Trans-perineal versus endo-anal ultrasound in the detection of anal sphincter tears.

Objective: To compare endo-anal and trans-perineal ultrasonography in the detection of anal sphincter lesions.

Study Design: Sixty-four patients sent for a uro-gynaecological consultation were given tests by two ultrasound methods using the same apparatus (Aloka) with different probes. The endo-anal ultrasound (EAUS) was carried out in a supine position using a rotary circular probe at 7.5 MHz. The trans-perineal ultrasound (TPUS) was carried out using a curved linear probe at 5 MHz, applied to the perineum in the transverse direction, allowing a proximal view of the sphincter. For each image the thicknesses of the two components of the sphincter (internal and external) were noted, as well as the presence of any ultrasonographic tear, its position, and its width on the sphincterian circumference.

Results: The average of the internal and external thickness of the sphincters was of 2.8 and 5.6 mm, respectively for the TPUS, and 2.1 and 6.2 mm for the EAUS. Among the 64 patients, 15 external lesions of the anal sphincter were found with the TPUS, and 14 with the EAUS. The kappa correlation coefficient was 48%, with a confidence interval of 95%.

Conclusion: The endo-anal technique, which provides a staged analysis of the anal sphincter muscle, remains the benchmark of sphincterian imaging. TPUS is a useful method, in that it gives good visualisation of anatomical structures, but its sensitivity in detecting sphincter lesions remain to be demonstrated.