MRI thresholds for discrimination between normal and mild temporomandibular joint involvement in juvenile idiopathic arthritis

Abstract

Background: Currently there is no consensus agreement on the degree of enhancement in normal temporomandibular joints (TMJ) in children, which makes it difficult for clinicians to distinguish between the presence/absence of mild synovitis. Quantitative measurements of synovial and condylar enhancement may be useful additions to current qualitative methods on early MRI diagnosis and follow up of TMJ involvement in JIA. The purpose of the study is to establish thresholds/tendencies for quantitative measures that enable distinction between mild TMJ involvement and normal TMJ appearance based on the degree of synovial and bone marrow enhancement in JIA patients.

Methods: TMJ MRI examinations in 67 children with JIA and in 24 non-rheumatologic children who underwent MRI for neurologic/orbit indications were retrospectively assessed. As a priori determined TMJs of JIA patients were categorized into three groups by experienced staff radiologists based on the degree of synovial and condylar enhancement: no active disease (rheumatologic control), mild and moderate/severe findings. The signal intensity (SI) of the synovial tissue around each condyle and of the bone marrow was measured to calculate the enhancement ratio (ER) and relative SI change. The ER was calculated using signal to noise ratios, while relative SI change was calculated using signal intensities alone. Quantitative measurements of synovial and condylar enhancement of TMJs with mild or moderate/severe findings were compared with the rheumatologic and non-rheumatologic controls.

Results: Mean ER values were significantly different between the TMJs without active disease and those with mild and moderate/severe synovial enhancement, with highest values in the moderate/severe group (P < 0.0001). Similar findings were seen for condylar enhancement with P < 0.005. Relative SI change was unable to differentiate TMJs with mild synovitis from the two controls (P > 0.10). 27/60 (45%) TMJs without active disease had osteochondral changes. 8/40 (20%) TMJs in the mild group did not demonstrate any synovial thickening.

Conclusions: Quantitative signal to noise ratios of TMJ synovial and condylar enhancement generate thresholds/tendencies, which offer additional information to differentiate mild synovitis from normal TMJs in JIA patients. Osteochondral changes and synovial thickening may not be reliable indicators of active TMJ involvement and should be differentiated from synovial enhancement.

Fig. 1

Regions of interest used to measure the synovial (1) and condylar (2) enhancement. Pre- (a) and post- (b) contrast coronal T1 weighted (W) images with the region of interest and the corresponding post contrast T1W axial image (c) showing that the two coronal images represent similar regions in the sagittal plane

Fig. 2

Representative images of various degrees of synovitis and condylar enhancement on qualitative assessment. Coronal T1 weighted pre- (top) and post contrast (bottom) images of TMJs with: no evidence of synovitis or condylar enhancement (a, b), mild synovitis without condylar enhancement (c, d) and moderate/severe synovitis with mild condylar enhancement (e, f)

Fig. 3

Pre- (a) and post- (b) contrast coronal T1 images of moderate/severe condylar and synovial enhancement

Fig. 4

Graphic representation comparing synovial enhancement ratios of mild JIA, moderate/severe JIA, rheumatologic and non-rheumatologic controls. The enhancement ratios of the two control groups are shown in (a) and (b). The 1.5 T and 3.0 T non-rheumatologic control cases have been grouped together in this figure. TMJs with mild or moderate/severe synovitis are shown in (c) and (d), respectively. It is interesting to note that there is more variability in the range of enhancement ratios for the moderate/severe JIA group as compared to the other groups

Fig. 5

Various cutoff synovial enhancement ratios and their sensitivities and specificities

Fig. 6

Graphic representation comparing condylar enhancement ratios of the same four groups as Fig. 4. The enhancement ratios of the two control groups are shown in (a) and (b). TMJs with mild or moderate/severe condylar enhancement are shown in (c) and (d), respectively. Excluding the outlier for the moderate/severe JIA group concerning condylar enhancement, there is less variability in the range of condylar enhancement ratios for the moderate/severe JIA group compared to synovial enhancement ratios for the same JIA group (Fig. 4)

Fig. 7

Various cutoff condylar enhancement ratios and their sensitivities and specificities