The Meninges

Question 1

What is meningitis?

Answer 1

Infection of the meninges, very dangerous

Question 2

What are the 3 layers of the meninges?

Answer 2

1. Dura mater
2. Arachnoid mater
3. Pia mater

Question 3

Describe the outermost meninges layer, ‘cranial dura mater’

Answer 3

Has two layers, the periosteal and meningeal layers. However these are very hard to seperate (unless on histological slide)

Periosteal Layer: acts as a skull seal to protect from infection. This layer has different names throughout the cavity. Doesn’t go to SC but instead seals off outer layer.

Meningeal layer: Goes just down to the spinal cord, hence why there is only ONE dura layer in the spinal cord

Question 4

What is a dural partition and what does it do?

Answer 4

Extension of the meningeal dura mater layer, seperates

1. The hemispheres Faux cerebri
2. The cerebrum from cerebellum Tentorium cerebelli
3. The two parts of the cerebellum Falx cerebelli

Also has the infundibulum, a membrane covering the pituitary gland

Question 5

The main blood supply of the dura mater comes from the _______ arteries, more specifically the ______________ artery.

This artery splits into _____ and ______ divisions

Answer 5

The main blood supply of the dura mater comes from the meningeal arteries, more specifically the middle meningeal artery.

The middle meningeal artery splits into anterior and posterior divisions which supply the skull (remember the anterior runs behind the pterion)

Question 6

List the parts of the dura mater that are innervated by a specific nerve.

Answer 6

Opthalamic [V₁] division of the trigeminal nerve → Falx cerebri, tentorium cerebelli

Mandibular [V_2/3] division of the trigeminal nerve → other parts of the tentorium cerebelli

Question 7

What are the ‘intracranial venous structures’ and what do they do?

Answer 7

Another unique structure of the dura mater.

Along the borders of the partition we have sinuses that are drained via intracranial venous structures and that all eventually lead back to the internal jugular vein

Question 8

Describe the relationship between all the sinuses of the skull

Answer 8

Superior sagital sinus meets the straight sinus to form the ‘confluence of sinuses’. From here the L/R transverse sinuses leave laterally, become the sigmoid sinus which moves through the jugular foramen.

Question 9

Why is the cavernous sinus so important?

Answer 9

The internal carotid artery and cranial nerve 6 (VI), as well as other nerves (3, 4 and 5-1/2 that run along the wall) run through the cavernous sinus.

If anything happens to this sinus, then 5 nerves plus the brains main blood supply can be compromised!

As it lies either side of the turkish saddle (where the pit. gland sits)

Question 10

The opthalamic vein drains into the cavernous sinus, why is this dangerous?

Answer 10

Because if you get an onfection, eg periotribital cellulitis the draining opthalamic vein can spread that infection to the cavernous sinus → clot → cavernous sinus thrombosis → death in a few hours

Question 11

What are ‘Raccoon eyes’

Answer 11

Not to do with eyes! is when, due to a fracture, blood from the skull accumulates in the potential space between the periosteal layer and the skin.

Question 12

How does the venous drainage of the skull work?

Answer 12

Emissary veins: drain between the external skull to the sinuses → cavernous sinus. This means an infected skull wound can cause infection within the brain

Diploic Vein: Drains from within the skull back to the sinuses

Cerebral vein: Drain the brain itself, back to the sinuses

Question 13

List the properties of Arachnoid Mater

Answer 13

• Avascular membrane
• Trabeculae
• Subarachnoid space is the gap
• Doesn’t enter grooves or fissures except the main longitudinal fissure!
• Arachnoid granulations drain CSF → sinuses

Question 14

Describe the properties of the pia mater

Answer 14

Like an onion skin, invests the surface of the brain, covering every groove/fissure

• You can’t detach from brain

Question 15

List the layers of the skull and where the arteries/ veins sit. WHat happens if this vasculature gets damaged?

Answer 15

Skull

meningeal arteries

Periosteal dura mater

Meningeal Dura mater: cerebral veins cross

Arachnoid mater: cerebral veins cross

sub arachnoid space: cerebral arteries

Pia mater

If damaged: intracranial bleeding

Question 16

What type of intracranial haemorrage happens if:
The meningeal artery is damaged → ______

The venous strucutres are damaged → _____

The Cerebral artery is damaged → ______

Answer 16

The meningeal artery is damaged → extradural haemorrage (between skull and dura, usually around the pterion)
**extradural usually always ARTERIAL DAMAGE

Venous damage → Subdural Haemorrage
(between meningeal layer of dura)
***subdural usually due to VENOUS DAMAGE, in elderly

Cerebral artery damage → Subarachnoid haemorrage
In the subarachnoid space
**as cereb. arteries run in subarachnoid space, can also be due to venous

Question 17

What is the most common cause of extradural haemorrage?

Answer 17

Damage to the middle meningeal artery

Question 18

Take away message from student presentation

Answer 18

The pterion is 2.6cm behind and 1.3cm above the posterio-lateral border from the zygomatic arch/border