Agreement and reproducibility in identification of endometriosis using magnetic resonance imaging

Magnetic resonance imaging (MRI) is a promising technique in the study of endometriosis, allowing a complete mapping of lesions before surgery. However, the value of MRI in the diagnosis of endometriosis in the bladder, in superficial peritoneal lesions, and in ovarian foci and uterosacral ligaments is still under debate.

To assess inter- and intra-observer agreement in the evaluation of endometriosis in different anatomical locations using MRI.

From June 2006 to February 2008, 83 female patients (mean age 39, range 19-49 years) who had undergone MRI examination for suspected endometriosis were evaluated by two radiologists. MRI at 1.5 Tesla was performed with SE and TSE sequences, T1- and T2-weighted with and without fat suppression. Each examination was completed with gadolinium administration. Each dataset was independently evaluated by the radiologists for the presence or absence of endometriosis. The location (ovaries, uterosacral ligaments (USLs), pouch of Douglas, vagina, rectosigmoid, rectovaginal septum, and bladder) of suspected lesions was recorded. Cohen kappa statistical analysis was performed to calculate agreement between measurements. After 2 months the data were analyzed again by the two observers to assess intra-observer agreement.

Of the 83 MRI examinations performed, 12 patients demonstrated no evidence of endometriosis. In the remaining 71 studies, 157 endometriotic lesions ranging in size from 0.4 to 6.2 cm were detected. Of the 157 lesions, 53 (33.75% incidence) were smaller than 1 cm. In the ovaries, the inter-observer agreement was 92.77% and the kappa value was 0.802 (95% CI, 0.695-0.91). In the bladder the inter-observer agreement was 96.39% and the kappa value was 0.553 (95% CI 0.056-1). In the USLs the inter-observer agreement was 90.96% and the kappa value 0.583 (95% CI, 0.381-0.784). In the rectovaginal septum the inter-observer agreement was 94.58% and the kappa value 0.739 (95% CI, 0.572-0.905). In the rectovaginal pouch the inter-observer agreement was 88.55% and the kappa value 0.608 (95% CI, 0.443-0.774). In the vaginal fornix the inter-observer agreement was 94.58% and the kappa value 0.726 (95% CI, 0.552-0.901). In the rectosigmoid the inter-observer agreement was 89.76% and the kappa value 0.589 (95% CI, 0.389-0.768).

The results of our study indicate that MRI has a high inter- and intra-observer agreement in the identification of endometriosis located in the ovary, rectosigmoid, and rectovaginal septum, whereas the agreement is suboptimal for the identification of endometriosis located in the USLs.