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Where does it come from and what does it do?

Cerebrospinal fluid (CSF) is a clear, acellular fluid secreted by the choroid plexus of the lateral, third and fourth ventricles. In adults around 500ml of CSF is produced daily. It bathes the brain and the spinal cord, protecting against trauma. It prevents compression of nearby cranial nerve roots and vessels by the brain and the spinal cord. It also supplies nutrients to the brain and spinal cord and removes waste products.

Where does it go?

CSF flows from the lateral ventricles to the third ventricle via the interventricular foramina and then into the fourth ventricle through the cerebral aqueduct. Some CSF enters the subarachnoid space via the median and lateral apertures, however most gathers in subarachnoid cisterns, which are widened areas of the subarachnoid space.

CSF then finds it way into the venous system by passing through processes called arachnoid granulations which extend from the subarachnoid space into the superior sagittal dural sinus. The size and number of arachnoid granulations increase with age. CSF is absorbed into the venous system when the pressure of the CSF is higher than that of the venous pressure. Normally a balance is maintained between production and reabsorption of the CSF. Water, gases and lipid- soluble molecules from the blood can pass into the cerebrospinal fluid, however large molecules like protein can not.


CSF pressure is measured in mm of water and its normal range is within 70- 180. Respiration and contraction of the heart can alter this slightly. A rise in CSF pressure can occur due to and increase in:

  • intracranial pressure secondary to a tumour
  • blood volume following a haemorrhage or,
  • CSF in hydrocephalus