Usefulness of hydrogen peroxide enhancement in diagnosis of anal and ano-vaginal fistulas.

Our objective was to assess if contrast-enhanced (CE) anal endosonography (AES) with hydrogen peroxide is useful in the diagnosis of anal and ano-vaginal fistulas. A Bruel and Kjaer scanner with a 7.0-MHz transducer was used. After visualization of the fistula tract in non-contrast (NC) AES, hydrogen peroxide was introduced into the fistula tract through the external opening in 22 patients with different types of anal fistulas. Both CE and NC AES revealed 13 transsphincteric, 3 intersphincteric, 2 suprasphincteric and 4 ano-vaginal fistulas. Simple tracts were found in 16 cases and complex in 6 cases in non-contrast AES. The CE AES revealed 19 simple and 3 complex fistulas. Fifteen internal openings visible in NC AES were confirmed in CE AES in 6 cases, which additionally found 11 more internal openings. Surgery confirmed all types of fistulas found in NC and CE AES; however, the latter two found 18 simple and 4 complex fistulas, and 21 internal openings. Both NC and CE AES are able to correctly differentiate types of anal fistulas and are of comparable value in differentiating simple from complex fistulas, although a false-negative result was found in CE AES. In the preoperative assessment of the internal opening, CE AES is superior to NC AES.