Differences in signal intensities of temporomandibular joint (TMJ) effusion on fluid-attenuated inversion recovery (FLAIR) images

Objectives Joint effusion is demonstrated by high signal intensity in the upper and lower temporomandibular joint (TMJ) spaces on T2-weighted images. The fluid-attenuated inversion recovery (FLAIR) technique can be applied to analyze joint effusion in the TMJ. FLAIR signal intensity can be more sensitively influenced by the contents of joint effusion than T2-weighted signal intensity. The purpose of this study was to analyze the signal intensity of joint effusion on FLAIR images and to investigate the changes in joint effusion contents according to the status of TMJ disorders. Methods A total of 48 joints (45 patients) with joint effusion were investigated by magnetic resonance (MR) imaging. Regions of interest were placed over the joint effusion and gray matter on FLAIR images. The joints were categorized as normal disk position (NL), disk displacement with reduction (DWR), disk displacement without reduction (DWOR), and osteoarthritis (OA). The signal intensity ratio of joint effusion was calculated using gray matter as the reference point. The Kruskal–Wallis test and Steel test were applied. A probability of less than 0.05 was considered statistically significant. Results The median signal intensity ratios of joint effusion differed significantly among the four joint categories ( p = 0.02, Kruskal–Wallis test). The median signal intensity ratio of joint effusion in the OA category was significantly higher than that in the NL category ( p = 0.04, Steel test). Conclusions The present findings suggest that FLAIR images can demonstrate the changes in joint effusion contents according to the status of TMJ disorders.