Anorectal Abscess and Fistula

Anorectal Abscess & Fistula - Genesis & Germs

• Anorectal Abscess: Acute infection in spaces around the anus/rectum.
• Fistula-in-ano: Chronic abnormal tract connecting the anal canal to perianal skin.
• Genesis (Cryptoglandular Hypothesis):
  • Infection originates in anal glands (Hermann's glands) in the intersphincteric space.
  • These glands drain into anal crypts (of Morgagni).
  • Duct obstruction → stasis → bacterial infection → abscess.
  • Abscess may drain spontaneously or require surgery, potentially forming a fistula.
• Causative Organisms (Polymicrobial):
  • Escherichia coli (most common aerobe)
  • Bacteroides fragilis (common anaerobe)
  • Staphylococcus aureus
  • Enterococcus spp.
  • Streptococcus spp.

⭐ The cryptoglandular theory is the most accepted etiology for common, non-specific anorectal abscesses and fistulas.

Anorectal Abscess & Fistula - Mapping the Maze

Anorectal Abscesses: Origin: Cryptoglandular infection.

• Types & Features:

  Type	Location	Key Feature
  Perianal	Subcutaneous	Most common (60%), fluctuant
  Ischiorectal	Ischiorectal fossa	Large, tender
  Intersphincteric	Intersphincteric	Deep pain, difficult Dx
  Supralevator	Above levator ani	Sepsis, deep pain

Fistula-in-Ano: Chronic sequela of abscess.

• Parks Classification:

  Type	Pathway	Frequency
  Intersphincteric	Intersphincteric	~70%
  Transsphincteric	Crosses ext. sphincter	~25%
  Suprasphincteric	Over puborectalis	~5%
  Extrasphincteric	Outside sphincters	<1%

• Goodsall's Rule: Predicts internal opening.
  • Anterior: straight track.
  • Posterior: curved to posterior midline.
  • Exception: Anterior >3cm from verge may curve.

⭐ Perianal abscess is the most common type of anorectal abscess.

Anorectal Abscess & Fistula - Signs & Scrutiny

• Symptoms:
  • Abscess: Acute throbbing pain, localized swelling, erythema, fever.
  • Fistula: Chronic purulent/serosanguinous discharge, recurrent abscess, external opening, pruritus ani.
• Examination:
  • Inspection: External opening, induration, inflammation.
  • Palpation: Tenderness, fluctuance (abscess), tract (fistula).
  • DRE: Pain may limit (abscess); identify internal opening (fistula).
  • Probing: Gentle; often under anaesthesia (EUA) to trace tract.
• Investigations:
  • Anoscopy/Proctoscopy: Visualize internal opening.
  • Complex/Recurrent Fistulas:
    • Endoanal Ultrasound (EAUS/ERUS): Sphincter integrity, tract relation.
    • MRI Pelvis: Gold standard; delineates entire tract, extensions, abscesses.

  ⭐ MRI is the gold standard investigation for complex or recurrent fistula-in-ano.

• Diagnostic Algorithm:

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Anorectal Abscess & Fistula - Fixing the Flow

• Abscess Management: Prompt Incision & Drainage (I&D) is mainstay; cruciate or radial incisions close to anal verge. Antibiotics: only if significant cellulitis, systemic signs (fever, ↑WBC), immunocompromised, or prosthetic heart valves.
• Fistula Surgery Principles:
  • Eradicate tract, prevent recurrence.
  • Preserve anal sphincter function & continence.
  • Identify primary (internal) opening. 📌 Goodsall's Rule aids this.
• Surgical Options (Fistula):
  • Simple/Low: Fistulotomy/Fistulectomy.
  • High/Complex: Seton (draining/cutting), LIFT (Ligation of Intersphincteric Fistula Tract), VAAFT, Advancement flap, Fibrin glue/plug, FiLaC (Fistula laser closure).

⭐ The primary goal of fistula surgery is to cure the fistula while preserving continence.

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High‑Yield Points - ⚡ Biggest Takeaways

• Cryptoglandular infection in the intersphincteric space is the primary cause.
• Perianal abscess is most common; supralevator abscesses can be deep and insidious.
• Goodsall's rule predicts fistula tracks: anterior openings = straight paths, posterior = curved paths.
• Intersphincteric fistulas are the most frequent type.
• MRI is gold standard imaging for complex or recurrent fistulas.
• Abscesses require prompt incision and drainage; fistulas often need fistulotomy or seton.
• Consider Crohn's disease with multiple, recurrent, or complex fistulas.