Role of transcutaneous perianal ultrasonography in evaluation of fistulas in ano

Objective. The purpose of this study was to evaluate the role of transcutaneous perianal ultrasonography in evaluation of fistulas in ano and to assess its possible role as a first-line investigation, for follow-up, and as a possible substitute for magnetic resonance imaging. Methods. Transcutaneous perianal ultrasonography was per-formed in 30 patients with fistulas in ano with the use of a 3- to 6-MHz sector probe, a 7- to 11-MHz linear probe, and a 5- to 7-MHz endocavitary probe. Patients were followed clinically and at surgery to assess the accuracy of transcutaneous perianal ultrasonography. Results. A total of 43 fistulas, sinus tracts, or both were found in 26 patients. They appeared as hypoechoic tracts. Eleven of 30 patients had the presence of a collection or abscess, which appeared as hypoechoic areas. Twenty-four of 29 patients with positive findings underwent surgery. In these, 35 of 39 tracts were surgically confirmed (positive predictive value, 90%). The positive predictive value for demonstration of an internal opening was 85% (22/26) when compared with direct visualization or probing. Sensitivity for detection of tracts was 100%, and that for demonstration of an internal opening was 96% (26/27). The negative predictive value for sinus/fistulous tracts was nearly 100%. Transcutaneous perianal ultrasonography could not adequately evaluate suprasphincteric-type fistulas. However, it is a good, inexpensive modality in the evaluation of patients with fistulas in ano and also helps in follow-up of these patients. It can also be used to select patients who need magnetic resonance imaging. Conclusions. Transcutaneous perianal ultrasonography has the potential to become the first investigation in patients with perianal fistulas and abscesses.