Foramen Magnum: Sectional Anatomy And Imaging

Part I: Foramen Magnum: thin sectional anatomy with CT and MRIObjective: To study the thin sectional anatomy and CT and MR imaging of Foramen Magnum (FM).Materials and methods: Eight formalin fixed (10%) specimens including head and neck were selected, each specimen was imaged with CT and MRI. 5 specimens were sectioned with frozen section technique, the others were sectioned with plastination. 20 normal subjects who had performed CT and MRI respectively were also selected. Serial thin sections of FM were observed and they were compared with the images of CT and MRI.Results: Serial sections of 3.0mm slice thickness for the axial, coronal and sagittal levels of FM sectioned with frozen section technique were obtained; data set of serial thin sections of 0.25mm and 0.5mm slice thickness for the axial levels sectioned with frozen section technique were obtained; serial sections of 1.0mm slice thickness for the axial, coronal and sagittal levels of FM sectioned with plastination were obtained. The resulting sections demonstrated excellent distinction of bone and joint, ligaments, nerves and blood vessels of FM and their adjacent structures. We found a good overall correlation between sections and images of CT an MRI.Conclusions: In combination with CT and MRI, serial thin sections of FM offers a better understanding of the complex anatomy of FM and provides a morphological basis for imaging diagnosis and therapy of FM. This combined approach is also a valuable tool in learning radiographic anatomy of FM.Part II: Visualization and three dimensional reconstruction of CT in Foramen MagnumObjective: To build digitized visible model of FM, to evaluate the value of three dimensional (3D) reconstruction of CT and reconstructive techniques in FM.Materials and methods: Two formalin fixed (10%) specimens including head and neck were selected, each specimen was imaged with CT and then sectioned with frozen section technique. The 3D CT reconstruction was processed in the CT workstation. 3D visualization of FM was generated from cross sectional images using a personal computerand imaging software. One with axial fracture and atlantoaxial dislocation was also evaluated with 3D CT reconstruction.Results: The final 3D visible model demonstrated structures of FM very well, the structures could be displayed singly or in small groups, could be cut freely and continuously rotated in 3D space at different velocities. 3D CT reconstruction could clearly delineate the bone and joint of FM, also fracture and dislocation of FM, especially with volume rendering technique and surface shaded display technique.Conclusions: The 3D visible model has an obvious advantage in the study of the complex anatomy of FM and offer unique insights into it. 3D CT reconstruction was of important value in diagnosis and therapy of bone and joint diseases of FM.Part III: MRI measurement of Foramen Magnum in vivoObjective: To provide the criterion for imaging diagnosis of FM through MRI measurement.Materials and methods: 60 normal subjects who had performed MRI were grouped according to sex equally. The anteroposterior diameter of the FM (AD), the basilar angle (BA), the length of clivus (LC), the distance between the tonsillar tip and FM (DT), the distance between the tip of odontoid process and Chamberlain's line (DO) were measured on sagittal MRI in all subjects. The data were analyzed statistically.Results: AD, BA, LC, DT and DO of male's (female's) was 37.03 3.28mm (36.32 3.50), 133.70 3.95 (134.93 4.83), 45.79 3.08mm(44.74 2.79), 0.77 1.25mm (1.59 2.19) and -1.50 2.26mm (-0.73 1.53) respectively. There was not significant difference between male group and female group (P>0.05).Conclusions: MRI measurement of FM in vivo aid us to understand the complex anatomy of FM and it is very useful in the diagnosis of FM malformation.Part IV: MRI in the diseases of Foramen MagnumObjective: To analyze the imaging characteristics of diseases of FM and to evaluate the value of MRI in diagnosis of these diseases.