From the Guidelines
CT scan with contrast is the recommended imaging method for assessing fistulas in Crohn's disease, as it provides optimal visualization of abnormal connections and associated inflammation. The procedure involves intravenous administration of iodinated contrast material, which helps highlight fistulas and other complications of Crohn's disease 1. Patients should fast for 4-6 hours before the scan and inform their doctor about any allergies to contrast agents, kidney problems, or if they are pregnant. Oral contrast may also be given 1-2 hours before the scan to better visualize the intestinal tract. The scan typically takes 15-30 minutes to complete.
Key Considerations
- CT with contrast is preferred over non-contrast CT because fistulas are often subtle and the contrast enhancement improves detection by highlighting abnormal connections and associated inflammation 1.
- MRI is an alternative that provides excellent soft tissue detail without radiation exposure, but CT remains widely used due to its availability, speed, and ability to detect both intestinal and extra-intestinal complications of Crohn's disease 1.
- The sensitivity of CT-based evaluation for fistula detection ranges from 68% to 100%, with variable performance depending on the specific type of fistula and the presence of other complications 1.
Clinical Recommendations
- CT scan with contrast is suitable for the initial imaging of suspected Crohn's disease with no prior diagnosis, as well as for the imaging of known Crohn's disease with suspected acute exacerbation 1.
- MR enterography or CT enterography is recommended for disease surveillance and monitoring therapy of known Crohn's disease 1.
- The choice between CT and MRI should be based on individual patient factors, such as age, symptoms, and contraindications to certain imaging modalities 1.
From the Research
Assessment of Fistulas in Crohn's Disease
To assess for fistulas in Crohn's disease, various diagnostic methods can be employed, including imaging techniques. The use of a CT scan with contrast is one such method.
Diagnostic Methods
- CT scan with contrast: This method can be used to assess for non-perianal fistulas, as it provides complete anatomical definition 2.
- MRI: Pelvic Magnetic Resonance is the principal technique in patients with perianal disease, offering precise and fine detail images of the sphincter complex 3.
- Ultrasonography: This method has comparable accuracy to barium radiology and CT in detecting internal fistulae 4.
- Contrast radiography: This method can be used in combination with ultrasonography to improve diagnostic accuracy in detecting internal fistulae 4.
CT Scan with Contrast
- A CT scan with contrast can be used to evaluate the extent of the disease throughout the entire gastrointestinal tract 2.
- The accuracy of CT in detecting internal fistulae and abscesses is comparable to ultrasonography and barium radiology 4.
- CT enterography (CTE) has similar diagnostic accuracy to MR enterography (MRE) for the diagnosis of Crohn's disease and its complications 3.
Limitations and Considerations
- The presence of abscesses can be correctly detected by CT in 86.4% of cases, although accuracy may be higher for CT than for ultrasonography due to false positive results in US studies 4.
- The use of CT scans with contrast should be considered in the context of other diagnostic methods, such as MRI and ultrasonography, to provide a comprehensive assessment of fistulas in Crohn's disease 3.