Computed tomography of posterior longitudinal ligament ossification: its appearance and diagnostic value with special reference to thoracic lesions.

An earlier review of the lateral chest radiographs of 8,610 Hiroshima and Nagasaki Adult Health Study subjects revealed 48 persons with posterior longitudinal ligament ossification (PLLO) in the thoracic region. Seven additional PLLO cases detected outside that observation period brought the total to 55. Among them, 15 patients with neurological signs and/or the greatest degree of thoracic PLLO were selected for computed tomography (CT) of the spine in the present study. Computed tomography proved extremely valuable in identifying the location, shape, and severity of PLLO. In two cases, CT differentiated some lesions previously regarded to be PLLO as actually due to hypertrophic margins of vertebral bodies. Possible explanations are included for the development of the laminated or tandem type PLLO, and PLLO that is located laterally rather than in midline.