Cerebral Vasculature Flashcards
Why is the brain in particular vulnerable if blood supply is impaired?
The brain makes up 2% of body weight but uses 10-20% of the bodies cardiac output, consumes 20% of the bodies oxygen and 66% of liver glucose.
Sufficient cerebral circulation is required in order to ensure that the brain is supplied adequately with glucose, and respiratory substrates, in addition to the effective removal of waste products.
Explain how blood is supplied to the brain starting from the aorta.
The cerebral vasculature originates from the aorta, branching off into the brachiocephalic trunk and subsequently bifurcating into the right common carotid artery and right subclavian artery posterior to the sternoclavicular joint. At the level of the laryngeal prominence, the common carotid artery further bifurcates into the internal and external carotid artery. The internal carotid artery directly supplies the brain, passing through the carotid canal (within the temporal bone) into the cranial cavity. Vertebral arteries arise from the subclavian arteries, traversing upwards and posteriorly through the transverse foramen of the cervical vertebrae (Protective effect reducing the susceptibility of a bleed). Vertebral arteries enter the cranial cavity via the foramen magnum. Paired arteries (Right and left vertebral arteries)
What is the anterior and posterior vasculature of the circle of Willis supplied by?
Anterior vasculature - carotid arteries
Posterior vasculature - vertebral arteries
Outline the posterior circulation of the circle of Willis.
Paired vertebral arteries fuse into the basilar artery, residing on the base of the pons Bifurcation into two posterior cerebral arteries.
The posterior communicating arteries connect the posterior and middle cerebral arteries.
Posterior cerebral artery supplies the occipital lobe and the inferior part of the temporal lobe.
Outline the anterior circulation of the circle of Willis.
- Middle cerebral artery - Supplies the temporal and parietal lobes
- Anterior cerebral artery - Frontal lobes & superior medial parietal lobes.
The anterior cerebral arteries are connected via the anterior communicating artery.
Note: A vascular atherosclerotic blockage within a cerebral artery can theoretically be compensated by the opposite respective branch.
What is the basic order of drainage for the venous drainage of the brain?
Cerebral veins > venous sinuses in the dura mater > internal jugular vein
Outline the venous drainage of the brain in detail.
Superficial veins drain into dural sinuses, sinuses arise from the separation of the periosteal and meningeal dural layers. The superior sagittal sinus aligns the longitudinal fissure, the presence of arachnoid granulations absorbs cerebrospinal fluid (CSF) from the meninges. This then drains into the confluence of sinuses besides the occipital lobe. The straight (Large cerebral vein of Galen) and occipital sinuses also drain into the confluence. Laterally, the transverse sinuses drain into the sigmoid sinuses and then to the internal jugular vein.
List the types of haemorrhage and their respective common causes.
Extradural - trauma, immediate clinical effects (arterial, high pressure)
Subdural - trauma, can be delayed clinical effects (venous, lower pressure)
Subarachnoid - ruptured aneurysms
Intracerebral - spontaneous hypertensive
What is an extradural haemorrhage?
An extradural (epidural) haemorrhage is a collection of blood that forms between the inner surface of the skull and the outer layer of the dura (endosteal layer).
It causes an increase in intracranial pressure. Pressure can strip the endosteal layer away from the cranial cavity. A rising level of intracranial pressure will eventually cause midline shift and tentorial herniation.
Compression of brainstem (Centres supressed)
What is the pterion?
The weakest point of the cranial cavity therefore vulnerable to trauma as it is the fusion point between the parietal, sphenoid, frontal and temporal bones.
What will trauma to the pterion most likely lead to?
Trauma to the pterion will most likely lead to the rupture of the middle meningeal artery.
Symptoms are immediate.
Leads to a ‘lemon’ shaped bleed, seen
on MRI and CT imaging.
Where do subarachnoid haemorrhages most often present and due to what?
Subarachnoid bleeds typically present at the base of the brain, most often due to aneurysmal ruptures. Blood accumulation within the subarachnoid space. Berry aneurysms are arterial swellings usually at the junction of arterial bifurcation.
What do intracerebral haemorrhages usually arise from?
Intracerebral haemorrhages usually arise from ruptures of an arteriosclerotic small artery that has been weakened predominantly by chronic arterial hypertension.
(Charcot-Bouchard aneurysms more likely to be found in lenticulostriate vessels (Anterior circulation of the Circle of Willis and supplies the basal ganglia). Chronic hypertension can result in cerebral microbleeds.)
Explain the pathophysiology of a Charcot-Bouchard aneurysm.
Blood from an intracerebral haemorrhage accumulates as a mass, compressing cerebral structures and leading to neuronal dysfunction. Large haematomas increase intracranial pressure.
What is a stroke?
What % are thrombi-embolic and what % due to a haemorrhage?
A cerebrovascular accident (CVA) - defined as a rapidly developing focal disturbance of brain function of presumed vascular origin and a duration of more than 24 hours.
Thrombo-embolic (85%)
Haemorrhage (15%)
