Transvaginal sonography of the anal sphincter: reliable, or not?

The purpose of this study was to validate the use of transvaginal sonography for anal sphincter evaluation, compare this technique with the more commonly used transanal technique, and explain a publication that suggested that transvaginal sonography is unreliable.

The study population consisted of 50 women, of whom 44 prospectively underwent transanal and transvaginal sonography. The six remaining patients with surgical confirmation underwent only transvaginal sonography. All images were interpreted by the examining radiologist and then reviewed by a second radiologist who was unaware of the first radiologist's interpretations. Defects in the external and internal anal sphincters, the status of the perineal body, and any perianal collections or fistulas were documented.

Twenty-five of the 50 patients showed sphincteric defects. Twenty-two had a defect in the external anal sphincter, of whom 16 had a matching internal anal sphincter defect. Four patients had an isolated internal anal sphincter defect. Surgery in nine of these 22 patients confirmed the defects seen on sonography. The 10th patient who underwent surgery had scar tissue rather than a tear in the external anal sphincter that corresponded with the defect seen on sonography. Defects were identified in all patients presenting with fecal incontinence who had undergone either a primary repair or an anterior sphincteroplasty. Of the 25 patients with intact sphincters on both transvaginal and transanal sonography, four had other significant findings including two perianal abscesses and two T3 rectal carcinomas. In 40 of the 44 patients who were prospectively imaged using both techniques, the sonographic findings were in agreement. Review, performed by a second radiologist who was unaware of the first radiologist's interpretations, verified the findings resulting in an 88.6% interobserver agreement. In all patients, perineal body assessment and assessment of perianal inflammatory disease was more accurate with the transvaginal technique.

Transvaginal sonography is a reliable method for evaluating the anal sphincter, with an accuracy equivalent to that of the transanal technique. Transvaginal sonography is preferable for evaluation of the perineal body and perianal inflammatory processes.