Temporomandibular joint

Normal anatomy and MRI technique

Magnetic resonance imaging is used for detailed assessment of the TMJ. The standard protocol includes 3 mm parasagittal slices, with the tilt angle aligned to the medial angulation of the condylar head. Proton density (PD)-weighted sequences, as well as T1WI and T2WI, are used during the study. The coronal plane is particularly useful for detecting lateral (medial or lateral) disc displacements.

Normally, the articular disc has a specific biconcave shape (resembling an "hourglass") and shows low signal intensity on tomograms. It must lie strictly between the articular fossa and the anterior part of the condyle in both closed and open mouth positions. Assessing joint space width on a standard radiograph has no diagnostic value for determining disc position.

Articular disc displacement variants

Pathological disc dislocation is a frequent cause of patient discomfort. There are two main mechanisms:

1. Anterior displacement with reduction: with the jaws clenched, the disc is displaced anteriorly, but upon mouth opening, it returns to the correct position over the condylar head. This process is usually accompanied by a characteristic click (click) that can be palpated by the physician.
2. Anterior displacement without reduction: the disc remains permanently anterior to the condyle, and during jaw movements, the head does not translate beneath it. This condition prevents normal condylar translation, causes painful joint locking (locking), and restricts mouth opening range. Prolonged pressure eventually leads to irreversible disc deformation.

Joint effusion can be detected on T2-weighted images. Its presence is traditionally considered a sign of synovitis, although its clinical significance remains controversial: it is characteristic of late stages of displacement without reduction, but is sometimes found in completely painless joints.

Degenerative and inflammatory arthritides

Osteoarthritis develops when the TMJ loses its ability to adapt to loads. Clinically, it may present with pain and crepitus (crepitus). Cone-beam computed tomography (CBCT) is indicated for accurate diagnosis of bone changes, as condyles are often obscured by other structures on panoramic radiographs. Tomograms demonstrate:

• Flattening and sclerosis of the anterosuperior surface of the condyle.
• Marginal osteophytes.
• Focal subchondral cysts (Erosive cysts / Élé's cysts).

Inflammatory diseases also destroy the joint. In rheumatoid arthritis, erosion formation and bone density loss occur, causing the condylar head to become pointed. Children may develop juvenile idiopathic arthritis, which causes intermittent synovial inflammation, renders the condyle radiolucent, and can severely impair mandibular growth.

Traumatic injuries and ankylosis

Isolated fractures of the condylar neck frequently accompany mandibular trauma (e.g., a blow to the chin). From a biomechanical standpoint, the thin neck acts as a stress-shielding zone: by fracturing, it reduces the risk of the condyle protruding into the middle cranial fossa. In a displaced fracture, the fragment is typically pulled anteriorly and medially due to contraction of the lateral pterygoid muscle.

Acute dislocation occurs from trauma to the jaw with the mouth open, whereas recurrent dislocations are characteristic of systemic dysplasias (Marfan and Ehlers-Danlos syndromes). Severe complications of trauma and infections include hemarthrosis and ankylosis (bony fusion), which leads to persistent trismus and requires CT to assess the extent of involvement.

Deep spaces of the suprahyoid region

When analyzing TMJ images, the radiologist also evaluates adjacent soft tissues of the neck. The suprahyoid region is divided by fascial planes into compartments:

• Parapharyngeal space is filled with fat, making it an excellent natural contrast. Displacement of this adipose tissue helps determine the origin of a tumor.
• Parotid space contains the salivary gland, facial nerve, and retromandibular vein.
• Retropharyngeal and danger spaces are indistinguishable on tomograms, but are of critical importance. Infections from these zones can directly descend downward. Therefore, if a retropharyngeal abscess is suspected, the scan range must include the superior mediastinum.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Radiological manifestations of synovial osteochondromatosis of the TMJ (calcified loose bodies).
• Impact of juvenile idiopathic arthritis on mandibular development and growth.
• Differential diagnosis of retropharyngeal abscess and simple edema on MRI.
• Anatomic boundaries and contents of the masticatory and parotid spaces of the neck.

Other topics in the Neuroimaging section

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