Systematic review and meta-analysis of 3D-EAUS, unenhanced MRI, and CE-MRI for anal fistula classification

RATIONALE AND OBJECTIVES: Anal fistula severely impacts patients' quality of life, and accurate preoperative Parks classification is critical for surgical planning and anal sphincter preservation. This systematic review and meta-analysis evaluated the diagnostic efficacy of 3D-endoanal ultrasound (3D-EAUS) and unenhanced/contrast-enhanced (CE) magnetic resonance imaging (MRI) for anal fistula classification. MATERIALS AND METHODS: Following PRISMA guidelines, PubMed, Embase and Cochrane Library were searched for studies (2010-2025) comparing the two modalities, with diagnostic indices extracted and meta-analyzed via RevMan 5.3. RESULTS: A total of 32 studies involving 4104 anal fistula cases were included. The summary receiver operating characteristic curves of 3D-EAUS, unenhanced MRI, and contrast-enhanced MRI (CE-MRI) showed that most points fell on or in the upper-left corner of the curves, indicating good diagnostic performance for all three modalities. 3D-EAUS exhibited high sensitivity and specificity for intersphincteric (SEN: 0.89, SPE: 0.94) and transsphincteric anal fistulas (SEN: 0.96, SPE: 0.86), but lower diagnostic sensitivity for suprasphincteric (SEN: 0.72) and extrasphincteric (SEN: 0.75) fistulas. unenhanced MRI demonstrated high specificity (>0.94) for all classifications and moderate sensitivity (>0.85), except for suprasphincteric fistulas (SEN: 0.71). CE-MRI showed the highest diagnostic accuracy, with both sensitivity and specificity exceeding 0.90 for most classifications. CONCLUSION: Both 3D-EAUS and MRI can effectively diagnose anal fistulas. 3D-EAUS is the preferred initial examination, and CE-MRI is recommended for complex or unclear cases, providing an evidence-based basis for clinical decision-making and improving patient prognosis.