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.
Diagnosis & workup
Diagnostics & workup: - Order CT head before LP if increased ICP suspected (papilledema, focal deficits) - Order CSF analysis: cell count, glucose, protein, Gram stain, culture - Order opening pressure measurement via manometer - Order CSF cytology if malignancy suspected - Order blood glucose simultaneously for CSF:serum glucose ratio - Order oligoclonal bands and IgG index if MS suspected - Order xanthochromia assessment if SAH suspected
Risk factors: - Increased intracranial pressure (herniation risk) - Coagulopathy/thrombocytopenia - Local infection at puncture site - Spinal deformity - Obesity - Anticoagulant therapy - Previous lumbar surgery