Perirectal Abscess

Basics

Description

Localized infection and accumulation of purulent material adjacent to anus or rectum

Etiology

  • Anal crypt gland infection, with spread to adjacent areas separated by muscle and fascia:
    • Perianal:
      • Most common
      • Usually with red bulge near anus
    • Ischiorectal:
      • Large potential space
      • May become very large before diagnosed
      • Can communicate posteriorly with other side forming a “horseshoe” abscess.
    • Intersphincteric:
      • Contained at primary site of origin between internal and external sphincters
    • Supralevator:
      • Above levator ani muscle
      • Needs operative debridement under general anesthesia but can be used as adjuncts
      • Often systemic symptoms manifest before the diagnosis is made
  • Bacterial cause is typically a mix of stool species

Diagnosis

History

  • Perianal pain:
    • Aggravated by defecation, sitting, coughing
  • Dull, deep pelvic or rectal pain:
    • Less pain if the abscess arises above the dentate line (ischiorectal and supralevator)
  • Rectal or perirectal drainage
  • Fever/chills

Physical Exam

  • Perianal swelling, erythema, induration, fluctuance, tenderness
  • Inner cleft buttock abscess = red flag:
    • Rectal abscess can track out to buttock
  • Rectal exam is the most important diagnostic intervention:
    • Rectal swelling or tenderness
    • Fistula can be probed, or palpated as a cord

Essential Workup

  • Careful history and physical exam with rectal exam are paramount in making diagnosis
  • Have high index of suspicion for any constant perirectal pain

Diagnostic Tests And Interpretation

No labs or imaging routinely indicated

Lab

  • CBC: Leukocytosis with left shift
  • Wound or blood culture: Not typically indicated

Imaging

  • Bedside ultrasound:
    • Linear probe most common
    • Endocavitary probe can be used to perform endoanal ultrasound
  • CT with IV contrast
  • MRI (helpful with detecting fistulas)

Diagnostic Procedures

Incision and drainage (I&D) can be diagnostic and therapeutic

Differential Diagnosis

  • Anal fissure
  • Anal fistula
  • Thrombosed or inflamed hemorrhoids
  • Prolapsed internal hemorrhoid
  • Anal ulcer (ie, HIV)
  • Proctitis (ie, gonococcal)
  • Anorectal carcinoma
  • Sentinel pile in the posterior midline or anterior midline

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