Three-dimensional endoanal ultrasound assessment of the anal sphincters during rest and squeeze

Current ultrasound assessment of the anal sphincter is based on measurements during rest. However, active constriction plays a role in maintaining continence. Here we assess female anal dimensions during rest and squeeze.

Thirty women were recruited for a cross-sectional endoanal ultrasound study after written consent according to an ethically approved protocol: nine 0-gravida, 10 with normal vaginal delivery, and 11 with complicated vaginal delivery (babies >4,500 g, operative vaginal delivery or perineal rupture). Endoanal three-dimensional (3D)-ultrasound volume was obtained during rest and squeeze. Length of anal canal and volume of the external and internal sphincters were determined.

In the 0-gravida group, the mean anal canal at rest was 3.28 cm (SD: +/-0.63) compared with 2.30 (+/-0.77) in those who had given birth (p =0.002). Correspondingly, the volume of the external sphincter was 7.61 cm(3) (+/-2.63) versus 4.80 (+/-2.02) (p =0.004), and for the internal sphincter 2.63 (+/-1.18) versus 2.68 (+/-1.30) (p =0.98). There were no differences between rest and squeeze within the 0-gravida, but after a traumatic vaginal delivery the internal sphincter was smaller during squeeze (p =0.01), and the overlap between external and internal sphincter was 0.76 cm (+/-0.41), insignificantly shorter (p =0.09) than in the 0-gravida group at 1.21 (+/-0.62).

Women with vaginal delivery had a shorter anal canal and smaller external sphincter than 0-gravida. Active squeeze had no effect on the dimensions of the sphincter apart from a reduction of the internal sphincter in those who had undergone a complicated delivery, possibly due to a dislodging upwards during squeeze.