Comparison of Percutaneous Instillation of Aqueous Jelly with Intravenous Contrast for Magnetic Resonance Fistulography- A Prospective Cohort Study

Introduction: The perianal fistulae are complex clinical scenarios, often complicated by direct or blind surgical exploration. A precise preoperative evaluation of the perianal fistulous tract is not only an essential diagnostic requirement but a presurgical prognostic determinant. The usefulness of Magnetic Resonance Imaging (MRI) in such instances is established, but if aqueous jelly can be used instead of regular contrast during fistulography is not clear.

Aim: To evaluate the diagnostic accuracy of Magnetic Resonance (MR) percutaneous aqueous jelly compared to intravenous (i.v.) contrast enhanced MR fistulography in perianal fistulous tracts.

Materials and Methods: A prospective cohort study was carried out on 40 participants who were referred for MR fistulography (with suspected anal fistulae) to the Department of Radiology, Mahatma Gandhi Medical College and Research Institute, Puducherry, India, form March 2017 to October 2019. Total 40 subjects presented with signs and symptoms of perianal fistula were injected with i.v. contrast and MR Fistulography sequences were obtained. Same subjects were injected with aqueous jelly two days prior to surgery and MR fistulography sequences were obtained. Both the sequences obtained were compared with respect to primary tract, internal opening and lateral ramification. These MR fistulography results were compared with intraoperative findings. Presence and absence of internal opening was analysed using Chi-square test for comparison of intraoperative internal opening and aqueous jelly internal opening. The specificity, sensitivity, Positive Predictive Values (PPV), Negative Predictive Values (NPV) and accuracy were estimated.

Results: Patients included in the study ranged from 25-65 years with a mean age of 41.5±7.3 years. Among the 40 subjects included, 37 were male and three were females. Aqueous jelly showed a good sensitivity of 96.67% overall in diagnosing internal opening as compared to intravenous (i.v.) contrast. Sensitivity and specificity of aqueous jelly in identifying internal opening was found to be 89.47% and zero respectively with an accuracy of 85% as compared to intravenous (i.v.) contrast in Grade I and II intersphincteric fistula. The PPV was 94.44% and NPV was found to be zero with respect to comparison of aqueous jelly with i.v. contrast grade I and II fistula.

Conclusion: Overall results of this study demonstrated that the instillation of the aqueous jelly is safe and provided diagnostic accuracy in identifying internal openings as compared to surgical findings.