A patient with cryptococcal meningitis has elevated CSF opening pressure of 45 cm H2O. CSF protein is 120 mg/dL and glucose is 35 mg/dL (serum 110 mg/dL). The primary site of CSF reabsorption in normal physiology — and its impairment in this context — involves:

• A Choroid plexus reabsorbs 80% of CSF; inflammation impairs this active transport
• B Arachnoid villi (granulations) projecting into the dural venous sinuses reabsorb CSF by pressure-dependent bulk flow; meningeal inflammation impairs these granulations ✓
• C Ependymal lining of ventricles reabsorbs CSF through aquaporin-4 channels; inflammation downregulates these channels
• D Cerebral lymphatics along perivascular spaces (glymphatic system) are the primary route; inflammation occludes these channels

Explanation

CSF is produced primarily by the choroid plexus (~500 mL/day, with total CSF volume ~150 mL, turning over ~3-4×/day). Reabsorption occurs predominantly through arachnoid villi (granulations) — finger-like projections of arachnoid mater into the dural venous sinuses (superior sagittal sinus and transverse sinuses). Flow across arachnoid villi is pressure-dependent and occurs when CSF pressure exceeds venous sinus pressure. In cryptococcal meningitis, protein and fungal cellular debris block arachnoid villi and disrupt reabsorption, causing communicating hydrocephalus and elevated ICP. The glymphatic system plays a role in brain waste clearance but is not the primary reabsorption route.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.