CSF and Intracranial Pressure

Question 1

New brain anatomy words

Answer 1

Virchow Robin spaces: Invaginations of pia mater due to the arteries

Tentorial notch: where the brain stem comes out

Question 2

Where is CSF produced

Answer 2

In the choroid plexus, mainly in the lateral ventricles.

Process: ultrafiltration across choroidal capillary endothelium; active secretion by choroidal epithelium

Question 3

Choroid plexus structure

Answer 3

Is a capillary network surrounded by epithelial cells.
Capillaries are fenestrated
Epithelium have tight junctions and lots of lysosomes, vesicles and a brush border of microvilli

Question 4

Path of CSF

Answer 4

From choroid plexus in lateral ventricles, to third ventricle, then through cerebral aqueduct to the fourth ventricle, then out to the subarachnoid space in spinal cord and around the brain.

Question 5

CSF amounts

Answer 5

Not much, 150mL and 15-25mL in the ventricles, most in SAS.

Fairly constant production and turnover 3-4 times per day (can take some, and rapidly replaced)

Question 6

CSF absorption

Answer 6

In the arachnoid villi and granulations, Hernaitions into the dura, into the lumen of the superior sagittal veins.

Unidirectional bulk flow, and is dependent on the hydrostatic pressure. Passive

Question 7

Lumbar puncture

Answer 7

Way to sample CSF, usually done at L3/L4 between the vertebra (due to cauda equina and larger space)

Question 8

CSF composition

WBCs; neutrophils; RBC’s; protein; glucose

Answer 8

WBC's: < 5x10^6
no neutrophils
no RBC's
protein < 0.45 g/L
glucose > 2.5 mmol/L (dependent on blood glucose and metabolism by brain)

Question 9

CSF changes in disease

Answer 9

Meningitis: increase WBC’s, increase in protein, may or may not decrease glucose. Neck stiffness
Subarachnoid haemorrhage: RBC’s, xanthochromia (yellow tint)

Question 10

Function of the CSF

Answer 10

Homeostasis: BBB, constant environ for neurons and glia
Protection: cushion
Counters sudden increase in ICP

Question 11

Functions of the BBB

Answer 11

• Regulates ionic balance in the brain
• Facilitates transport of essential substrates for the brain
• Prevents entry of harmful molecules to the brain

Thus metabolites must be selectively transported across endothelial cells

Question 12

What does the BBB consist of?

Answer 12

• Specialised endothelial cells (many mitochondria, tight junctions, fewer vesicles, present astrocytic processes)
• Thick basement membranes
• astrocytic processes on capillaries

Question 13

What are the ways substrates move across the BBB?

Answer 13

Diffusion of lipid soluble things, like oxygen, alcohol etc
AT of things like glucose, amino acids, vitamins
Ion channels

Question 14

What factors affect the crossing of a substance across the BBB?

Answer 14

Size; lipid solubility; protein binding; ionisation; means of getting across

Question 15

What are some disease processes targeting the BBB?

Answer 15

• Alteration of tight junctions, making them leaky
• BM disrupted
• astrocyte interactions
• transport mechansim altered
• angiogenesis making leaky capillaries

E.g tumour casuing oedema; meningitis causing BBB breakdown

Question 16

Measurement of ICP

Answer 16

-Lumbar puncture or pressure reader in the head placed by surgeon

Normal is 65-195 mm of water (5-15 mmHg)

Question 17

What is the Monro-Kellie doctrine

Answer 17

That there are three components to ICP, brain blood and CSF. If any one of these is to ise, there has to be a decrease of another due to the intracranial volume being fixed by the skull.

If this decrease does not occur, the ICP goes up

Question 18

What are some compensatory mechanisms to alter an increase in ICP

Answer 18

• CSF shunted to spinal cord
• cerebral veins collapse
• increase in CSF absorption

Question 19

Causes of ICP

Answer 19

• Increase in brain volume e.g tumour or oedema
• Increase blood volume e.g venous obstruction, loss of autoregulation
• Increase in CSF, hydrocephalus due to an obstruction to flow, decreased absorption or increase production

Question 20

What are Cushing’s signs and what are they a result of?

Answer 20

As a result of ICP, when there is a reduction of blood flow to the medulla, or medullary distortion, you get

• Arterial hypertension
• slow heart rate
• slow resp rate

Question 21

Cerebral herniations

transtentorial; tonsillar; subfalcine ; upward

Answer 21

As a result of ICP, can displace brain tissue:

• from one intracranial compartment to another
• through the foramen magnum into the spinal cord

Causing compressions of the brain, arteries and cranial nerves

Question 22

Herniations through the tentorial notch can cause problems with? (transtentorial)

Answer 22

Third cranial nerve, posterior cerebral arteries (midbrain compression)

Question 23

Cerebrovascular autoregulation and the cranial perfusion pressure.

CPP is?
What happen when autoregulation is lost

Answer 23

CPP is the MAP-ICP, so increased ICP will lower the CPP

Autoregulation maintains cerebral blood flow over a wide range of CPP’s (60-150) by use of vasoactive substances on small cerebral arteries

When this is lost, cerebral blood flow becomes proportional to the CPP, so at lower BP’s, the CPP is lower than normal, it is not tightly regulated so th brain is hyperperfused. (diagram in slides)

Can happen in stroke

Question 24

Ways to alter the ICP (increase)

Answer 24

Increase venous pressure; increase intrathoracic pressure; arterial blood pressure; posture (lying will increase venous pressure); increase PaCO2 will increase CBF, increasing ICP; decrease in O2; increase temperature increases CBF

if you want to lower ICP opposite of these