S2) Meningeal Layers, Dural Folds and Dural Venous Sinuses Flashcards
There are 3 membranous sacs that surround the brain.
Identify them
Outer layer to inner layer:
- Dura
- Arachnoid
- Pia
all continuous
pia and arachnoid are known as the leptomeninges
Describe the structure of the three membranous layers around the brain
- Dura: tough fibrous membrane, effectively touches arachnoid as arachnoid is pushed up due to CSF
- Arachnoid: soft translucent membrane, space between arachnoid and Pia is full of CFS
- Pia: microscopically thin (can’t pull away), delicate closely adherent to surface of brain, goes into lots of dips
What additional feature is found between the membranous layers of the brain?
Potential spaces:
- Subarachnoid space – between pia and arachnoid mater, maintains pressure through CSF. Contains cerebral arteries and veins
- Subdural space – between dura and arachnoid mater
The dura consists of two layers.
Identify and describe them
- Periosteal: endosteum lining inner bones of skull aka stuck to bone (cranial floor) (outer surface)
- Meningeal: layer adjacent to arachnoid (inner surface)
The periosteal and meningeal layers are closely adhered but separate in some areas.
What is the result of this?
- Dural folds
- Dural venous sinuses (spaces which become venous channels)
– in this image you see a fold and a dural venous sinus being created
Identify the some 2 dural folds
- Falx cerebri
- Tentorium cerebelli
Describe the structure of the tentorium cerebelli
- Tentorium cerebelli is a strong fold of dura mater roofing over the posterior cranial fossa
- stabilises the brain in an up and own movement
- It has a tentorial notch and is attached at the midline to the falx cerebri for blood to pass through
Describe the structure and function of the falx cerebri
Falx cerebri is a large fold of meningeal layer of dura mater that descends vertically between the cerebral hemispheres
- stabilise the brain from any right to left movements
- dural venous sinus running In its superior and inferior margin
Generally, dural folds stabilise the brain.
Explain how these folds can contribute to herniation
- A rise in pressure inside the skull leads to herniation
- Can be secondary to a bleed, compressing and displacing the brain against rigid dural folds and/or through foramen magnum
What are dural venous sinuses?
Dural venous sinuses are venous blood filled spaces created by the separation of meningeal from periosteal layer of dura
Describe the drainage of blood into dural venous sinuses
Venous blood from cerebral veins (in the subarachnoid space) traverses the subarachnoid space and drains into the sinuses
Describe the drainage of blood from the dural venous sinuses
Dural venous sinuses drain into internal jugular vein (eventually)
Describe the location of the dural venous sinuses
Major dural venous sinuses lie at the margins of borders of falx cerebri and tentorium cerebelli and on cranial floor
Identify the following dural venous sinuses:
- Superior sagittal sinus
- Inferior sagittal sinus
- Transverse sinus
- Sigmoid sinus
- Cavernous sinus
- two transverse sinus (one in both sides)
- two sigmoid sinus
- two cavernous sinus that connect with dural venous sinus system
- overall, are the sinus are connected and drain into the internal jugular vein
What is an intracranial haemorrhage?
An intracranial haemorrhage is bleeding in ‘spaces’ between meningeal layers due to head trauma or the rupture of a blood vessel (aneurysm)
Bleeding from blood vessels in the meningeal layers will cause accumulation of blood in which potential spaces?
- Extradural
- Subdural
- Subarachnoid
Bleeding can also occur within the brain tissue itself.
What is this called?
Intracerebral haemorrhage
E.g. contusions, tearing of white matter
Why are intracranial haemorrhages so dangerous?
Addition of ‘volume’ to an already fixed space (the skull) leads to rise in pressure and damage to brain tissue and other structures e.g. cranial nerves that can be compressed/ stretched
Briefly, what type of bleeding occurs in an extradural haemorrhage?
Arterial bleed – middle meningeal artery runs between the inner periosteum and the inner table of bone
- injury to the lateral side if the head can damage this vessel
- in a CT you will see a white blob of blood (fresh blood is white)
- lateral extension of bleed is limited to the length of the bone and the sutures either side of the bone
- HISTORY → will be normal for a while then suddenly an hour later will have significant deterioration (lucid interval)
Briefly, what type of bleeding occurs in a subdural haemorrhage?
Venous bleed – bridging veins
- has the potential to fill all the dural space right around a single hemisphere
- can be common in elderly due to brain shrinkage putting tension on bridging veins
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Briefly, what type of bleeding occurs in a subarachnoid haemorrhage?
Arterial bleed – cerebral arteries, circle of Willis
How does a subarachnoid haemorrhage occur?
- Secondary to trauma or spontaneous rupture of blood vessel e.g. aneurysm
- Blood leaks into subarachnoid space, mixing with CSF
– sudden, often fatal
– so can do a lumbar puncture and see if old blood has mixed with CSF
What is the common cause of subarachnoid haemorrhages?
A branch of ‘Circle of Willis’ ruptures (the arterial circuit responsible for supplying brain structures)
Describe the CT imaging of the head for a subarachnoid haemorrhage
- 93% picked up if within 24 hours and 100% if within 6 hours
- Lumbar puncture if CT inconclusive: sample CSF to identify presence of blood
name two important venous connections between the dural and venous sinuses
- intracrainally: cerebral veins → connect to sinus via bridging veins
- extracranially: scalp veins → connect to sinus via emissary veins that pass through bones
what is a bridging vein?
- runs from the subarachnoid space and passes the subdural space then going the wall of the dural venous sinus
- point at which it is at its weakest is the bend
- if it snaps it will fill the subdural space and cause a haemorrhage
what Is a scalp vein?
- connection between venous structures outside the skull to venous structures inside the skull
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what does a subdural haemorrhage look like on a CT scan
- it is a long white line across skull as no limitations
- rapid deterioration
what does a CT image of a subarachnoid haemorrhage look like
starshaped
blood collects in the basal cisterns
what are the two tests for meningitis?
Kernig’s sign
Brudzinski’s sign.
describe a positive Kernigs sign
- pain with extension of the knee due to stiffness of the hamstrings
- if positive it is a sign for a subarachnoid haemorrhage
describe a positive brudzinskis sign
- neck stiffness, flexion of the neck causes involuntary flexion of the hip and the knee
- this shows signs of meningitis
