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

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  • 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.


    A multicenter, international, retrospective, diagnostic accuracy study was carried out between January 2016 and April 2018 on women with suspected pelvic endometriosis.


    Four different centers with advanced ultrasound and laparoscopic services were recruited (1 for temporal validation and 3 for external validation).


    Women with pelvic pain and suspected endometriosis.


    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).


    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.


  • Espada, Mercedes
  • Leonardi, Mathew
  • Aas-Eng, Kristina
  • Lu, Chuan
  • Reyftmann, Lionel
  • Tetstall, Emma
  • Slusarczyk, Basia
  • Ludlow, Joanne
  • Hudelist, Gernaud
  • Reid, Shannon
  • Condous, George

publication date

  • January 2021