A Multicenter International Temporal and External Validation Study of the Ultrasound-based Endometriosis Staging System

Study Objective: The aim of this study was to validate temporally and externally the ultrasound-based endometriosis staging system (UBESS) to predict the level of complexity of laparoscopic surgery for endometriosis. Design: A multicenter, international, retrospective, diagnostic accuracy study was carried out between January 2016 and April 2018 on women with suspected pelvic endometriosis. Setting: Four different centers with advanced ultrasound and laparoscopic services were recruited (1 for temporal validation and 3 for external validation). Patients: Women with pelvic pain and suspected endometriosis. Interventions: All women underwent a systematic transvaginal ultrasound and were staged according to the UBESS system, followed by classification of laparoscopic level of complexity according to the Royal College of Obstetricians and Gynaecologists (RCOG) levels 1 to 3. Measurements and Main Results: UBESS I, II, and III were then correlated with RCOG levels 1, 2, and 3, respectively. A comparison between temporal and external sites (skipping “A”) and between each site was performed in terms of the diagnostic accuracy of UBESS to predict RCOG laparoscopic skill level. A total of 317 consecutive women who underwent laparoscopy with suspected endometriosis were included. Complete transvaginal ultrasound and laparoscopic surgical outcomes were available for 293/317 (92.4%). At the temporal site, the accuracy, sensitivity, specificity, positive predictive value, negative predictive value, positive likelihood ratio, and negative likelihood ratio of UBESS I to predict RCOG level 1 were 80.0%,73.8%, 94.9%, 97.2%, 60.2%, 14.5%, and 0.3%, respectively; of UBESS II to predict RCOG level 2 were 81.0%, 70.6%, 82.0%, 26.7%, 96.8%, 3.9%, and 0.3%, respectively; of UBESS III to predict RCOG level 3 were 91.0%, 85.7%, 92.4%, 75.0%, 96.1%, 11.3%, and 0.2%, respectively. At the external sites, the results of UBESS I to predict RCOG level 1 were 90.3%, 92.0%, 88.4%, 90.2%, 90.5%, 7.9%, and 0.1% respectively; UBESS II to predict RCOG level 2 were 89.2%, 100.0%, 88.5%, 37.5%, 100.0%, 8.7%, and 0.0%, respectively; and UBESS III to predict RCOG level 3 were 86.0%, 67.6%, 98.2%, 96.2%, 82.1%, 37.8%, and 0.3%, respectively. When patients requiring ureterolysis (i.e., RCOG level 3) in the absence of bowel endometriosis were excluded (n = 54), the sensitivity of UBESS III to correctly classify RCOG level 3 increased from 85.7% to 96.7% at the temporal site (n = 42) and from 67.6% to 96.0% at the external sites (n = 12) (p <.005). Conclusion: The results from this external validation study suggest that UBESS in its current form is not generalizable unless there is either or both bowel deep endometriosis and cul-de-sac obliteration present. The major limitation appears to be the misclassification of women who require surgical ureterolysis in the absence of bowel endometriosis.