Guidelines on postoperative magnetic resonance imaging in patients operated for cryptoglandular anal fistula: Experience from 2404 scans

Abstract

Magnetic resonance imaging (MRI) is considered the gold standard for the evaluation of anal fistulas. There is sufficient literature available outlining the interpretation of fistula MRI before performing surgery. However, the interpretation of MRI becomes quite challenging in the postoperative period after the surgery of fistula has been undertaken. Incidentally, there are scarce data and no set guidelines regarding analysis of fistula MRI in the postoperative period. In this article, we discuss the challenges faced while interpreting the postoperative MRI, the timing of the postoperative MRI, the utility of MRI in the postoperative period for the management of anal fistulas, the importance of the active involvement and experience of the treating clinician in interpreting MRI scans, and the latest advancements in the field.

A Novel MRI and Clinical-Based Scoring System to Assess Post-Surgery Healing and to Predict Long-Term Healing in Cryptoglandular Anal Fistulas

“…The reason for this was that before 3 months, it is difficult to differentiate between post-operative tissue inflammation, healing granulation tissue and active fistula tract. 19 , 22 Therefore, a cut-off of 3 months was chosen, though it is known that healing granulating tissue can, at times, take longer than 3 months to convert into fibrous tissue. 19 , 22 No doubt, extending the cut-off to 6 months would have made scoring more accurate, but it was felt that waiting for 6 months to confirm fistula healing would be practically difficult.…”

“… 19 , 22 Therefore, a cut-off of 3 months was chosen, though it is known that healing granulating tissue can, at times, take longer than 3 months to convert into fibrous tissue. 19 , 22 No doubt, extending the cut-off to 6 months would have made scoring more accurate, but it was felt that waiting for 6 months to confirm fistula healing would be practically difficult. Additionally, it would increase both patients’ anxiety and expense (more follow-up visits).…”

“…To assign non-subjective weights to each of these parameters in terms of their predictive ability for healing (non-healing), we selected four researchers with extensive surgical and radiological experience in managing anal fistulas. 18 , 19 They were independently asked to assign weights to each of these parameters on a scale of 0–5 where lower weights meant lower ability to characterize and higher weights meant better ability to characterize healing/non healing. Once these researchers rated the parameters and provided the weights, we obtained the mean of these weights for each parameter rounded-off to the closest integer.…”

“…All the MRI scans were interpreted by two independent experts (BK, PG) (BK has 20 years and PG has 12 years of experience of MRI imaging in anal fistula patients 18 , 19 ). All MRI scans were interpreted independently and then discussed to reach a consensus.…”

“…Cases in which consensus could not be reached were excluded from the analysis. Since radiological healing takes at least 10–12 weeks in most cases, 19 it was decided that MRI assessment and scoring would be done at least three months after surgery.…”