P15.08: Three‐dimensional ultrasound of rectosigmoid endometriosis: intra and interobserver variation of lesion size

An ongoing study from our group relates growth of rectosigmoid endometriosis to the patient's symptoms of disease. For that reason, there is a need for knowledge of the intra- and interobserver variation when measuring growth of rectosigmoid endometriosis by the use of three-dimensional ultrasound. This study investigates variation within and between observers measuring volume of rectosigmoid endometriosis by the use of transvaginal three-dimensional ultrasound. Three-dimensional ultrasound scans of rectosigmoid endometriosis were collected using a Voluson® E8 machine (GE Healthcare, Wauwatosa, WI, USA) with a 6–12 MHz vaginal probe. Scans were chosen for analysis on the basis of quality of the scan and the demarcation of the rectosigmoid lesion. Virtual Organ Computer-aided analysis within the software of 4D View® was used to measure the volume of each lesion. Only the growth into the muscularis propria in the rectosigmoid wall was evaluated. Testing for systematic difference was done using paired t-test. Thirty three-dimensional ultrasound scans were measured. The average volume of rectosigmoid endometriosis was 1.71 cm3. A statistically significant mean difference between observers of 0.10 cm3 (95% CI: 0.02; 0.19) was found. 95% limits of agreements for the interobserver variation were −0.35 to 0.58 cm3. Intraobserver differences for measuring the same volume twice was 0.15 cm3 (0.07; 0.23) cm3 and statistically significant. 95% limits of agreements for the intraobserver variation was −0.27 to 0.58 cm3. This study shows small intra- and interobserver variation when measuring volume of rectosigmoid endometriosis by vaginal three-dimensional ultrasound. Therefore, measurement of a three-dimensional ultrasound scan can, indeed, be applied in the clinical setting. Based on the results of the average volume of rectosigmoid endometriosis and the intra- and interobserver variation, our recommendation is to consider a 10% change or more of the volume of rectosigmoid endometriosis clinically relevant.