OC12.05: Normal values for quantitative piriformis muscle and sacral nerves ultrasonography with gynecological transvaginal ultrasound

To investigate the feasibility to visualise the intrapelvic part of the piriformis muscle (PM) and the sacral (S1-S3) nerves with gynecological transvaginal ultrasound (TVS). Secondly to provide normative ultrasonography data for antero-posterior (AP) diameters of the nerves entering the pelvis at the sacral foramina and the belly of the PM at the height of the S3 spine. A multicentric prospective observational study including two tertiary referral centres for endometriosis. Consecutive women scheduled for routine gynecological ultrasound examination were involved between December 2022 and December 2023. A standardised assessment of the pelvic organs was performed and visualization of both S1-S2-S3 nerves and PM was attempted in all cases. The time needed to identify the sacral nerves, success rate and AP diameters of both PM and nerves were recorded. A total of 305 patients were included in the study. Visualization rate of the PM was 96.4% (294/305) on the right and 96.0% (293/305) on the left side. Median AP diameter was 18.3 (IQR: 17-19.2)mm on the right and 18.4 (IQR: 17-19.2)mm on the left side. S1 nerves were visualised in 81.6% (249/305) on the right and 81.0% (247/305) on the left side. Visualization time was 8 seconds and median AP diameter 4.8mm on both sides. S2 nerve visualization rate was 83.9% (256/305) on the right side and 74.8% (228/305) on the left side. Visualization time was 8 seconds on the right and 7 seconds on the left side. Median AP diameters were 4.3mm on both sides. S3 nerves were visualised in 67.2% (205/305) on the right and 69.5% (212/305) on the left side. Visualization time was 6 seconds and median AP diameter 3.2mm on both sides. We present a novel approach which provides the consistent measurement of AP diameters of the PM and the S1-S3 nerves on TVS and normative data for them. Integrating assessment of the sacral nerves and PM into routine pelvic TVS may be helpful particularly for women suffering from deep endometriosis.