3D visualization of perianal fistulas using parametric models

Magnetic resonance imaging (MRI) is used as a standard for assessment of complex perianal fistulas. Apart from textual description of the case, 3D reconstructed models from MRI further aid in understanding the entire anatomy of the fistula tract and its relation to the pelvic floor. This information is crucial as it helps surgeons to understand the extent and complexity of the disease before surgical treatment. However, 3D model generation from MRI is a time-consuming step for a radiologist as it requires tedious manual delineations to be performed on every slice of the images. The aim of this study was to develop a method that could enable radiologists to present enhanced information to surgeons for treatment of complex perianal fistulas while simultaneously reducing the manual efforts and time required to generate the information.

A method was proposed to depict relevant anatomies of complex perianal fistula as parametric models in three-dimensional (3D) space. A plugin inside 3D Slicer software was developed for the generation of the parametric models from MRI. The levator ani muscle, internal sphincter, and external sphincter are represented as tubular structures, whereas fistula tracks and abscess are presented as splines.

Parametric models were generated to depict three cases of complex perianal fistulas and similarity measures were computed for ten cases. Visual comparison of the parametric models was made with the 3D models generated by the standard approach. The parametric models took less time to create and were able to visually present enriched information as compared to the 3D models generated by the standard approach.

The proposed method, using parametric models, shows potential for faster generation and better visualization of the 3D information required for the treatment of complex perianal fistula cases.