Peroxide-enhanced anal endosonography: technique, image interpretation, and clinical applications.

Because current techniques for examination and imaging of perianal fistulas tend to underestimate the extent, location, and course of perianal fistulas--information essential for decisions about surgical management--the use of hydrogen peroxide was investigated as an image-enhancing contrast agent for confirmation of the presence of and improvement in the depiction of fistulas during endoanal ultrasonography (US). After conventional endoanal US was performed with a side-fire 7.5- or 10.0-MHz rotating endoprobe, external perianal openings were cannulated and approximately 1 mL of peroxide was administered. After reinsertion of the endoprobe, the entire course of the echogenic fistula, including its relation to the internal and external sphincters and the levator ani muscle, was depicted in real time in three dimensions. This depiction of fistulas permits accurate classification, which facilitates surgical planning. In experience with more than 60 patients, peroxide-enhanced endoanal US was found to be a useful technique for documentation of the presence, number, and internal course of perianal fistulas and for characterization of abnormalities seen at endosonography performed without use of contrast enhancement. In addition, the technique permitted surgeons to stratify patients into treatment groups and has been especially useful for planning surgical treatments.