Intra- and interobserver reproducibility of transvaginal ultrasound for the detection and measurement of endometriotic lesions of the bowel

Abstract

Introduction: The number and invasion depth of endometriotic bowel lesions, total length of bowel affected by endometriosis, lesion-to-anal verge distance, and extent of pouch of Douglas obliteration are important factors in preoperatively determining risk and complexity of endometriosis surgery. The intra- and interobserver reproducibility of transvaginal ultrasound in the evaluation of many of these parameters has not yet been investigated. Our study aimed to assess the intra- and interobserver reproducibility of transvaginal ultrasound between an experienced and less experienced examiner for all of these parameters.

Material and methods: This prospective observational cross-sectional study was conducted between July 2019 and November 2020. Fifty consecutive premenopausal women who underwent transvaginal ultrasound examination in our clinic for the first time, were examined by the same two operators during the same attendance. Outcomes of interest were the inter-rater reproducibility of transvaginal ultrasound for detecting the presence, number, depth and size of bowel endometriotic nodules, lesion-to-anal-verge distance, total length of bowel affected, and pouch of Douglas obliteration. The intraobserver reproducibility was assessed for the continuous parameters. Cohen's kappa (κ) statistic, Cohen's weighted kappa (κ), proportions of agreement, intraclass correlation coefficient (ICC) and Bland-Altman limits of agreement were used to assess the reproducibility of the parameters.

Results: The inter-rater agreement and reliability were very good for identifying bowel endometriosis, the number and invasion depth of bowel nodules, determining whether the maximum nodule length was <3 cm, and lesion-to-anal-verge distance <8 cm (proportion of agreement 0.92, 0.94, 0.97, 0.94, 0.96; κ 0.92, 0.91, 0.92, 0.82, 0.89). The inter-rater agreement and reliability were good for assessing pouch of Douglas obliteration (proportion of agreement 0.86, κ 0.80). The intra-rater reliability for the mean nodule diameter (ICC 0.93 and 0.97) and total length of bowel affected (ICC 0.94 and 0.91) were excellent for operators A and B, respectively. The inter-rater reliability for the mean nodule diameter was good (ICC 0.80), and moderate for the total length of bowel affected (ICC 0.70). The Bland-Altman limits of agreement demonstrated clinically acceptable ranges for these two parameters.

Conclusions: This study demonstrated a high intra- and inter-rater reproducibility of transvaginal ultrasound in the diagnosis of bowel endometriosis and measurement of its various components.

Keywords: bowel endometriosis; deep endometriosis; rectosigmoid colon; reliability; reproducibility; surgery planning; transvaginal ultrasound.

FIGURE 1

Illustration of the female pelvis and the anatomical relation of bowel to internal genitals. Definition of bowel segments according to the International Deep Endometriosis Analysis (IDEA) consensus. The anal canal ends at the dental line, followed by the lower rectum, which is retroperitoneal, thus not visible during diagnostic laparoscopy. The beginning of the upper rectum corresponds approximately to the pouch of Douglas/retrocervical area, where this bowel segment is first only anteriorly intraperitoneal while the posterior wall is still in the retroperitoneal space and immobile. When bending to the left, the rectosigmoid enters the peritoneal cavity also posteriorly, becoming completely intraperitoneally both on the anterior and posterior surface. The rectosigmoid junction is defined to be approximately at the uterine fundus, from where the sigmoid colon continues. The numbers (2, 8, 12) indicate the distance from the anal verge and their corresponding landmarks in centimeters (cm). The anatomy is consistent in‐between people. The dental line is at 2 cm distance from the anal verge; the second anal valve is found at 8 cm and the third anal valve at 12 cm. B, bladder; O, ovary; P, pouch of Douglas; U, uterus.

FIGURE 2

Transvaginal ultrasound, B‐mode, illustrating the different layers of the bowel wall and endometriotic nodules of the bowel. (A) Normal bowel anatomy without endometriosis. (B) Endometriotic nodule (N) confined to the anterior bowel muscularis, with no involvement of other parts of the bowel wall. (C) Endometriotic nodule (N) invading the anterior submucosal layer of the bowel. Note the loss of normal anatomy of the anterior bowel which is replaced by deep endometriosis nodule. The submucosal (SMc) and muscularis (M) layers are only discernible within the posterior bowel wall. In, layer interface; Mc, mucosal layer; M, muscularis layer; N, endometriotic nodule; S, serosal layer; SMc, submucosal layer.

FIGURE 3

Illustration of the approach to measure the lesion‐to‐anal verge distance (LAVD). LAVD was measured in a stepwise fashion (A–D), starting at the most distal point of the lesion (A) and following the hypoechoic line of the muscularis layer of the bowel down to the anal verge, taking measurements successively between identifiable anatomical landmarks and adding them together to calculate the total distance (D) at the end. B, bladder; C, cervix; N, endometriotic nodule; V, vaginal wall.

FIGURE 4

Flow chart summarizing the inclusion and exclusion of eligible women in the study. TVUS, transvaginal ultrasound.

FIGURE 5

Bland–Altman plots for measurements on transvaginal ultrasound. The red lines represent the mean differences between the measurements, the blue lines represent the upper and lower limits of agreement (95% confidence interval). All measurements are indicated in millimeters (mm). Images (a) represent interobserver agreement between operators (Op A; Op B); Images (b) represent the intraobserver agreement for Operator A (Op A); Images (c) represent intraobserver agreement for Operator B (Op B) for the respective measurements.