# Seeing Beyond the Tract: The Superiority of 3 Tesla (3T) MRI Over X-ray Fistulography in Perianal Fistula Evaluation

## TL;DR

3T MRI is more accurate than X-ray for evaluating perianal fistulas, providing better visualization and diagnostic accuracy.

## Contribution

Demonstrates the diagnostic superiority of 3T MRI over X-ray fistulography in perianal fistula evaluation.

## Key findings

- 3T MRI showed significantly longer and wider fistula tracts compared to X-ray.
- MRI had 100% sensitivity and specificity for fistula detection and high agreement with surgical findings.
- X-ray frequently missed secondary tracts and internal openings, showing poor diagnostic accuracy.

## Abstract

Background

Perianal fistulas are a prevalent anorectal condition, often resulting from cryptoglandular infections. They cause significant morbidity due to chronic discharge, pain, and recurrent infections, affecting patient's quality of life. Accurate preoperative imaging is crucial for defining the fistulous tract, identifying internal and external openings, and planning surgical intervention to prevent recurrence. X-ray fistulography is outdated due to its poor visualization of soft tissues and inability to adequately image complex anatomical structures, making it a less preferred method in modern clinical practice. High spatial resolution magnetic resonance imaging (MRI), especially using 3 Tesla (3T) scanners, has emerged as the preferred modality due to its excellent soft tissue characterization and multiplanar imaging capability.

Aim

This study aims to evaluate and compare the diagnostic efficacy of 3T MRI fistulogram and conventional X-ray fistulography in patients with clinically suspected perianal fistulas and to correlate imaging findings with intraoperative surgical observations.

Materials and methods

A prospective cross-sectional study was conducted over 24 months in a tertiary care center in Lucknow. A total of 52 patients with clinical suspicion of perianal fistulas were enrolled. All patients underwent both X-ray fistulography and 3T MRI fistulography prior to surgical management. Imaging findings were evaluated for tract length, width, complexity, internal and external openings, and secondary extensions. MRI-based classification was performed using the St. James University Hospital (SJUH) grading system. Intraoperative findings served as the reference standard. Data were statistically analyzed to assess agreement and diagnostic accuracy.

Results

The mean age of patients was 37.4 ± 11.03 years, with a male predominance (92.3%). All patients presented with perianal pus discharge; 55.8% also reported pain. MRI showed significantly longer (mean: 6.21 ± 0.93 cm) and wider (mean: 3.59 ± 0.43 mm) tracts compared to X-ray (length: 5.50 ± 1.10 cm; width: 3.13 ± 0.53 mm), with p < 0.01. MRI more accurately detected internal and external openings and complex tracts. According to the SJUH system, 76.9% were complex fistulas, with 55.8% graded as grade 4. MRI findings had high agreement with surgical findings (κ = 0.820). The sensitivity and specificity of MRI for fistula detection were both 100%. For detecting high-grade fistulas (grades 4 and 5), MRI showed a sensitivity of 96.6% and specificity of 93.9%. X-ray fistulography frequently missed secondary tracts and internal openings and showed poor agreement with surgical outcomes.

Conclusion

3T MRI fistulography is a highly accurate and superior imaging modality for preoperative assessment of perianal fistulas. It offers a detailed visualization of tract morphology and strong concordance with intraoperative findings, significantly outperforming conventional X-ray fistulography. MRI is expected to remain the imaging gold standard for the evaluation of fistula-in-ano, whereas the role of X-ray fistulography is anticipated to further decline given its limited diagnostic value.