Meninges and Intercranial Circulation

Question 1

Describe the venous drainage of the brain

Answer 1

1. Cortical bridging veins > superior sagital sinus
2. Inferior sagittal sinus > straight sinus
3. Straight sinus + superior sagittal sinus + occipital sinus > confluens of sinuses
4. Confluens of sinuses > transverse sinuses
5. Transverse sinus + superior petrosal sinus (from cavernous sinus) > sigmoid sinus
6. inferior petrosal sinus + sigmoid sinus > jugular foramen

Question 2

Describe the arterial circulation of the brain.

Answer 2

1. The vertebral arteries each give off 2 branches
   - a posterior spinal artery
   - branches that join in the midline as the anterior spinal artery
2. The vetebral arteries give off another branch before they meet known as the posterior inferior cerebellar artery
3. The vertebral arteries meet at the midline to form the basillar artery and promptly gives off an anterior inferior cerebellar artery.
4. The basillar artery gives off many short pontine arteries.
5. The basillar artery then gives off an anterior inferior cerebellar artery
6. the basillar then gives off a superior cerebelllar artery before it splits
7. The basillar splits into the posterior cerebral arteries
8. The posterior cerebral arteries connect to the internal carotid artery via the posterior communicating arteries.
9. The internal carotids give off the middle cerebral arteries which run laterally on the brain
10. The internal carotid also gives off anterior cerebral arteries which runs on the medial sides of the hemispheres. They are connected between themselves with the anterior communicating artery.

Question 3

Which cranial nerves are commonly impinged with sites of cerebral aneurysms?

Answer 3

1. Optic nerve (II) at the junction between the anterior cerebral artery and anterior communicating artery. (MOST COMMON)
2. Optic Chiasm (junction of the internal carotid, middle cerebral, anterior cerebral)
3. Oculomotor (where basillar divides into posterior cerebral arteries)
4. Abducens (Where the vetebral arteries and the space between anterior and labrynthe arteries)

Question 4

Describe the meninges, the layers from the bone of the skull.

Answer 4

1. Against the bone is the periosteal dura.
2. Meningeal dura is pressed against the periosteal except for the sinuses where the meningeal dura detaches.
3. Next is the arachnoid
4. Between the arachnoid and the pia mater is the subarachnoid space containing the CSF.
5. Pia mater is tightly associated with the brain.

Question 5

Describe an epidural hematoma.

Answer 5

It is lesion of the middle meningeal artery, pressed between the periosteal dura and the bone of the skull (creating the grooves)

It runs along the lateral side of the skull which is also the most vulnerable.

The periosteal dura is tightly associated at the suture lines and in imaging wouldn’t cross suture lines.

Question 6

Describe a subdural hematoma.

Answer 6

This occurs with the cortical bridging veins which go along the surface of the brain, through the arachnoid and into the meningeal dura.

When the brain moves while the skull and its dura doesn’t move. This can cause tearing of the bridging veins, releasing blood between the meningeal dura and the arachnoid membrane.

This hematoma can cross suture lines.

Question 7

Describe the recycling of CSF

Answer 7

CSF is made in the ventricles which contain choroid plexus. It is in the two lateral ventricles.

Then it travels down the interventricular foramen (Monroe)

Into the third ventricle.

From there it travels down the cerebral aqueduct into the fourth ventricle.

From the fourth ventricle it can travel anteriorly (lateral foramina - Lushka) or posterior (medial foramina - Magendie)

The CSF enters the subarachnoid space.

Then it goes through arachnoid granulations (communication between the subarachnoid space and the superior sagittal sinus.

Question 8

What is communicating hydrocephalus?

What is non-communicating hydrocephalus?

Answer 8

Communicating - problems with the arachnoid granulations.

Non-communicating - problems with the ducts and foraminas that allow the ventricles to communicate with each other and the subarachnoid space.
(most common site is the cerebral aqueduct)

Question 9

What is a subarachnoid hemorrhage?

Answer 9

Its when a cerebral artery ruptures when its running on the pia mater. The blood fills the subarachnoid space leading to bloody cerebrospinal fluid.

Question 10

What nerves are running through the cavernous sinus and when clots form in the sinus, what nerve is the first to be affected?

Answer 10

Oculomotor, trochlear, abducens, V1, V2.

Abduction is the first thing to go.