POSITIONALLY DEPENDENT SPINAL STENOSIS - CORRELATION OF UPRIGHT FLEXION-EXTENSION MYELOGRAPHY AND COMPUTED TOMOGRAPHIC MYELOGRAPHY

Objective: Upright flexion-extension myelography has shown marked vari ation in the severity of lumbar dural sac stenosis during flexion and extension in some patients (''positionally dependent'' stenosis). Axia l computed tomography (CT) of the lumbar spine while the patient is su pine may not demonstrate the maximal spinal stenosis shown by flexion- extension myelography. This study compares the severity of central lum bar spinal stenosis on CT myelograms and on upright flexion-extension myelograms in patients with positionally dependent spinal stenosis. Pa tients and methods: From January 1995 to December 1996, 210 patients u nderwent upright flexion-extension lumbar myelography for the assessme nt of back pain, radiculopathy or neurogenic claudication. In 33 of th ese patients (in whom 39 lumbar levels were seen) there was a differen ce of 30% or more in the diameter of the dural sac seen on anteroposte rior lateral myelograms during flexion and extension. These findings w ere compared with the dural sac compression shown on the CT myelograms for these patients. Results: In 10 of the 33 patients (12 levels), th e CT myelogram underestimated spinal stenosis, as compared with the up right flexion-extension myelogram. In 5 levels, stenosis of 70% or mor e seen on flexion-extension myelography was measured as 50% or less on CT myelography. Conclusion: In patients with positionally dependent s pinal stenosis, CT myelograms may underestimate the severity of the sp inal stenosis, compared with upright flexion-extension myelograms. Whi le upright flexion-extension myelography is not a first-line imaging m odality for patients with spinal stenosis, it should be considered for patients whose symptoms are not explained by routine cross-sectional imaging studies to exclude positionally dependent spinal stenosis.