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Ano-rectal Abscess
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: commonest (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 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.
- 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.
- Inflammatory bowel disease
- Anal carcinoma
- Colorectal cancer
- 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:1
- Location of any fistula tracts
- Location of the internal and external opening(s) of any fistula
- Location of deep abscesses
- The state of the ano-rectal wall and the perirectal spaces
- Any damage to the anal sphincter
Fistula-in-ano
- Fistulas occur in 30-60% of patients with anorectal abscesses. Anorectal fistulas also may 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 fistulas: lay open with either fistulotomy or fistulectomy2
- High fistulas: may require a defunctioning proximal colostomy; there is also a risk of post-operative faecal incontinence.
- Systemic infection
- Fissure-in-ano occurs in up to 30% of patients (the risk is reduced by early surgical drainage)
- Recurrence
- Scarring
- 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.3
- The number of recurrences requiring surgery can be significantly reduced by initial fistulotomy.2
- Infants and toddlers usually recover very quickly.
Document references
- Cuenod CA, de Parades V, Siauve N, et al;
J Radiol. 2003 Apr;84(4 Pt 2):516-28. [abstract] - 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. [abstract]
- Hebra A; Perianal Abcess; eMedicine, March 2006
DocID: 1805
Document Version: 20
DocRef: bgp238
Last Updated: 31 Oct 2007
Review Date: 30 Oct 2009
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