Clinical Correlation and MRI Finding in the Management of Fistula in Ano

Predictors of outcome in cryptoglandular anal fistula according to magnetic resonance imaging: A systematic review

Background and Aims

Anal fistula (AF) with cryptoglandular origin tends to recur, and multiple risk factors are implicated. Recently, some magnetic resonance imaging (MRI) findings with predictive value for disease outcomes have been proposed. These intrinsic anatomic features include those of the AF and its surrounding structures. This study aims to clarify the prognostic role of MRI in AF.

Methods

We performed a systematic search of PubMed, Embase, and EBSCO databases. Two independent reviewers conducted the search and screened the articles. We selected studies that used MRI to assess AF and reported its relationship to disease outcome. We extracted data regarding the study design, type of intervention, outcome, MRI-measured items, and their significance.

Results

Out of 1230 retrieved articles, 18 were eligible for final inclusion, and a total of 4026 patients were enrolled in the selected studies. For preoperative MRI, the significant items affecting the outcome were the length of the fistula, horseshoe type, presence of multiple tracts, supralevator extension, and apparent diffusion coefficient (ADC) value. Other studies investigated the healing process using postoperative MRI.

Conclusion

This review found that MRI can be useful in the management of AF, both preoperatively and postoperatively. Factors, such as fistula length, horseshoe type, presence of multiple tracts, supralevator extension, and ADC value were found to be significantly associated with treatment outcomes. The presence of the fistula tract and the development of new abscesses on postoperative MRI was found to hinder the healing process. Further studies are needed to confirm these findings.

Introducing 3D modelling of MRI in the preoperative mapping of perianal fistula: How it could help the surgeons?

Background

Surgeons find treating perianal fistula difficult because insufficient drainage and failure to eradicate perianal sepsis could increase the risk of recurrence and postoperative complications. For better planning of the most suitable surgical technique, surgeons must consider the risk factors of recurrence with an accurate pre-operative assessment of perianal fistulae. The most common imaging method for grading primary perianal fistulas, identifying their complications, and locating occult extensions is magnetic resonance imaging (MRI). However, surgeons may find it challenging to read the lengthy reports of complex tracts, particularly for complicated patients. The creation of three-dimensional (3D) models has gained traction recently as a genuinely useful diagnostic tool for pre-operative planning. The authors evaluated the value of these surgical models. Inspecting the 3D models in addition to the routine two-dimensional study caused four out of five skilled colorectal surgeons to re-evaluate how far the fistulae extended. This made promise that 3D models would be helpful, simple to understand, and quick to interpret for colorectal surgeons. The purpose of the study is to assess the value of adding 3D modelling of MRI to standard two-dimensional MRI protocol for more accurate delineation of perianal fistula and its complications aiming at better surgical outcomes.

Results

Regarding 3D models, the highest degree of accuracy was in detecting supra-levator extension (100%) by both the third radiologist and the surgeon. There was a statistically high diagnostic inter-observer agreement between both, with a p-value < 0.0001. The highest inter-observer agreement was in the supra-levator extension (50/50, 100%), and the lowest agreement was in the side branches detection (44/50, 88%).

Conclusions

Pre-operative 3D MRI modelling provided the surgeon with a pre- and intra-operative road map that improved the surgeon’s orientation and ability to see complex perianal fistulas and their consequences, especially those with supra levator extension, thus helping the surgeon achieve better surgical results and decrease the preoperative risk factors of recurrence. Surgeons should utilise it in complex and recurrent cases reducing preoperative risk factors and improving outcomes. Although this technique is expensive, its cost–benefit ratio is low relative to recurrent hospitalisation and complications.

High failure rates following ligation of the intersphincteric fistula tract for transsphincteric anal fistulas: are preoperative MRI measurements of the fistula tract predictive of outcome?

AIM

Treatment of transsphincteric fistulas (TSFs) with fistulotomy after an indwelling seton is tempered by risks of incontinence and litigation. Thus, ligation of the TSF tract has been popularized as an alternative option. We previously reported on 107 patients who underwent ligation of the intersphincteric fistula tract (LIFT), with a 46% failure rate. Posterior fistula was the only predictor of recurrence. The aim of the present work was to investigate whether the length, width or depth of the fistula measured on preoperative MRI was correlated with recurrence.

METHOD

Following institutional review board approval, a retrospective analysis of our prospective Complex Anal Fistula Database from 1 January 2011 to 31 August 2019 was performed. Patients with TSF who underwent preoperative MRI and LIFT were included. Fistula location was classified as anterior, posterior or lateral. MRI measurements of fistula length, width and depth (in the intersphincteric groove) were performed. The type and rate of postoperative recurrence were analysed.

RESULTS

173 patients underwent MRI for an anal fistula; of these 40 underwent LIFT and 22/40 (55%) had preoperative MRI. There was no difference in the length, width or depth of anterior (n = 9), posterior (n = 7) or lateral (n = 6) fistula tracts. The overall recurrence rate was 9/22 (41%). Posterior TSFs had the highest recurrence rate (5/7, 71%).

CONCLUSION

The mean length, width, and depth of the fistula tract, measured at the preoperative site of LIFT in the intersphincteric groove, did not correlate with recurrence regardless of fistula location.