Innovation in the imaging perianal fistula: a step towards personalised medicine

Abstract

Background: Perianal fistula is a topic both hard to understand and to teach. The key to understanding the treatment options and the likely success is deciphering the exact morphology of the tract(s) and the amount of sphincter involved. Our aim was to explore alternative platforms better to understand complex perianal fistulas through three-dimensional (3D) imaging and reconstruction.

Methods: Digital imaging and communications in medicine images of spectral attenuated inversion recovery magnetic resonance imaging (MRI) sequences were imported onto validated open-source segmentation software. A specialist consultant gastrointestinal radiologist performed segmentation of the fistula, internal and external sphincter. Segmented files were exported as stereolithography files. Cura (Ultimaker Cura 3.0.4) was used to prepare the files for printing on an Ultimaker 3 Extended 3D printer. Animations were created in collaboration with Touch Surgery™.

Results: Three examples of 3D printed models demonstrating complex perianal fistula were created. The anatomical components are displayed in different colours: red: fistula tract; green: external anal sphincter and levator plate; blue: internal anal sphincter and rectum. One of the models was created to be split in half, to display the internal opening and allow complexity in the intersphincteric space to better evaluated. An animation of MRI fistulography of a trans-sphincteric fistula tract with a cephalad extension in the intersphincteric space was also created.

Conclusion: MRI is the reference standard for assessment of perianal fistula, defining anatomy and guiding surgery. However, communication of findings between radiologist and surgeon remains challenging. Feasibility of 3D reconstructions of complex perianal fistula is realized, with the potential to improve surgical planning, communication with patients, and augment training.

Keywords: 3D printing; MRI; innovation.

Figure 1.

Two-dimensional axial scans with fistula complex segmented. The various anatomical components are displayed in different colours (red: fistula tract; green: external anal sphincter (EAS) and levator plate; blue: internal anal sphincter (IAS) and rectum).

Figure 2.

Three-dimensional perianal anal fistula models. (1) Trans-sphincteric fistula with an infralevator extension; (2) trans-sphincteric fistula with a horseshoe; (3) complex trans-sphincteric and intersphincteric fistula.

Figure 3.

Animation demonstrating a magnetic resonance fistulography, a ‘fly through’ of the fistula tract as it passes through the sphincter complex (the animation is available on the journal site as the online supplementary material).