Validation of the ultrasound-based endometriosis staging system


An external validation multicenter international study, in the hands of expert ultrasound examiners, has concluded that the ultrasound-based endometriosis scoring system (UBESS) is accurate in predicting the level of surgical complexity in the presence of bowel deep endometriosis or obliterated pouch of Douglas.

“However, we were unable to prove that UBESS is useful in predicting ureterolysis, which is a complex surgical procedure that requires a deep understanding of the pelvic anatomy and advanced surgical skills,” said senior author Mercedes Espada, MD, PhD, a provisional fellow in the Acute Gynecology, Early Pregnancy and Advanced Endosurgery Service at Nepean Hospital in Kingswood, New South Wales, Australia. “Therefore, we believe that UBESS, in its current version, should be used with caution.”

Published in The Journal of Minimally Invasive Gynecology, the retrospective study was conducted between January 2016 and April 2018 on 317 consecutive women with pelvic pain and suspected endometriosis who underwent laparoscopy at four centers (three in Australia and one in Austria) with advanced ultrasound and laparoscopic services.

Intervention consisted of a systematic transvaginal ultrasound (TVS) and all women 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 1-3.

UBESS I, II and III were then correlated with the RCOG level 1, 2 and 3, respectively. Comparison between temporal and external sites, as well as each site, was performed to determine the diagnostic accuracy of UBESS for predicting RCOG laparoscopic skill level.

Complete TVS and laparoscopic surgical outcomes were available for 92.4% (293 of 317) women.

At the temporal site, the accuracy, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratio (LR)+ and LR- of UBESS I to predict RCOG level 1 were 80.0%, 73.8%, 94.9%, 97.2%, 60.2%, 4.5 and 0.3, respectively. For UBESS II to predict RCOG level 2, the percentages/ratios were 81.0%, 70.6%, 82.0%, 26.7%, 96.8%, 3.9 and 0.3; respectively; whereas for UBESS III they were 91.0%, 85.7%, 92.4%, 75.0%, 96.1%, 11.3 and 0.2, respectively.

At the external sites, UBESS I to predict RCOG level 1 were 90.3%, 92.0%, 88.4%, 90.2%, 90.5%, 7.9 and 0.1, respectively; for UBESS II, 89.2%, 100.0%, 88.5%, 37.5%, 100.0%, 8.7 and 0.0; and for UBESS III, 86.0%, 67.6%, 98.2%, 96.2%, 82.1%, 37.8 and 0.3.

When patients requiring ureterolysis 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 < 0.005).

“​Our findings confirm that the concept of obtaining perfect accuracy with diagnostic tools is hard to achieve, and hence it is a field for constant improvement,” Dr. Espada told Contemporary OB/GYN.

Results highlight the importance of accurate preoperative awareness of disease stage in order to optimize surgical outcomes and minimize surgical complications, according to Dr. Espada. “Our research also raises the question of whether patients with suspected endometriosis on ultrasound should be managed by generalists or minimally invasive gynecologic surgeons, in the absence of obliterated pouch of Douglas or bowel deep endometriosis,” she said.

Moreover, because of a potential correlation between the size of the uterosacral ligament (USL) deep endometriosis implant/ovarian immobility/presence of ovarian endometrioma and risk of ureteral involvement, “these ultrasound markers could hold the key to the prediction of ureterolysis, even in the absence of ultrasound diagnosed ureteric or bowel deep endometriosis,” Dr. Espada said.

Future studies, she said, should focus on incorporating ultrasound markers, which potentially can overcome the documented deficiencies of the current UBESS.


  1. Espada M, Leonardi M, Aas-Eng K, et al. A Multicenter International Temporal and External Validation Study of the Ultrasound-based Endometriosis Staging System [published online ahead of print, 2020 Apr 11]. J Minim Invasive Gynecol. 2020;S1553-4650(20)30184-9. doi:10.1016/j.jmig.2020.04.009
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