CSF sampled simultaneously from the lateral ventricle, the cisterna magna, and the lumbar cistern will show which pattern of total protein concentration?

• A Highest in the lumbar cistern, lowest in the ventricle ✓
• B Highest in the ventricle, lowest in the lumbar cistern
• C Equal at all three sites because protein diffuses freely along the neuraxis
• D Highest at the cisterna magna, lowest in the ventricle

Explanation

CSF protein rises progressively along its caudocranial flow path: approximately 15 to 25 mg/dL in the ventricles, 25 to 35 mg/dL in the cisterna magna, and 15 to 45 mg/dL normally up to about 45 mg/dL in the lumbar sac, reflecting addition of protein during transit. This rostrocaudal gradient explains why lumbar reference ranges are higher than ventricular ones and why a lumbar value must be interpreted against lumbar norms.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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