S2) Meningeal Layers, Dural Folds and Dural Venous Sinuses

Question 1

There are 3 membranous sacs that surround the brain.

Identify them

Answer 1

• Dura
• Arachnoid
• Pia

Question 2

Describe the structure of the three membranous layers around the brain

Answer 2

• Dura: tough fibrous membrane
• Arachnoid: soft translucent membrane
• Pia: microscopically thin, delicate closely adherent to surface of brain

Question 3

What additional feature is found between the membranous layers of the brain?

Answer 3

Potential spaces:

• Subarachnoid space – between pia and arachnoid mater
• Subdural space – between dura and arachnoid mater

Question 4

The dura consists of two layers.

Identify and describe them

Answer 4

• Periosteal: endosteum lining inner bones of skull (cranial floor)
• Meningeal: layer adjacent to arachnoid

Question 5

The periosteal and meningeal layers are closely adhered but separate in some areas.

What is the result of this?

Answer 5

• Dural folds
• Dural venous sinuses (spaces which become venous channels)

Question 6

Identify the two dural folds

Answer 6

• Falx cerebri
• Tentorium cerebelli

Question 7

Describe the structure of the tentorium cerebelli

Answer 7

• Tentorium cerebelli is a strong fold of dura mater roofing over the posterior cranial fossa
• It has a tentorial notch and is attached at the midline to the falx cerebri

Question 8

Describe the structure and function of the falx cerebri

Answer 8

Falx cerebri is a large fold of meningeal layer of dura mater that descends vertically between the cerebral hemispheres

Question 9

Generally, dural folds stabilise the brain.

Explain how these folds can contribute to herniation

Answer 9

• 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

Question 10

What are dural venous sinuses?

Answer 10

Dural venous sinuses are venous blood filled spaces created by the separation of meningeal from periosteal layer of dura

Question 11

Describe the drainage of blood into dural venous sinuses

Answer 11

Venous blood from cerebral veins (in the subarachnoid space) traverses the subarachnoid space and drains into the sinuses

Question 12

Describe the drainage of blood from the dural venous sinuses

Answer 12

Dural venous sinuses drain into internal jugular vein (eventually)

Question 13

Describe the location of the dural venous sinuses

Answer 13

Major dural venous sinuses lie at the margins of borders of falx cerebri and tentorium cerebelli and on cranial floor

Question 14

Identify the following dural venous sinuses:

• Superior sagittal sinus
• Inferior sagittal sinus
• Transverse sinus
• Sigmoid sinus
• Cavernous sinus

Answer 14

Question 15

What is an intracranial haemorrhage?

Answer 15

An intracranial haemorrhage is bleeding in ‘spaces’ between meningeal layers due to head trauma or the rupture of a blood vessel (aneurysm)

Question 16

Bleeding from blood vessels in the meningeal layers will cause accumulation of blood in which potential spaces?

Answer 16

• Extradural
• Subdural
• Subarachnoid

Question 17

Bleeding can also occur within the brain tissue itself.

What is this called?

Answer 17

Intracerebral haemorrhage

E.g. contusions, tearing of white matter

Question 18

Why are intracranial haemorrhages so dangerous?

Answer 18

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

Question 19

What type of bleeding occurs in an extradural haemorrhage?

Answer 19

Arterial bleed – middle meningeal artery

Question 20

Briefly, what type of bleeding occurs in a subdural haemorrhage?

Answer 20

Venous bleed – bridging veins

Question 21

Briefly, what type of bleeding occurs in a subarachnoid haemorrhage?

Answer 21

Arterial bleed – circle of Willis

Question 22

How does a subarachnoid haemorrhage occur?

Answer 22

• Secondary to trauma or spontaneous rupture of blood vessel e.g. aneurysm
• Blood leaks into subarachnoid space, mixing with CSF

Question 23

What is the common cause of subarachnoid haemorrhages?

Answer 23

A branch of ‘Circle of Willis’ ruptures (the arterial circuit responsible for supplying brain structures)

Question 24

Describe the CT imaging of the head for a subarachnoid haemorrhage

Answer 24

• 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

Question 25

Describe the characterisitcs of an extradural bleed

Answer 25

• Biconvex shape on CT - bleeding between periosteal layer and inner table of bone - strips periosteal dura from bone
• As periosteal layer tigghtly adhered at suture edges of bone once bleeding etends here it cannot extend further
• Typical history - blunt head trauma, lose conciousness, come to and seems normal, an hour later have significant deterioration in neurological function = lucid interval

Question 26

Describe the characterisitcs of an subdural bleed

Answer 26

• Crecent shaped as not limited by bown sutures so can fill right round the hemisphere