All patients underwent postoperative MRI which showed excellent decompression of cord and dural sac in all cases.

Conclusion: Quantitative assessment of sagittal dural sac diameters is comparable between lumbar myelography and positional MR imaging.

A small but statistically significant positional dependence of the dural sac diameter was found in the lower lumbar spine.

The midsagittal diameter of the dural sac was measured at the level of the disks on MR images and myelograms.

Dynamic cervical magnetic resonance imaging was used, revealing the classic findings of epidural venous plexus dilation and anterior displacement of the dural sac.