Anatomy of Blood Flow in CNS and Consequences of disruption

Question 1

What percentage of the CO and body’s glucose consumption does the brain use?

Answer 1

10-20% of CO

66% of glucose consumption

Question 2

What are the sources of blood to the brain?

Answer 2

Internal carotid arteries–internal branch of the common carotid go through the carotid canal in the base of the skull.

Vertebral arteries (a branch of the subclavian artery) –protected in the vertebral transverse foramina - goes through the foramen magnum and then fuse to form the basilar artery–forms posterior circulation to the brain.

Question 3

Describe the locations of the arteries in the brain.

Answer 3

two vertebral arteries coming up from foramen magnum -> two arteries fuse at level of pons and run as basilar artery under the pons ->bifurcates at cerebellum to posterior cerebral arteries -> internal carotids come through floor of cranial cavity -> middle cerebral artery is the main branch coming off- > small anterior cerebral artery
posterior and anterior communicating arteries complete anastomotic circuit

Question 4

What is venous drainage mediated by?

Answer 4

Cerebral veins.

Venous sinuses.

Dura mater –folds in this are the venous sinuses.

Internal jugular vein.

Question 5

What is a falx?

Answer 5

folds in the dura

Question 6

What are the sinuses in the brain?

Answer 6

biggest is the superior sagital sinus -> falx cerebri between the hemispheres -> inferior sagital sinus

a lot of blood from the brain drains through the cerebral vein (vein of galen) -> drains through straight sinus -> confluence of sinuses (in occipital region)

transverse sinus -> sigmoid sinus -> internal jugular vein via jugular foramen

Question 7

Which of the arteries in the circle of willis is unpaired? What is the advantage of this arrangement

Answer 7

anterior communicating artery

anatomotic circuit allows compensatory flow

Question 8

What is a stroke?

Answer 8

A cardiovascular accident (CVA)

Definition –rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours’ duration

Caused by infarction (85%)or haemorrhage (15%).

50% of survivors are permanently disabled and 70% show an obvious neurological deficit.

Question 9

What are the risk factors of stroke?

Answer 9

age
hypertension
cardiac disease
smoking
diabetes mellitus

Question 10

What is a transient ischaemic attack?

Answer 10

rapidly developing focal disturbance of brain function of presumed vascular origin that resolves completely within 24 hours (normally resolve in minutes)

Normally a precursor to a full-blown stroke.

Question 11

What is an infarction?

Answer 11

degenerative changes that occur in any tissue following the occlusion of an artery.

Question 12

What is cerebral ischaemia?

Answer 12

lack of sufficient BLOOD SUPPLY to nervous tissue resulting in permanent damage if blood flow is not restored quickly (hypoxia or anoxia are different as they are describing JUST oxygen).

Question 13

What are causes of occlusion?

Answer 13

Thrombosis - formation of a solid blood clot

embolus - plugging of a small vessel by debris carried from larger vessels

Question 14

What are the areas supplied by the anterior, middle and posterior arteries?

Answer 14

anterior = strip on top of brain from temporal -> parieto-occipital sulcus

middle = most of the brain, also supplies some of the sub-cortical grey matter towards the centre of the brain

posterior = occipital area

Question 15

What would a disturbance in the anterior cerebral artery cause?

Answer 15

Paralysis of contralateral leg (more so in the leg than arm) - as you have the upside down homunculus map of the body in the brain

Disturbance of intellect, executive function and judgement (collectively known as aboulia) - frontal lobe

Loss of appropriate social behaviour.

Question 16

What would a disturbance in the middle cerebral artery cause?

Answer 16

“CLASSIC STROKE

Contralateral hemiplegia (arm>leg however).

Contralateral hemi-sensory deficits.

Hemianopia–blindness over half the field of vision.

Aphasia(left-sided lesion) –inability to understand or produce speech

Question 17

What would a disturbance in the posterior cerebral artery cause?

Answer 17

visual deficits :
- Homonymous hemianopia –loss of half of the field of view on the same side in both eyes.

-Visual agnosia –inability to recognise things.

Question 18

What is a lacunar infarct?

Answer 18

lacune = small cavity.

These appear in deep structures as a result of small vessel occlusion.

The deficit is of course dependant on anatomical location –often occur in basal ganglia.

Area has often been infarcted and then cleared away by phagocytosis leaving a lacuna.

Associated with chronic hypertension.

Question 19

What are the different types of haemorrhagic storkes?

Answer 19

Extradural - from trauma with immediate effect - high pressure arterial bleed - main cause is blow to side of head (pterion) bursts middle meningeal artery

Subdural - from trauma with delayed effect- lower pressure venous bleed

Subarachnoid - from ruptured aneurysms (congenitally weak vessels – e.g. Berry aneurism)

Intracerebral - from spontaneous hypertensive events/bleeding