Case 8.6 – Perianal Abscess & Fistula

History and Examination:

• Complete GIT history - bowel habits, previous perianal problems, IBD symptoms, immune status
• Thorough GIT examination
• Visual and digital rectal examination
• Proctoscopy
• Cardinal signs of infection are usually present:
  • Pain
  • Fever
  • Redness
  • Swelling
  • Loss of function

Pathophysiology

• Cryptoglandular origin: Most anorectal abscesses are believed to start with obstruction of the perianal glands that are located between the internal and external sphincters (intersphincteric space)
• Perianal glands normally discharge their secretions at the level of the anal crypts that are located at the base of the columns of Morgagni
• As the early intersphincteric abscess increases in size, it tends to spread along the planes of lesser resistance

Classification of Anorectal Abscesses

Type	Location	Frequency
Perianal abscess	Superficial to external sphincter, most common presentation of intersphincteric abscess	Most common (90% combined with ischiorectal)
Ischiorectal abscess	Located in the ischiorectal fossa, outside the external sphincter mechanism and below the level of the levator ani muscle	Common (90% combined with perianal)
Intersphincteric abscess	Between internal and external sphincters	Uncommon (early stage)
Supralevator abscess	Above the levator ani muscles (rare, may be very difficult to diagnose clinically)	Rare

Clinical Features

• Except for early intersphincteric abscesses and supralevator abscesses, perianal pain and swelling are readily apparent in perirectal abscesses
• Spontaneous drainage of pus may occur

Primary Treatment

• Thorough and complete drainage of the abscess is essential
• Failure to do this will likely result in ongoing pain, sepsis and overall treatment failure
• Drainage usually requires general anaesthesia and surgical incision

Role of Antibiotics

• Antibiotics alone have NO role in the primary treatment of an abscess
• However, antibiotics may be used in conjunction with surgical incision and drainage in specific circumstances:
  • Immune-compromised patients
  • Patients with diabetes
  • Patients with leukaemia
  • HIV/AIDS patients
  • Patients undergoing chemotherapy

Key Principles

• Early surgical drainage prevents progression and complications
• Complete drainage is critical for treatment success
• Appropriate antibiotics should be considered for high-risk patients

Definition

• After drainage of a perirectal abscess, the patient has a 50% chance of developing a chronic fistula-in-ano
• An anorectal fistula is an abnormal communication between the anus at the level of the dentate line and the perirectal skin, through the bed of the previous abscess

Classification of Fistulae

Fistulae are named in relation to the sphincteric mechanism:

Type of Fistula	Origin	Anatomy
Intersphincteric	Result of perianal abscesses	Between internal and external sphincters
Transphincteric	Result of ischiorectal abscesses	Traverses through sphincter mechanism
Suprasphincteric	Result of supralevator abscesses	Above the sphincter mechanism
Extrasphincteric	Various causes	Bypasses the anal canal and sphincteric mechanism, opens high up in the rectum

Clinical Presentation

• Chronic drainage of pus from the skin opening
• Sometimes drainage of stool from the external opening
• Fistulae rarely (if ever) heal spontaneously
• Therefore, surgical correction is usually indicated to eliminate symptoms

Purpose

Goodsall's rule helps the examiner to predict the trajectory of the fistulous tract and the probable location of the internal anal opening.

How to Apply Goodsall's Rule

• With the patient in the lithotomy (or knee-chest) position, an imaginary line is drawn at the level of the anus, parallel to the floor

The Rule

External Opening Location	Fistula Tract Path
Anterior to the imaginary line	The fistula tract usually goes radially straight into the anal crypt
Posterior to the imaginary line	The fistula tract generally curves around, and the internal opening is in a frank midline position

Limitations

• The greater the distance between the anus and the external opening, the less reliable and helpful Goodsall's rule becomes
• The trajectory of complex anal fistulae is unpredictable

Fistulotomy - Basic Technique

• Fistulotomy consists of "unroofing" the fistula tract, allowing the fistula to heal slowly by secondary intention
• Preliminary identification of the fistula tract by gentle insertion of a probe into the external skin opening, through the tract, until the internal anal opening is found
• Allows intra-operative evaluation of the structures that need division

Staged Fistulotomy with Seton Suture

• A Seton suture/nylon sling permits immediate division of all non-sphincteric structures and partial fistulotomy if appropriate
• Judgement must be exercised to avoid cutting a large portion of the sphincter muscle which may lead to incontinence

Newer Techniques

• Fibrin glue - minimally invasive approach
• Rectal advancement flaps to cover the internal opening

Important Considerations

• The key principle is to preserve sphincter function while eliminating the fistula
• Balance between complete fistula treatment and maintaining continence
• Recurrence and/or minor incontinence can be seen with more complex fistulae

Surgical Goals

1. Identify the entire fistula tract
2. Eliminate the fistula while preserving sphincter function
3. Prevent recurrence
4. Minimize risk of incontinence