EP304 - Guiding Surgical Strategy for Perianal Fistulas with MRI – From Conventional Acquisition to 3D Modeling

Purpose/Background: What is the most relevant information in the magnetic resonance imaging report to best assist in making decisions about surgical technique? Do 3D models have an application in the preoperative evaluation of patients with perianal fistula?

Methods/Interventions: A comprehensive review was performed to identify the most relevant MRI features and descriptors for perianal fistula evaluation that can assist in surgical planning. Data were synthesized from current literature and expert consensus, focusing on the internal opening's position, size, and height; tract course and relationship to the sphincter complex; presence and configuration of secondary tracts; external openings; fluid collections; and inflammatory activity. The correlation of these imaging descriptors with the suitability of specific surgical techniques-such as fistulotomy, Ligation of the Intersphincteric Fistula Tract (LIFT), Video-Assisted Anal Fistula Treatment (VAAFT), Fistula-tract Laser Closure (FiLaC), and advancement flaps-was evaluated. The role and technical considerations of generating 3D models from MRI datasets were also analyzed, including their potential integration into preoperative planning.

Results/Outcomes: MRI reports that include precise descriptors of the internal opening (radial and vertical location), fistulous tract anatomy (classification, angulation, length, diameter), secondary extensions (horseshoe, supralevator), external openings, and associated abscesses or collections provide the most value for surgical decision-making. Specific anatomical characteristics can guide or contraindicate certain procedures; for example, horseshoe extensions may preclude LIFT, while long, narrow tracts may favor FiLaC. 3D modeling, when based on accurate segmentation by experienced radiologists, enhances the surgeon's understanding of complex anatomy, facilitates multidisciplinary planning, and may reduce operative time. Preliminary evidence suggests high inter-observer agreement and improved surgical confidence with 3D models, though time and cost constraints remain.

Conclusion/Discussion: Magnetic Resonance Imaging (MRI) plays a pivotal role in the management of perianal fistulas, providing critical anatomical details that inform surgical strategy, reduce recurrence rates, and minimize complications. This review has synthesized current knowledge on optimizing MRI utilization, from conventional image acquisition and reporting to the emerging applications of 3D modeling.

3D reconstruction fused with sagittal T2-weighted images: transsphincteric fistula in red, seton in 42 yellow
3D reconstruction fused with sagittal T2-weighted images: transsphincteric fistula in red, seton in yellow.