Perirectal Abscess

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
Contiguous spread of infection in to ischiorectal space
1. Infection spreads through the internal anal sphincter, and into the intersphincteric plane
Causative organisms: Mixed infection with fecal flora
1. Bacteroides fragilis (most common in adults)
2. Escherichia coli (most common in children)

Superficial: Perianal Abscess (60%)
1. Local Perianal Abscess
2. Immediately adjacent to anal verge
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)

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

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
Purulent drainage may be seen via perianal skin tract
1. See Fistula-in-ano

CT Pelvis
1. Indicated for evaluation of deep space or complicated abscess
MRI Pelvis
1. Indicated for complicated Anal Fistula evaluation
Endorectal Ultrasound
1. Indicated in some cases of complicated Perirectal Abscess

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
General Measures
1. Keep area clean and dry
2. Stool Softeners (e.g. Colace)
3. Sitz baths
4. Frequent dressing changes
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

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