Adenomyosis: specificity of 5 mm as the maximum normal uterine junctional zone thickness in MR images

Our objective was to investigate the specificity of the criterion stating that a diagnosis of adenomyosis can be made confidently from MR images of the uterus when the junctional zone is thicker than 5 mm. Twenty clinically normal women volunteers (chosen by strict criteria) underwent MR imaging of the uterus. Images were independently evaluated by two experienced observers who measured the greatest thickness of the junctional zone in the anterior, posterior, right and left walls of the uterine corpus and at the top of the fundus. The mean value of the greatest junctional zone thickness (averaged for both observers) was 4.4 +/- 2.1 mm (mean +/- SD, range, 1-9 mm) for the anterior and posterior walls of the corpus, 4.3 +/- 2.1 mm (range, 1-10 mm) for the right and left walls, and 2.3 +/- 1.1 mm (range, 1-5 mm) for the fundus. At least one region of the junctional zone was found to be thicker than 5 mm by at least one observer in 13 (65%) of the 20 subjects; at least one region was found to be thicker than 5 mm by both observers in eight (40%) subjects. At least two regions were measured as thicker than 5 mm by both observers in six (30%) subjects. Serial studies of three volunteers showed transient irregular focal or diffuse thickening (up to 12 mm) of the junctional zone and focal myometrial bulging, probably due to myometrial contractions. Our results suggest that if a diagnosis of adenomyosis is based solely on junctional zone thickness in MR images, 5 mm should not be assumed as the upper limit of normal, because this assumption may result in a high false-positive rate.