The eye and intracranial pressure

Question 1

From which embryological structure does the ventricular structure of the brain arise?

Answer 1

The neural canal

Question 2

What do the choroid plexuses form from and what is their function?

Answer 2

Form from cells in the wall of the ventricles and produce cerebrospinal fluid

Question 3

Where is the choroid plexus found in the adult brain?

Answer 3

3rd, 4th and lateral ventricles

Question 4

Which structures are being indicated here (1-5)?

Answer 4

1. Superior sagittal sinus
2. Choroid plexus
3. 4th ventricle
4. 3rd ventricle
5. Lateral ventricles

Question 5

How does CSF circulate in the brain?

Answer 5

Produced by choroid plexus

Flows directionally through the ventricular system

Flows into the subarachnoid space between dura mater and pia mater

Returns to venous blood through arachnoid granulations into the superior sagittal sinus

Question 6

What does the blood brain barrier consist of?

Answer 6

The capillary enthothelium, its basal membrane and perivascular astrocytes

This forms a barrier between blood and brain

Question 7

In total, how much CSF is in the CNS?

Answer 7

150ml

Question 8

How much CSF is produced daily?

Answer 8

500-600ml per day, at a similar rate to kidney or pancreatic ducts

Question 9

What is the purpose of CSF analysis?

Answer 9

Aiding the diagnosis of infectious and non-infectious inflammatory conditions of the brain, meninges and spinal cord as well as CT-negative subarachnoidal haemorrhages and leptomeningeal disease

Question 10

What in the CSF is analysed clinically?

Answer 10

Protein

Albumin

Immunoglobulin

Glucose

Lactate

Cellular changes

Specific antigen and antibody testing for infectious agents

Question 11

What can be seen on examination of the fundus that indicates raised ICP?

Answer 11

Papilloedema - swollen discs

Edge of disc is blurred

Question 12

What is the definition of papilloedema?

Answer 12

Swollen optic discs secondary to raised intracranial pressure

Question 13

What is the pathophysiology of papilloedema?

Answer 13

The subarachnoid space of the brain is continuous with that around the eyes

Increased pressure is transmitted to the SAS and this to the optic nerve

This compresses the optic nerve and thus interrupts the normal flow of venous blood

The build up of blood causes the optic discs to swell

Question 14

What three components is the intracranial pressure a sum of?

Answer 14

The brain (80%)
The blood (10%)

The CSF (10%)

Question 15

What is the Monro-Kellie hypothesis?

Answer 15

The sum of the blood, brain and CSF must remain constant to maintain ICP

An increase in one variable will result in a decrease of one/both other variables

Question 16

Why is raised ICP a medical emergency?

Answer 16

The cranial vault does not expand to accomodate raised ICP

The only opening is the foramen magnum

If the ICP is raised, the brain is squeezed through the foramen magnum, compressing the brainstem

This causes the patient to stop breathing

Question 17

What three ways can the CSF cause raised ICP?

Answer 17

Obstruction to CSF circulation
Overproduction of CSF
Inadequate absorption

Question 18

What happens if disc swelling becomes chronic?

Answer 18

Disc swelling subsides, discs become atrophic and pale
Loss of visual function occurs and blindness may result

Question 19

What are the symptoms and signs of raised ICP?

Answer 19

Transient blurred vision
Double vision
Loss of vision
Papilloedema

Pupillary changes

Question 20

What is the sensory supply to the dura mater?

Answer 20

CN V

Question 21

What is the function of the dura mater?

Answer 21

This is the external layer and is the ‘hard’ layer

Encloses dural venous sinuses

Question 22

Which layer of mater adheres to the brain?

Answer 22

Pia mater