Updated: 6/1/2019

Perirectal / Perianal Abscess

Review Topic
  • A 41-year-old man presents to the emergency department with 2 days of worsening fever and severe pain in his rectum, worse with defecation. His medical history is significant for type 2 diabetes mellitus and morbid obesity. On physical exam, he has a fever of 39°C and a warm, fluctuant 2-cm mass is palpated immediately adjacent to the anus with surrounding cellulitis. Incision and drainage is performed at the bedside, and the patient is discharged with a course of oral ciprofloxacin and metronidazole.
  • Clinical definition
    • an abscess of the rectum, anus, or adjacent tissues
  • Epidemiology
    • demographics
      • 2:1 male to female
      • middle age
        • roughly 20-60 years of age with a mean age of 40 for both sexes
      • occurs rarely in children
    • risk factors
      • Crohn disease
      • immunodeficiency
        • diabetes
        • chronic corticosteroid use
  • Pathogenesis
    • obstruction and infection of an anal gland
    • may spread to contiguous areas (e.g. perianal, ischiorectal, and intersphincteric) through the extensive branching of the anal gland network
  • Genetics
    • not inherited
    • increased susceptibility in inherited immunodeficiencies
  • Associated conditions
    • Crohn disease
    • fistula-in-ano/perianal fistula
  • Symptoms
    • perirectal/perianal pain
    • fever
    • local swelling
    • less commonly diarrhea and/or constipation
  • Physical exam
    • perirectal/perianal tenderness
    • palpable mass
    • fever
    • surrounding cellulitis
  • Diagnostic testing
    • diagnostic approach
      • diagnosis is based on history and clinical exam
      • if clinical exam cannot be performed in the office (e.g., due to pain)
        • examination under anesthesia (EUA) may be necessary
    • imaging
      • generally not required for the diagnosis of anorectal abscesses
        • may be necessary to diagnose occult abscesses or to define the extent of large or complicated abscesses
        • used in patients with concurrent Crohn disease
      • no clear first-line among the following modalities
        • endoanal ultrasound
        • MRI with contrast
        • CT with contrast
  • Anal fissure
    • differentiating factors
      • visualizable tear, bleeding, no mass, and no signs of infection
  • Hemorrhoids
    • differentiating factors
      • bleeding and no signs of infection
  • Pilonidal abscess
    • differentiating factors
      • location alone
  • First-line
    • incision and drainage
      • early, adequate, and dependent drainage yields best results
        • more superficial abscesses may be drained in the office
        • deeper may require the operating room
  • Other treatments
    • antibiotics
      • never indicated alone
        • only in addition to drainage
      • indications
        • accompanying cellulitis
        • systemic signs of infection
        • immunosuppressed patients
          • including
            • HIV/AIDS
            • diabetes
            • morbid obesity
      • typically metronidazole and a fluoroquinolone (e.g., ciprofloxacin)
        • covers MRSA and gut flora
  • Anorectal fistula/fistula-in-ano
    • 30-70% will present with concurrent fistula
    • an additional 33% will eventually develop a fistula after drainage
  • Recurrent abscess
  • Sepsis

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