Expansion
Produced by choroid plexus, circulates through the ventricles, absorbed by arachnoid granulations
Expansion
- Production: about 500 ml a day (0.35 ml/min), mostly by the choroid plexus, by active secretion rather than filtration, so it is largely independent of blood pressure
- Total volume: about 150 ml, so turnover is three to four times daily
- Circulation: lateral ventricles, foramina of Monro, third ventricle, aqueduct, fourth ventricle, foramina of Luschka and Magendie, then subarachnoid space
- Absorption: arachnoid granulations into the dural venous sinuses, by bulk flow driven by the pressure gradient, with some through lymphatics
Composition differs from plasma: lower protein, glucose about two-thirds of plasma, lower potassium and calcium, higher chloride and magnesium.
Hydrocephalus
- Communicating: impaired absorption, as after subarachnoid haemorrhage or meningitis
- Non-communicating (obstructive): blockage within the ventricular system, classically at the aqueduct
Acetazolamide reduces production, and is used in idiopathic intracranial hypertension.