Perirectal Abscess

Aka: Perirectal Abscess, Anorectal Abscess

1. See Also
   1. Fistula-in-ano
2. Epidemiology
   1. More common in men
3. Pathophysiology
   1. Infection of the 6-12 anal glands and crypts that surround the anus
      1. Occurs at mucocutaneous junction (Dentate Line)
   2. Contiguous spread of infection in to ischiorectal space
   3. Causative organisms: Mixed infection with fecal flora
      1. Bacteroides fragilis (most common in adults)
      2. Escherichia coli (most common in children)
4. Types
   1. Perianal Abscess (60%)
      1. Local Perianal Abscess
      2. Immediately adjacent to anal verge
   2. Intersphincteric Abscess
      1. Proximal infection spread through the internal and external anal sphincter
   3. Ischiorectal Abscess (25%)
      1. Inferior to levator ani
      2. Two to 3 cm from anal verge
   4. 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)
5. Risk Factors
   1. Crohn's Disease
   2. Diabetes Mellitus
   3. Immunodeficiency
   4. Pregnancy
6. Symptoms
   1. Constant, throbbing perianal pain
7. Signs: General
   1. Palpable, tender mass in perianal area or in Rectum
   2. Drainage may be seen via perianal skin tract
      1. See Fistula-in-ano
8. 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
9. Management
   1. Surgical drainage is critical
      1. See types above for specific approach
   2. General Measures
      1. Stool Softeners (e.g. Colace)
      2. Sitz baths
      3. Frequent dressing changes
   3. Antibiotics usually not indicated
      1. Special Indications
         1. Systemic signs of infection
         2. Accompanying Cellulitis
         3. Valvular heart disease
         4. Diabetes Mellitus
         5. Immunocompromised patient
      2. Antibiotic coverage (Anaerobes, Gram Negatives)
         1. See Diverticulitis for nuanced antibiotic coverage (Perianal Abscess is treated the same)
         2. Example Regimen: Ciprofloxacin 500 mg PO bid and Metronidazole 500 mg PO tid
10. Complications
    1. Fistula-in-ano (complicates up to 50% of Perirectal Abscess)
11. 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. Surrell in Pfenninger (1994) Procedures, Mosby, p. 969