Anal fistula surgery

Surgical principles

Define anatomy
Ensure resolution of sepsis
- Initial placement of seton is appropriate
- Fistula can't be definitively treated until sepsis resolved
Preserve anal sphincter function
- Division of internal sphincter is usually well-tolerated
- Division of external third of external sphincter is usually safe

Lots of options, but realistically most fistulas fall into two categories
- Superficial, inter-sphincteric, or low trans-sphincteric fistulas get a fistulotomy
- High trans-sphincteric fistulas can be temporised with a seton and treated definitively with LIFT, advancement flap, fibrin glue or collagen plug
Supra-sphincteric and extra-sphincteric are a bit different

Balance between curing the acute problem, and causing incontinence later in life
High-risk factors for incontinence:
- 12 o'clock tract, especially in women
- Involving >20% of external sphincter (traditionally, dividing internal sphincter is not as risky)
- Poor pre-op sphincter function
Good candidates for fistulotomy:
- Posterior
- Superficial
- Inter-sphincteric
- Consider it for low trans-sphincteric, but there will always be a risk of impaired sphincter function
Cannulate and divide tissue over probe
Recurrence rate for these will be 2-8%, with functional impairment 0-17%
- ~30% risk of flatus and mucus incontinence

Allows continuous drainage of sepsis, rather than intermittent build-up of pus
Promotes fibrosis and maturation of fistula tract, in preparation for second-stage procedure
Ensure not too tight
Second-stage procedure 6-8 weeks later
For some Crohn's or other high-risk patients, seton can be definitive
Draining setons are good for recurrent infections or to mature a fistula tract for definitive future treatment
- Probe the tract. Tie a silk ligature to the probe and pull it through. Then tie the ligature to a vessel loop and pull that through. Use two artery forceps to clamp an appropriate length ready for tying. Tie three separate silk ligatures on the overlapping part of vessel loop, then trim the ends. Try to pull the seton through so the ties are on the inside.
Cutting setons are for trans-sphincteric or extra-sphincteric fistulas
- Only rarely used now
- Tighten every month
- Do not tighten the seton over intact skin

First described 2007
Cannulate and widen external opening
Particularly useful in those where advancement flap is difficult - stenosed anus or very high internal opening
1-2cm curvilinear incision at intersphincteric groove, over the tract, which is then developed bluntly
Isolate fistula tract circumferentially without disrupting it
Probe removed
Both ends of tract suture-ligated with 3-0 absorbable
Divide tract sharply
Inject hydrogen peroxide as a leak check
Reapproximate anoderm
Primary healing rates 47-95%, with worsening of incontinence rare
- Real success rate in real-world practice seems to be lower than that

'gold standard' sphincter-preserving operation
Indications: high fistula tracts, suprasphincteric tracts, low tracts in high-risk patients
Technique
- EUA
- Excise a patch of mucosa with diathermy, down to but not including muscle, but do try and take a decent chunk of the fistula
- Close the defect with 3/0 Vicryl or Vicryl Rapide, either primarily or with an advancement flap (uncommon to need an actual flap). Generally make a few muscular sutures then a good continuous mucosal suture from one end to the other, and maybe back again if defect is not neatly closed the first time.
- Curette the external opening
- Spongostan

Idea is to block off the tract
Can be repeated multiple times
Early results were very good with closure, but long-term results seem to be very poor - about 15-20% successful closure
Although they are not particularly risky or harmful, they are expensive, and most surgeons would consider them to be outdated and a waste of time

Delivers a controlled burn along the fistula tract - intended to de-epithelialize the tract, but doesn't affect the underlying pathology
Ideally used when the underlying disease state is controlled as well as possible