Skull Vault, Cranial Cavity and Meninges 3

Question 1

How do venous sinuses communicate with extracranial veins?

Answer 1

By means of emissary veins – these pass all the way through the skull in emissary foramina in the vault bones.

Question 2

What is the function of diploic foramina?

Answer 2

They transmit diploid veins from the diploe to either the inside or the outside of the vault.

However, they dont pass all the way through the vault bones like the emissary foramina.

Question 3

Where is the superior sagittal sinus found?

Answer 3

It is found in the upper border of the falx cerebri.

Question 4

What happens to the superior sagittal sinus towards the posterior end?

Answer 4

It increases in size.

Question 5

What happens to the falx cerebri at the point where it meets the tentorium?

Answer 5

It turns to the right to become the right transverse sinus.

Question 6

What is the path of the right transverse sinus?

Answer 6

It travels around the side of the cranial cavity in the attached margin (outer margin) of the tentorium cerebelli and then it follows an S shaped curve downwards towards the jugular foramen.

Question 7

What is the latter S shaped section of the right transverse sinus called?

Answer 7

It is called the sigmoid sinus.

Question 8

What happens to the sigmoid sinus as it passes down through the jugular foramen?

Answer 8

It becomes the internal jugular vein.

Question 9

Where are most of the venous sinuses?

Answer 9

They occupy slits that sit between the dura and the periosteum.

Question 10

Which 2 sinuses are found entirely between the 2 dural folds?

Answer 10

The inferior sagittal sinus and the straight sinus.

Question 11

Where is the inferior sagittal sinus found?

Answer 11

In the lower free edge of the falx.

Question 12

How does the inferior sagittal sinus become the straight sinus?

Answer 12

It joins the great cerebral vein from the brain to form the straight sinus.

Question 13

What is the path of the straight sinus?

Answer 13

It continues posteriorly to the attached margin of the tentorium to form the left transverse sinus and occassionaly it can form the right transverse sinus.

Question 14

Where are the cavernous sinuses found?

Answer 14

They are found on each side of the body of the sphenoid bone.

Question 15

Describe the cavernous sinuses?

Answer 15

These are large sinuses which are filled with a fine fibrous meshwork giving it a spongy consistency in real life.

Question 16

Which structures travel in the dura of the cavernous sinuses?

Answer 16

The cranial nerves travel in the dura of the lateral wall of the cavernous sinuses on their way to the orbital cavity and to the maxilla and the upper jaw.

Question 17

Which cranial nerves travel in the lateral wall of the cavernous sinuses?

Answer 17

• 3rd cranial nerve
• 4th cranial nerve
• 2 divisions of the trigeminal nerve
  
  • opthalmic
  • maxillary

Question 18

Which cranial nerve travels free in the substance of the cavernous sinus?

Answer 18

The 6th cranial nerve runs forwards through the cavernous sinus but it is free within the substance of the sinus. If approaches the sinus from the posterior cranial fossa and it passes underneath the petroclinoid ligament to enter the cavernous sinus.

In the cavernous sinus, it travels close to the internal carotid artery.

The internal carotid artery also courses through the cavernous sinus.

Question 19

Where does the 6th cranial nerve travel to?

Answer 19

It travels to the orbit.

Question 20

Does the internal carotid artery stay in the cavernous sinus?

Answer 20

No it eventually leaves the cavernous sinus and it supplies part of the brain with blood.

Question 21

Where do the cavernous sinuses recieve blood from?

Answer 21

From the veins of the orbit.

Question 22

How can an infection from the orbital cavity or mid face enter the cavernous sinus?

Answer 22

Infections can track down from the orbital cavity and mid face through the orbital veins to enter the cavernous sinus.

Question 23

How can we get cavernous sinus thrombosis?

Answer 23

The cavernous sinus communicates with veins below the skull base so if these is an infection of the back of the upper jaw, this can track up to the cavernous sinus through those veins.

If this is untreated it can cause thrombosis in the cavernous sinus.

Question 24

How do the 2 cavernous sinuses communicate with each other?

Answer 24

Across the midline.

Question 25

From the cavernous sinuses, where does blood drain into?

Answer 25

Blood drains into venous channels that run along the upper and lower borders of the petrous temporal bones therefore these are known as the petrosal sinuses.

Question 26

Where is the superior petrous sinus?

Answer 26

The superior petrosal sinus occupies the upper edge or the crest of the petrous temporal bone.

Question 27

What does the superior petrous sinus join posteriorly?

Answer 27

It joins the transverse sinus posteriorly.

Question 28

Where is the inferior petrosal sinus found?

Answer 28

It is found along the lower posterior edge of the petrous bone.

Question 29

What is the path of the inferior petrosal sinus?

Answer 29

It first drains blood from the inner ear by means of the labrynthine veins and then runs to the jugular foramen where it joins the sigmoid sinus and becomes the internal jugular vein.

Question 30

What is the subdural space?

Answer 30

The dura is in contact with the underlying arachnoid mater but there is a potential space between the them called the subdural space.

Question 31

How can we get a subdural haemotoma?

Answer 31

Many of the veins from the brain drain into the superior sagittal sinus and therefore they need to cross the potential space between the dura and the arachnoid. If these veins rupture because of a head injury then this could lead to a subdural haemotoma.

Question 32

How do we get an extradural haemotoma?

Answer 32

Rupture of the meningeal artery can cause an extradural haemotoma because this artery lies outside the dura or lateral to it. This could occur because of an injury to the vault bones.

Question 33

Describe the arachnoid.

Answer 33

• thin membrane
• outermost layer of the arachnoid consists of several layers of flattened cells that are all linked together as a continuous sheet with tight junctions and this sheet acts as a barrier to the free passage of ions and molecules into or out of the space between the arachnoid and pia mater.

Question 34

What is the name of the space between the arachnoid and the pia mater?

Answer 34

This is called the sub arachnoid space.

Question 35

Describe the sub arachnoid space.

Answer 35

• extensive
• it surrounds the brain and it is continuous with the subarachnoid space around the spinal cord
• it contains a clear fluid called the cerebrospinal fluid (CSF)

Question 36

Describe the pia mater.

Answer 36

• delicate membrane
• intimately covers the brain and the spinal cord
• dips deeply into the fissures on the surface of the brain.
• blood vessels that are destined for the brain lie on the surface of the pia and they anastomose freely
• blood vessels pierce the pia and enter the brain

Question 37

What are the 2 roles of the cerebrospinal fluid?

Answer 37

• protective role — surrounds and buffers the brain and the spinal cord against injury.
• regulatory role — regulates intracranial pressure which rises and falls with changes in cerebral blood flow.

Question 38

What are the choroid plexuses?

Answer 38

• these are a series of tufts which project into the cavity/ ventricles as a vascular network of the pia
  
  • the walls of the cavities are often only composed of a thin layer of epithelium.
• in the choroid plexus is therefore a vascular plexus where the CSF is formed
• the CSF that is formed in the choroid plexus escapes from the interior of the brain through small holes at the back of the brain and spinal cord into the subarachnoid space.

Question 39

What are subarachnoid cisterns?

Answer 39

After the CSF enters the subarachnoid space it circulates around in this space and in certain places, the subarachnoid space is large and it is here that the CSF forms pools called subarachnoid cisterns.

Question 40

Where is a cistern where we can easily tap CSF from the patient?

Answer 40

Near the lower end of the spinal cord there is a large lumbar cistern which is a useful place to tap fluid from a patient.

Question 41

How does absorption of the CSF take place.

Answer 41

Takes place through arachnoid villi.

Arachnoid villi are small protrusions of arachnoid mater through the bit of the dura that form the superior sagittal sinus.

Question 42

Describe the structure of the arachnoid villi.

Answer 42

They have minute tubules that pass through the middle of each villus and which open at the apex of the sinus

Question 43

What happens when the pressure of the CSF is greater than the pressure of the venous sinuses?

Answer 43

The arachnoid villi fill with cerebrospinal fluid which then flows into the venous sinus.

Question 44

What happens when the venous pressure is greater than the pressure of the cerebrospinal fluid?

Answer 44

The villi and their tubules collapse so that there is no flow of cerebrospinal fluid.

Question 45

What are collections of arachnoi villi called?

Answer 45

They are called arachnoid granulations.

Question 46

What happens with the arachnoid granulations as you grow older?

Answer 46

They become larger and they can be seen with the naked eye when examining the interior of the superior sagittal sinus.

Question 47

What is rhinorrhoea?

Answer 47

If we have a head injury to the anterior cranial fossa then the brain coverings in the region of the cribriform plate can be torn and this could cause CSF to leak downwards into the nasal cavity.

Question 48

What is otorrhoea?

Answer 48

If there is a fracture of the petrous temporal bone, CSF could leak through any of the cracks in the petrous temporal bone and into the ear.

Question 49

What is it important to ask a patient who has had a head injury?

Answer 49

It is important to ask them whether they have noticed any blood stained fluid coming out of their nose or out of their ears.

Question 50

Where does the blood supply to the brain come from?

Answer 50

From the vertebral arteries and the internal carotid arteries.