Perianal abscesses + fistulae

Question 1

What is a perianal abscess?

Answer 1

a pus collection in the perianal region

Question 2

What is a perianal fistula?

Answer 2

An abnormally chronically infected tract communicating between the rectum and the perineum

Question 3

Describe the pathophysiology of an abscess and fistula formation

Answer 3

1. Foreign material in anal crypts ->
2. Anal glands ducts blocked ->
3. Anal abscess ->
4. Pus travels to skin through tract= fistual

Anal abscesses are the acute manifestation of a purulent infection in the perirectal area, while anal fistulas are the chronic manifestation of such infections.

Question 4

What are some risk factors for perianal abscess/ fistulae?

Answer 4

IBD
Diabetes mellitus
Malignancy

Question 5

Summarise the epidemiology of anal abscesses and fistulae

Answer 5

COMMON
- M>F (2:1), 20-60 yrs old
- In about 30–60% of cases, anal abscesses progress into fistulas

Question 6

What are the different types of perianal fistula’s a patient may have?

Answer 6

1. Intersphincteric
   - Internal and anal sphincter -> space between internal, external anal sphincters (AKA intersphincteric plane) -> skin
2. Transsphincteric (U-shaped fistula)
   - Internal anal sphincter -> intersphincteric plane -> external anal sphincter -> skin
3. Suprasphincteric
   - Internal anal sphincter -> puborectalis muscle -> space between puborectalis, levator ani muscle -> skin

Question 7

What are the presenting symptoms of anal abscesses and fistula’s?

Answer 7

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

Question 8

What signs of an anal abscess/ fistulae can be found on physical examination?

Answer 8

1. Localised tender perineal mass (may be fluctuant)
2. Small skin lesion near the anus (opening of the fistula)
3. DRE
   - A thickened area over the abscess/fistula may be felt
   - DREs are not always possible due to pain and anal sphincter spasm

Question 9

What rule can be used to predict the position of the internal opening of the fistula, based on the position of the external opening?

Answer 9

Goodsall’s Rule:
- 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 

• 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 10

What investigations are used to diagnose/ monitor perianal abscesses/ fistulae?

Answer 10

1. CT/MRI or Anal Ultrasonography → confirmatory tests for deeper abscesses
2. MRI Pelvis - best investigation to characterise fistula course
3. Further testing to identify possible fistulae and comorbidities (malignancy, IBD) → endoscopy, MRI, fistula probe

Question 11

How are perianal abscesses/ fistulae managed?

Answer 11

a. Requires Surgical Treatment
1. Early surgical incision and drainage of abscess (under local anaesthetic)
- Prevent spread of infection which may lead to sepsis
- Postoperative → sitz baths, analgesics & stool softeners, antibiotics (if individuals are immuocompromised)
2. Fistulotomy → cutting along the whole length of the fistula to open it in order to be drained
- Complex Perianal Fistulae (eg. in crohns) ⇒ seton placement (piece of surgical thread that is run through the fistula to allow continuous drainage while the fistula is healing, ensuring fistula doesn’t heal containing pus within causing further abscess formation)
b. Antibiotics

Question 12

What complications may arise from perianal abscesses/ fistulae?

Answer 12

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

Question 13

Summarise the prognosis for patients with perianal abscesses and fistulae

Answer 13

High recurrence rate without complete excision