Measuring intraobserver and intermethod reliability of endometriotic cyst volumes: A comparison between MRI and 3D transvaginal ultrasound in endometriosis

Objectives: To identify the intraobserver and intermethod reliability of three-dimensional transvaginal ultrasound (3D-TVUS) using the software VOCAL and XI VOCAL compared with magnetic resonance imaging (MRI) for volumetric measurement of ovarian endometrioma. Methods: The intermethod and intraobserver reliability of endometrioma volumes were assessed in 16 women diagnosed with endometriosis through laparoscopy with histologic confirmation and presenting with uni- or bilateral endometriomas. In total, volumes of 23 endometriomas were assessed with two-dimensional and three-dimensional transvaginal ultrasound and 6 mm magnetic resonance imaging. Examinations took place at two moments in one menstrual cycle: day 2-4 (T0) and day 20-22 (T1). Results: The intraclass correlation for intraobserver reliability is good to very good for all three techniques ranging from the lowest value of 0.953 to the highest of 1.000. MRI has the most narrow limits of agreement (-3.93 to 4.53), followed by XI VOCAL (-5.16 to 5.65) while VOCAL has the widest limits of agreement (-10.22 to 11.39). Intraclass correlations are poor in the comparison of XI VOCAL to MRI, moderate between VOCAL and XI VOCAL, and good for the comparison between VOCAL and MRI. Limits of agreement vary per technique. When comparing 3D imaging techniques with 2D TVUS, XI VOCAL versus 2D TVUS provide the smallest limits of agreement. Conclusions: MRI and XI VOCAL provide the best intraobserver reliability. The different imaging techniques are not interchangeable. As TVUS is a more readily available and cost-efficient imaging technique the usage of XI VOCAL is advised.