Perineal Abscesses & Fistulae

Question 1

Definition (abscess)

Answer 1

a pus collection in the perineal region

Question 2

Definition (fistula)

Answer 2

an abnormal chronically infected tract communicating between the perineal skin and either the anal canal or the rectum

Question 3

Aetiology

Answer 3

• Bacterial infection
• Fistulae develop as a complication of an abscess

• Fistulae can develop as a complications of Crohn’s disease
o The development of multiple perineal fistulae in Crohn’s disease is called pepper pot perineum

Question 4

Risk factors

Answer 4

o IBD
o Diabetes mellitus
o Malignancy

Question 5

Epidemiology

Answer 5

COMMON

Question 6

Presenting symptoms

Answer 6

• Constant throbbing pain in the perineum
• Intermittent discharge (mucus or faecal staining) near the anal region
• Personal or family history of IBD

Question 7

Signs on physical examination

Answer 7

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

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

Question 8

Goodsall’s Law

Answer 8

o This is a rule that allows you to correlate the location of the internal fistula
opening based on the location of the external fistula opening

o If the external fistula opening is ANTERIOR to the anal canal (i.e. lies anterior to the transverse anal line), the fistula runs radially and directly into the anal canal

o A fistula that is 3 cm away and any fistula that has an external fistula opening lying posterior to the transverse anal line will follow a curved path and open internally in the posterior midline

Question 9

Investigations

Answer 9

• Bloods
o FBC
o CRP
o ESR
o Blood culture 

• Imaging
o MRI

• Endoanal Ultrasound
o Less useful than MRI

Question 10

Management plan

Answer 10

• Requires SURGICAL treatment
• Open Drainage of Abscess

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

o Low Fistula
• Fistulotomy
• Care must be taken to prevent damage to the anal sphincter

o High Fistula
• Fistulotomy would cause INCONTINENCE so is NOT performed
• Seton - a non-absorbable suture that is threaded through the fistula and
allows drainage

• Antibiotics

Question 11

Possible complications

Answer 11

• Recurrence
• Damage to internal anal sphincter
• Incontinence
• Persisting pain

Question 12

Prognosis

Answer 12

• High recurrence rate without complete excision