Perianal abscesses and fistulae

Question 1

Define Perianal abscesses and fistulae

Answer 1

Perianal abscess = infection of the soft tissues around the anus

Perianal fistulae = chronic, abnormal communication between the epithelialized surface of the anal canal and the perianal skin

Question 2

How are perianal abscesses and fistulae classified?

Answer 2

Categorised based on relationship to sphincter muscles
o	Inter-sphincteric
o	Trans-sphincteric
o	Supra-sphincteric
o	Extra-sphincteric

Question 3

What is the aetiology of perianal abscesses and fistulae?

Answer 3

Abscesses
Majority result from infections of anal glands (cryptoglandular infections)
6-14 anal glands in the plane between the internal and external sphincters
Ducts from the glands drain into anal crypts as the dentate line
The glands become infected when a crypt is occluded by impaction of food, oedema from trauma or as a result of adjacent inflammation (e.g. Crohn’s)
Usually caused by gut organisms
45% are perianal

Fistula
Most are formed by the rupture of an abscess
Also found as a result of Crohn’s disease, perianal sepsis, TB, diverticular disease, immunocompromised and rectal carcinoma

Question 4

What are the risk factors for perianal abscesses and fistulae?

Answer 4

Abscesses
o	Anal fistula
o	Crohn’s
o	Male
o	DM
o	Malignancy

Fistula
o	Crohn’s
o	Anal abscesses
o	HIV
o	Diverticular disease
o	Malignancy
o	TB

Question 5

What is the epidemiology of perianal abscesses and fistuale?

Answer 5

Abscesses are very common
o 0.18% of general population
o 33% of Crohn’s patients

Abscesses are 2x more common in men
Highest occurrence during spring and summer

Question 6

What are the symptoms of perianal abscesses and fistulae?

Answer 6

Abscesses
o	Perianal pain - Constant, throbbing, worse on sitting down
o	Perianal/rectal induration
o	Change in bowel habits
o	Purulent/bloody discharge 

Fistula
o	Skin maceration
o	Pruritis ani (itching)
o	Recurrent malodorous perianal drainage
o	Perianal pain - Throbbing, constant

Question 7

What are the signs of perianal abscesses and fistulae?

Answer 7

Abscesses
o Perianal swelling
o Low grade fever
o Tachycardia

Fistula
o Tenderness
o Skin maceration
o Goodsall’s rule - If the fistula is anterior the tract is in a straight line (radial). If the fistula is posterior, the internal opening is always at the 6 o’clock position

Question 8

What are the investigations for perianal abscesses and fistulae?

Answer 8

Primarily based on history and physical examination
o DRE - Anaesthetic if inter-sphincteric

IF unclear
o CT/MRI
o Endoanal US scan

Question 9

What is the management for perianal abscesses and fistulae?

Answer 9

Abscess
o Surgical drainage - Post-op: 2-3 daily warm water baths, high fibre/water diet
o ABs if elderly/diabetic

Fistula
o Fistulotomy - If superficial
o Seton placement - If more than 25% of sphincter mechanism involved

Question 10

What are the possible complication of perianal abscesses and fistulae?

Answer 10

Abscesses
o Anal fistula
o Necrotising soft tissue infection

Fistulae
o Faecal impaction - Pain discourages people from defecating
o Surgical complications- Urinary retention, bleeding, incontinence
o Carcinoma

Question 11

What is the prognosis for patients with perianal abscesses and fistulae?

Answer 11

• Abscesses usually quickly improve with drainage

* Anal fissures often have recurrent abscesses (37%)