Topic 4 extracranial cerebral vessels Flashcards
Describe which parts of the brain are supplied by which vessels.
The anterior brain is supplied by the carotids. The posterior brain is supplied by the vertebrals.
Where do the carotid arteries arise from?
The right carotid artery arises from the innominate artery which is the first branch of the aorta. The left carotid artery arises directly from the aorta as the second branch
Where do the vertebral arteries arise from?
The vertebral arteries both arise from the respective subclavian branch (innominate artery on the right and aortic arch on the left). They form the basilar artery at the base of the brain.
List the branches of the external carotid artery.
Superior temporal artery Facial artery Lingual artery Superior thyroid artery Occipital artery Maxillary artery Posterior auricular artery Ascending pharyngeal artery
Describe the anterior circulation of the brain.
The first branch of the ICA is the opthalmic artery as it passes through the cavernous sinus. ICA branches into the middle and anterior cerebral arteries. Anterior and middle cerebral arteries supply mostly the frontal and parietal cortices, but also supply occipital and temporal cortices. The MCA is the largest branch of the anterior circulation.
Describe the posterior circulation of the brain.
The basilar artery begins at the pontomedullary sulcus and courses along the pons. Gives branches to the cerebellum and pons. Divides into the posterior and superior cerebral arteries.
Describe the circle of Willis
The CoW is formed by small arteries communicating from the posterior cerebral arteries to the distal ICA. The circle is completed by the two anterior cerebral arteries communicating via the anterior communicating artery.
Describe the development of atherosclerosis
Atherosclerosis is initiated by the lipid incorporation into the arterial wall which initiates inflammation. Extra-cellular lipids transform microscopic lesions into atheromas. Progression of inflammation promotes accumulation of lipid and necrosis of the surrounding tissue. Necrotic lesions form a fibrous cap and this creates lesions which are not hemodynamically significant. Fibrous cap thins over years and becomes susceptible to rupture. Calcification increases causing larger deposits which may become exposed to the lumen.
What are the causes of TIA?
85% is caused by ischaemia or by occlusion from atherosclerosis or emboli released from an atheroma or the heart. 15% is caused by cerebral haemorrhage of the intracranial arteries.
What is the difference between a stroke and a TIA?
In a stroke, symptoms last for more than 24 hours. In a TIA, symptoms last for less than 24 hours. In a stroke, residual function defecit persists or only partially resolves. In a TIA, symptoms completely resolve.
What is crescendo TIA?
Multiple TIA episodes within 7 days. These patients are at a high risk of stroke
What is amaurosis fugax?
Transient monocular blindness. Occurs in one eye. Typically resolves in a short period of time. Can be caused by emboli from carotid plaque.
What is a reversible ischaemic neurologic deficit?
It is a stroke in evolution. Symptoms usually last longer than 24 hours but can completely resolve.
Describe a dissection.
There is separation of the intimal layer. Can be caused by blunt trauma, heavy exertion or spontaneously. Spontaneous dissection can be associated to fibromuscular dysplasia or cystic medial degeneration.
What is giant cell arteritis ?
It is a type of vasculitis. Temporal arteritis and Takyasu’s arteritis is often associated with inflammation of the aorta and its proximal branches. Affects mid-large size arteries. Patients can present with headache, jaw claudication and transient vision loss.
Describe the sonographic appearance of giant cell arteritis
There is uniform thickening of the arterial wall. There may be a halo around the temporal artery due to inflammation. There may be a stenosis present.
What is the most common cause of aneurysm?
Atheroma
Describe vertebrobasilar ischaemia.
Number of conditions which impair the posterior circulation. Blood flow may be disturbed by embolic occlusion, external compression or stenosis. Symptoms include dizziness, vertigo, diplopia, paresthesia, tinnitus and drop attacks.
List some causes of vertebrobasilar ischaemia
- stenosis of the vertebral artery which may result in thrombus formation and occlusion of the artery
- stenosis of the subclavian artery can cause a fall in blood pressure in the subclavian and vertebral arteries
- pressure reduction in the subclavian artery may be enough to cause retrograde flow in the vertebral and basilar arteries
- embolic occlusion of the vertebral artery or one of its branches
- compression by osteophytes in the C-spine
What is subclavian steal syndrome?
Subclavian steal syndrome results from severe proximal subclavian artery stenosis or retrograde flow in the ipsilateral vertebral
What is the difference between subclavian steal syndrome and subclavian steal phenomenon?
Subclavian steal phenomenon refers to steno-occlusive disease of the proximal subclavian artery with retrograde flow in the ipsilateral vertebral artery.
Subclavian steal syndrome is the same as subclavian steal phenomenon with the addition of cerebral ischaemic symptoms.
What are the symptoms of subclavian steal syndrome ?
- Arm claudication
- Decreased blood pressure in that arm
- weak or absent pulse
- visual changes
- vertigo
- ataxia
List some causes of subclavian steal syndrome
- Atherosclerosis
- Takayasu arteritis
What is a carotid body tumour?
Carotid body tumours are paragangliomas. They usually occur in the bifurcation of the carotid artery. They can form along the vagus nerve up to the base of skull. Can cause tinnitus, dysphagia and hoarseness.
What is fibromuscular dysplasia?
FMD is the abnormal growth and connective tissue deposition in the media of an artery. It forms a series of thickened ridges which display a string of beads appearance. Symptoms include that of TIA, amaurosis fugax or stroke
Describe a carotid endarterectomy
Longitudinal incision in the artery with the removal of the diseased segment. The incision is stitched closed.
Describe an eversion endarterectomy
This involves a transverse incision through which atheroma is removed from the CCA, ICA and ECA. Atherome is removed from the cut end of the artery while pulling back on the artery to assist with atheroma removal. Stitches around the circumference of the artery therefore does not constrict the artery radially.
