Changes in cross-sectional measurements of the spinal canal and intervertebral foramina as a function of body position: In vivo studies on an open-configuration MR system

OBJECTIVE, The purpose of this study was to evaluate physiologic changes of the cross-sectional area of the spinal canal and neural foramina in young asymptomatic volunteers. SUBJECTS AND METHODS. Twelve asymptomatic volunteers were examined in a 0.5-T open-configuration MR system. T2-weighted fast spin-echo sequences were obtained in upright neutral, upright flexed, upright extended, and supine extended positions. The cross-sectional area of the spinal canal and the thickness of the ligamentum flavum were measured on angled axial images at the L4-L5 level. The anteroposterior diameter of the spinal canal and cross-sectional areas of the neural foramina were measured on sagittal images from L1 to S1, RESULTS. At disk level, the cross-sectional area of;he spinal canal vaned significantly between body positions, most notably between the upright flexed (mean, 268 mm(2)) and the upright extended (mean, 224 mm(2)) positions (p < .0001), The maximum thickness of the Ligamenta flava increased in the extended positions (p < .0001). The cross-sectional area of the neural foramina underwent position-dependent variations of as much as 44.4%. The smallest cross-sectional areas were found in the extended positions. CONCLUSION. In asymptomatic volunteers, MR imaging is able to show position-dependent changes in the cross-sectional areas of the spinal canal and the intervertebral foramina, The extended positions best reveal important findings.