Can fistulas from Crohn's disease be visualized on a computed tomography (CT) scan of the abdomen with intravenous (IV) contrast?

CT Abdomen with IV Contrast Can Detect Crohn's Fistulas, But Performance is Variable

Yes, CT abdomen with IV contrast can visualize fistulas from Crohn's disease, but sensitivity is highly variable (20-100%) and depends significantly on fistula type and location. 1

Understanding CT Performance for Fistula Detection

Overall Detection Rates

• Standard CT abdomen/pelvis with IV contrast demonstrates variable sensitivity for fistula detection, ranging from 68% to 100% across studies 1
• The wide range reflects significant differences in fistula type, with some being much harder to detect than others 1

Critical Limitation: Enteroenteric Fistulas

• Enteroenteric fistulas (bowel-to-bowel connections) have particularly poor detection rates, with one study showing only 20% sensitivity 1
• This represents a major clinical pitfall, as these internal fistulas can be completely missed on standard CT 2

Better Detection for Other Fistula Types

• Extraenteric fistulas (connecting bowel to other structures or skin) are detected more reliably, with 81% appearing as hyperenhancing tracts on CT enterography 3
• Most fistulas (86%) demonstrate hyperenhancement compared to adjacent bowel loops when IV contrast is used 3
• Contrary to expectation, most fistulas (68%) contain no internal air or fluid, making them harder to identify 3

Why IV Contrast is Essential

Contrast Enhancement Patterns

• IV contrast is absolutely necessary for optimal fistula assessment, as it allows visualization of the hyperenhancing inflammatory tract that characterizes most fistulas 1
• Without IV contrast, fistulas can only be inferred by secondary findings and performance is markedly poorer 1

Comparison with Non-Contrast CT

• Non-contrast CT has "poorer performance" and should not be used for evaluating suspected Crohn's complications 1
• The American College of Radiology emphasizes that processes like fistula formation require IV contrast for optimal assessment 1

CT Enterography vs Standard CT

Optimal Protocol

• CT enterography (with neutral oral contrast and IV contrast) is the preferred imaging protocol when patients can tolerate it, as it provides better bowel distention and improved detection of complications 1
• Standard CT with positive oral contrast may actually improve fistula detection in some cases, as the contrast can track through fistulous tracts 1

When Standard CT is Appropriate

• In acutely ill patients who cannot tolerate large volumes of oral contrast, standard CT with IV contrast is acceptable 1
• For suspected complications like abscess or fistula in acute presentations, standard CT with IV contrast remains a suitable option 1

Comparative Performance with Other Modalities

CT vs Other Imaging

• A pediatric study showed high agreement between standard CT and MR enterography for fistula detection (k = 1.00) 1
• Ultrasound and barium studies showed comparable accuracy (85.2% vs 84.8%) for internal fistula detection in one prospective study, though both had sensitivity around 70% 4
• Combining imaging modalities significantly improves diagnostic accuracy for internal fistulas 4

Surgical Correlation Studies

• When compared to intraoperative findings, CT enterography had 50% sensitivity for fistulas, with a false-negative rate of 50% 5
• MR enterography performed slightly better with 60% sensitivity and 40% false-negative rate for fistulas 5
• These false-negative rates led to unexpected intraoperative findings requiring modification of planned surgical procedures in 26% of patients 5

Clinical Implications and Pitfalls

Do Not Rule Out Fistulas Based on Negative CT

• A negative CT does not exclude fistulas, particularly enteroenteric fistulas, which have very poor detection rates 1, 2
• The American College of Radiology recognizes that imaging findings can be absent even in patients with known active complications 2

When to Pursue Additional Evaluation

• If clinical suspicion for fistula remains high despite negative CT, consider complementary endoscopy or MR enterography 2, 6
• CT enterography detected clinically occult fistulas in 50% of patients who had no or remote suspicion at pre-imaging assessment 3
• These findings resulted in changes in medical management (61%) or interventional procedures (18%) 3

Abscess Detection is More Reliable

• CT performs much better for abscess detection (86-100% sensitivity) compared to fistulas 1
• Both CT and ultrasound show excellent accuracy for abscess identification (>90%) 4

Practical Recommendations

Optimize Your Imaging Protocol

• Request CT enterography when possible for better overall assessment of Crohn's complications 1
• Always ensure IV contrast is administered unless contraindicated 1
• Consider adding positive oral contrast if fistula or abscess is specifically suspected 1

Interpret Results Cautiously

• Recognize that a negative CT for fistulas, especially enteroenteric fistulas, does not rule them out 1, 2
• Look specifically for hyperenhancing extraenteric tracts, which represent 81% of detectable fistulas 3
• Do not expect to see air or fluid within most fistulous tracts 3

Surgical Planning Considerations

• Surgeons should actively search for additional lesions intraoperatively, as unexpected findings occur in approximately 26% of cases 5
• Counsel patients preoperatively about the possibility of unexpected interventions based on intraoperative findings 5