Perirectal Abscess



  • Abscess in the perirectal area
  • May be associated with fistula-in-ano
  • Classification of the abscess is based on the location in relation to the levator and sphincteric muscles of the pelvic floor.
  • Classification by decreasing frequency: perianal, ischioanal, intersphincteric, and supralevator


  • May occur at any age
  • More common in males 2:1
  • In children, more common in those <2 years


  • Most often originates from an occluded anal gland with subsequent bacterial overgrowth and abscess formation
  • Infection from within the anal glands, penetrates through the internal sphincter, and ends in the intersphincteric space
  • Chronic infection and inflammation may result in the formation of fistula-in-ano. This occurs in up to 50% as a result of persistent anal sepsis or an epithelialized tract.
  • Also can be associated with transmural inflammation and fistulization of the rectosigmoid mucosa due to Crohn disease

Commonly Associated Conditions

  • Nonspecific anal gland infection
  • Crohn disease
  • Immune deficiency (e.g., neutropenia, diabetes mellitus, AIDS)
  • Perforation by a foreign body
  • External trauma
  • Tuberculosis
  • Chronic granulomatous disease (CGD)
  • Tumor (e.g., carcinoma, rhabdomyosarcoma)


Signs and symptoms

  • General
    • Constant anal or perianal pain that often precedes local findings
    • Localized swelling, erythema, and fluctuance
    • Painful defecation or ambulation
    • Constitutional symptoms (e.g., fever or malaise)
  • Perianal abscess
    • Result of distal vertical spread of the infection to the anal margin
    • Presents as tender, fluctuant mass
    • Most common type of perianal abscess
  • Ischiorectal abscess
    • Secondary to horizontal spread of infection across the external anal sphincter into the ischiorectal fossa
    • Infection may track across the internal anal sphincter into the anal canal.
    • Presents as diffuse, tender, indurated, fluctuant area
    • Patients may have pain and fever prior to visible swelling.
  • Intersphincteric abscess
    • Limited to the intersphincteric space between the internal and external sphincters; therefore, often does not cause perianal skin changes
    • Associated with painful defecation
    • Accounts for only 2–5% of all anorectal abscesses
  • Supralevator abscess
    • May arise from two different sources
      • Proximal vertical spread from the gland through the intersphincteric space to the supralevator space
      • Pelvic inflammation or infection (e.g., Crohn disease)
    • Presents with pelvic or anorectal pain, fever, and, at times, urinary retention
    • Rectal exam usually reveals an indurated swelling above the anorectal ring.
    • Imaging may be necessary to establish the diagnosis.
  • Horseshoe abscess
    • Secondary to abscessed anal gland located in the posterior midline of the anal canal
    • Due to presence of anococcygeal ligament, the infection is forced laterally into the ischiorectal fossae and is therefore known as “horseshoe.”
    • May be unilateral or bilateral
    • Presents with pain

Differential Diagnosis

  • Pilonidal infection
  • Bartholin abscess
  • Presacral epidermal inclusion cyst
  • Hidradenitis suppurativa
  • Rectal duplication cyst

Diagnostic Tests and Interpretation

Initial Tests

  • CBC
  • Abscess culture
  • Magnetic resonance imaging (MRI)
    • Preferred modality, as it provides excellent spatial and contrast resolution
    • Enables comprehensive evaluation of the entire peritoneum and lower pelvis
  • Computed tomography (CT) scan
    • Has limited soft tissue contrast resolution which makes distinguishing perineal musculature and fistula tracts difficult, although organized fluid collections larger than 1 cm are generally seen
    • This modality also uses ionizing radiation, which is less desirable in the pediatric population.
  • Ultrasound (US)
    • Endoscopic and transperineal US have been used but do not always show the full extent of inflammation.
    • Deeper structures may not be visualized, owing to the lack of sound wave penetration.
    • Endoscopic US may be used to diagnose, characterize, and monitor rectal abscesses.


General Measures

  • Lack of fluctuation should not delay treatment.
  • Abscess should be drained with placement of a seton or drainage catheter.
  • Abscess should be cultured at time of drainage to direct therapy in the case antibiotics are needed.
  • Antibiotics are reserved for situations in which the infection does not appropriately respond to drainage infections with adjacent cellulitis, of infections secondary to an enteric organism on culture. Antibiotics are also indicated for infection in an immunocompromised patient, a patient with abnormal cardiac valves, or a patient with Crohn disease.
  • Sitz baths may be helpful with drainage.

Diagnostic Procedures/Other

  • Drainage may be performed either with conservative incision and drainage or with judicious probing for fistulae.
  • It is a matter of debate as to whether a fistulotomy or fistulectomy should be performed at the time of drainage for an accompanying fistula.

Ongoing Care

  • If abscess recurs, consider other associated conditions (e.g., neutropenia, HIV, diabetes mellitus, Crohn disease, rectal duplication cyst).
  • Exploration for fistula-in-ano is recommended to prevent recurrence.


  • Prognosis is good if there is early detection and drainage of abscesses.
  • Patients typically recover well after surgical drainage without the need for antibiotics.


  • Sepsis
  • Fistula formation
  • Crohn disease should be considered in patients with perirectal abscess with or without fistula-in-ano.
  • Signs and symptoms that increase suspicion for Crohn disease include weight loss or poor growth, chronic diarrhea, or abdominal pain.

Additional Reading

  1. Caliste X, Nazir S, Goode T, et al. Sensitivity of computed tomography in detection of perirectal abscess. Am Surg. 2011;77(2):166–168.  [PMID:21337873]
  2. Chang HK, Ryu JG, Oh JT. Clinical characteristics and treatment of perianal abscess and fistula-in-ano in infants. J Pediatr Surg. 2010;45(9):1832–1836.  [PMID:20850628]
  3. Hammer MR, Dillman JR, Smith EA, et al. Magnetic resonance imaging of perianal and perineal Crohn disease in children and adolescents. Magn Reson Imaging Clin N Am. 2013;21(4):813–828.  [PMID:24183527]
  4. Huang A, Abbasakoor F, Vaizey CJ. Gastrointestinal manifestations of chronic granulomatous disease. Colorectal Dis. 2006;8(8):637–644.  [PMID:16970572]
  5. Lejkowski M, Maheshwari A, Calhoun DA, et al. Persistent perianal abscess in early infancy as a presentation of autoimmune neutropenia. J Perinatol. 2003;23(5):428–430.  [PMID:12847542]
  6. Malik AI, Nelson RL, Tou S. Incision and drainage of perianal abscess with or without treatment of anal fistula. Cochrane Database Syst Rev. 2010;(7):CD006827.  [PMID:20614450]
  7. Marcus RH, Stine RJ, Cohen MA. Perirectal abscess. Ann Emerg Med. 1995;25(5):597–603.  [PMID:7741334]
  8. Niyogi A, Agarwal T, Broadhurst J, et al. Management of perianal abscess and fistula-in-ano in children. Eur J Pediatr Surg. 2010;20(1):35–39.  [PMID:19899037]
  9. Rosen NG, Gibbs DL, Soffer SZ, et al. The nonoperative management of fistula-in-ano. J Pediatr Surg. 2000;35(6):938–939.  [PMID:10873039]
  10. Whiteford MH, Kilkenny J III, Hyman N, et al; for The Standards Practice Task Force. Practice parameters for the treatment of perianal abscess and fistula-in-ano (revised). Dis Colon Rectum. 2005;48(7):1337–1342.  [PMID:15933794]



  • 566 Abscess of anal and rectal regions
  • 565.1 Anal fistula


  • K61.1 Rectal abscess
  • K60.3 Anal fistula
  • K61.3 Ischiorectal abscess
  • K61.4 Intrasphincteric abscess


  • 91669008 Perirectal abscess (disorder)
  • 197150008 anal fissure and fistula (disorder)
  • 36046008 Ischiorectal abscess (disorder)
  • 197163002 Supralevator abscess (disorder)


  • Q: What are complications of this problem?
  • A: Fistula formation is seen in up to 50% of patients, with a predilection for males.
  • Q: What are the most common organisms of the abscess?
  • A: Staphylococcus species
  • Q: What other disease may perirectal abscess be associated with?
  • A: Crohn disease. If there has been exposure, tuberculosis should also be excluded.
  • Q: What treatments can be done other than surgery?
  • A: Sitz baths and warm compresses may be able to help with smaller more superficial abscess.


Naamah Levy Zitomersky, MD

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