Vaginal high-pressure zone assessed by dynamic 3-dimensional ultrasound images of the pelvic floor

Objective: The purpose of this study was to determine the shape and characteristics of the vaginal high-pressure zone (HPZ) by imaging a compliant fluid-filled bag that had been placed in the vaginal HPZ with the 3-dimensional ultrasound system. Study Design: Nine nulliparous asymptomatic women underwent 3-dimensional ultrasound imaging and vaginal pressure measurements. A compliant bag was placed in the vagina and filled with various volumes of water. Three-dimensional ultrasound volumes of the pelvic floor were obtained at each bag volume while the subjects were at rest and during pelvic floor contraction. Results: At low volumes, the bag was collapsed for a longitudinal extent of approximately 3.3 ± 0.2 cm (length of vaginal HPZ). With increasing bag volume, there was opening of the vaginal HPZ in the lateral dimension before the anteroposterior dimension. Pelvic floor contraction produced a decrease in the anteroposterior dimension but not the lateral dimension of the bag in the region of the vaginal HPZ. Conclusion: We propose that the shape and characteristics of the vaginal HPZ are consistent with the hypothesis that the puborectalis muscle is responsible for the genesis of the vaginal HPZ.