CT and MRI characteristics of ossification of the ligamenta flava in the thoracic spine

The purpose of this study was to compare MRI findings with CT findings of m ass-forming calcification/ossification of the thoracic ligamenta flava (OTL F). Twenty-one Chinese patients presented with clinical evidence of chronic and progressive thoracic spinal cord compression which included: difficult y in walking; weakness; and/or numbness of the extremities, back pain, and lower extremity paresthesias. Axial and sagittal Tl-weighted imaging (T1WI) and T2-weighted imaging (T2WI) were performed through the thoracic spine o n a 1.0-T Impact unit (Siemens, Erlangen, Germany). Axial CT was obtained w ith 5-mm contiguous sections through the thoracic region. Decompressive sur gery with resection of the OTLF were carried out in all patients. Low signa l intensity of the mass-forming OTLF was demonstrated at a single level (n = 1) or at multiple levels (n = 20) on both T1WI and T2WI. The distribution of OTLF was bilateral at all levels identified in 6 cases, unilateral at a ll levels in 5 patients, and both unilateral and bilateral at different lev els in 10 cases. Ossification of the thoracic ligamenta flava involved the upper thoracic spine (T1-4) in 3 cases, midthoracic spine (T5-8) in 3 cases , lower thoracic spine (T9-12) in 10 cases, and more than one thoracic spin al subregion in 5 cases. Computed tomography confirmed the MR findings rega rding the location and distribution of OTLF in all cases, as well as the as sociated evidence of central spinal canal stenosis. In addition, 5 patients revealed associated ossification of the posterior longitudinal ligament. A ll patients demonstrated gradual, but incomplete, clinical improvement of t he radiculomyelopathy following decompressive surgery. Ossification of the posterior longitudinal ligament resulting in thoracic central spinal canal stenosis and clinical radiculomyelopathy is not uncommon in the Asian peopl e. Ossification of the thoracic ligamenta flava can be accurately evaluated equally well by CT and MR with regard to level(s) and side(s) of involveme nt, as well as to the relative degree of central spinal canal stenosis and the associated compression of the thoracic spinal cord.