CT Number Characteristics of Malpositioned TMJ Menisci: Diagnosis With CT Number Highlighting (Blinkmode)

Christiansen EL, Thompson JR, Hasso AN, Hinshaw DB Jr, Moore RJ, Roberts D, Kopp S. CT number characteristics of malpositioned TMJ meniscidiagnosis with CT number highlighting (blinkmode). Invest Radiol 1987;22:315–321.The use of computed tomography (CT) number highlighting (“blinkmode”) for diagnosing malpositioned temporomandibular joint menisci was investigated. By determining the average CT number, standard deviation, and range for specific periarticular tissues, it is possible to tell how much their attenuation values overlap and, therefore, whether there is a sound basis for distinguishing the disc from adjacent tissues.Fresh and fresh-frozen cadaver specimens, were scanned in axial and direct sagittal planes with 1.5-mm thick overlapping soft-tissue sections. CT number measurements were made for tendon, muscle, fat, and meniscus. Patients also were scanned with overlapping 1.5-mm thick axial soft-tissue sections in order to compare the range of CT numbers in cadavers with that in living subjects. Cadaver joints were cryosectioned at 0.5-mm intervals in the same planes as their CT sections, and the tissue sections were compared with their respective CT highlighted sections. For patients the average CT numbers in Hounsfield units were 88 for tendon, 67 for muscle, -25 for fat, and 100 for meniscus. Fresh unembalmed cadavers showed a higher CT average number for tendon and a lower average CT number for fat. The anatomic sections confirmed the meniscal position seen in the highlighted sections in nine of ten joints (90%) and was equivocal in one. Misshapen and malpositioned discs are seen readily with the blinker function; thinned and normal discs are not. The tendinous insertion of the lateral pterygoid muscle may be confused for meniscus in the medial aspect of the TMJ. CT highlighting does not consistently depict meniscal form, most probably because of intrameniscal tissue inhomogeneities.