Zones of the uterus: discrepancy between US and MR images

The location of the boundaries among the endometrium, inner myometrium (dark), and outer myometrium (intermediate or bright) were compared on T2-weighted magnetic resonance (MR) and intravaginal ultrasound (US) images obtained within 24 hours of each other. Twelve women with normal reproductive cycles underwent a total of 21 pairs of examinations. The endometrium, inner myometrium (junctional zone), and outer myometrium were measured by three independent observers. The endometrial thickness was thinner with MR imaging (6.5 mm with MR imaging vs 7.9 mm with US early in the cycle [P = .001]; 9.9 mm with MR imaging vs 11.3 mm, respectively, late in the cycle [P = .045]). The junctional zone was thicker with MR imaging (4.4 vs 2.3 mm early [P less than .001]; 3.9 vs 2.2 mm late [P = .003]). The combined thickness of the endometrium and junctional zone was thicker with MR imaging (15.5 vs 12.7 mm early [P = .002]; 17.3 vs 15.8 mm late [P = .064]), confirming that the boundary between the junctional zone and outer myometrium is different with MR imaging versus US.