Dynamic physiologic changes in lumbar CSF volume quantitatively measured by three-dimensional fast spin-echo MRI

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 thi s 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 end radionuclide myelo graphy 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 co ntrast-laden CSF was visualized using these techniques. Methods. Four adult volunteers had lumbar MRI using a fat-saturated T2-weig hted three-dimensional fast spin-echo sequence. Quantitative analysis of im ages was used to measure lumbar CSF volume; the technique was validated usi ng a water phantom. Lumbar CSF volume was measured 1) at rest, 2) with hype rventilation, 3) with abdominal compression, and 4) with both hyperventilat ion and abdominal compression. Results. Resting lumbar CSF volume ranged from 28 to 42 mL. Reversible chan ges in lumbar CSF volume resulting from physiologic maneuvers are visualize d by MR myelography and measured. The volume change (10% reduction in volum e with hyperventilation, 28% with compression, and 41% with combined hyperv entilation and abdominal compression) is directly visualized to be caused b y 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.