Pathophysiology
Clinical meaning
Lumbar puncture accesses the subarachnoid space at L3-L4 or L4-L5 (below the conus medullaris at L1-L2 to avoid spinal cord injury). CSF is produced by choroid plexus at ~500mL/day with ~150mL circulating at any time. Opening pressure measured by manometer (normal 10-20 cmH2O). CSF analysis differentiates bacterial (neutrophilic, low glucose, high protein) from viral (lymphocytic, normal glucose) meningitis, SAH, and malignancy.