Imaging and pathogenic characteristics of thoracic ossification of the ligamentum flavum complicated with dural ossification

Abstract

Objective To investigate the imaging characteristics and pathogenic manifestations of thoracic ossification of the ligamentum flavum complicated with dural ossification. Methods CT and MRI imaging data of 62 segments from 29 patients with thoracic ossification of the ligamentum flavum (TOLF) treated with en bloc resection of lamina and ossified were retrospectively analyzed. There were 19 males and 10 females, aged 54.9±10.25 years (36-77 years), 16 segments in 11 cases with dural ossification (DO) and 46 segments in 18 cases without DO. The ossified mass shape, the relationship between ossified mas and dura mater on cross section of CT bone window and MRI T2WI, and the ossified mass occupational rate (OR) of the spinal canal were investigated. Pathologic features of TOLF-DO from 2 patients were analyzed by H&E staining. Results The shape of ossified mass was as followed, in 16 segments with DO, 7 segments (43.8%) by CT and 2 segments (12.5%) by MRI showing ossification layer on the dural sac side of ligamentum flavum; 1 segment (6.3%) by CT and 2 segments (12.5%) by MRI showing typical Tram track sign. The relationship between ossified mass and dura mater was that 7 segments (43.8%) by CT and 7 segments (43.8%) by MRI with C sign and 7 segments (43.8%) by CT and 8 segments (50.0%) by MRI with V sign. The ossified mass OR was 60.5%±13.0% in the group with DO and 42.2%±12.3% in the group without DO. There was a significant difference between the two groups (t=5.192, P<0.001). Among the 16 segments with DO, the ossified mass OR of 7 segments with C sign was 68.8%±12.8% and that of the other 9 segments without C sign was 54.39%±9.9%. There was significant difference between the two groups (t=2.45, P=0.028). Histological examination showed that there were two pathological phenomena in the dura tissue adjacent to ossified mass. The one, there were fibrocartilage, cartilage and osteogenesis in the dura mater. The other, the unossified dura mater fused with the ossified mass but with clear histological demarcation, while the dura mater on the ventral side of the ossified ligamentum flavum atrophies or disappeared. Conclusion The occurrence of dural sac ossification is associated with the ossification of ligamentum flavum beginning at the side of the dural sac and the persistent thickening of the ossified mass. The pathological manifestations of DO are ossification of dural tissue or fusion of dural with ligamentum flavum ossification. Key words: Ligamentum flavum; Ossification, heterotopic; Dura mater; Tomography, X-ray computed; Magnetic resonance imaging; Histology