Lecture 5 - Meningeal Layers, Dural Folds & Dural Venous Sinuses

Question 1

What are the 3 meningeal layers that surround and protect the brain and SC from outside to in & their composition?

Answer 1

D.A.P

1) Dura Mater - tough fibrous membrane essentially touching arachnoid mater
2) Arachnoid Mater - translucent membrane enclosing surface of the brain, doesn’t extend into gyri/sulci or into lateral fissures, but does into longitudinal fissure.
3) Pia Mater - microscopic layer, adhered to surface of brain, follows every fold

Question 2

What are the 2 spaces between meningeal layers and what is contained within them?

Answer 2

1) Subdural space - this is a potential space when in good health
2) Sub-arachnoid space - filled with CSF which exerts fluid to keep layers separated, also with vertebral & internal carotid arteries (cerebral vessels) which supply and drain the brain.

Question 3

What are the 2 layers of dura that are closely adhered appearing as one?
What 2 things does separation of these layers form? - give 2 examples

Answer 3

1) Periosteal layer - part of the periosteum of adjacent bone 2) Meningeal layer - part adjacent to arachnoid.

1) Dural folds (long extensions that form partitions) - e.g.: dural fold extending into longitudinal fissure on cranial vault
2) Dural venous sinuses (spaces filled with venous blood) - e.g.: cavernous sinus on cranial floor.

Question 3

What are the 2 layers of dura that are closely adhered appearing as one?
What 2 things does separation of these layers form? - give 2 examples

Answer 3

1) Periosteal layer - part of the periosteum of adjacent bone 2) Meningeal layer - part adjacent to arachnoid.

1) Dural folds (long extensions that form partitions) - e.g.: dural fold extending into longitudinal fissure on cranial vault
2) Dural venous sinuses (spaces filled with venous blood) - e.g.: cavernous sinus on cranial floor.

Question 4

What is the role of dural folds in the brain?
Identify 2 main dural folds that can be identified from a sagittal section and state their specific roles.
What can cause herniation of dural folds?

Answer 4

Act as partitions/rigid dividers to stabilise the brain

1) Falx cerebri - stops left to right movement
2) Tentorium cerebellum - stops movement up and down

Rise in intracranial pressure causes compression & displacement (herniation) of dural folds, causing displacement of other brain tissue and neurological complications (see slide 11 for pic)

Question 5

What do dural venous sinuses (venous filled blood spaces) receive blood from & where do they drain blood into?

Answer 5

• Receive blood from cerebral veins (draining the brain)

- Drain into the internal jugular vein

Question 6

Locate & describe the course of the main dural venous sinuses within the brain, starting at the superior sagittal sinus (8)

Answer 6

• Superior sagittal sinus superior to falx cerebri. At inferior margin, we reach confluence of sinuses, where straight sinus, occipital sinus and transverse sinus are formed.
• Straight sinus connects to inferior sagittal sinus, inferior to falx cerebri
• Transverse sinus moves toward jugular foramen, twisting in an S-shape bend to form sigmoid sinus, with a connection to the cavernous sinus

Question 7

How are dural venous sinuses connected to cerebral veins within the sub-arachnoid space?

Answer 7

• Via ‘bridging’ veins

Question 8

How are dural venous sinuses connected to scalp veins?

What could a scalp injury lead to?

Answer 8

• Via ‘emissary’ veins, which transverse through the skull

- Presence of infection which could spread inside skull and involve intra-cranial structures via emissary veins.

Question 9

Good summary pic of all the layers of the brain from the outside of the hemisphere through to the head.

Answer 9

Thanks m8

Question 10

What are the 3 types of intra-cranial haemorrhages that occur in the ‘spaces’ between meningeal layers?

What is the potential consequence of these haemorrhages?

Answer 10

1) Extra-dural
2) Sub-dural
3) Sub-arachnoid

NB: can also occur within brain tissue itself - intracerebral haemorrhage

• Addition of volume via blood within fixed space (skull) can cause rise in intracranial pressure and damage brain tissue, brain stem an other important structures such as CN’s

Question 11

Where does bleeding occur in an extradural haemorrhage?
Which branch of which artery is typically affected?
What is the characteristic findings in a patient history + CT-scan?

Answer 11

• Outside dura, in between periosteal and and meningeal layers.
• Anterior branch of the middle meningeal artery, runs in-between these layers over the pterion
• Trauma to lateral side of head, unconscious for a couple minutes then normal for about an hour (lucid interval), then deteriorate, behavioural changes and go unconscious.
• Lentiform/bi-convex shape on CT-scan

Question 12

Where does bleeding occur in a subdural haemorrhage?
Where is the blood coming from?
How does it present itself?

Answer 12

• Into the space below the dura, but stays on one side because of the downwards direction of the dura. Can occur even in minor head injuries, esp in elderly.
• Blood is coming from snapping of bridging veins which extend into the subdural space from the dural venous sinus.
• Similar presentation to extradural (i.e.: lucid interval) with bright white crescent shape on CT-scan

Question 13

How do sub-arachnoid haemorrhages occur?

How are they diagnosed?

Answer 13

• Secondary to trauma or spontaneous rupture of blood vessel (aneurysm), usually a branch of the circle of willis
• Blood leaks into sub-arachnoid space, mixing with CSF, often sudden and fatal.
• Picked up with CT scan (needs to be within 24 hours), lumbar puncture if inconclusive (blood for blood within CSF …)