Contrast-enhanced endosonography for the diagnosis of anal and anovaginal fistulas

PURPOSE: We assessed whether contrast-enhanced anal endosonography (AES) with hydrogen peroxide improves the identification of anal fistulas and their internal openings compared with non-contrast AES. METHODS: The study group comprised 12 patients who had various types of anal fistulas with visible external openings. AES was performed before and about 15 seconds after injection of 1 ml of 3% hydrogen peroxide into the fistula tract through the external opening. RESULTS: Both contrast and non-contrast AES revealed 7 transsphincteric, 2 intersphincteric, 1 suprasphincteric, and 2 anovaginal fistulas. Simple tracts were found in 8 cases and complex tracts in 4 cases on non-contrast AES. Contrast-enhanced AES revealed 9 simple and 3 complex fistulas. One fistula that appeared complex on the non-contrast study appeared simple after contrast agent administration. Contrast-enhanced AES demonstrated more internal openings than non-contrast AES did. Surgery confirmed 11 of the fistulas; an internal opening could not be located surgically for the other tract. CONCLUSIONS: Contrast-enhanced AES appears to be superior to non-contrast AES in the preoperative assessment of anal and anovaginal fistulas and in demonstrating and locating their internal openings.