Content provided by Jon Lund
Clinical Associate Professor, School of Graduate Entry Medicine & Health University of Nottingham

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COLORECTAL SURGERY

CONDITIONS - Fistula-in-ano

1. Definition

A fistula is an abnormal connection between two epithelial lined surfaces. In this case it is an abnormal connection between the anal canal and the skin surface.

2. Examples of fistulae
Commonest fistulae- Ear piercing!
Commonest fistulae in medical practice- entero-enteric fistulae, but many are clinically silent
Commonest presenting fistula- fistula-in-ano

3. Classification of fistula-in-ano

Best to classify them according to their relationship to the anal sphincters
Subcutaneous + submucous - below sphincters
Low - traverses only the internal sphincter
High - traverses internal + external sphincter
Intersphincteric -travels between the two muscles with the opening being at variable levels
Pelvirectal - opens above the anorectal ring

4. Goodsall's rule

Pelvirectal - opens above the anorectal ring
With the patient in the lithotomy position a horizontal line is drawn from 9 o'clock through the centre of the anus to 3 o'clock.
If the external opening is below this plane, the fistula will follow a curved course to the posterior midline.
If the external opening is above this plane, the fistula will follow a straight radial course to the dentate line
 
5. Aetiology

Nearly always caused by previous perianal abscess formation
Crohn's disease
Diabetes
Immunosuppression
HIV infection
Malignancy
Trauma
Radiotherapy
 
6. Symptoms
 
Pain
Discharge - purulent or bloody
Pruritis ani
PR bleeding

7. Diagnosis

History and Examination
PR examination - area of induration, fibrous tract and internal opening may be felt
Proctoscopic inspection of anal canal
Signs
External opening
Perianal discharge
Skin excoriation
Inflammation + erythema
 
8. Imaging

MRI: When presented with a complex fistula, MRI is utilised to evaluate the primary course as well as any secondary extensions. Recurrence rates have been shown to improve following its use as unknown extensions, which would have otherwise been missed, are identified and treated

9. Management
 
Treatment depends on the level of the fistula
Enema is used in the morning prior to surgery
Anaesthesia of choice is used (GA, regional block, local)
Patient is placed in the lithotomy position
Before any surgical procedure is carried out an EUA + Rigid Sigmoidoscopy is performed
 
9.1 EUA
A full examination/inspection of the perineum + PR is then performed
This is also necessary as the patient is quite commonly too uncomfortable for full examination in outpatients
 
9.2 Rigid Sigmoidoscopy
This is performed to evaluate the rectal mucosa for any underlying disease process
 
9.3 Identification of the internal opening/course

A fistula probe is passed via the external opening to identify the course of the tract and the internal opening. Care must be taken when using the probe as too much pressure can lead to the formation of false passages.
If a tract cannot be found with the probe, injection of hydrogen peroxide into the external opening can reveal the internal opening
 
9.4 Low fistulas (subcutaneous, submucous, low)

9.4.1 Laying open (Fistulotomy)
After identifying the level of the internal opening with a probe, as well as the level of the internal sphincter, the tract is opened up with diathermy
This therefore does not compromise sphincter integrity
Granulation tissue is then removed using a curette
9.4.2 Fistulectomy
Complete excision of the fistula
Bigger wound is created
No advantage shown over fistulotomy
 
9.5 High fistulas

9.5.1 Seton suture placement
High fistula's cannot be laid open as described above as this would lead to division of the sphincters and faecal incontinence
Setons are usually made from rubber slings
2 types of seton suture can be placed
  
9.5.1.1 Cutting Seton
Slowly "cheese-wires" though the sphincter muscle
This suture is pregressively tightened every 2 weeks over 6-8 weeks
Allows fibrosis to take place behind as it gradually cuts through
9.5.1.2 Draining Seton
Facilitates draining of sepsis
Left loose and allows fistula to heal by fibrosis
 
9.6 Complex Fistulae

May require combinations of procedures such as fistulectomy, with a defunctioning stoma