High-resolution direct magnetic resonance imaging fistulography with hydrogen peroxide for diagnosing anorectal fistula: A preliminary retrospective study.

Background: Fistula-in-ano is an abnormal tunnel formation linking the anal canal with the perineum and perianal skin. Multiple imagining methods are available to evaluate it, among which magnetic resonance imaging (MRI) is the most advanced noninvasive preoperative method. However, it is limited in its visualization function.

Aim: To investigate the use of intraluminal MRI for perianal fistulas via a novel direct MRI fistulography method.

Methods: We mixed 3% hydrogen peroxide (HP) with gadolinium for HPMRI fistulography, retrospectively analyzing 60 cases of complex/recurrent fistula-in-ano using physical examination, trans-perineal ultrasonography (TPUS), low-spatial-resolution MRI, and high-resolution direct HPMRI fistulography. We assessed detection rates of fistula tracks, internal openings, their relationship with anal sphincters, and perianal abscesses using statistical analyses, including interobserver agreement (Kappa statistic), and compared results with intraoperative findings.

Results: Surgical confirmation in 60 cases showed that high-resolution direct HPMRI fistulography provided superior detection rates for internal openings (153) and fistula tracks (162) compared to physical exams, TPUS, and low-spatial-resolution MRI (Z > 5.7, P < 0.05). The effectiveness of physical examination and TPUS was also inferior to that of our method for detecting perianal abscesses (54) (Z = 6.773, 3.694, P < 0.05), whereas that of low-spatial-resolution MRI was not significantly different (Z = 1.851, P = 0.06). High-resolution direct HPMRI fistulography also achieved the highest interobserver agreement (Kappa: 0.89, 0.85, and 0.80), while low-spatial-resolution MRI showed moderate agreement (Kappa: 0.78, 0.74, and 0.69). TPUS and physical examination had lower agreement (Kappa range: 0.33-0.63).

Conclusion: High-resolution direct HPMRI fistulography enhances the visualization of recurrent and complex fistula-in-ano, including branched fistulas, allowing for precise planning and improved surgical outcomes.