Lo Re et al [23] retrospectively evaluated MRI in 31 patients with CD suspected of having perianal fistula and a surgical examination under anesthesia showing that short-tau inversion recovery sequences were equivalent to IV contrast-enhanced fat-suppressed T1-weighted sequences in detection and classification of anal fistula with sensitivity of 96%, specificity of 75%, positive predictive value (PPV) of 93%, and negative predictive value (NPV) of 86% for both sequences [23]. However, their study did not evaluate tract activity. In another retrospective study of 17 patients that underwent MRI prior to surgery, the contribution of MRI sequences to fistula classification was evaluated. All 3 readers showed statistically significant concordance between fistula classification and surgery with IV contrast-enhanced fat-suppressed T1-weighted sequences. The highest concordance for all 3 readers was reached Anorectal Disease with the combination of T2-weighted sequences and IV contrast-enhanced fat-suppressed T1-weighted sequences [24]. Finally, Dohan et al [19] evaluated the addition of diffusion imaging in a retrospective study of 24 patients with perianal fistula that went to surgery. The sensitivity for anal fistula detection for fat-suppressed FSE T2-weighted sequences was 91.2% and for diffusion imaging was 100%, with statistically significant greater fistula conspicuity on diffusion imaging than fat-suppressed FSE T2-weighted sequences. Radiography Pelvis Radiography is not useful in this clinical scenario because it cannot assess the presence or absence of an abscess or fistula tract. There is no relevant literature to support the use of radiography in the evaluation of perianal fistula. In a recent study of 122 patients by Sun et al [27], the reported sensitivity, specificity, and accuracy for the diagnosis of perianal fistula compared with surgery was 92%, 100%, and 93%, respectively. This study reported an accuracy of identification of the internal opening of the fistula of 95%.
Anorectal Disease. Lo Re et al [23] retrospectively evaluated MRI in 31 patients with CD suspected of having perianal fistula and a surgical examination under anesthesia showing that short-tau inversion recovery sequences were equivalent to IV contrast-enhanced fat-suppressed T1-weighted sequences in detection and classification of anal fistula with sensitivity of 96%, specificity of 75%, positive predictive value (PPV) of 93%, and negative predictive value (NPV) of 86% for both sequences [23]. However, their study did not evaluate tract activity. In another retrospective study of 17 patients that underwent MRI prior to surgery, the contribution of MRI sequences to fistula classification was evaluated. All 3 readers showed statistically significant concordance between fistula classification and surgery with IV contrast-enhanced fat-suppressed T1-weighted sequences. The highest concordance for all 3 readers was reached Anorectal Disease with the combination of T2-weighted sequences and IV contrast-enhanced fat-suppressed T1-weighted sequences [24]. Finally, Dohan et al [19] evaluated the addition of diffusion imaging in a retrospective study of 24 patients with perianal fistula that went to surgery. The sensitivity for anal fistula detection for fat-suppressed FSE T2-weighted sequences was 91.2% and for diffusion imaging was 100%, with statistically significant greater fistula conspicuity on diffusion imaging than fat-suppressed FSE T2-weighted sequences. Radiography Pelvis Radiography is not useful in this clinical scenario because it cannot assess the presence or absence of an abscess or fistula tract. There is no relevant literature to support the use of radiography in the evaluation of perianal fistula. In a recent study of 122 patients by Sun et al [27], the reported sensitivity, specificity, and accuracy for the diagnosis of perianal fistula compared with surgery was 92%, 100%, and 93%, respectively. This study reported an accuracy of identification of the internal opening of the fistula of 95%.