title: A unique 3D endoanal ultrasound feature of perianal Crohn's fistula: the 'Crohn ultrasound fistula sign'.
abstract: OBJECTIVE
  Using a high-resolution 3D endoanal ultrasound, we have observed that some perianal fistulas show a hypoechogenic fistula tract surrounded by a well-defined hyperechogenic area with a thin hypoechogenic edge in patients with Crohn's disease ['Crohn's Ultrasound Fistula Sign' (CUFS)], unlike conventional fistula tracks. The study aimed to determine the prevalence of CUFS in a consecutive series of patients with anal fistula.
  
  
  METHODS
  Of 157 patients (median age 45, range 14-86 years, 100 males) with perianal fistula were examined with 3D endoanal ultrasound. All 3D volumes were stored and analysed retrospectively by two independent observers blinded to the clinical information of the patients.
  
  
  RESULTS
  There were 29 patients with Crohn's disease of whom 20 (69%) showed CUFS. CUFS was absent in 125 (98%) of 128 patients without Crohn's disease. The positive and negative predictive value of CUFS for Crohn's disease was 87% and 93%, respectively. The kappa value of the two independent observers was 0.77, indicating a substantial interobserver agreement.
  
  
  CONCLUSIONS
  This study provides a new 3D endoanal ultrasound criterion, CUFS, of perianal fistula in patients with Crohn's disease. The sign can be used to discriminate a Crohn's from other types of fistula, which may be useful in the management of patients with anal fistula.
authors.affiliation: Department of Clinical Sciences, Surgery, Section of Pelvic Floor Centre, Skåne University Hospital, Lund University, Malmö, Sweden. antoni.zawadzki@med.lu.se
authors.forename: A
authors.initials: A
authors.lastname: Zawadzki
authors.forename: M
authors.initials: M
authors.lastname: Starck
authors.forename: M
authors.initials: M
authors.lastname: Bohe
authors.forename: H
authors.initials: H
authors.lastname: Thorlacius
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D003424:Crohn Disease / Q000150:complications / Q000000981:diagnostic imaging*; D019160:Endosonography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012003:Rectal Fistula / Q000000981:diagnostic imaging* / Q000209:etiology; D012189:Retrospective Studies; D012680:Sensitivity and Specificity