CSF and Intracranial Pressure

Question 1

What is cerebral-spinal fluid?

Answer 1

• Clear colourless fluid
• Found in ventricles of the CNS and the sub-arachnoid space
• Approximately 125ml in total
• Approximately 500ml made each day
• Process of CSF production and drainage

Question 2

Describe CSF production and circulation

Answer 2

-Made in the choroid plexus
-Most production is in the lateral ventricles
-Flows through the Interventricular foramina (foramina of Monro) to 3rd ventricle
-Cerebral aqueduct to 4th ventricle
-4 routes to the sub-arachnoid space
=Central canal of spinal cord
=Median aperture (foramen of Magendie)
=2 x Lateral apertures (foramina of Luschka)
-Absorbed in cerebral veins (dural venous sinuses) via arachnoid granulations

Question 3

What are the functions of CSF?

Answer 3

• Buoyancy =(gross brain weight 1.4-1.5 kg, net 25-50 g) would impair flow of blood to brain
• Protection from physical injury (”shock absorber”)
• Maintenance of brain perfusion (reduction in CSF production drops ICP, encouraging cerebral perfusion)
• Homeostasis (neurotransmitter exposure)
• Clearing waste (lymphatics)

Question 4

What is the Monro-Kellie Doctrine?

Answer 4

• The skull is a “bony box”
• There are 3 non-compressible components (brain, blood, CSF)
• Increasing volume of one component requires a reduction in one or both others to maintain the same ICP (intracranial pressure)

Question 5

What are the proportions of the 3 non-compressible components?

Answer 5

• CSF volume= 150ml (10%)
• Blood volume= 150ml (10%)
• Brain parenchyma volume= 1400ml (80%)

Question 6

What is the normal pressure range of CSF?

Answer 6

=10-18 cm H2O lying on side

=20-30 cmH2O sitting up

Question 7

What is the composition of CSF?

Answer 7

• RBC = 0
• WBC < 5 / μl
• Protein 0.1 – 0.45 g/l
• Glucose >50% blood level

Question 8

What are the special tests of CSF?

Answer 8

• Gram stain & culture= micro bacteria
• Oxyhaemoglobin & bilirubin= blood products
• Oligoclonal bands= immune system activity

Question 9

How is CSF sampled?

Answer 9

Lumbar puncture

Question 10

What are the features of high Intracranial pressure?

Answer 10

• Headache: worse when: lying down, coughing, sneezing, stooping, straining
• Visual obscurations: grey/black out with ICP spikes

Question 11

What are the causes of high intracranial pressure?

Answer 11

1) CSF overproduction:
Idiopathic intracranial hypertension (IIH)
2) Blocked CSF circulation:
“Obstruction” (physical mass, intracerebral bleeding)
3) Blocked CSF drainage:
Very high protein in CSF (subarachnoid haemorrhage, TBM- tuberculous meningitis)
Cerebral venous sinus thrombosis (CVST)
4) An increase in blood or “brain tissue” within the skull:
Intracerebral haemorrhage
Cerebral oedema (trauma)
Intracerebral mass (e.g. brain tumour, abscess)

Question 12

What are the features of low intracranial pressure?

Answer 12

• Headache: worse when: sitting or standing up

- Blurred vision, “Dizziness”

Question 13

What are the causes of low intracranial pressure?

Answer 13

1) Underproduction:
Dehydration, drugs
2) CSF leak:
Iatrogenic (post-Lumbar Puncture), spontaneous