A simplified method for determining hiatal biometry.

INTRODUCTION: The levator hiatus is the largest potential hernial portal in the human body. Its dimensions are measured in the axial plane and are strongly associated with female pelvic organ prolapse. We aimed to compare two commonly used methods for measuring hiatal dimensions.
METHODS: We performed offline analysis of 100 consecutive 4D ultrasound volume datasets of women seen in a tertiary urogynecological clinic. Hiatal measurements were obtained in sectional planes (SP, Method A) and rendered volumes of 1-2 cm thickness (RV, Method B).
RESULTS: A test-retest series in 20 women showed similar repeatability for both methods, with an intraclass correlation (ICC) of 0.85 (CI 0.81-0.88) for Method A (SP) and of 0.88 (CI 0.85-0.9) for Method B (RV). Measurements taken from rendered volumes were generally lower than those taken in axial plane slices, reaching significance for area on Valsalva (P=0.005), sagittal diameter and area on pelvic floor contraction (P=0.009 and 0.044). Method B seemed more strongly associated with symptoms of prolapse than Method A (P=0.008 vs P=0.027).
CONCLUSIONS: We recommend that hiatal dimensions be measured in rendered volumes whenever possible because this method seems more valid and at least as repeatable. This is probably due to the fact that the plane of minimal hiatal dimensions is non-Euclidean, i.e., warped, which can be compensated for by measuring in a rendered volume of 1-2 cm thickness.