Preoperative MRI of perianal fistula evaluation and its impact on surgical outcome

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.

Role of MRI special diffusion weighted imaging/diffusion tensor imaging techniques in the assessment of perianal fistula activity

Background

Pre-operative MRI examination is currently considered as an evolving tool for assessment of perianal fistula types, extensions, and complications to achieve proper treatment plan. Proper assessment of fistula activity can also have a major contributing role to the treatment plan, through deciding the type of prescribed medications, proper surgical approach as well as the proper operative intervention timing. Reviewing literature, only few studies have mentioned the importance of diffusion tensor imaging (DTI) sequences in diagnosing perianal fistula activity, yet many studies have discussed the perianal fistula activity assessment using other diffusion weighted imaging (DWI) sequences. In the present study, the main objective was to prove the MRI quantitative DTI sequences’ ability of diagnosing perianal fistulae inflammatory activity.

Results

This study was a prospective analysis in which fistular activity was confirmed by intra-operative findings (considered as the standard reference). The cases included in the study were divided into two groups, based on their surgical findings, positive inflammatory and negative inflammatory groups. Both groups were pre-operatively assessed using MRI imaging and additionally used diffusion weighted and tensor imaging (DWI and DTI) sequences by special post-processing quantitative assessment of DTI FA and ADC values. There was significant statistical difference between the mean ADC value of the PIA and NIA groups in the track, edema, ipsilateral and contralateral sphincter areas with P values (P = 0.000, 0.000, 0.002 and 0.000 respectively). There was also significant difference between the mean FA value of the PIA and NIA groups in the track, edema, ipsilateral and contralateral sphincter areas with P values (P = 0.000, 0.000, 0.000 and 0.008 respectively).

Conclusion

This study results revealed that FA are relatively lower in positive inflammatory activity lesions than in negative inflammatory activity lesions while the ADC values were relatively higher in positive inflammatory activity lesions than in negative inflammatory activity lesions and the differences were statistically significant having a fundamental role in the assessment of perianal fistula activity especially at the track area being of highest sensitivity and specificity. Unlike conventional MRI sequences which revealed only high specificity being a good negative modality.