Perineal abscess and fistulae

Question 1

what is an anal fistula?

Answer 1

Anal fistula , or fistula-in-ano, is a chronic abnormal communication between the epithelialised surface of the anal canal and (usually) the perianal skin.

Question 2

Aetiology and risk factors?

Answer 2

Bacterial infection

Fistulae develop as a complication of an abscess

Fistulae can develop as a complications of Crohn’s disease

The development of multiple perineal fistulae in Crohn’s disease is called pepper pot perineum

diverticulitis, surgery in the area 
Risk Factors 
IBD - personal or FHx
Diabetes mellitus  
Malignancy

Question 3

Presenting symptoms?

Answer 3

Constant throbbing pain in the perineum

Intermittent discharge (mucus or faecal staining) near the anal region

skin maceration (softening, thinning)

unpleasant odour

thick discharge

some - bowel incontinence

Question 4

Signs on examination of either fistulae or abscess?

Answer 4

Localised tender perineal mass (may be fluctuant)
Small skin lesion near the anus (opening of the fistula)

DRE;
A thickened area over the abscess/fistula may be felt
DREs are not always possible due to pain and anal sphincter spasm

Goodsall’s Law;
used to determine the location of the internal fistula based on the external opening.

Question 5

Invx for anal fistulae?

Answer 5

clinical diagnosis

DRE
Proctoscopy – where a special telescope with a light on the end is used to look inside your anus

Ultrasound scan, magnetic resonance imaging (MRI) scan - more useful than US.

Question 6

Management plan?

Answer 6

Requires SURGICAL treatment

Open Drainage of Abscess (no abx unless accompanied cellulitis)

Laying Open of Fistula
A probe is inserted to explore the fistula
A dye can be inserted into the external opening to allow you to find the internal opening

Low Fistula;
Fistulotomy - cut open the legnth of the fistula so it heals into a flat scar. Care must be taken to prevent damage to the anal sphincter

High Fistula;
Fistulotomy would cause INCONTINENCE so is NOT performed. Seton - a non-absorbable suture called a seton is placed in the fistula from internal to external opening and tied outside. another proceedure is later required to close the fistula.

NO Antibiotics needed !!
other options; fibrin glue, fistula plug

Question 7

Complications and prognosis?

Answer 7

Recurrence
Damage to internal anal sphincter
Incontinence
Persisting pain

prognosis;
High recurrence rate without complete excision