Background: To assess the accuracy of transperineal ultrasound (TPUS), in comparison with magnetic resonance imaging (MRI), in classifying perianal Crohn's disease (CD) according to Parks' classification and the American Gastroenterological Association criteria.
Methods: Fifty-nine consecutive patients with confirmed or suspected perianal CD underwent TPUS and MRI within 10 days. An independent expert surgical evaluation, which took into account proctological and MRI findings, was used as the gold standard. Fistulae and perianal disease were classified according to Parks' classification and American Gastroenterological Association criteria, respectively.
Results: Forty-six patients showed 64 fistulae (9 intersphincteric, 34 transsphincteric, 2 suprasphincteric, 9 extrasphincteric, and 10 anovaginal) and 23 abscesses were also found. Fifty-one of 54 perianal fistulae (per-lesion sensitivity: 94.4%) and 9 of 10 anovaginal fistulae (sensitivity: 90.0%) were detected and 58 were correctly classified by TPUS (sensitivity: 90.6%; positive predictive value: 93.4%). Overall, TPUS correctly detected and classified the fistulae in 89% of patients and the agreement for classifying perianal fistulae between TPUS and MRI was excellent (K value: 0.783). In contrast, 11 of 23 abscesses were correctly diagnosed by TPUS (sensitivity: 47.8%); although 14 abscesses were diagnosed by TPUS, only 11 were confirmed by MRI (positive predictive value: 78.6%). Overall, TPUS correctly detected and classified fistulae and associated abscesses in 67.3% of patients. Agreement between MRI and TPUS in discriminating simple (15) and complex (29) perianal disease was fairly good (K value: 0.57).
Conclusions: TPUS is a simple and accurate diagnostic method for classifying perianal fistulae in CD and could be used for the preliminary assessment and follow-up of perianal CD.