|ESSR 2016 / P-0048|
|MR-Assessment of the Temporomandibular Joint - Where to look and what to look for|
Imaging findings OR Procedure Details
Standard MR-protocols for imaging the TMJ consist of PD and/or T2w sagittal oblique slices in closed and maximum open mouth position as well as coronal oblique in closed mouth position (figure 1) for evaluation of the intraarticular structures and disc position. At least one plane in T1 is necesseray to fully evaluate the bony structures. T2w with fatsaturation helps in detecting joint effusion and together with T1 in evaluating bone marrow edema. Dynamic TMJ-series can be acquired as fast spinecho PD or T2 in cine mode. Optimal slice orientation is shown in figure 1, sagittal oblique along long axis of condyle, coronal oblique perpendicular to the long axis.
Normal gross anatomy of the TMJ and MR-correlation is presented in figure 2, 3 and 4 for closed and open mouth position. The posterior attachment of the articular disc consists of macroscopically three parts, the bigger temporal and condlyar part and the smaller intermediate part. On MR - if the resolution and image quality is superior - we can often see the so called bilaminar zone with superior and inferior (temporal and condylar) part of posterior disc attachment. While opening the mouth, both, the condyle and the intraarticular disc translate together in a forward direction to their anterior position upon the articular eminence.
The most common disorder of the TMJ is "internal derangement" with partial or total displacement of the intraarticular disc. Anterior (sagittal plane) as well as mediolateral (coronal plane) disc displacement in closed mouth position can be categorized into 3 levels, as seen on figure 5 and 6. MR-examples of partial and total anterior and mediolateral disc displacements are given in figures 7 and 8.
Opening the mouth in a case of disc displacement can result in recapture or no-recapture of the displaced intraarticular disc (figure 7, 8) with a correct or incorrect position of the disc in open mouth position. Advanced internal derangement can lead to degenerative osteoarthritis with typical features as flattening of the condyle (figure 8, closed mouth), osteophytes, joint space narrowing, subchondral cysts, erosions and subchondral edema (figure 9).
Less common disorders of the TMJ inlcude inflammatory changes (rheumatoid or juvenile arthritis), neoplastic lesions (metastasis, primary tumors rare) or traumatic changes. An example of inflammatory osteoarthritis of the TMJ is given in figure 10. MR and CT are complementary modalities in less common TMJ disorders except in trauma, where CT is the modality of choice.
Structured reporting of a TMJ-scan inlcudes statements abouts:
1. Condylus: position, morphology (normal, flattened, erosions, osteophytes), bone marrow
3. Disc morphology and signal: normal bow tie, thinning, signal changes
2. Disc position: normal, anterior displacement (sagittal plane), medial or lateral dispclacement (coronal plane)
4. Joint and disc motion: normal, reduced or no anteriortranslation of condyle, recapture or no-recapture of disc (open mouth sagittal plane, dynamic series)
5. Joint Effusion
6. Masticator space and surrounding tissue: incidental findings or other nearby causes for TMJ-discomfort