MR Imaging of the TMJ: A Pictorial Essay

Chris Roth, MD; Robert J. Ward, MD; Scott Tsai, MD; Wendy Zolotor, MD; Richard Tello, MD, MSME, MPH

Disclosures

Appl Radiol. 2005;34(5):9-16. 

In This Article

Internal Derangement

An abnormal position of the disk constitutes internal derangement. The cause is usually not elicited; postulated causes include trauma, malocclusion, bruxism, stress, and primary osseous abnormalities.[3] The disorder is 3 to 5 times more common in females and commonly manifests by the fourth decade. Initially, there is anterior displacement of the disk that reduces with jaw opening. As the fibers of the posterior bilaminar zone loosen, the disk no longer reduces. Disk deformity ultimately results and secondary osseous and articular abnormalities ensue.

Abnormal disk morphology and position are the earliest and most sensitive signs of internal derangement. The earliest finding is often T2 hyperintensity in the bilaminar zone. Disk degeneration is reflected as desiccation or loss of signal that is typically intermediate on T1weighted images and hyperintense on T2-weighted images.[9] Disk deformity may also develop; the disk may become biconvex, thickened, or folded among other previously described morphologic abnormalities. Late in the course of the disease, the disk or bilaminar zone may perforate.

The position of the disk must be assessed first on sagittal closed-mouth images. The disk most commonly displaces anteriorly or anterolaterally. However, the disk can become displaced in any direction; medial and lateral disk displacements account for up to 30% of cases.[4] Early in the course of the disease, the disk may reduce in position (Figure 3). With progression, the disk does not reduce during mouth opening (Figure 4). Finally, an irreducible disk may become adherent and remain fixed anteriorly during both mouth opening and closing (Figure 5). Fluid may accumulate within the joint. Cortical erosions, followed by condylar head flattening and anterior osteophytosis, develop. Subchondral marrow edema followed by low-signal sclerosis is the natural progression.

A 32-year-old man with a displaced, but reducible, disk. (A) Closed-mouth sagittal T1-weighted image shows the anteriorly displaced disk (arrow). (B) Open-mouth sagittal T1-weighted image shows the normal position of the disk (arrow) between the mandibular condyle (arrowhead) and articular eminence. A B A B

A 32-year-old man with a displaced and irreducible disk. (A) Closed-mouth sagittal T1-weighted image shows the anteriorly displaced disk (arrow). (B) Open-mouthed sagittal T1-weighted image shows the normal translation of the mandibular condyle without a reducible disk (white arrow) that maintains a position anterior to the condyle (black arrowhead).

A 42-year-old woman with a displaced, irreducible, and adherent disk. (A) Closed-mouth sagittal T1-weighted image shows the anteriorly displaced disk (arrow). (B) Open-mouth sagittal T1- weighted image shows translation of the mandibular condyle (arrowhead) without a reducible disk (small arrow) that is unchanged in position and adherent to the articular eminence (large arrow).

Internal derangement An abnormal position of the disk constitutes internal derangement. The cause is usually not elicited; postulated causes include trauma, malocclusion, bruxism, stress, and primary osseous abnormalities. 3 The disorder is 3 to 5 times more common in females and commonly manifests by the fourth decade. Initially, there is anterior displacement of the disk that reduces with jaw opening. As the fibers of the posterior bilaminar zone loosen, the disk no longer reduces. Disk deformity ultimately results and secondary osseous and articular abnormalities ensue.

Abnormal disk morphology and position are the earliest and most sensitive signs of internal derangement. The earliest finding is often T2 hyperintensity in the bilaminar zone. Disk degeneration is reflected as desiccation or loss of signal that is typically intermediate on T1-weighted images and hyperintense on T2-weighted images.9 Disk deformity may also develop; the disk may become biconvex, thickened, or folded among other previously described morphologic abnormalities. Late in the course of the disease, the disk or bilaminar zone may perforate.

The position of the disk must be assessed first on sagittal closed-mouth images. The disk most commonly displaces anteriorly or anterolaterally. However, the disk can become displaced in any direction; medial and lateral disk displacements account for up to 30% of cases.4 Early in the course of the disease, the disk may reduce in position (Figure 3). With progression, the disk does not reduce during mouth opening (Figure 4). Finally, an irreducible disk may become adherent and remain fixed anteriorly during both mouth opening and closing (Figure 5). Fluid may accumulate within the joint. Cortical erosions, followed by condylar head flattening and anterior osteophytosis, develop. Subchondral marrow edema followed by low-signal sclerosis is the natural progression.

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