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Fistula-in-ano

Contents

1. Definition
2. Examples of Fistulae
3. Classification of fistula-in-ano
4. Goodsall's Rule
5. Aetiology
6. Diagnosis
7. Imaging
8. Management
1. EUA
2. Rigid Sigmoidoscopy
3. Identification of the Internal Opening/Course
4. Low Fistulas (Subcutaneous, submucous, low)
   1. Laying open (Fistulotomy)
   2. Fistulectomy

5. High Fistulas
   1. Seton Suture placement
      1. Cutting Seton
      2. Draining Seton
6. Complex Fistulae

 

1. Definition

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