Cerebrospinal Fluid (CSF) Production and Absorption
CSF is produced by the choroid plexus that lines the ventricles.
Choroid plexus = Infoldings of blood vessels of piamater + Modified ciliated ependymal cells
Tight junctions of the choroid plexus cells form Blood-CSF barrier.
CSF is reabsorbed by arachnoid granulations to enter dural venous sinuses.
Turnover of entire volume of CSF is 3-4 times per day.
- There is approximately 120mL (average 90-150 ml) of CSF at any one time.
- It is formed and reabsorbed at a rate of 0.33 mL/min.
- During Lumbar puncture (LP), depending on the purpose, the amount of fluid withdrawn ranges few milliliters to as much as 40 ml; however, in a typical lumbar puncture roughly 12mL of fluid is withdrawn.
- What percent of the CSF in the nervous system is this? 10%.
- And how quickly is it replaced? In about half-an-hour (or, more exactly, in 36 min).
Normal Composition of CSF
Clear fluid, isotonic with serum (290-295 mOSm/L)
Mononuclear cells upto 4 cells/µl
Glucose levels = 66% of blood glucose level (50-75 mg/dl)
Protein levels = 15-45 mg/dl
CSF pressure = 80-180 mm of water
Compared to serum:
- ↓↓ protein and immunoglobulins
- ↓ [glucose]
- ↓ pH (7.33 compared to arterial blood 7.4 and venous blood 7.36)
- equal [Na+]
- ↑ [Cl-] and [Mg2+]
- ↓ [K+], [Ca2+], [HCO3-]
Ventricular System and CSF circulation
- CSF from the lateral ventricles passes through the interventricular foramina of Monro into the 3rd ventricle.
- CSF from the 3rd ventricle passes through the cerebral aqueduct into the 4th ventricle.
- 4th ventricle is continuous with the spinal canal which progressively obliterates by the 2nd decade.
- CSF from the 4th ventricle passes through the 2 lateral (foramen of Luschka) and 1 middle (formane of Magendie) into the subarachnoid space.
Functions of CSF
- Cushion of the brain
- Transports hormones and hormone releasing factors
- Removes metabolic waste products through absorption
CSF composition in meningitis
Choroid plexus papilloma = Overproduction of CSF = Communicating hydrocephalus
Arachnoid granulations adhesions (post-meningitis) = Decreased CSF absorption = Communicating hydrocephalus
Obstruction at foramen of monro or cerebral aqueduct or formane of Magendie or Luschka = Non-communicating hydrocephalus
CSF not absorbed by arachnoid villi = Chronic dilation of ventricles and normal CSF pressure = Normal pressure hydrocephalus
- Wet: Urinary incontinence
- Wobbly: Apraxic gait
- Wacky: Dementia
Brain atrophy = Increased CSF = Hydrocephalus Ex-vacuo
- Alzheimer’s disease
- Advanced HIV
Pseudotumor Cerebri (Benign Intracranial Hypertension)
- Due to increased resistance to CSF at arachnoid villi
- Occurs in obese young women
- Papilledema without mass, elevated CSF pressure, deteriorating vision
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