CT evaluation of caudal versus lumbar access to the intradural space

Background: Percutaneous intraspinal navigation is a new procedure that enables visualization of the central nervous system using a lumbar puncture technique. Past research shows promising potential, but is limited by damage to expensive fiberscopes due to the sharp angle of manipulation at L3-L4. Our objective in this study is to analyse the feasibility of a novel access through the sacral hiatus to eliminate this problem. Methods: We retrospectively reviewed computed tomography images of the sacrum of 132 subjects, of which nine were excluded either secondary to incomplete imaging of the sacrum or variant anatomy that precluded any possible measurements. Of the remaining 123 patients, we measured kyphotic and lordotic curvature of the sacral canal in comparison to the angle of lumbar puncture. We also measured the anteroposterior diameters of the sacral canal at the distal, middle, and proximal portions. Results: There were no significant differences according to sex or age. The kyphotic angle was a wide angle with a mean value of 167.89±11.71°. The lordotic angle had a mean value of 133.35±7.84°, making it 25.52° more obtuse than the average angle for lumbar puncture. The smallest diameter of the sacral canal was at the sacral hiatus and had a mean value of 4.49±1.66 mm. Conclusion: The size and anatomy of the sacral canal is feasible for PIN procedure and appears more favorable as compared to entry via lumbar puncture. The canal opening is wide enough to accommodate most small-diameter fiberscopes without difficulty, and the angles are obtuse enough to limit damage to the expensive fiberscopes.