Accuracy of hydrogen peroxide enhanced endoanal ultrasonography in assessment of the internal opening of an anal fistula complex.

BACKGROUND

The aim of this study was to evaluate the accuracy of hydrogen peroxide-enhanced ultrasound in localizing the internal opening of the anal fistula.

METHODS

A retrospective review of all patients with anal fistula who underwent hydrogen peroxide-enhanced ultrasound was performed. The results of hydrogen peroxideenhanced ultrasound and intraoperative findings on the basis of operative reports were correlated.

RESULTS

A total of 57 patients (47 men) of mean age of 45.7 (range, 21-77) years underwent hydrogen peroxide-enhanced ultrasound with a diagnosis of anal fistula; 36 patients underwent surgery. The intraoperative internal opening correlated with the hydrogen peroxide-enhanced ultrasound report in 22 of 36 patients (61.1%). In 5 patients, the hydrogen peroxide-enhanced ultrasound yielded false-positive information with a positive predictive value of 84%. Four of the 7 patients with falsenegative hydrogen peroxide-enhanced ultrasound findings had supra- and extrasphincteric fistulas.

CONCLUSIONS

There is a 61.1% correlation between hydrogen peroxide-enhanced ultrasound and surgical findings of the internal opening with a positive predictive value of 84%. If no internal opening was seen on hydrogen peroxide-enhanced ultrasound, it strongly suggests the possibility of a supralevator or extrasphincteric fistula.