Anal Fistula

An anal fistula is an epithelialised or granulating tract connecting an internal opening within the anal canal or rectum to an external opening on the perianal skin.

Most arise after cryptoglandular anorectal abscess.

Anatomical classification according to sphincter relationship includes:

• Intersphincteric
• Transsphincteric
• Suprasphincteric
• Extrasphincteric

The management objective is cure while preserving continence.

Patients typically report intermittent purulent or bloody drainage from a perianal opening.

Pain often increases when the external opening temporarily seals and an abscess reforms, then improves when drainage resumes.

Examination may identify an external opening, palpable tract or associated abscess.

Simple fistulas can often be defined clinically and during examination under anaesthesia.

Pelvic MRI: preferred for recurrent, branching, complex or Crohn associated fistulas.

Do not blindly probe a tract in clinic because creation of false passages makes subsequent surgery more difficult.

A simple low fistula involving little external anal sphincter can undergo fistulotomy.

Lay open the tract, curette granulation tissue and allow healing by secondary intention.

Fistulotomy has the highest cure rate for appropriately selected low cryptoglandular fistulas.

Do not perform fistulotomy when the amount of sphincter division would create unacceptable continence risk.

For a transsphincteric tract where preservation is required, options include:

LIFT procedure: identify and divide the fistula within the intersphincteric plane while preserving both sphincter complexes.

Endorectal advancement flap: close the internal opening beneath a vascularised rectal mucosal flap.

A loose draining seton controls sepsis and maintains drainage when definitive repair must be delayed.

Cutting setons divide sphincter progressively and carry a continence risk. They should be used only selectively rather than as a routine strategy.

Recurrent abscess after supposed fistula repair usually means the internal opening or a secondary tract remains untreated.