TMJ meniscus and bilaminar zone: MR imaging of the substructure--diagnostic landmarks and pitfalls of interpretation.

Identification of the junction of the posterior band with the bilaminar zone is important to detect anterior displacements of the temporomandibular joint (TMJ) meniscus on magnetic resonance (MR) images. However, significant differences in tissue characteristics within the meniscus itself may cause a confusing appearance that is not easily reconciled with available anatomic references. Six cadaveric TMJ specimens were imaged sagittally at 1.5 T with various combinations of repetition time and echo time and with use of both standard surface coils and a specially developed solenoidal specimen coil. Corresponding histologic sections were correlated with the in vitro MR images to identify the anatomic structure and tissue characteristics. Comparison of these in vitro images with in vivo images of 100 joints identified a vertical, linear, low-signal-intensity band as an important landmark of the junction of the posterior band and bilaminar zone. Recognition of the signal-intensity characteristics of the center and the surfaces of the posterior band as well as the appearance of the insertion of the bilaminar zone also increased confidence of visualization and helped avoid possible false-positive diagnoses.