Quantifying Synovial Enhancement of the Normal Pediatric Temporomandibular Joint

Objectives: Juvenile Idiopathic Arthritis (JIA) is the most common type of arthritis in children. JIA of the temoporomandibular joint (TMJ) is often asymptomatic and not detected until irreversible changes have occurred. Magnetic resonance imaging (MRI) with gadolinium to assess the signaling intensity of the synovium has shown promise as a way of assessing TMJ involvement. No age-related normative values of synovial enhancement exist to make accurate comparisons. The purpose of the current study is to assess a new method for measuring synovial enhancement and to establish normal values for for the pediatric TMJ synovium.
Methods: This is a retrospective cohort study of pediatric patients (ages 0-16) undergoing MRIs with gadolinium for reasons other than TMJ symptoms or pathology. Coronal slices of a T1-weighted MRI containing the TMJ were used to assess the ratio of signal intensity of a 0.2mm² region of interest (ROI) within the superior and inferior synovium of the joint space to the longus-capitus muscle. Signal intensity was compared by age. . Data was analyzed using mixed model regression analysis. Intra and inter-rater reliability was assessed using Intra-class Correlation Coefficient (ICC).
Results: 159 subjects were included. Using the ratio of synovium to longus capitus was a reliable method of assessment (ICC > 0.8 for all raters)Synovial enhancement did not vary significantly with age. We estimate a specificity of 95% using a threshold of 1.52, 1.68, and 1.55 for superior, Inferior, and average of superior and inferior synovial cavities respectively.
Conclusions: Comparing signal intensity of the TMJ synovium to the longus capitus is a reliable method for assessment of enhancement. Normative values of this ratio were identified for each age group and can be used as comparison when determining the presence of synovitis in patients with JIA..