Anal fistula

Background

• Inflammatory tract originating from infected anal gland connecting anal canal with skin
  • May be intersphincteric, suprasphincteric, transsphincteric, or extrasphincteric
• Goodsall's Rule
  • Draw imaginary line horizontally through the anal canal
    • If external opening is anterior to this line fistula runs directly into the canal
    • If external opening is posterior to this line fistula curves to post midline of canal
• Causes:
  • Perianal/ischiorectal abscess, Crohn's, ulcerative colitis, malignancies, STI, anal fissures, foreign bodies, TB

Clinical Features

• Fistulous tract open: Persistent, painless, blood-stained, mucous, malodorous discharge
• Fistulous tract blocked: Bouts of inflammation that are relieved by spontaneous rupture
• Abscess
  • Throbbing pain that is constant and worse with sitting, moving, defecation
  • May be only sign of fistula
• Fistulous opening
  • Adjacent to anal margin suggests superficial connection (e.g. intersphincteric region)
  • Distant from anal margin suggests deeper, more superior abscess

Differential Diagnosis

Anorectal Disorders

• Anal tags
• Hemorrhoids
  • Internal hemorrhoid
  • External hemorrhoid
• Cryptitis
• Anal fissure
• Anal fistula
• Anorectal abscess
• Proctitis
• Rectal prolapse
• Rectal foreign body
• Pruritus ani
• Pilonidal cyst
• Constipation
• Condyloma acuminata
• Anal cancer
• Colorectal tumor
• Pedunculated polyp
• Crohn Disease
• Syphilitic fissure
• GC/Chlamydia

Evaluation

• Endocavitary ultrasound with 3% hydrogen peroxide for definitive diagnosis

Management

1. Ill-appearing
   1. Analgesia
   2. IVF
   3. Antibiotics
   4. Urgent surgical consultation
2. Well-appearing
   1. Antibiotics
      1. Ciprofloxacin 750mg PO BID AND metronidazole 500mg QID x7d
   2. Outpatient surgery referral
      1. Improperly excised fistulas may result in permanent fecal incontinence
   3. Spasm treatment
      1. Nitroglycerin, Lidocaine
      2. Sitz baths

See Also

Anorectal Disorders

References

Authors

Jordan Swartz, Claire, Ross Donaldson, Marissa Camilon, Neil Young