Endoanal ultrasonography may distinguish Crohn's anal fistulae from cryptoglandular fistulae in patients with Crohn's disease: a cross-sectional study.

Background: The aim of the study was a cross-sectional investigation into the types of anal fistulae in patients with Crohn's disease using 3-dimensional endoanal ultrasonography.
Methods: The study population consisted of 45 patients with established Crohn's disease referred in a 2-year period for treatment of anal fistula. The fistulae were classified according to the presence of three criteria: 1. bifurcation or secondary extension; 2. cross-sectional width ≥ 3 mm; and 3. content of hyperechoic secretions.
Results: The fistulae of 24 patients (53%) satisfied two or three criteria and were classified as true Crohn's fistulae, while the fistulae of 21 patients satisfied one or none of the criteria and were the cryptoglandular type. The fistulae in the two or three criteria group had been in existence for 8.4 years on average and those in the cryptoglandular group for 4.5 years on average (P = 0.283). The corresponding numbers of previous operations for fistula were 5.7 (range 0-32) and 1.5 (range 0-6), respectively (P = 0.0211). The presence of colitis or proctitis was similar across the groups, but the perianal Crohn's disease activity index was higher with a Crohn's type of fistula (P = 0.0097). Also, a larger proportion had been treated with anti-TNF-monoclonal antibody (0.0169).
Conclusions: Endoanal ultrasonography was capable of discerning two subgroups of fistula in Crohn's patients. These groups were clinically different indicating that the prospect of surgical cure is also different.