Study design: Lumbar MRI of normal adults. Image analysis to measure lumbar CSF volumes at rest and during physiologic maneuvers.
Objectives: 1) Validate an MRI technique to measure CSF volumes, 2) use this technique to measure the resting volume of lumbar CSF, 3) measure changes in CSF volume with physiologic maneuvers, and 4) demonstrate the anatomic basis for these volume changes.
Summary of background data: Studies using radiograph and radionuclide myelography in dogs and humans in the 1960s-1980s qualitatively showed decreases in spinal CSF volume with physiologic maneuvers. Theories were proposed to explain these changes, but they could not be confirmed because only the contrast-laden CSF was visualized using these techniques.
Methods: Four adult volunteers had lumbar MRI using a fat-saturated T2-weighted three-dimensional fast spin-echo sequence. Quantitative analysis of images was used to measure lumbar CSF volume; the technique was validated using a water phantom. Lumbar CSF volume was measured 1) at rest, 2) with hyperventilation, 3) with abdominal compression, and 4) with both hyperventilation and abdominal compression.
Results: Resting lumbar CSF volume ranged from 28 to 42 mL. Reversible changes in lumbar CSF volume resulting from physiologic maneuvers are visualized by MR myelography and measured. The volume change (10% reduction in volume with hyperventilation, 28% with compression, and 41% with combined hyperventilation and abdominal compression) is directly visualized to be caused by engorgement of the epidural venous plexus, compressing the thecal sac.
Conclusions: MRI provides a noninvasive means to measure spinal CSF volume and demonstrates the anatomic basis of physiologic volume changes. This has important implications for spinal anesthesia.