A large review of 45 studies involving over 4,100 people with anal fistulas found that two imaging methods are highly accurate for classifying the type of fistula. The review compared 3D-endoanal ultrasound (3D-EAUS), unenhanced MRI, and contrast-enhanced MRI (CE-MRI).
3D-EAUS was very good at identifying common fistulas, with sensitivity above 0.89 for intersphincteric and transsphincteric types. Unenhanced MRI had high specificity (over 0.94) for all types, meaning it rarely misdiagnosed a fistula when none was there. CE-MRI showed sensitivity and specificity exceeding 0.90 for most classifications.
The review suggests that 3D-EAUS is a good first choice for imaging anal fistulas, while CE-MRI may be better for complex or unclear cases. No safety concerns were reported in the studies reviewed.
Because this is a meta-analysis of existing studies, the results depend on the quality of those studies. However, the large sample size and consistent findings across multiple studies add confidence. Patients should discuss with their doctor which imaging test is best for their situation.