Anorectal abscesses and fistulae

Question 1

What is an anorectal abscess?

Answer 1

Infection of soft tissues around anus

Question 2

Aetiology of anorectal abscess?

Answer 2

• Majority due to infections of anal glands (cryptoglandular infections)
• Anal canal has 6-14 glands that lie in plane between internal and external anal sphincters. Ducts from glands pass through internal sphincters→ drain into anal crypts at dentate line.

Question 3

Anal glands may become infected when crypt occulded by…? (3)

Answer 3

• Impaction of faecal matter
• Oedema from trauma secondary to hard stool/ foreign body
• As result of adjacent inflamm (ie: Crohn’s)

Question 4

Risk factors for anorectal abscess?

Answer 4

• Anal fistula
• Crohn’s disease
• Male
• Hard stools

Question 5

Common signs and symptoms of anorectal abscess?

Answer 5

Perianal pain and swelling

Perianal/ rectal induration (thickening and hardening of soft tissue)

Low-grade fever

Tachycardia

Question 6

Uncommon signs and symptoms of anorectal abscesses?

Answer 6

• Change in bowel habits
• Rectal bleeding
• Urinary incontinence

Question 7

Ix: How is diagnosis of anorectal abscess usually reached?

Answer 7

Clinical diagnosis

Question 8

Ix: Other investigations (other than clinical diagnosis) for anorectal abscesses?

Answer 8

Examination under anaesthesia (when adequate exam can’t be done due to too much pain)

WBC count (non-specific but helps confirm diagnosis)

Colonoscopy (exclude other diseases)

Screen for STIs, IBD, diverticular disease and malignancy

Question 9

Management and subsequent care for anorectal abscesses (without complications)?

Answer 9

Surgical drainage of abscess (without delay!)

Post-op care:
- Warm baths to clean wound (2-3 times/ day)
- Absorbent dressing
- Ensure high-fibre and adequate fluids in diet

Fistulotomy (if assoc anal fistula)

Question 10

Management for anorectal abscesses with complications? (Assoc cellulitis/ immunocompromise/ systemic infection/ diabetes/ cardiac valvular dis)

Answer 10

Broad-spectrum ABs w anaerobic and gram-negative coverage
(IV broad-spec penicillin, etc)

Question 11

What is an anal fistula and what is its pathophysiology?

Answer 11

• Anal fistula: abnormal tunnel under skin that connects anal canal to skin of buttocks
• Most form in reaction to abscess
• Abscess ruptures→ fistula

Question 12

Aetiology and risk factors for anal fistula?

Answer 12

• Anal fistula
• Crohn’s disease
• Male sex
• Hard stools
• Colitis
• Chronic diarrhoea
• Radiation treatment for rectal cancer

Question 13

Signs and symptoms of anal fistula?

Answer 13

Same as anorectal abscess plus pus drainage near anal opening

Question 14

Investigations for anal fistula?

Answer 14

Same as anorectal abscess
Consider: fistula probe

Question 15

Surgical management of anal fistula? (4)

Answer 15

• Fistulotomy: opens up fistula to let it heal
• Fill fistula w special glue/ plug
• Reconstructive surgery
• Seton placement: place suture/ rubber band (seton) in fistula. It is then progressively tightened→ lets fistula heal behind seton