Anorectal abscess

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Anorectal Abscess
Other names: Perianal abscess, perirectal abscess, anal abscess, rectal abscess
Anorectal abscess types and locations
SymptomsRectal pain, fever, drainage from the anus, redness of the skin[1]
ComplicationsAnal fistula, sepsis, fecal incontinence, urinary retention, chronic pain[1]
Duration3 to 8 weeks[1]
TypesPerianal, ischiorectal, supralevator, intersphincteric, submucosal[1]
Diagnostic methodExamination, medical imaging[1]
Differential diagnosisAnal fissure, anal fistula, thrombosed hemorrhoid, pilonidal cyst, hidradenitis suppurativa[1]
TreatmentIncision and drainage, antibiotics, surgery[1]
Frequency1 in 10,000 per year[1]

An anorectal abscess is a collection of pus in the region of the anus or rectum.[2][3] Symptoms generally include rectal pain of sudden onset.[1] There may also be fever, drainage from the anus, and redness of the skin in the area.[1] Complications may include an anal fistula, sepsis, fecal incontinence, urinary retention, and chronic pain.[1]

Most cases are the result of an infection of a anal gland.[3] Risk factors include injury, smoking, Crohn's disease, sexually transmitted infections, and HIV/AIDS.[1] There is no relation to hygiene, anal sex, or diabetes.[1] Types include perianal, ischiorectal, supralevator, intersphincteric, and submucosal.[1] Diagnosis is generally by examination and occasionally medical imaging (CT scan, MRI, or ultrasound).[4]

A perianal abscess may be simple cut open and drained, while other types generally require antibiotics and potentially surgery.[1] After surgery laxatives, sitz baths, and pain medication are recommended.[1] Healing can take 3 to 8 weeks.[1] About 1 in 10,000 people are affected a year.[1] They are most common in those in their 30s and 40s and males are three times more commonly affected than females.[1]

Signs and symptoms

Symptoms generally include rectal pain of sudden onset.[1] The pain may be dull, aching, or throbbing. It is worst when the person sits down and right before a bowel movement. After the individual has a bowel movement, the pain usually lessens. Other signs and symptoms of anorectal abscess include constipation, drainage from the rectum, fever and chills, or a palpable mass near the anus.

The condition can become extremely painful, and usually worsens over the course of just a few days. The pain may be limited and sporadic at first, but may worsen to a constant pain which can become very severe when body position is changed (e.g., when standing up, rolling over, and so forth). Depending upon the exact location of the abscess, there can also be excruciating pain during bowel movements, though this is not always the case. This condition may occur in isolation, but is frequently indicative of another underlying disorder, such as Crohn's disease.


If left untreated, an anal fistula will almost certainly form, connecting the rectum to the skin. This requires more intensive surgery. Furthermore, any untreated abscess may (and most likely will) continue to expand, eventually becoming a serious systemic infection.


Abscesses are caused by a high-density infection of (usually) common bacteria which collect in one place or another for any variety of reasons. Anal abscesses, without treatment, are likely to spread and affect other parts of the body, particularly the groin and rectal lumen. All abscesses can progress to serious generalized infections requiring lengthy hospitalizations if not treated.

Historically, many rectal abscesses are caused by bacteria common in the digestive system, such as E. coli. While this still continues often to be the case, there has recently been an increase in the causative organism being staphylococcus, as well as the difficult to treat community-acquired methicillin-resistant S. aureus. Because of the increasing appearance of more exotic bacteria in anal abscesses, microbiological examination will always be performed on the surgical exudate to determine the proper course of any antibiotic treatment.


MRI image of U-shaped fluid collection around the anus, showing perianal abscess formation.

Diagnosis of anorectal abscess begins with a medical history and physical exam. Imaging studies which can help determine the diagnosis in cases of a deep non-palpable perirectal abscess include pelvic CT scan, MRI or trans-rectal ultrasound. These studies are not necessary, though, in cases which the diagnosis can be made upon physical exam.


Anorectal abscesses are classified according to their anatomic location and the following are the most common types; Perianal abscess, Ischiorectal abscess, Intersphincteric abscess and Supralevator abscess.[5][6]

Perianal abscess, which represents the most common type of anorectal abscesses accounting for about 60% of reported cases, are superficial collections of purulent material just beneath the skin of the anal canal.[7]

Ischiorectal abscess is formed when suppuration transverses the external anal sphincter into the ischiorectal space.[8]

Intersphincteric abscess results from suppuration contained between the internal and external anal sphincters .Supralevator abscess forms from cephalad extension of the intersphincteric abscess above the levator ani or from caudal extension of a suppurative abdominal process like appendicitis, diverticular or gynaecologic sepsis.

Differential diagnosis

This condition is often initially misdiagnosed as hemorrhoids, since this is almost always the cause of any sudden anal discomfort. The presence of the abscess, however, is suspected when the pain quickly worsens over one or two days and usual hemorrhoid treatments are ineffective in bringing relief. Furthermore, any serious abscess will eventually begin to cause signs and symptoms of general infection, including fever and nighttime chills.

A physician can rule out a hemorrhoid with a simple visual inspection, and usually appreciate an abscess by touch.


Treatment is generally with incision and drainage.[9] Antibiotics (such as amoxicillin/clavulanate) may also be given if infection of the overlying skin, poor immune function, fast heart rate, or fever is present.[9][10] Packing is generally not needed.[9] Treatment may be possible in an emergency department under local anesthesia, but surgery in an operating room under general anesthesia may be required.

Generally speaking, a fairly small but deep incision is performed close to the root of the abscess. The surgeon will allow the abscess to drain its exudate and attempt to discover any other related lesions in the area. This is one of the most basic types of surgery, and is usually performed in less than thirty minutes by the anal surgical team. Generally, a portion of the exudate is sent for microbiological analysis to determine the type of infecting bacteria. The incision is not closed (stitched), as the damaged tissues must heal from the inside toward the skin over a period of time.

The affected individual is often sent home within twenty-four hours of the surgery, and may be instructed to perform several 'sitz baths' per day. These involve a small basin which is filled with warm water, and possibly with salts; usually fits over a toilet; and soaks the affected area for a period of time. Another method of recovery involves the use of surgical packing. The initial packing is inserted by the surgical team, with redressing generally performed by hospital staff or a district nurse. During the week following the surgery, many people will receive antibiotics, and pain management, consistent with the nature of the abscess.

It is unclear whether internal packing of the perianal abscess influences time taken for healing, wound pain, development of fistulae, or abscess recurrence.[11]

The person usually experiences an almost complete relief of the severe pain associated to his/her abscess upon waking from anesthesia; the pain associated with the opening and draining incision during the post-operative period is often mild in comparison.


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 Turner, SV; Singh, J (January 2020). "Perirectal Abscess". PMID 29939672. {{cite journal}}: Cite journal requires |journal= (help)
  2. Taylor, Robert B. (2002). Manual of Family Practice. Lippincott Williams & Wilkins. p. 337. ISBN 978-0-7817-2652-8. Archived from the original on 2021-08-27. Retrieved 2020-10-30.
  3. 3.0 3.1 "Abscess and Fistula Expanded Information | ASCRS". Archived from the original on 31 October 2020. Retrieved 30 October 2020.
  4. Madoff, Robert D.; Melton-Meax, Genevieve B. (2020). "136. Diseases of the rectum and anus: perianal abscess". In Goldman, Lee; Schafer, Andrew I. (eds.). Goldman-Cecil Medicine. Vol. 1 (26th ed.). Philadelphia: Elsevier. p. 935. ISBN 978-0-323-55087-1. Archived from the original on 2023-03-15. Retrieved 2023-03-15.
  5. "Anorectal Abscess: Background, Anatomy, Pathophysiology". 2018-11-28. Archived from the original on 2019-01-20. Retrieved 2019-01-20. {{cite journal}}: Cite journal requires |journal= (help)
  6. Janicke DM, Pundt MR (November 1996). "Anorectal disorders". Emerg. Med. Clin. North Am. 14 (4): 757–88. doi:10.1016/S0733-8627(05)70278-9. PMID 8921768.
  7. "Anorectal Abscess: Background, Anatomy, Pathophysiology". 2018-11-28. Archived from the original on 2019-01-20. Retrieved 2019-01-20. {{cite journal}}: Cite journal requires |journal= (help)
  8. "Anorectal Abscess: Background, Anatomy, Pathophysiology". 2018-11-28. Archived from the original on 2019-01-20. Retrieved 2019-01-20. {{cite journal}}: Cite journal requires |journal= (help)
  9. 9.0 9.1 9.2 Turner, Steven V.; Singh, Jasvinder (2023). "Perirectal Abscess". StatPearls. StatPearls Publishing. Archived from the original on 25 April 2023. Retrieved 24 July 2023.
  10. Vogel, JD; Johnson, EK; Morris, AM; Paquette, IM; Saclarides, TJ; Feingold, DL; Steele, SR (December 2016). "Clinical Practice Guideline for the Management of Anorectal Abscess, Fistula-in-Ano, and Rectovaginal Fistula" (PDF). Diseases of the colon and rectum. 59 (12): 1117–1133. doi:10.1097/DCR.0000000000000733. PMID 27824697. Archived (PDF) from the original on 13 May 2023. Retrieved 24 July 2023.
  11. Smith, Stella R; Newton, Katy; Smith, Jennifer A; Dumville, Jo C; Iheozor-Ejiofor, Zipporah; Pearce, Lyndsay E; Barrow, Paul J; Hancock, Laura; Hill, James (2016-08-26). Cochrane Wounds Group (ed.). "Internal dressings for healing perianal abscess cavities". Cochrane Database of Systematic Reviews (8): CD011193. doi:10.1002/14651858.CD011193.pub2. PMID 27562822.

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