Transvaginal versus anal endosonography for detecting damage to the anal sphincter

We undertook this study to establish the accuracy of transvaginal endosonography for detecting damage to the anal sphincter.

Anal endosonography was performed in 47 parous patients and one nulliparous patient using a sonographic scanner, an 1850 endoprobe, and a 10-MHz transducer protected by a water-filled hard plastic cone. This procedure was followed by transvaginal sonography using the same system but with a water-filled balloon in 43 and a dedicated vaginal probe Type 8551 of 10-MHz frequency in five. Axial images were obtained as low in the perineum as possible. The transvaginal images were reviewed with the observer unaware of the findings from anal endosonography and were then compared with the anal endosonograms.

The transvaginal images were inadequate for review in three patients. In the remaining 45 patients, anal endosonography showed internal sphincter defects in 18 and external sphincter tears in 21. Transvaginal endosonography showed eight internal and 10 external sphincter defects only, giving a sensitivity of 44% and a specificity of 96% for the detection of internal sphincter defects and a sensitivity of 48% and a specificity of 88% for external sphincter tears.

Transvaginal examination is not accurate for assessing the anal sphincter because of the anatomic limitations this approach imposes on axial imaging of the anal canal.