Diagnostic Performance of Three-Dimensional Endoanal Ultrasound Compared with MRI in Anal Fistula: A Systematic Review and Meta-analysis

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. 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. 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. 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.