A 35-year-old woman on lithium therapy for bipolar disorder develops headache, nausea, and papilledema. CSF opening pressure is 32 cmH2O with normal cell count and protein. The CSF absorption pathway normally responsible for maintaining ICP homeostasis involves:
- A Ependymal cell reabsorption back into choroid plexus capillaries
- B Lymphatic absorption via perineural sheaths of cranial nerve rootlets predominantly
- C Drainage via arachnoid granulations (pacchionian bodies) into the dural venous sinuses, driven by a CSF-to-venous pressure gradient ✓
- D Trans-ependymal reabsorption into periventricular white matter and then into veins
Explanation
CSF, produced by the choroid plexus (~500 mL/day in adults, total volume ~150 mL, turnover ~3–4 times/day), flows from the lateral ventricles through the foramina of Monro to the third ventricle, aqueduct of Sylvius to the fourth ventricle, and then into subarachnoid cisterns. Reabsorption occurs primarily via arachnoid granulations (villi) that project into the dural venous sinuses (mainly superior sagittal sinus). CSF absorption is driven by a hydrostatic pressure gradient (CSF > venous sinus pressure) and is largely passive. Idiopathic intracranial hypertension (pseudotumor cerebri—suspected in this case) involves impaired arachnoid granulation absorption. Perineural/lymphatic routes account for a minor fraction of CSF absorption.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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Written and medically reviewed by the StethoPrep medical team.