Flashcards in Lecture 5 - Meninges And Dural Folds Deck (44)
What are the 3 meningeal layers form deep to superficial?
Where do you find the pia?
It is firmly adhered to the brain and goes deep into the grooves
Where is the arachnoid found?
It is separated from the pia by the subarachnoid space which is filled with
CSF and cerebral vessels.
It goes into the fissures of the brain (the gaps between the hemispheres) but not the grooves of the brain.
Arachnoid is very delicate and can be peeled off.
What is the name of the structure between the arachnoid and pia and what is found within it?
Within it is CSF and cerebral vessels.
What is the function of the CSF in subarachnoid space?
It acts as a cushion/provides buoyancy that helps protect the brain if there is movement of the brain in the skull.
It also creates pressure that pushes the arachnoid away rom the pia and up against the dura.
Where else is the subarachnoid space found?
It is continuous down the spinal cord - where we take CSF in a lumbar puncture
Is the space between the dura and the arachnoid a space or a potential space?
It is a potential space because the arachnoid is not stuck to the dura. It becomes a space when things start to accumulate there.
Describe the dura and where is it found?
The dura is the outermost meningeal layer and is very tough and can’t be torn easily. The dura and all of the meningeal layers are continuous down the length of the vertebral column and continue around the spinal cord.
What is the difference between the dura inside the skull and the dura found in the vertebral column?
The difference between dura inside the skull compared to dura in the vertebral column is that there is a space between the bony circle formed by the vertebrae and the dura itself - an epidural space in the vertebral canal that can be used for various therapeutic reasons
In the skull, the dura is different - it is stuck to the inside of the skull/calvaria and stuck to the cranial floor
What are the meninges?
Three membranous layers that surround and protect the brain and spinal cord.
What is the order of the meningeal structures from superficial to deep?
Dura: tough fibrous membrane
Potential space - space doesn’t exist until something pathological starts to fill it
Arachnoid: soft, delicate, translucent membrane
Subarachnoid space - CSF, cerebral vessels
Pia: microscopically thin, delicate, adherent to surface of brain, follows every fold
What would you see if the calvaria was removed?
The dura would be stuck to the inner table of bone.
The arachnoid is transparent - can see the grooves fo the brain - underneath the arachnoid would be CSF containing cerebral vessels and it can be peeled off.
Pia is stuck to the brain - it is part of the surface of the brain - wouldn’t be able to be peeled off.
What does the dura fuse with found lining the inner travel of skull bones?
As the dura fuses with the periosteum, it effectively has two layers within the skull. What are hey?
Periosteal - part against the inner table of bone
Meningeal - part adjacent to the arachnoid
Do the two layers of dura appear as one?
For the most part, the two layers are closely adhered (appearing as a single layer) but there are areas where they separate.
When the two layers of the dura separate, what do they form?
Dural venous sinuses (spaces filled with venous blood)
Where is periosteum found in relation to bone?
It is continuous around the bone - the entire bone is completely encircled by periosteum.
How are dural folds and dural venous sinuses created?
The meningeal layer of dura separates from the periosteal layer of dura.
What is the falx cerebri?
It is a dural fold found between the two hemispheres. It attaches to the crista galli anteriorly and the tentorium cerebelli posterioly.
What is the tentorium cerebelli and where is it found?
It is a dural fold.
Whilst the falx runs in a vertical direction down the middle of the two hemispheres, the tentorium cerebelli tents over the posterior cranial fossa and runs in a more horizontal plane.
The tentorium cerebelli is found beneath the occipital lobe and above the cerebellum (it tents over the cerebellum).
What structure does the brainstem travel through?
Tentorial notch (which is quite sharp)
Where is the cavernous sinus found?
Cavernous sinus sits on either side of the sella turcica - this is where there is a separation of the meningeal dura from periosteal dura to create the space for the cavernous sinus.
Which branches of the ICA and basilar artery form the circle of Willis?
ICA - anterior and lateral cerebral arteries
Basilar - left and right posterior cerebral arteries.
What is the function of the dural folds and how can this be problematic?
The dural folds help to stabilise the brain and act as rigid dividers. They prevent side to side movement of the brain.
However, a rise in pressure inside the skull e.g. secondary to a bleed or tumour can lead to compression and displacement of parts of the bran against/(under) rigid dural folds and/or through the foramen magnum.
Herniation - one of the first structures to herniate are the tonsils of the cerebellum.
Brain can herniate against the dural folds or be pinched on/squashed against their edges which are quite sharp
What are dural venous sinuses?
Venous blood filled spaces created by separation of the meningeal layer of dura from the periosteal layer at different points around the skull.
Where are dural venous sinuses found?
They are found throughout the skull, surrounding the brain where the two layers fo dura have separated from each other.
What blood do the dural venous sinuses receive?
They receive venous blood from the cerebral veins draining the brain.
The dural venous sinuses are connected to each other.
Where do the dural venous sinus drain into?
The IJV and then the heart.
See lecture slide for how the dura can form gaps when separating from each other for the sinuses in the brain.
Sinuses such as the superior sagittal, inferior sagittal, straight, transverse sigmoid etc.
How is the cavernous sinus connected to the sigmoid sinuses?
By superior and inferior petrosal sinuses.
How do cerebral veins within the subarachnoid space drain into the dural venous sinuses?
Via bridging veins that traverse the subdural space.
Bridging vein - not an emissary vein
Why are dural venous sinuses present?
We have dural venous sinuses because if we didn’t, there would be no way to remove venous blood from the brain - the ICA brings lots of arterial blood to the brain tissue but there is no system to receive blood from the cerebral veins which is why there are dural venous sinuses
What is the significance of bridging veins and potential spaces?
There is a potential space between the arachnoid and dura where the bridging vein runs - this is the subdural space which is not normally present because the arachnoid is pushed the surface of the dura.
What would happen if something tore the bridging vein?
If something tears the bridging vein where it enters the dura, the blood from the vein can fill the subdural space
What connects the scalp veins to the dural venous sinuses?
The emissary veins that traverse through the skull
Head trauma can lead to bleeding n ‘spaces’ between meningeal layers. What is this known as?
Blood vessels run along or traverse between the meningeal layers. Injury and bleeding from these blood vessels will cause accumulation of blood in the ‘space’ between the meningeal layers.
What are the 3 kinds of intracranial haemorrhage?
Which of the intracranial haemorrhages are caused by arterial blends and which are caused by venous bleeds?
Extradural - arterial - mostly MMA
Subdural - venous - bridging veins
Subarachnoid - arterial - spontaneous rupture of blood vessels e.g. aneurysm.
Bleeding can also occur within the brain tissue itself (e.g. contusions, tearing of white matter). What is this known as?
What does Addison of ‘volume’ to an already fixed space (the skull) lead to?
A rise in pressure and damage to brain tissue, brainstem and other important structures e.g. cranial nerves and blood vessels.
In the case of an extradural haemorrhage where the MMA bleeds, what would you see on a CT scan?
The MMA runs between the inner table of bone and periosteal layer of dura (periosteum lining the inner table of bone). Because the periosteum travels through suture lines, the margins of an extradural bleed will never extend beyond the edges of the bone under which it has occurred - get the classical lentiform appearance.
A subdural haemorrhage is caused by a venous bleed usually from bridging veins. How does this bleeding usually occur and what would you see on an a CT?
Bumping the head and even sudden movements of the head/small injuries can shear bridging veins away from dural venous sinuses, then they bleed into subdural space. This is more likely to happen in old people where the bridging veins are under tension due to cerebral atrophy. -
Typical crescent shape appearance of a subdural haemorrhage which appears white when fresh.
How do subarachnoid haemorrhages due to arterial bleeds occur?
• Secondary to trauma or the spontaneous rupture of a blood vessel e.g. aneurysm
• Usually a branch of the ‘Circle of Willis’ (the arterial circuit
responsible for supplying brain structures)
• Blood leaks into subarachnoid space, mixing with CSF
– Sudden, often fatal