Perirectal Abscess

Aka: Perirectal Abscess, Anorectal Abscess

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II. Epidemiology

  1. More common in men (twice risk of women)
  2. Anorectal Abscess Incidence: >100,000 cases per year in U.S.
  3. Age: 20 to 60 years old (mean 40 years old)

III. Pathophysiology

  1. Infection of the 6-12 anal glands and crypts that surround the anus circumferentially
    1. Occurs at mucocutaneous junction (Dentate Line)
    2. Intestinal columnar epithelium lies proximal to the Dentate Line
    3. Squamous epithelium is present distal to the Dentate Line
  2. Contiguous spread of infection in to ischiorectal space
    1. Infection spreads through the internal anal sphincter, and into the intersphincteric plane
  3. Causative organisms: Mixed infection with fecal flora
    1. Bacteroides fragilis (most common in adults)
    2. Escherichia coli (most common in children)

IV. Risk Factors

  1. Crohn's Disease
  2. Diabetes Mellitus
  3. Immunodeficiency
  4. Pregnancy
  5. Chronic Corticosteroid ues
  6. Anorectal Trauma
  7. Radiation fibrosis
  8. Perirectal tumor

V. Types: Anorectal Abscess

  1. Superficial: Perianal Abscess (60%)
    1. Local Perianal Abscess
    2. Immediately adjacent to anal verge
  2. Deep: Perirectal Abscess
    1. Intersphincteric Abscess
      1. Proximal infection spread through the internal and external anal sphincter
    2. Ischiorectal Abscess (25%)
      1. Inferior to levator ani
      2. Two to 3 cm from anal verge
    3. Pelvirectal Abscess (Supralevator Abscess)
      1. Abscess superior to levator ani
      2. Complicated, deep abscess spread from perianal, intersphincter and Ischiorectal Abscesses
      3. May also spread from Pelvis (PID, Diverticulitis, Ruptured Appendicitis)

VI. Symptoms

  1. Constant, throbbing perianal pain
  2. Pain may be made worse with Defecation
  3. Systemic symptoms (e.g. fever, chills, Nausea, Vomiting) may be present with deep space infection

VII. Signs: General

  1. Palpable, tender mass in perianal area or on Rectal Exam
    1. Perianal Abscess is superficial and is easily identified as a red, tender fluctuant perianal mass
    2. Deeper, Perirectal Abscesses may only be identified on Rectal Exam or on imaging
  2. Purulent drainage may be seen via perianal skin tract
    1. See Fistula-in-ano

VIII. Differential Diagnosis

  1. Buttock Skin Abscess
  2. Internal Hemorrhoid
  3. External Hemorrhoid
  4. Anal Fissure
  5. Anal Fistula
  6. Pilonidal Abscess
  7. Hidradenitis Suppurativa

IX. Imaging

  1. CT Pelvis
    1. Indicated for evaluation of deep space or complicated abscess
      1. Intersphincteric Abscess
      2. Ischiorectal Abscess
      3. Pelvirectal Abscess (Supralevator Abscess)
  2. MRI Pelvis
    1. Indicated for complicated Anal Fistula evaluation
  3. Endorectal Ultrasound
    1. Indicated in some cases of complicated Perirectal Abscess

X. Management

  1. Complete surgical abscess drainage is critical (including breaking up loculations)
    1. See types above for specific approach
    2. Perianal Abscess is typically drained bedside
    3. Deep, Perirectal Abscess is typically drained in the operating room
    4. Perianal Abscess and Ischiorectal Abscess incision should be made as close to anal verge as possible
      1. Minimizes length of potential fistula formation
    5. Wound cultures are not typically useful (polymicrobial)
    6. Wound packing is not typically recommended (does not alter course)
      1. Sterile saline irrigation of the abscess cavity may be performed
      2. However, incision should be long enough to continue to effectively drain
  2. General Measures
    1. Keep area clean and dry
    2. Stool Softeners (e.g. Colace)
    3. Sitz baths
    4. Frequent dressing changes
  3. Antibiotics are recommended to reduce Anal Fistula formation
    1. Treat for 5 day Antibiotic course
    2. Additional Indications
      1. Systemic signs of infection
      2. Accompanying Cellulitis
      3. Valvular heart disease
      4. Diabetes Mellitus
      5. Immunocompromised patient
    3. Antibiotic coverage (Anaerobes, Gram Negatives)
      1. See Diverticulitis for nuanced Antibiotic coverage (Perianal Abscess is treated the same)
      2. Example Regimens (choose one)
        1. Ciprofloxacin 500 mg orally twice daily AND Metronidazole 500 mg orally three times daily
        2. Amoxicillin-Clavulanate (Augmentin) 875 mg orally twice daily

XI. Complications

  1. Fistula-in-ano (complicates up to 50 to 70% of Perirectal Abscess)
  2. Untreated Anorectal Abscess
    1. Fecal Incontinence
    2. Chronic Pain
    3. Constipation
    4. Recurrent Anorectal Abscess

XII. References

  1. Goroll (2000) Primary Care Medicine, Lippincott, p. 426
  2. Jhun and Cologne in Herbert (2015) EM:Rap 15(9): 17-8
  3. Marx (2002) Rosen's Emergency Medicine, p. 1951
  4. Roberts (1998) Procedures, Saunders, p. 649-51
  5. Sherman, Bahga and Vietvuong (2022) Crit Dec Emerg Med 36(7): 23-9
  6. Surrell in Pfenninger (1994) Procedures, Mosby, p. 969

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