CSF formed by the choroid plexus circulates through the ventricular system and subarachnoid space. Through which structures is it principally reabsorbed into the venous system?

• A Perivascular spaces draining into the deep cerebral veins
• B Choroid plexus of the fourth ventricle
• C Arachnoid granulations projecting into the superior sagittal sinus ✓
• D Pia mater along the dorsal roots of the cauda equina

Explanation

Arachnoid granulations, herniations of arachnoid through the dural wall of the superior sagittal sinus and other venous sinuses, act as one-way valves allowing bulk flow of CSF into venous blood down a pressure gradient. Obstruction of this route raises intracranial pressure with normal ventricular size, as seen in idiopathic intracranial hypertension. The choroid plexus produces rather than absorbs CSF, and perivascular glymphatic drainage plays only a minor supplementary role.

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

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