Biometry of the pubovisceral muscle and levator hiatus by three-dimensional pelvic floor ultrasound

Objective: Until recently, magnetic resonance was the only imaging method capable of assessing the levator ani in vivo. Three-dimensional (3D) ultrasound has recently been shown to be able to demonstrate the pubovisceral muscle. The aim of this study was to define the anatomy of the levator hiatus in young nulliparous women with the help of 3D ultrasound. Methods: In a prospective observational study, 52 nulligravid female Caucasian volunteers (aged 18-24 years) were assessed by two-dimensional (2D) and 3D translabial ultrasound after voiding whilst supine. Pelvic organ descent was assessed on Valsalva maneuver. Volumes were acquired at rest and on Valsalva maneuver, and biometric indices of the pubovisceral muscle and levator hiatus were determined in the axial and coronal planes. Results: In the axial plane, average diameters of the pubovisceral muscle were 0.4-1.1 cm (mean 0.73 cm). Average area measurements were 7.59 (range, 3.96-11.9) cm². The levator hiatus at rest varied from 3.26 to 5.84 (mean 4.5) cm in the sagittal direction, and from 2.76 to 4.8 (mean 3.75) cm in the coronal plane. The hiatus area at rest ranged from 6.34 to 18.06 (mean 11.25) cm² increasing to 14.05 (6.67-35.01) cm ² on Valsalva maneuver (P = 0.009). There were significant correlations between pelvic organ mobility and hiatus area at rest (P = 0.018 to P < 0.001) and on Valsalva maneuver (all P < 0.001). Conclusions: Biometric indices of the pubovisceral muscle and levator hiatus can be determined by 3D ultrasound. Significant correlations exist between hiatal area and pelvic organ descent. These data provide support for the hypothesis that levator ani anatomy plays an independent role in determining pelvic organ support.