Anal fissures and fistulas

Anal Anatomy

  • Surgical anal canal: the length between the anal verge  / intersphincteric groove to the anorectal ring
  • Anatomical anal canal: anal verge to the dentate line
  • Anal verge: anocutaneous line approximately 2 cm to the dentate line
  • Dentate line: Junction of ectoderm and endoderm of anal canal
  • Internal anal sphincter: Smooth muscle not under voluntary control; most distal part of the circular part of the tunica musuclaris of the gut
  • External anal sphincter: Voluntary muscle that merges with the puborectalis and levator ani

Anal fissure

  • Definition
    • Linear tear in the distal anal canal which involves the epithelium and variably, the full thickness of anal mucosa
  • Presentation
    • Severe pain during defecation >  not pooping > constipation > hard stools > more pain
    • Bright red blood on TP
    • Acute fissure: just a tear
    • Chronic fissure: fibres of internal anal sphincter visible, enlarged anal skin tag and proximal anal papillary hypertrophy commonly present
  • Medical Management
    • Stool softener + laxatives
    • Sitz bath post defecation > relives spasm > less pain, more healing
    • GTN/nifedipine pintment
    • Botulism toxin (=chemical sphincterotomy)
  • Surgical Management
    • Sphincter dilatation (not commonly used due to impaired continence)
    • Lateral internal sphincterotomy
      • Procedure of choice
      • Cut through hypertrophied internal sphincter to reduce tension


  • Definition – tract lined with granulation tissue that allows communication between the anal canal to the perianal skin
  • The Goodsall rule – fistuals with anterior openings will follow a staight radial line to the dentate; fistulas with posterior openings will follow a curved line
  • Typical follows anal abscess
  • Surgical options
    • Fistulotomy
    • Seton placement – cord/rubber band that runs through the fistula and joins up outside to prevent one end sealing up and forming an abscess

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