An anorectal abscess is a collection of pus in the anal or rectal region. It may be caused by infection of an anal fissure, sexually transmitted infections or blocked anal glands:
- Perianal abscess: the most common (around 50%) - caused by direct extension of sepsis in the intersphincteric plane caudal to the perianal skin.
- Ischiorectal abscess: (22-39%) - results from extension of sepsis through the external sphincter into the ischiorectal space.
- Intersphincteric abscess: (0-18%) - depending on the effort made to find them, sepsis confined to intersphincteric space.
- Supralevator abscess: (2-9%) - produce horseshoe abscess track.
- Postanal abscess: posteriorly based below the level of the anococcygeal ligament.
- High-risk groups include diabetics, immunocompromised patients, people who engage in receptive anal sex, and patients with inflammatory bowel disease.
- Deep rectal abscesses may be caused by intestinal disorders such as Crohn's disease or diverticulitis.
- Add notes to any clinical page and create a reflective diary
- Automatically track and log every page you have viewed
- Print and export a summary to use in your appraisal
- Symptoms include painful, hardened tissue in the perianal area, discharge of pus from the rectum, a lump or nodule, tenderness at the edge of the anus, fever, constipation or pain associated with bowel movements.
- The perianal pain is usually constant, throbbing and worse when sitting down.
- A rectal examination may confirm the presence of an anorectal abscess.
- Superficial perianal abscesses may occur in infants and toddlers. The abscess often appears as a swollen, red, tender lump at the edge of the anus. The infant may have discomfort but no other symptoms.
- A digital rectal examination is usually sufficient for the diagnosis and the treatment planning of anal abscesses and fistulae.
- Initial investigation will depend on presentation but may include a screen for sexually transmitted diseases, and/or investigation for inflammatory bowel disease, diverticular disease or lower gastrointestinal tract malignancy.
- Proctosigmoidoscopy may be performed to exclude associated diseases.
- Ultrasound scan
- MRI scan: allows the assessment of:
- Location of any fistular tracts
- Location of the internal and external opening(s) of any fistula
- Location of deep abscesses
- The state of the anorectal wall and the perirectal spaces
- Any damage to the anal sphincter
- Fistulae occur in 30-60% of patients with anorectal abscesses. Anorectal fistulae may also be associated with diverticular disease, inflammatory bowel disease, malignancy, tuberculosis and actinomycosis.
- 80% of recurrent abscesses are associated with a fistula.
- Goodsall's rule: an external opening situated behind the transverse anal line will open into the anal canal in the midline posteriorly. An anterior opening is usually associated with a radial tract.
- Fistulae may be classified as intersphincteric (70%), transphincteric (25%), suprasphincteric (5%), extrasphincteric (less than 1%). Extrasphincteric fistulae are usually not associated with intersphincteric sepsis.
- Prompt surgical drainage
- Medication for pain relief
- Antibiotics are usually not necessary unless there is associated diabetes or immunosuppression
- Low fistulae: lay open with either fistulotomy or fistulectomy
- High fistulae: may require a defunctioning proximal colostomy; there is also a risk of postoperative faecal incontinence
- Systemic infection
- Fissure-in-ano occurs in up to 30% of patients (the risk is reduced by early surgical drainage)
- The outcome is good if the abscess is treated promptly.
- However approximately two thirds of patients with rectal abscesses treated by incision and drainage or by spontaneous drainage will develop a chronic anal fistula.
- The number of recurrences requiring surgery can be significantly reduced by initial fistulotomy.
- Infants and toddlers usually recover very quickly.
Further reading & references
- Lewis RT, Maron DJ; Anorectal Crohn's disease. Surg Clin North Am. 2010 Feb;90(1):83-97, Table of Contents.
- Cuenod CA, de Parades V, Siauve N, et al; MR imaging of ano-perineal suppurations. J Radiol. 2003 Apr;84(4 Pt 2):516-28.
- Knoefel WT, Hosch SB, Hoyer B, et al; The initial approach to anorectal abscesses: fistulotomy is safe and reduces the chance of recurrences. Dig Surg. 2000;17(3):274-8.
- Hebra A; Perianal Abcess, eMedicine, Feb 2009.
|Original Author: Dr Colin Tidy||Current Version: Dr Gurvinder Rull|
|Last Checked: 21/05/2010||Document ID: 1805 Version: 21||© EMIS|
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.