Qualitative assessment of Gadolinium-enhanced MRI (magnetic resonance imaging) is the typically used diagnostic technique for the diagnosis of temporomandibular joints (TMJs) synovitis associated with Juvenile Idiopathic Arthritis (JIA). The authors of this study were successful in applying the much needed, quantitative analysis of synovial enhancement to MRIs of patients with JIA.

Juvenile Idiopathic Arthritis (JIA) frequently affects the temporomandibular joints (TMJs) and is often undetected by history, examination and plain imaging. Qualitative assessment of gadolinium-enhanced magnetic resonance images (MRI) is currently the standard for diagnosis of TMJ synovitis associated with JIA. The purpose of this study is to apply a quantitative analysis of synovial enhancement to MRIs of patients with and without JIA to establish a disease threshold, sensitivity and specificity for the technique.

This is a retrospective case-control study of children (≤16 years) who had MRIs with gadolinium including the TMJs. Subjects were divided into a “JIA group” and a “control group.” From a coronal T1-weighted image, a ratio (“enhancement ratio”, ER) of the average pixel intensity within three 0.2mm2 regions of interest (ROI) in the TMJ synovium to that of a 50mm2 ROI of the longus capitis muscle was calculated. Receiver operating characteristic (ROC) curves were used to determine sensitivity and specificity. Inter- and intra-examiner reliabilities were evaluated with Bland-Altman plots and two-way mixed, absolute agreement intraclass correlation coefficients (ICC).

There were 187 and 142 TMJs included in the JIA and control groups, respectively. An ER threshold of 1.55 had a sensitivity and specificity for detecting synovitis of 91% and 96%, respectively. Inter- and intra-examiner reliability were excellent.

Calculating a ratio of pixel intensity between TMJ synovium and the longus capitis muscle is a reliable way to quantify synovial enhancement. An ER of 1.55 differentiates normal TMJs from those affected by inflammatory arthritis.