Anal fistula

Section: Colorectal Sub-section: Proctology Curriculum: Curriculum, page 19

Definition

Idiopathic

• Majority non-specific, idiopathic or cryptoglandular, their exact aetiology having not been fully proven

Associated with:

• Lymphogranuloma venereum
• Presacral dermoids
• Rectal duplication
• Aactinomycosis
• Trauma
• Foreign bodies
• Crohn’s disease
• Tuberculosis
• Pilonidal disease
• Hidradenitis suppurativa

Epidemiology

M:F 2-4:1 3rd-5th decade

Pathophysiology

Cryptoglandulary hypothesis

• Anal glands in intersphincteric space
• Drain via anal sinuses onto dentate line
• Sinuses block with debris
• Impaired gland drainage
• Stasis
• Infection
• Abscess
• If abscess cannot drain back into the anal canal then slow increase in pressure until drain by another path
• perianal/subcutaneous, intersphincteric, ischioanal and supralevator
• This path can then either heal or become Epithelialised and a fistula

Clinical

Define:

1. Location of the internal opening;
2. Location of the external opening;
3. Course of the primary track;
4. Presence of secondary extensions;
5. Presence of other diseases complicating the fistula.

Parkes classification 45%, 30%, 20%, 5% and EL are based on different aetiologies

Colorectal Surgery A Companion to Specialist Surgical Practice 1, page 224

1. Inter-sphincteric (45%)
   • Usually simple
   • Or can have:
     • High blind track
     • High opening into the rectum
     • No perineal opening
     • Pelvic extension
     • Arise from pelvic disease
2. Trans-sphincteric (30%) - through the external sphincter into the ischiorectal fossa
   • Can be uncomplicated
   • Or can have:
     • High blind track
       • That terminates above or below the levator ani
3. Supra-sphincteric (20%)
   • Run up to a level above the puborectalis and then curl back down through the levators and into the ischiorectal fossa to reach the skin
4. Exrta-sphincteric (5%)
   • Run without relation to the sphincters

Simple - Parkes 1 (intersphincteric) and Parkes 2 (transsphincteric) which are low lying = <30% sphincter involvement Complex - all others

Draw backs of Parks

• Superficial fistulas are not in Parks classification
• There can be clinical difficulty in differentiating between a simple intersphincteric fistula and a very low trans- sphincteric fistula that crosses the lowermost fibres of the subcutaneous portion of the external sphincter.
• And some argue whether suprasphincteric tracks can be part of a classification based on cryptoglandularpathology (arguing indeed that many are iatrogenic).

Goodsall’s Rule

• Describes predicted location of internal opening based on transverse anal line
• External openings anterior - radial tract to internal opening
• External openings posterior - curvilinear tract to internal opening to 6 o’clock
• Exceptions
  • External opening >3cm from anal verge
  • Complex fistula
  • Long anterior fistula

Investigations

MRI

Differential diagnosis

• Hidradenitis
• Pilonidal
• Fissure
• Bartholin’s
• TB
• Crohn’s
• STI
• Benign - pilonidal, hidradenitis, fissures, cryptoglandular, TB, Crohns, radiation, divertic
• Malignant - adeno, scc, amelanotic melanoma

Treatment

Parkes Classification

• Superficial (not part of the types)
• Intersphincteric type 1 - 45% ⇒ CANT LIFT
• Transsphincteric type 2 - 30% → LIFT
• Suprasphincteric type 3- 20%
• Extrasphincteric type 4 - 5%

Goals

• Drain sepsis
• Define anatomy - Openings, track, extensions
• Eradicate fistula track
• Prevent recurrence
• Preserve sphincters
• Treat underlying pathology

Fistulotomy Principle

• Anteriorly sphincter is thinner for males and females (more so for females) How to
• Curette the tract to prevent recurrence
• Marsupialise the track to promote healing Mx → how much max sphincter involvement to allow fistulotomy
• Male
  • Posterior - 50%
  • Anterior - 33%
• Female
  • Posterior - 33%
  • Anterior - 0% Outcomes
• Recurrence - 5%
• Incontinence - variable, up to 10%

Cutting setons

• Painful
• High incontinence rate up to 40%

FIbrin glue

• 50% success
• Easy and repeatable
• No sphincter disruption

Fistula plug

• 50% success
• Surgisis mesh material - porcine collagen
• Sutured in place

Mucosal advancement flap for fistual in ano

• 50- 70% success
• Excise, suture internal opening with prolene and MAF

Ligation of the intersphincteric fistula tract

• 60-80% success

Summary

• Fistulotomay/ectomy
  • Success: 90%
  • Incontinance risk: 10%
• LIFT
  • Success: 50-80%
  • Incontinance risk: 10-30%
• Anorectal advancement flap
  • Success: 50-70%
  • Incontinance risk: 10-30%
• Fibrin glue
  • Success: 50%
  • Incontinance risk: Minimal
• Plug
  • Success: 50%
  • Incontinance risk: Minimal