L5: meningeal layers, dural folds and dural venous sinuses Flashcards
Describe the three meningeal layers
Pia mater – microscopically thin, adherent to surface of brain, follows every fold
Arachnoid mater – soft, fibrous translucent membrane
Dura mater – tough fibrous membrane
(Pia & arachnoid = leptomeninges)
List functions of the meninges
Provide a supportive framework for the cerebral and cranial vasculature
Acting with CSF to protect the CNS from mechanical damage
What are the different spaces found between the meningeal layers?
Potential subdural space
Subarachnoid space – CSF and cerebral vessels
Describe the dura
Dura fuses with the periosteum lining inner table of skull bones
Has two layers:
1) Periosteal = part against the inner table of bone
2) Meningeal = part adjacent to arachnoid
The two layers are closely adhered, but there are areas where they separate = dural folds and dural venous sinuses
List the important dural folds
1) Falx cerebri – projects downwards to separate the right and left cerebral hemispheres
2) Tentorium cerebelli – separates the occipital lobes from the cerebellum and contains a space anteromedially for passage of the midbrain (tentorial notch)
3) Falx cerebelli – separates the right and left cerebellar hemispheres
Describe the function of the dural venous sinuses
Located between the two layers of dura mater
Responsible for the venous drainage of the cranium and empty into the internal jugular veins
Describe the vascular supply to the meningeal layers
Pia mater – highly vascularised, with blood vessels perforating through the membrane to supply the underlying neural tissue
Arachnoid mater – avascular
Dura mater – receives its own vascular supply from middle meningeal artery and vein
Describe the connection between the dural venous sinuses and cerebral veins
Cerebral veins drain brain tissue directly – connect and drain into dural venous sinuses via bridging veins at certain points (particularly along the length of the superior sagittal sinus)
Head injuries – brain can move a little bit -> can cause traction of the bridging veins and cause them to snap
-leads to extravasation of venous blood which fills the plane between the dura and arachnoid = SUBDURAL HAEMORHAGE
Describe the connection between the dural venous sinuses and scalp veins
Scalp veins also connect with dural venous sinuses – emissary veins traverse through the skull
Not uncommon for scalp injuries -> infections may rise in this area
-deep infections of the scalp could involve intracranial structures due to spread
What is an intracranial haemorrhage?
Bleeding in ‘spaces’ between meningeal layers
Blood vessels run along/traverse between the meningeal layers
-injury and bleeding from these blood vessels will cause accumulation of blood
-extradural, subdural & subarachnoid
Bleeding can also occur within the brain tissue itself -> intracerebral haemorrhage
Describe an extradural haemorrhage
Origin = middle meningeal artery (between periosteal layer of dura and inner table of bone)
CT scan: biconvex in shape – starts to strip the periosteal layer from the inner table of bone
-can’t extend at the edges of bone as it is strong at the connections
Patient experiences lucid interval – patient faints, feels okay and then an hour or so later, significant deterioration occurs
Describe a subdural haemorrhage
Venous bleed usually from the bridging veins
CT scan: crescent shaped
Can occur in a minor head injury, specifically in the elderly -> brain shrinks & tension of bridging vein to venous sinuses increases
-gradual decline as venous blood starts to accumulate
Describe a subarachnoid haemorrhage
Secondary to trauma/spontaneous rupture of blood vessels (usually a branch of ‘circle of willis’)
Blood leaks into subarachnoid space, mixing with CSF (sudden, often fatal)
CT imaging of head to diagnose & do lumbar puncture if CT is inconclusive
-sample CSF to identify presence of blood
