Added Value of Diffusion Weighted Imaging in Evaluation of Perianal Fistula in comparison with conventional MRI Fistulogram

Background: Perianal fistulas are common inflammatory conditions of the anal canal and perianal tissues with a high morbidity rate. Magnetic resonance imaging (MRI) is currently considered the ideal imaging modality for detailed preoperative assessment of perianal fistula and its related complications. Post contrast study is considered the ideal sequence for characterizing a perianal fistula. Diffusion weighted imaging (DWI) has been under extensive research to assess its additive value to other MRI sequences in assessment of perianal inflammation. Objective: To explore the added value of DWI in evaluation of perianal fistula in comparison to conventional MRI fistulogram and whether it can be used as an alternative to post contrast study. Patients and Methods: the current study included 50 cases with perianal fistula who were subjected to full history taking and clinical examination. Radiological examination involved MRI assessment with the following sequences: T1, T2, post-contrast T1 sequences in addition to DWI. Post-surgical data has been used as reference for evaluating the diagnostic efficacy. Results: There was a significant statistical difference between the different MRI sequences as regard visibility scores (p= 0.020). Visibility score 2 was reported in 90%, 84%, 94% and 96% in T2, DWI, T2 + DWI and post contrast T1 respectively. The mean ADC value of fistulas was higher than that of the associated abscesses (1.34 ± 0.15 versus 0.95 ± 0.21 x10-3 mm2/s). As regard the diagnostic accuracy of different MRI sequences in detection of primary fistula, the highest accuracy (100%) was reported with the combination of T2+ T1-post contrast and combined T2 +DWI sequences. Conclusions:Our study confirmed the significant added value of DWI in comparison to T2WI alone in evaluation of perianal fistulas and its related complications. DWI should be routinely included in the MRI protocol for perianal fistula.