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Topic

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Intermediate zone of articular disc

The intermediate zone of the articular disc is the thinnest central portion of the fibrocartilaginous disc located between the condyle of the mandible and the temporal bone in the temporomandibular joint (TMJ). This zone plays a crucial role in facilitating smooth movement within the joint by distributing load and reducing friction during jaw movement. It is distinctly narrower compared to the anterior and posterior bands of the disc and is primarily composed of dense, well-organized collagen fibers. Understanding the morphology and imaging characteristics of the intermediate zone is essential for accurate diagnosis of TMJ disorders.

Synonyms

  • Central zone of articular disc

  • Intermediate band of articular disc

  • Central part of TMJ disc

  • Central zone (TMJ disc)

MRI Appearance

  • Proton Density (PD) Sequence

    • The intermediate zone appears as a thin, hypointense (dark) linear structure between the brighter signals of synovial fluid and adjacent bone.

    • It provides clear delineation of the disc’s thinnest segment.

    • Useful for assessing disc position and morphology due to good soft tissue contrast.

  • Short Tau Inversion Recovery (STIR) Sequence

    • The intermediate zone remains hypointense relative to the surrounding joint fluid, which is hyperintense (bright).

    • STIR is sensitive to fluid, so inflammation or edema in the disc or adjacent tissues appears bright, helping differentiate the normal disc from pathologic conditions.

    • The normal intermediate zone should not show increased signal on STIR; a high signal may indicate degeneration or tear.

  • T1-Weighted Sequence

    • The intermediate zone appears as a thin, low-signal (dark) band between the higher-signal condylar bone and temporal bone marrow.

    • T1 is less sensitive for subtle disc changes but helps in anatomical localization.

    • Normal disc tissue, including the intermediate zone, has low to intermediate signal intensity on T1.

MRI images

Intermediate zone of articular disc