Fistula in Ano


  • Hollow tract lined with granulation tissue connecting a primary opening inside the anal canal to a secondary opening in the perianal skin
  • Common condition-prevalence 1:10,000
  • Males-4th decade

What are Causes:

  • History of an abscess-about 50% of anal abscess lead to anal fistula
  • Crypto glandular theory 90%: Anal canal glands at the dentate line afford a path for infecting organisms to reach the intramuscular space
  • Crohn’s dsease-35% of pts with CD -perianal fistula as first presentation
  • Radiation
  • TB
  • Actinomycosis

What is Differential diagnosis

  • Pilonidal infection
  • Hidradenitis suppurativa
  • Crohn’s disease
  • Tuberculosis
  • Intrapelvic sepsis

What are types of Anal Fistulae – (Parks classification)

4 Types of fistulae:

  • A-Inter-sphincteric -70%
    Common course - Via internal sphincter to the inter-sphincteric space and then to the perineum
  • B-Trans-sphincteric-25%
    Common course - Low via internal and external sphincters into the ischiorectal fossa and then to the perineum
  • C-Supra-sphincteric -5%
    Common course - Via inter-sphincteric space superiorly to above puborectalis muscle into ischiorectal fossa and then to perineum
  • D-Extra-sphincteric
    Common course - From perianal skin through levator ani muscles to the rectal wall completely outside sphincter mechanism

Only 1 % of all anal fistulae

What is Surgical Management

  • Depends on if low or high fistula and whether it is simple or complex fistula
  • If asymptomatic-not treated but still needs EUA . But of patient is immunocompromised-treated even if asymptomatic
  • If diagnosed at time of drainage of perianal abscess and it is low -can be layed open otherwise wait untill tract mature
  • LAY OPEN-only if simple and low

If complex

  • LIFT

What Investigations are needed

  • MRI
  • Anorectal USS
  • CT scan
  • EUA

What are principles of surgical treatment

  • Location internal opening
  • Location external opening
  • Closure of the primacy tract
  • Closure of the secondary tract
  • Assess sphincter involvement

Laying Open Fistula

Seton Placement

  • Setons keep fistula tract open and prevent recurrence of abscess
  • Reserved for high fistula
  • Control the sepsis and granulate the tract
  • Commonly are draining type setons to prevent tract closing and forming abscess
  • Stay in for 3 months and again change or do partial fistulotomy
  • Can be uncomfortable

Biological Mesh Plug

  • Usually bovine or porcine –can be human
  • Treated –sterilized and disinfected collagen –intestinal mucosa
  • Induce granulation tissue

Fibrin Glue

  • Not very popular

LIFT-ligation of fistula tract