What is the normal volume of cerebrospinal fluid (CSF)?
- Overall volume is between 100-150ml
- 2⁄3 within the ventricles
- 1⁄3 within the subarachnoid space around the spinal cord (35ml)
- Equates to ~10% of intracranial volume
What is the pressure of cerebrospinal fluid (CSF)?
- CSF pressure is gravitational and varies with position
- In the lateral position normal pressure is 5-20 cm of H2O
- In the sitting position:
- Pressure in the lumbar region rises to 20-50 cmH20
- Pressure in the cervical region may be sub-atmospheric
Where is CSF produced and through which processes?
- Produced by the four choroid plexuses:
- Located in the two lateral, third, and fourth ventricles
- Highly vascular invaginations of pia mater
- Covered by specialised ciliated ependymal cells
- Produced by a combination of:
- Filtration of plasma through the fenestrated capillaries
- Active transport of solutes
- Control of substances entering is regulated by the blood-CSF barrier (distinct from the BBB)
How much CSF is normally produced?
- Normal rate of production is 0.3-0.4ml/min or 20ml/hour or 500ml/day
- Results in effective replacement of CSF volume 3x daily
- Production is largely independent of ICP:
- Raised ICP is compensated by increased absorption of CSF reducing total volume
- Decreased when CPP <70 mmHg due to reduction in choroid plexus blood flow
How and where is CSF reabsorbed?
- Reabsorbed by the arachnoid granulations:
- Villi arising from the arachnoid mater
- Project into venous sinuses and veins
- Reabsorption occurs throughout the brain and spine
- 90% by villi of the sagittal and sigmoid Dural sinuses
- 10% by spinal villi
- Reabsorption due to differences in pressure between CSF and veins
- Pressure of CSF typically 15 cm H2O and venous blood typical 8cm H2O
- Removal of CSF increases with rising intracranial pressure.
