P–319 Measuring intraobserver and intermethod reliability of endometriotic cyst volumes: a comparison between MRI and 3D transvaginal ultrasound

Study question Are three-dimensional imaging techniques, MRI and three-dimensional transvaginal ultrasound reliable for the volume measurement of endometriotic cysts? Summary answer MRI and XI VOCAL 3D-transvaginal ultrasound both provide a very good intraobserver reliability. The imaging techniques are however not advised to be used interchangeably. What is known already Two-dimensional transvaginal ultrasound (2D-TVUS) and MRI are commonly used in endometriosis care. However, three-dimensional ultrasound (3D-US) has gained more attention in recent years. The use of 3D-US, more specifically VOCAL and XI VOCAL software has proven to be a reliable tool in the measurement of volumes such as splenic volumes and uterine niche volumes. Up to date, 3D-TVUS has not been evaluated for volume measurements in endometrioma. Study design, size, duration A prospective case-control study was performed in an academic endometriosis centre. In total, 23 endometriosis cysts from 16 patients were included. Participants/materials, setting, methods Women diagnosed with endometriosis through laparoscopy with histological confirmation presenting with uni- or bilateral endometrioma on TVUS were included in this study. All women had a regular menstrual cycle (28 days ± 3 days). Women were seen for examinations at two time points during one menstrual cycle: on cycle day 2–4 (T0) and cycle day 20–22 (T1). At both time points a 2D and 3D TVUS and an MRI at 1,5T were performed. Main results and the role of chance 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 – 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. The limits of agreement are widest for XI VOCAL versus MRI (–36.96 –10.54). Similar limits of agreement are found between VOCAL versus XI VOCAL (–7.80 –23.40) as between VOCAL versus MRI (–18.27–8.96). Limitations, reasons for caution No absolute volume measurements were obtained during subsequent surgery to compare the imaging data to. This makes it more difficult to determine an acceptable error margin for the 3D imaging techniques used. Wider implications of the findings: Being able to determine (small) volumetric changes in endometrioma can give more insight into the development and circumstances under which endometrioma grow or decrease in size. For reliable and accurate follow up of endometrioma a single measuring technique must be used as three-dimensional imaging techniques are not interchangeable. Trial registration number Trial NL2106 (NTR2223)