What is a Fistula?

• Bailey and Love's Short Practice of Surgery defines it as: "an abnormal communication between two epithelium-lined surfaces."

How Do Fistulas Form?

• Infection / abscess - pus breaks through tissue, creating a channel
• Inflammation (e.g., Crohn's disease, diverticulitis)
• Surgery or trauma - especially in the head/neck, abdomen, or pelvic region
• Radiation therapy - damages tissue integrity
• Childbirth injury - particularly in obstetric fistulas
• Congenital defects - present from birth (e.g., tracheo-oesophageal fistula)
• Malnutrition / poor healing - increases risk especially after surgery

Types of Fistulas

Symptoms

• Discharge of pus, stool, urine, or gas from an abnormal opening
• Recurrent infections or abscesses
• Pain and swelling in the affected area
• Foul-smelling discharge
• In vaginal fistulas: leakage of stool/urine into the vagina, pain with intercourse

A Special Case: The AV Fistula (Surgically Created)

Management

1. Conservative (small/uncomplicated fistulas):
   • Wound care and dressing changes
   • Nutritional support (enteral feeding, nil by mouth)
   • Antibiotics for infection control
   • Treating the underlying disease (e.g., immunosuppressants for Crohn's)
2. Surgical (large, persistent, or dangerous fistulas):
   • Fistulotomy / fistulectomy - laying open or excising the tract (anal fistula)
   • Flap repair - using vascularized tissue to close the defect (e.g., pectoralis major flap for pharyngocutaneous fistula)
   • Surgical excision and primary repair - for vesicovaginal, rectovaginal fistulas
3. Complications if untreated:
   • Chronic infection and abscess formation
   • Sepsis
   • Carotid artery blowout (pharyngocutaneous fistulas near great vessels)
   • Delayed cancer treatment (radiation cannot proceed if active fistula present)

Anal Fistula - A Complete Overview

Definition

• Goldman-Cecil Medicine defines it as: "the chronic form of a perianal abscess in which the tract from the infected anal gland to the abscess cavity does not adequately heal."

Epidemiology

• Incidence: approximately 8.6 per 100,000 population
• 2-3x more common in men than women
• Occurs in 30-50% of patients following a perianal abscess
• Crohn disease-associated fistulas occur in 13-54% of Crohn patients

Pathophysiology (Cryptoglandular Theory)

1. Bacteria enter an anal gland (located in the crypts at the dentate line)
2. The gland becomes infected, forming a perianal abscess
3. The abscess drains (spontaneously or surgically), but the internal opening at the dentate line remains patent
4. This persistent tract = an anal fistula

• Goldman-Cecil Medicine: "After a perianal abscess is drained, the internal opening - the site at the dentate line where the infected gland originated - can remain patent, thereby leaving a source for recurrent infection."

Parks Classification (by relationship to sphincter complex)

Goodsall's Rule

• Posterior external opening (behind the line): tract curves to open in the posterior midline of the anal canal
• Anterior external opening (in front of the line): tract runs in a straight line to the nearest anal crypt

Clinical Features

• Recurrent perianal abscesses (often same location)
• Persistent or intermittent purulent / bloody discharge from a perianal opening
• Perianal pain, swelling, and itching
• Intermittent healing followed by re-flare ("feels like a boil forming, rupturing, and relieving")
• In Crohn fistulas: may have multiple external openings, more complex anatomy

• External opening visible on perianal skin (may have granulation tissue)
• Fibrous tract may be palpable along the course toward the anal canal
• Internal opening sometimes visible on anoscopy (but not always necessary for diagnosis)

Differential Diagnoses

Investigations

1. Clinical examination (usually sufficient for simple fistulas)
2. Examination under anesthesia (EUA) with a probe - identifies tract length and sphincter involvement
3. Endoanal ultrasound - shows tract in relation to sphincters, useful for internal opening identification

1. MRI pelvis (modality of choice for complex fistulas) - fat-suppressed T2W sequences show the fistula tract as high signal against the sphincter complex; detects supralevator extensions and abscesses; preoperative MRI reduces recurrence rates
2. Hydrogen peroxide injection into external opening (with or without endoanal US) - helps identify smaller fistulas
3. Fistulography with water-soluble contrast - for complex, recurrent, or Crohn fistulas

Management

Simple / Low Fistulas

• Success rate up to 90%
• Safe when < 30% of sphincter is involved and baseline continence is normal
• The unroofed tract heals by secondary intention
• Caution in women: the anterior anal sphincter is shorter; anterior fistulotomy risks incontinence

Complex / High Fistulas

• A suture, Silastic loop, or other material passed through the fistula tract and secured
• Keeps the external opening patent (prevents recurrent abscess)
• Over weeks, the tract scars and becomes fibrotic around the seton
• Can be used as a draining seton (long-term symptom control) or progressively tightened as a cutting seton (gradually erodes through sphincter)
• Cutting seton success: up to 94%, but incontinence risk: 23-22%

• A flap of mucosa + internal sphincter muscle is raised over the internal opening
• Tract is curetted, internal opening sutured closed, flap advanced and sutured over it
• Success rate: 66-87%

• After seton placement allows fibrosis, the intersphincteric tract is exposed, ligated, and divided
• Incision over the intersphincteric groove; both ends of tract ligated
• Success rate: 40-95%

• Fibrin glue instillation - high recurrence
• Fistula plug - high recurrence

Crohn-Associated Fistulas

• Asymptomatic fistulas in Crohn disease do not need treatment
• First step: unroof branching tracts to create a single track
• Anti-TNF therapy (e.g., infliximab) for medical management - can achieve symptomatic control
• Long-term draining setons combined with medical therapy are the mainstay
• Fistulotomy reserved only for most superficial fistulas
• Temporary defunctioning stoma (diversion) may help complex cases heal
• Proctectomy for severe, refractory perianal Crohn disease

Prognosis

Recent Evidence