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Perianal Fistula

  • Chronic abnormal communication running outwards from anorectal lumen to an external opening on
    • The skin of perineum
    • The skin of buttock
    • The skin of vagina
  • The fistula usually originates in the infected crypt (internal opening) and tracks to the external opening, usually at the site of prior drainage
  • The course of the fistula can often be predicted by the anatomy of the previous abscess

Clinical features

  • Intermittent purulent discharge – pain until discharge is completed
  • Skin irritation
  • Anorectal sepsis

Classification – Parks Classification

  • 1 – Intersphincteric (70%)
    • Found between internal and external sphincter
  • 2 – Transphincteric (23%)
    • As a result of ischio-rectal abscess
    • Extends through both internal and external anal sphincter
  • 3 – Suprasphincteric (2%)
    • Originates from the intersphincteric space and tracks up and around the entire external sphincter
  • 4 – Extrasphincteric (5%)
    • Originates in rectal wall, tracks around both sphincters
    • Exits laterally in the ischiorectal fossa

Goodsall’s rule 
  • The rule is used to predict the trajectory of a fistula tract depending on the location of the external opening in relation to the transverse anal line
  • If the external opening is located anterior to the transverse anal line – the fistula will have a straight tract
  • If the external opening is located posterior to the transverse anal line – the fistula will have a curved tract
    • May present with multiple external openings all connected to a single internal opening

Investigations

  • Fistulography + CT
  • MRI – gold standard
  • Proctosigmoidoscopy under general anaesthesia
  • Dilute hydrogen peroxide instilled via the external opening – demonstrates the site of internal opening

Treatment

  • Treat the concomitant abscess
  • Sitz bath and fibre therapy

Fistulotomy – for low anal fistulas

  • Probe is inserted into tract (from external to internal)
  • Base of wound and granulation tissue removed
  • Surgery for complex fistula – i.e. high transphincteric, suprasphincteric, extrasphincteric
Seton technique – for high fistulas

  • Striated muscle superficial to the fistula tract is encircled with seton and tied
  • It is left in situ to create ischaemic necrosis
    • Divides the muscle slowly without allowing it to spring apart, avoiding gutter deformity
  • Allows fistula to granulate and heal from above and close completely

Other procedures

  • Fibrin glue – easy to use, avoids sphincter division
    • Tract is debrided, then glue is injected
  • Anal fistula plug – better than glue

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Perianal Fistula

  • Chronic abnormal communication running outwards from anorectal lumen to an external opening on
    • The skin of perineum
    • The skin of buttock
    • The skin of vagina
  • The fistula usually originates in the infected crypt (internal opening) and tracks to the external opening, usually at the site of prior drainage
  • The course of the fistula can often be predicted by the anatomy of the previous abscess

Clinical features

  • Intermittent purulent discharge – pain until discharge is completed
  • Skin irritation
  • Anorectal sepsis

Classification – Parks Classification

  • 1 – Intersphincteric (70%)
    • Found between internal and external sphincter
  • 2 – Transphincteric (23%)
    • As a result of ischio-rectal abscess
    • Extends through both internal and external anal sphincter
  • 3 – Suprasphincteric (2%)
    • Originates from the intersphincteric space and tracks up and around the entire external sphincter
  • 4 – Extrasphincteric (5%)
    • Originates in rectal wall, tracks around both sphincters
    • Exits laterally in the ischiorectal fossa

Goodsall’s rule

  • The rule is used to predict the trajectory of a fistula tract depending on the location of the external opening in relation to the transverse anal line
  • If the external opening is located anterior to the transverse anal line – the fistula will have a straight tract
  • If the external opening is located posterior to the transverse anal line – the fistula will have a curved tract
    • May present with multiple external openings all connected to a single internal opening

Investigations

  • Fistulography + CT
  • MRI – gold standard
  • Proctosigmoidoscopy under general anaesthesia
  • Dilute hydrogen peroxide instilled via the external opening – demonstrates the site of internal opening

Treatment

  • Treat the concomitant abscess
  • Sitz bath and fibre therapy

Fistulotomy – for low anal fistulas

  • Probe is inserted into tract (from external to internal)
  • Base of wound and granulation tissue removed
  • Surgery for complex fistula – i.e. high transphincteric, suprasphincteric, extrasphincteric

Seton technique – for high fistulas

  • Striated muscle superficial to the fistula tract is encircled with seton and tied
  • It is left in situ to create ischaemic necrosis
    • Divides the muscle slowly without allowing it to spring apart, avoiding gutter deformity
  • Allows fistula to granulate and heal from above and close completely

Other procedures

  • Fibrin glue – easy to use, avoids sphincter division
    • Tract is debrided, then glue is injected
  • Anal fistula plug – better than glue
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