Comparison of different magnetic resonance imaging sequences for assessment of fistula-in-ano

Abstract

AIM:To assess agreement between different forms of T2 weighted imaging (T2WI), and post-contrast T1WI in the depiction of fistula tracts, inflammation, and internal openings with that of a reference test. METHODS:Thirty-nine consecutive prospective cases were enrolled. The following sequences were used for T2WI: 2D turbo-spin-echo (2D T2 TSE); 3D T2 TSE; short tau inversion recovery (STIR); 2D T2 TSE with fat saturation performed in all patients. T1WI were either a 3D T1-weighted prepared gradient echo sequence with fat saturation or a 2D T1 fat saturation [Spectral presaturation with inversion (SPIR)]. Agreement for each sequence for determination of fistula extension, internal openings, and the presence of active inflammation was assessed separately and blindly against a reference test comprised of follow-up, surgery, endoscopic ultrasound, and assessment by an independent experienced radiologist with access to all images. RESULTS:Fifty-six fistula tracts were found: 2 intersphincteric, 13 trans-sphincteric, and 24 with additional tracts. The best T2 weighted sequence for depiction of fistula tracts was 2D T2 TSE (Cohen's kappa = 1.0), followed by 3D T2 TSE (0.88), T2 with fat saturation (0.54), and STIR (0.19). Internal openings were best seen on 2D T2 TSE (Cohen's kappa = 0.88), followed by 3D T2 TSE (0.70), T2 with fat saturation (0.54), and STIR (0.31). Detection of inflammation showed Cohen's kappa of 0.88 with 2D T2 TSE, 0.62 with 3D T2 TSE, 0.63 with STIR, and 0.54 with T2 with fat saturation. STIR, 3D T2 TSE, and T2 with fat saturation did not make any contributions compared to 2D T2 TSE. Post-contrast 3D T1 weighted prepared gradient echo sequence with fat saturation showed better agreement in the depiction of fistulae (Cohen's kappa = 0.94), finding internal openings (Cohen's kappa = 0.97), and evaluating inflammation (Cohen's kappa = 0.94) compared to post-contrast 2D T1 fat saturation or SPIR where the corresponding figures were 0.71, 0.66, and 0.87, respectively. Comparing the best T1 and T2 sequences showed that, for best results, both sequences were necessary. CONCLUSION: 3D T1 weighted sequences were best for the depiction of internal openings and active inflammatory components, while 2D T2 TSE provided the best assessment of fistula extension. Key words: Fistula; Magnetic resonance imaging; Diagnosis Core tip: Both T1 (post-contrast) and T2 weighted sequences are needed for the best assessment of fistulain-ano; T2 weighted imaging: 2D turbo-spin-echo (2D T2 TSE) is most useful for depiction in relation to sphincter muscles. 3D T2 TSE cannot replace 2D T2 TSE. Post-contrast 3D T1 weighted prepared gradient echo sequence with fat saturation is necessary for the CASE CONTROL STUDY

The role of magnetic resonance imaging in the preoperative evaluation of anal fistulas

“…20 reported that MRI had a high accuracy rate (94% and 93% respectively) in detecting primary tracts. Our study, as well as previous studies, support the concept that MRI is the imaging modality of choice in the preoperative assessment of anal fistulas 8,15,16 . In our study, MRI was found to misclassify 10% of primary tracts compared with the reference standard.…”

“…In this study, we used the diameter-based criteria, proposed by Torkzad et al . 16 , to classify fluid collections, i.e., a roundish fluid collection ≥ 10 mm was identified as an abscess while an elongated fluid collection < 10 mm was identified as a fistula (Fig. 2).…”

“…Torkzad et al . 16 have indicated that T2W sequences must be included in the MRI protocol for the most reliable evaluation of fistula-in-ano in conjunction with post-contrast T1W sequences. Conversely, Singh et al .…”

Diagnostic Accuracy of Short Tau Inversion Recovery as a Limited Protocol for Diagnosing Perianal Fistula

“…Preoperative MRI can help in reducing the recurrence and is also helpful in the evaluation of complex fistulous disease process [15]. MRI sequences that are usually performed for perianal fistula assessment include plain and postcontrast T1-weighted and T2-weighted sequences [10]. STIR sequences have also been used [12].…”

“…MRI provides accurate details regarding anal canal anatomy and effectively delineates fistulous tracts along with other findings such as abscesses or secondary tracts [9]. In MRI pelvis, T1 weighted, T2 weighted, short tau inversion recovery (STIR) and T1 post-contrast with fat suppression sequences are commonly used to evaluate fistula-in-ano [10]. Recently, the role of diffusion-weighted imaging (DWI) has also been evaluated [11].…”