How to classify an enterocutaneous fistula?

Classification of Enterocutaneous Fistulas

Enterocutaneous fistulas are best classified based on their output volume: low (<200 ml/day), moderate (200-500 ml/day), and high (>500 ml/day). 1

Primary Classification System: Output-Based

This output-based classification system is the preferred approach according to the European Crohn's and Colitis Organisation (ECCO) and European Society of Coloproctology (ESCP) consensus guidelines, as it directly guides management decisions and predicts outcomes. 1

• Low output: <200 ml/day - these fistulas may respond to medical therapy with immunomodulators and biologics 2
• Moderate output: 200-500 ml/day - require careful monitoring and may need surgical intervention 1
• High output: >500 ml/day - typically require surgery for symptom control and have significant risk of fluid/electrolyte derangements 2, 3

The output volume directly correlates with morbidity and mortality risk, as high-output fistulas lead to severe dehydration, electrolyte imbalances, and malnutrition. 4, 3

Secondary Classification: Anatomic Description

While output is the primary classification, anatomic description provides essential complementary information. 1

Anatomic classification should indicate the bowel segment of origin followed by the target organ (e.g., ileo-cutaneous, jejuno-cutaneous, colo-cutaneous). 1

This anatomic detail is critical because:

• The site of origin affects spontaneous closure rates (proximal fistulas have lower closure rates) 5, 6
• It determines nutritional management strategies 4, 3
• It guides surgical planning when operative intervention is needed 7

Additional Classification Considerations

Complexity Assessment

Fistulas should also be characterized as simple (single tract) or complex (multiple tracts, asterisk-shaped configuration involving multiple structures). 1

• Complex fistulas have reduced healing rates with anti-TNF therapy and increased need for surgery 2
• Complexity increases mortality risk 2

Associated Complications

Document the presence of:

• Bowel strictures at the fistula origin - nearly always present with penetrating disease and require surgical intervention 1
• Intra-abdominal abscesses - must be drained before initiating anti-TNF therapy 2
• Active inflammation at the fistula site - influences medical therapy decisions 2

Diagnostic Imaging

MRI is the preferred diagnostic tool for enteric fistulas, with the highest sensitivity and specificity. 1, 2

MRI can identify:

• Fistula tracts appearing as tubular structures with fluid or air content and peripheral enhancement 1
• Associated complications (abscesses, strictures, inflammatory masses) 1
• Multiple fistula tracts in complex disease 1

Common Pitfalls to Avoid

• Do not classify solely by anatomy - output volume is the primary determinant of management strategy and must always be documented 1
• Do not overlook associated strictures - they are nearly always present at the site of fistula origin and affect treatment planning 1
• Do not use ambiguous terms like "phlegmon" - specify whether there is a drainable abscess or inflammatory mass 1
• Do not fail to assess complexity - multiple tracts significantly worsen prognosis and alter management 2