ABSTRACT
CONDENSATION: A mathematical formula to estimate the levator ani subtended volume parameter based on magnetic resonance imaging linear measurements from one axial and one sagittal view. OBJECTIVE: To estimate the levator ani subtended volume based on MRI linear measurements. METHODS: The 3D Slicer was used to obtain the Levator Ani Subtended Volume (LASV) from 35 women with Pelvic Organ Prolapse (POP), that were assumed as reference values. The linear measurements that best fitted our criteria were chosen. The subjects were divided in two groups, 1 and 2. The coefficients of the mathematical equation were obtained from group 1 through a regression analysis using the 3D rendering volume as a dependent variable. To validate the mathematical equation, two observers, blinded to POP ordinal stages, performed new measurements. The 3D rendering and the estimated volumes were compared and correlated with POP-Q measurements and POP ordinal stages. A residual analysis was performed to validate the mathematical equation. Finally, a reliability analysis was performed. RESULTS: The predictors chosen were M-line, H-line, and width of levator hiatus. An equation to estimate the volume was determined: eLASV = -72.838 + 0.598H-line + 1.217M-line + 1.136WLH1. The estimated values showed similar correlation with POP-Q individual measurements and ordinal stages. The residual analysis showed normal distribution of the estimate values and the errors, from both observers. The intra and interclass evaluation of the estimated values indicated a good reliability of the eLASVs. CONCLUSION: The LASV can be estimated using well known Magnetic Resonance linear measurements, showing good correlation with correspondent 3D rendering volumes. The clinical relevance of this parameter should be proved in further studies.
