Description of a new ultrasound sign to distinguish Crohn's anal fistula from cryptoglandular fistula: The rosary sign

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Abstract
Aim: Endoanal and endorectal ultrasound are essential diagnostic tools for perianal fistula. Recent studies have examined ultrasound signs that help differentiate cryptoglandular anal fistula from perianal fistulizing Crohn's disease. The main aim of this work was to describe a new ultrasound sign for perianal fistula and to evaluate its ability to differentiate Crohn's disease from cryptoglandular anal fistula.Method: This study included 363 patients (113 women; mean age 46.5 ± 14.3 years). Overall, 287 (79.1%) patients had a cryptoglandular perianal fistula and 76 (20.9%) had fistulizing Crohn's disease. All patients underwent three‐dimensional anal endosonography for perianal fistula. The reading was carried out by two observers.Results: Observer 1, who was an experienced sonographer and colorectal surgeon, observed the ultrasound sign in 120 patients (33.1%), while observer 2, who was inexperienced, observed it in 129 patients (35.5%). The overall interobserver agreement was 67.22%. The Kappa coefficient measuring interobserver agreement was 0.273 (0.17–0.38). Among those patients with Crohn's disease, 48.68% had the sign and 16% did not (p = 0.001). A logistic regression study showed that the sign was a predictor of Crohn's disease (p = 0.001), with an odds ratio of 2.33 (1.39–3.91). Sensitivity, specificity, positive predictive value, negative predictive value and accuracy were 38.68%, 71.08%, 30.83%, 83.95% and 66.39%, respectively.Conclusion: This study provides a new ultrasound sign for perianal fistula (the rosary sign) in patients with Crohn's disease. The sign can be used to differentiate Crohn's disease from other types of fistula. This is useful in the management of patients with anal fistula.

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