Urogenital Hiatus Stress Test (UGST): Development and Feasibility

Objectives: An enlarged POP-Q genital hiatus (GH) is associated with increased risk of prolapse development and surgical failure. However, POP-Q GH measurements are done during Valsalva when the prolapse may dilate the hiatus rendering the independent status of the GH uncertain. So we developed a 3D endovaginal ultrasound-based (US) urogenital hiatus stress test (UGST) to characterize hiatal distention and perineal complex structure changes that occur under increasing distention pressures, independent of prolapse status and Valsalva effort.

Methods: A 0.5 mm thick polyethylene bag, that can expand freely up to 8 cm in diameter, was sealed over a 3D endovaginal US probe using a closed-cell foam gasket and a filling tube. The UGST was performed by placing the probe and bag assembly into the participant’s vagina. The UGH was dilated step-wise by instilling fluid into the bag at 10-30 cmH2O pressure. 3D US images were taken at each step when participants were instructed to be relaxed. Using 3D Slicer software, we quantified Level III measures including pubovisceral muscle (PVM) length and UGH.

Results: : We successfully performed the UGST and acquired ultrasound (US) data during hydrostatic distension in 7 patients. Women who participated were on average 38 ± 5 years old, with BMI 28.7 ± 5.9 kg/m2, and were at least 5 years from their first vaginal delivery. We were able to capture 3D US images in all subjects that visualized the distended bag size and its relationship with hiatus and level III structures simultaneously (Fig. 1). Fig 2A showed enlarged hiatus with increasing pressure in 3D. There was a large variation in both initial UGH area (range: from 7.5 to 20.5 cm2) and also in the slope of the area-pressure curves (range: from 0.08 to 0.49 cm2/cmH2O) revealing variation in GH resistance to dilation. Noted is the large difference in two women with medium POP-Q GH (3-3.5 cm). PVM length changes with increasing pressure exhibited smaller variation than UGH area (Fig. 2B).

Conclusions: The GHST successfully revealed substantial variability in hiatus size and resistance to dilation not captured by POP-Q. It also demonstrated changes in adjacent muscles. Comment: The GHST provides an objective assessment of Level III function unaffected by prolapse. It also offers a method to study the Level III structural failures responsible for an enlarged hiatus.