Endometrium-myometrium Ratio: A Newly Proposed Diagnostic Parameter on Magnetic Resonance Imaging Assessment of Myometrial Invasion by Endometrial Cancer

In order to improve the accuracy of magnetic resonance (MR)imaging assessment of myometrial invasion by endometrial cancer,the usefulness of a new diagnostic parameter, the endometriummyometrium(EM) ratio has been evaluated. EM ratio is the proportion ofthe widest length of endometrium to the length of myometriummeasured at the same line, this being vertical to the parallelof the long axis of the uterine body in the sagittal plane ofthe MR images. Myometrial invasion was defined as a value ofthe EM ratio > 1 , and the tumor was limited to the endometriumfor values < 1 . In 25 consecutive patients, both the EMratio-based assessment and the well-established junctional zone-basedasessment with T2-weighted MR imaging and enhanced MR imagingwith gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA)were compared with the results from pathological examinationsof postoperative specimens. In identifying moymetrial invasionby endometrial cancer, the sensitivity of the EM ratio-basedassessment was better than that of the junctional zone-basedassessment. The overall sensitivity of the former was 96% inboth the T2-weighted and enhanced MR imaging with Cd-OTPA, whereasthat of the latter was 84% in the T2-weighted MR imaging and72% (P<0.05) in the enhanced MR imaging. The use of the EMratio with MR imaging improves the ability to assess myometrialinvasion by endometrial cancer.