in-office procedure; deeper abscesses may require drainage in the operating room.
Patients with absolute neutropenia (< 1000/mcL [1 × 109/L]) should be treated with antibiotics alone.
Antibiotics are not indicated for healthy patients with superficial abscesses.
Anorectal fistulas may develop after drainage.
Key Points
Anorectal abscesses may be superficial or deep.
Superficial abscesses may be diagnosed clinically and drained in the office or emergency department.
Deep abscesses often require imaging with CT scan and typically must be drained in the operating room.
Patients with fever, immunocompromise, or diabetes and those with extensive cellulitis should receive antibiotics.
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
American Society of Colon and Rectal Surgeons: Clinical practice guideline for the management of anorectal abscess, fistula-in-ano, and rectovaginal fistula (2016)
