Estimation of uterine volume: A comparison between Viewpoint and 3D ultrasound estimation in women undergoing laparoscopic hysterectomy

Objectives: To assess the three-dimensional (3D) tool, Virtual Organ Computed-aided AnaLysis™ (VOCAL) in the calculation of pre-operative uterine volume and to correlate the measurements with those obtained with Viewpoint, using uterine dry weight (UDW) as the gold standard. Methods: Prospective observational study of women consented for a laparoscopic hysterectomy (LH) at Nepean Hospital between October 2008 and November 2011. All women underwent detailed transvaginal scan (TVS) at the pre-operative assessment. Two-dimensional (D) images of the uterus were obtained both in the mid-sagittal and transverse planes. 3D volumetric acquisitions were also obtained for each uterus in the mid-sagittal plane. 2D measurements of the uterus in millimetres (Anterio-Posterior, longitudinal and transverse) were recorded in Viewpoint software package (GE Healthcare ViewPoint, Germany); which then generated an estimated uterine volume (ml) using the ellipsoid formula. The 3D uterine volumetric datasets were reviewed using SonoView Pro and uterine volumes were estimated with off-line processing using VOCAL™. The gold standard for comparison was UDW in grams (g), measured by the histopathologist at the time of analysis of the LH specimens. The relationship between the estimated uterine volumes and actual UDW was evaluated using correlation analysis. P-values were calculated to ascertain the significance of these findings; P values &< 0.05 represented statistical significance. Results: 76 women underwent LH during the study period. Complete data were available in 96% (74/76) of cases. The mean age of the women was 43.7 years and 92% were multiparous. The mean Viewpoint uterine volume was 283 ml, the mean VOCAL™ uterine volume was 249 ml and the mean UDW was 295 g. There was a significant correlation between UDW and estimated uterine volumes both for Viewpoint (R = 0.83, P < 0.001) and VOCAL™ (R = 0.97, P < 0.001), respectively. Viewpoint systematically overestimated weight by 43.1 g, whereas VOCAL™ underestimated by an average of 42.4 g, and this difference was statistically significant (P < 0.001). In terms of absolute values, the mean prediction error for VOCAL™ was -18.0 g and for Viewpoint it was 27.6 g (P &< 0.0001). Conclusion: VOCAL™ was found to be significantly more accurate than Viewpoint in the estimation of uterine volumes, and it was better correlated with UDW.