OC09.02: The influence of severe endometriosis on the accuracy of transvaginal ultrasound diagnosis of uterosacral ligament endometriosis

The uterosacral ligaments (USLs) and torus uterinus (TU) are common sites for deep endometriosis (DE) but are challenging to diagnose through transvaginal ultrasound (TVS). Anatomical distortion caused by severe endometriosis, including pouch of Douglas (POD) obliteration and bowel DE, may contribute to poor diagnostic performance. This study aims to assess the impact of severe endometriosis and anatomic distortion on TVS diagnosis of DE in the USLs and TU. We performed a secondary analysis on data from a prospective diagnostic test accuracy study conducted at the McMaster University Medical Center, Tertiary Endometriosis Clinic, using consecutively recruited participants. The index test was TVS performed by an advanced sonologist. Diagnostic accuracy parameters were calculated for each site relative to the reference standard at 1) baseline, 2) excluding those with POD obliteration, and 3) excluding DE of the bowel. Fifty-four consecutive participants were included. Baseline diagnostic performance for the left USL, right USL, and TU without exclusion was: accuracy 92.6%, 94.4%, 100%, sensitivity 82.6%, 75.0%, 100%, and specificity 100%, 100%, 100%, respectively. Upon excluding those with POD obliteration, the diagnostic performance was: accuracy 90.2%, 97.6%, 100%, sensitivity 73.3%, 85.7%, 100%, and specificity 100%, 100%, 100%, respectively. Comparatively, diagnostic performance excluding those with DE of the bowel was: accuracy 93.2%, 95.5%, 100.0%, sensitivity 82.4%, 71.4%, 100%, and specificity 100%, 100%, 100%, respectively. Despite the challenges posed by severe endometriosis, which distorts the anatomical environment with extensive adhesions, potentially making it difficult to map normal and diseased tissue, our results demonstrate strong diagnostic performance regardless of disease complexity. Our findings show robustness in diagnosing and detecting DE through TVS.