Cerebral vasculature Flashcards
Describe blood supply to the brain
Blood supply is mainly formed from vertebral arteries and the internal carotid artery which arises from the common carotid. Vertebral arteries are protected initially as they run through the foramina transversarium of the spine. They then converge to form the basilar artery which feeds into the circle of Willis. Internal carotids enter through the carotid canal.
Describe circle of Willis
The basilar artery then divides into the 2 posterior cerebral arteries. Main branch of ICs is the middle cerebral artery with another branch being anterior cerebral arteries. There are also anterior and posterior communicating arteries to complete the circuit.
What is an advantage of the circle of Willis arrangement?
In the potential case that there is a blockage of one of these arteries e.g. if there is atherosclerotic blockage of the common carotid in the neck, it can be compensated by flow from other side through communicating arteries. However, compensatory mechanisms are often insufficient esp between anterior and posterior as posterior communicating arteries are very thin.
What is an extradural haemorrhage?
An extradural haemorrhage is when there is damage to the bone of the skull. If pterion impacted, main artery supplying dura runs directly beneath so it can be ruptured by impact (this type of haemorrhage is almost always caused by trauma). If ruptured, as it is arterial, immediate clinical effects are observed and high pressure of blood can strip away the dura and increase intracranial pressure. Therefore, blood must be removed and craniotomy resealed.
What is a subdural haemorrhage?
Usually caused due to trauma and a slow, venous subdural bleeding. May have been a head injury followed by loss of consciousness but patient is later fine - however, must be observed as this usually has a delayed clinical presentation due to venous bleed. May take hours or days to present as blood is at low pressure.
What is a subarachnoid haemorrhage?
Usually due to a ruptured aneurysms occuring in circle of Willis where a vessel may have weakened walls. Usually in hypertensive patients and aneurysms are congenital + symptomless so may be spotted when scanning for something else.
What is an intracerebral haemorrhage?
Usually spontaneous, seen in patients with chronic hypertension.
How is a stroke defined?
Cerebrovascular accident (CVA). Defined as rapidly developing focal disturbance of brain function of presumed vascular origin and of >24 hours duration. 85% of strokes are thromboembolic in nature (caused by a blockage) while 15% are haemorrhagic (caused by a bleed).
Define transient ischaemic attack
Defined as rapidly developing focal disturbance of brain function of presumed vascular origin and resolves completely within 24 hours. Often a warning for a subsequent stroke and patient presentation is that of random blankouts of confusion.
Define infarction
Degenerative changes which occur in tissue following occlusion of an artery
Define cerebral ischaemia
Lack of sufficient blood supply to nervous tissue resulting in permanent damage if blood flow is not restored quickly.
Define thrombosis
Formation of a blood clot (thrombus)
Define embolism
Plugging of smaller vessel by material carried by larger vessel e.g. thrombi from the heart or atherosclerotic debris from internal carotid.
Why is stroke a major public health issue?
3rd most common cause of death. 100,000 deaths in the UK per annum. 50% of survivors are permanently disabled and 70% show an obvious neurological deficit.
What are the risk factors for stroke?
Age, Hypertension, Cardiac disease, Smoking and Diabetes Mellitus
CHADS
