Meningeal Layers, Dural Folds

Question 1

What are the layers of meninges

Answer 1

• Three membranous layers that surround and protect the brain
• Dura - tough fibrous membrane
• Arachnoid - soft translucent membrane
• Pia - microscopically thin, delicate closely adherent to surface of brain

Question 2

Where do CSF and blood vessels lie within the meningeal layers

Answer 2

Subarachnoid space

Some blood vessels also lie between the dura and inner table

Question 3

What are the layers of the dura

Answer 3

• Periosteal - endosteum lining inner bones of skull
  
  • Acts as periosteum of inner table
• Meningeal - layer adjacent to arachnoid

Question 4

How do dural venous sinuses form

Answer 4

• For the most part, the periosteal and meningeal layers are closely adhered
• Where they separate, they form dural folds and dural venous sinuses
  
  • Blood drains through dural venous sinus before out of skull

Question 5

Describe the locations of the two types of dural folds

Answer 5

• Falx cerebri separates the two hemispheres
• Tentorium cerebelli separates the cerebellum from the occipital lobes
• Notch through tentorium cerebelli allows passage of brainstem to connect two hemispheres

Question 6

What is the role of dural folds and what can happen with a rise intracranial pressure

Answer 6

• Act to stablise the brain and act as rigid dividers
• However a rise in pressure can lead to compression and displacement of brain against rigid dural folds or through the foramen magnum (herniation)

Question 7

Outline how venous blood from brain drains to the heart

Answer 7

• Cerebral veins within subarachnoid space drain into dural venous sinuses
• Bridging veins transverse the subdural space and connect the subarachnoid space to dural venous sinus
• Superior sagittal sinus -> confluence of sinuses -> transverse sinus -> sigmoid sinus -> internal jugular vein

Question 8

How can intracerebral haemorrhages occur

Answer 8

• Bleeding can also occur within brain tissue itself

- Eg. Contrusions (rupture of capillaries), tearing of white matter

Question 9

What are extradural haemorrhages

Answer 9

• Bleeding between dural meningeal layer and inner table of skull
• Cannot spread beyond suture lines
• Egg shaped bleed

Question 10

What is subdural haemorrhage

Answer 10

• Venous bleeding from bridging veins between subarachnoid and dural venous sinus
• In elderly, constant sheering of bridging veins
• Subdural haemorrhage cannot spread to other hemisphere due to falk cerebri
• Banana shaped bleed

Question 11

What is a subarachnoid haemorrhage

Answer 11

• Arterial bleed secondary to trauma or spontaneous rupture of blood vessel (aneurysm)
• Blood leaks into subarachnoid space, mixing with CSF - often fatal
• CT imaging of head - need to be identified quickly
  
  • Lumbar puncture if CT inconclusive - sample CSF to identify presence of blood (haemoglobin degradation products)
• Blood can be seen gathering at base of brain