Examination techniques for endosonography of the anal canal

Background: To determine whether patient position or sphincter contraction influences sphincter thickness or defect assessment. Methods: Anal endosonography was performed on 35 consecutive patients (30 women, five men). Twenty-five were scanned in the left lateral and prone positions, and the internal sphincter thickness was measured. In 10 patients, the internal sphincter, longitudinal muscle, external sphincter, and length of any defect were measured at rest and during anal squeeze. Results: There was no significant difference in internal sphincter thickness measured in the prone and left lateral positions (95% limits of agreement, -0.12 to 0.06). The thickness of the internal sphincter, longitudinal muscle, and external sphincter at rest did not change significantly during straining (95% limits of agreement, -0.44 to 0.3, -0.28 to 0.24, and 0.33 to 0.71, respectively). The squeeze maneuver did not influence defect appearance or length (95% limits of agreement, -2.845 to 2.379). Greater symmetry of the anterior part of the external sphincter and improved visualization of perineum was achieved in the prone position. Conclusion: Examination in the prone position is preferred. Squeeze maneuvers are of no diagnostic benefit.