Session 3: Meningeal Layers, Dural Folds and Dural Venous Sinuses Flashcards
State the three membranous layers that surround the brain and spinal cord.
Pia mater
Arachnoid mater
Dura mater
Briefly explain the pia mater.
A microscopically thin layer adherent to the surface of the brain. This layer follows every sulcus, gyrus and fissure.
Briefly explain the arachnoid mater.
A loose connective tissue layer that is said to make the brain ‘smoother’. It follows every fissure but it does not go into gyri.
Briefly explain the dura mater.
A dense irregular connective tissue. It consists of two layers. It does not go into any gyri or fissures.
What are the two layers of the dura mater?
Periosteal dura Meningeal dura
What are the leptomeninges?
That is what the pia mater and the arachnoid mater is collectively called.
What is the space between the dura and arachnoid called?
It is called subdural space. However it is only potential subdural.
Why is the subdural space only a potential space?
Because the arachnoid layer is usually pushed up against the dura mater and the space becomes ‘sealed’.
What is the space between the arachnoid and pia called?
The subarachnoid space.
What is found in the subarachnoid space?
CSF Cerebral vessels supplying and draining the brain.
What makes the arachnoid mater be pushed up against the dura mater?
The cerebrospinal fluid.
What is the periosteal layer of the dura?
It is dura which is the same as the ‘periosteum lining’ that lines the inner table of the skull bones.
What is the meningeal layer of the dura?
The inner part of the dura mater that is adjacent to the arachnoid.
Are the two layers of the dura separate?
For most part the two layers closely adhere so they appear as a single layer. However in some areas they separate.
What does the separation of these two layers form?
Dural folds and dural venous sinuses.
What is a dural fold?
When the meningeal dura separate from the periosteal by the great longitudinal fissure it goes into the fissure where as the periosteal layer follow along the skull bone. The two layers of meningeal dura will meet in the fissure and adhere to each other.
That is a dural fold.
What is the tentorium cerebelli?
An extension of the meningeal dura that separates the cerebellum from the inferior occipital lobes.
What are some issues with the dural folds?
A rise in pressure inside the skull can lead to compression and displacement (herniation) of parts of brain under rigid dural folds.
Parts of the brain can also herniate through the foramen magnum.
Briefly explain extradural haemorrhage.
Trauma to the head, commonly by the pterion.
It is an arterial bleed commonly due to rupture of the middle meningeal artery.
This causes a tear between the periosteal layer of the dura and the inner table of the skull. This means that the haematoma will be found superficial to the dura mater and since the skull is fixed it can’t grow outwards so will press on inwards instead.
The bleeding will go as far as the next suture line.
Briefly explain subdural haemorrhage.
This is in the potential subdural space. It is usually a venous bleed from bridging veins. Where the bridging veins enter the DVSs is a point of weakness. As you get older there will be more and more tension on the bridging veins and trauma can pull a bridging vein away and fill the subdural space instead.
Briefly explain subarachnoid haemorrhage.
It is an arterial bleed that is secondary to trauma or spontaneous rupture of blood vessels like an aneurysm most commonly found from a branch of circle of willis.
The blood leaks into the subarachnoid space and will mix with the CSF.
This is often sudden and often fatal.
