[Value of MRI in the visualization of the meniscus in temporomandibular joints]

Modern imaging techniques, among which nuclear magnetic resonance currently ranks first, have made it much easier to understand the internal disorders of the temporomandibular joint. While computed tomography still is the ideal technique for all bony affections in the articular region, especially for injuries. MRI now is an essential first-intention complementary examination. It allows assessing the location of the meniscus and very well defines the pathology being explored: reducible or irreducible dislocation of the meniscus, either purely anterior or anterolateral, the latter being better visible on coronal views (which are not systematically taken). The examination includes T1-weighted parasagittal views perpendicular to the axis of the condyle, taken with a surface coil (knee coil). Two sequences are performed, one with the mouth open and one with the mouth shut. The meniscus appears as a biconcave hypointense signal, which normally lies on the head of the condyle both when the mouth is open and when it is shut. T2-weighted sequences have the advantage of revealing possible effusion or intra-articular adhesion between the capsule and the synovial membrane. They may also better demonstrate a possible myxoid degeneration of the meniscus. The considerable increase in scanning time required for these sequences accounts for their unfrequent use. The condition of the bone can also be assessed, but we find MRI less accurate than direct sagittal CT scans. The future prospects include shorter imaging times owing to fast-imaging sequences (short T1 with partial flip angle).