• B Coulier.
• Service d'Imagerie Médicale, Clinique St Luc, Bouge, Namur, Belgium.
• JBR-BTR. 2000 Apr 1;83(2):61-7.

AbstractThough CT and MRI are presently the most frequently required noninvasive methods for the diagnosis of lumbar spinal stenosis (LSS), imaging of a supine patient may not demonstrate the maximal spinal stenosis shown by upright flexion-extension myelography (FEM). Our prospective study tries to assess the averaging discrepancies between the supine CT-myelograms and the upright FEM in 50 patients. Considering all L2-L3 to L4-L5 vertebral levels, a mean underestimation of 16% of the diameter of the dural sac is found when and CT-myelograms are compared with extension myelography. Meaningful clinical discrepancies of 30% and more are found in 15.5% of these levels, the L5-S1 level remaining rather stable. Marked variations--but of less critical diagnostic interest--are also found between flexion and extension with, for flexion, a mean underestimation of 20% and discrepancies of 30% and more in 18.33% of L2-L3 to L4-L5 levels. Paradoxical results--CT diameters inferior to extension diameters--concern 22% of all studied levels but are of little clinical significance; only small discrepancies of 8.2% are found in a majority of non stenotic levels--with a maximal intensity for the L5-S1 level rarely implicated in LSS-. Measuring the mean cross-sectional surface occupied by the neural elements in the dural sac on CT-myelograms (189 evaluations), our study also empirically confirms a 60 to 80 mm2 are++ being the landmark of absolute stenosis. Finally, measurements of the cross-sectional area of the dural sac-109 L2-L5 levels inferior to 8.5 mm on CT myelograms or CT studies--show a large dispersion of areas for diameters superior to 6.5 mm and confirm cross-sectional area of the dural sac to be a much reliable parameter of LSS than diameter of the dural sac. We conclude that upright FEM--while not a first-line imaging modality for LSS--should be performed to exclude functional or dynamic position-dependent LSS in the patients whose symptoms are not explained by routine cross-sectional imaging, as long as no other upright technology is available.

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