Development of a mathematical model of the cervical spinal canal and its use in detecting early pathologic changes

Detection of subtle osseous changes on plain film roentgenograms of the cervical spine is essential in expediting the evaluation of suspected intraspinal tumors. It is our experience that the earliest osseous changes in such cases involve thinning or erosion of the adjacent pedicles and/or lamina and a subsequent increase in the oblique diameter of the cervical spinal canal. A statistical model is established which accurately describes the normal cervical vertebral column in terms of its spinal canal size (sagittal and oblique diameters) as well as pedicle and lamina thickness. Data was obtained from a series of 86 normal exams. Six surgically proven cases of cervical intraspinal tumors were analyzed using this model. Variations from expected normal values reveal statistically significant osseous changes involving thinning of the lamina and increased oblique diameter of the spinal canal, while the sagittal diameter of the canal remains normal. Because of these findings we feel that oblique cervical spine films should be included in the initial evaluation of neural canal tumors.