Perianal abscesses and Fistulae

Question 1

Define Perianal abscesses

Answer 1

Collection of pus in the perianal region

Submucous | Subcutaneous | Inter-sphincteric | Ischiorectal | Pelvirectal abscess

Question 2

Define Perianal fistulae

Answer 2

Abnormally chronically infected tract communicating between peritoneal skin and either canal or rectum

Types: Superficial | intersphincteric | Trans-sphincteric | Suprasphincteric | Extrasphincteric
Alternative classification: Low anal (below puborectalis) or High anal (at or above puborectalis) and Pelvirectal (inv. Levator ani)

Question 3

Aetiology of Perianal abscesses and Fistulae

Answer 3

Fistula can cause abscesses and abscesses can cause fistulae

Obstruction and stasis of anal crypt glands -> superinfection spreads to perianal tissues

Fistulae may develop once abscess discharges or has been evacuated

Fistulae may be a complication of Crohn’s disease (multiple fistulae -> pepper pot perineum)

Question 4

Risk factors for Perianal abscesses and Fistulae

Answer 4

Crohn's 
Diabetes
Malignancy (rectal carcinoma)
Clogged anal glands and anal abscess
Radiation
Trauma

Question 5

Symptoms of Perianal abscesses and Fistulae

Answer 5

Constant throbbing pain in perineum (around anus) NOT related to defecation

Fistulae with intermittent discharge (mucous of blood-stained) near the anal region, may be foul smelling

Systemic: fever and chills

Question 6

Signs of Perianal abscesses and Fistulae on examination

Answer 6

Localised tender perianal swelling
Small skin opening with discharge near the anus (open fistula)

DRE: area of induration corresponding to abscess or fistula tract

Question 7

What is Goodsall’s rule

Answer 7

rule of thumb to correlate location internal fistula opening based on location of external fistula opening

* If external opening is anterior to anal canal, the fistula runs radially and directly into the anal canal
* If external opening is posterior to anal canal, fistula tract follows curved path, opening internally in posterior midline

Question 8

Investigations for Perianal abscesses and Fistulae

Answer 8

Clinical diagnosis

FBC/CRP/ESR/Blood cultures: check for infection

MRI: internal pelvic abscesses seen
USS: Can be used to visualise abscesses if DRE is tool painful

Question 9

Management for Perianal abscesses and Fistulae

Answer 9

Surgery ± antibiotics

Abscess incision and drainage (most common)
Hydrogen peroxide or methylene blue injection
Fistulotomy
Seton
Advancement flap
Xenograft (fistula plug)
Fibrin glue

Question 10

Complications of Perianal abscesses and Fistulae

Answer 10

Recurrence (high rate without complete excision)
Sepsis if untreated
Incontinence due to surgery