Warping of the levator hiatus : how significant is it?

Objectives: The levator hiatus is the largest potential hernial portal in the human body. Excessive distensibility is associated with female pelvic organ prolapse (FPOP). Distension occurs not just laterally but also caudally, resulting in perineal descent and hiatal deformation or 'warping'. Methods: This is a retrospective study utilizing records of patients referred between November 2012 and March 2013. Patients underwent a standardized interview, ICS POPQ and 4D translabial ultrasound (US). The craniocaudal difference in the location of minimal distances in midsagittal and coronal planes was determined by offline analysis, as a numerical measure of warping. We tested potential predictors of warping such as demographic factors, signs & symptoms of prolapse, levator avulsion and levator distensibility. Results: Full data sets were available for 190 women. The mean craniocaudal difference in location of minimal distances in mid-sagittal and coronal planes was -1.26mm (-6.7 to 4.6) (P< 0.001). This measure of 'warping' was associated with area on Valsalva (r=-0.284) (p<0.0001) and signs of significant prolapse on clinical examination and ultrasound (all p <0.0001). Conclusions: The plane of minimal dimensions of the levator ani hiatus is non-Euclidean, i.e. warped, and the degree of warping is associated with hiatal distension or 'ballooning', and with FPOP. However, the degree of warping is minor, with the largest difference in the location of planes of minimal dimension 6.7 mm. Hence, our results support the determination of hiatal area in a rendered volume of 1-2 cm in depth.