Explain the main acute & chronic conditions that atherosclerosis of the carotid & cerebral arteries can cause (ensure that you can provide definitions from Haem week)
Chronic:
- Atherosclerosis (chronic inflammation within the wall of an artery) reduces vascular elasticity and the diameter of the artery lumen thus reducing blood supply to the brain accelerating the atrophy (apoptosis) that is already an inevitable part of ageing.
- Loss of functional tissue in the brain can cause a form of dementia referred to as vascular dementia when caused by atherosclerosis.
- Atrophied brains put people at greater risk of sub-dural haematomas as while the brain atrophies it produces more CSF and the brain can shift more within the skull. Sudden displacement of the brain within the skull can lead to tearing of the bridging veins.
Acute:
- Atherosclerosis increases the risk of thrombus (attached blood clot) formation due to turbulent blood flow and localised hypercoagulability in the affected artery.
- A thrombus may get so large that it occludes the vessel completely leading to an ischaemic (lack of blood supply) stroke (necrosis) Or a piece of thrombus may break off and travel with the flow of blood as an embolus (anything undissolved travelling in the blood), which in the carotids or cerebral arteries results in ischaemic stroke, which will inevitable cause oedema and a rise in ICP but is typically less dangerous that a haemorrhagic stroke.
- Atherosclerosis also weakens the wall of the artery and predisposes it to the formation of an aneurysm (localised abnormal dilatation of the artery), which constitutes a space-occupying lesion or SOL. SOLs can cause atrophy but in the case of aneurysms if they rupture the result is a sub-arachnoid or intracerebral haemorrhage or ‘haemorrhagic stroke’. This arterial bleed results in a rapid rise in intracranial pressure that can result in herniation of the brain and death.
Revise cell death, neoplasia, inflammation & repair in the nervous system
What is the purpose of myelin & an example of a demyelinating disease that affects the CNS?
Multiple Sclerosis
Transverse myelitis
List key features of subarachnoid, subdural & epidural haematomas
Epidural haemorrhage -
frequently the result of rupture of the dural arteries ususally following trauma to the temporal area of the skull, the high arterial pressure results in
rapid accumulation of blood/haematoma between the skull and dura - ICP is increasing and will predispose towards herniation and
death
Subdural haematomas are frequently the result of tearing of the bridging veins between the dura mater and arachnoid layers. These veins tear due to displacement of the skull, the brain moves within the CSF stretching the veins and predisposing them to tearing - Elderly people and those with atrophy of the brain are at greatest risk - Subdural haematomas progress more
slowly, resulting in vague symptoms up to 48 hours following the event. Subdural haematomas are usually self-limiting with lysis and organisation occurring over weeks and months following the bleed
Subarachnoid haematomas are frequently the result of trauma causing an arterial haemorrhage from a congenital aneurysm - Being arterial, there is a rapid rise in ICP due to a rapidly accumulating haematoma
What determines whether a SOL causes atrophy or herniation?
Generally the speed of the accumulation, if something accumulates gradually, the brain has time to adapt through atrophy whereas a fast accumulation will result in herniation
List how microbes enter the CNS
- Blood - Bacterial endocarditis
- Direct implantation - trauma, sergery
- peripheral nervous system (PNS)
- Extension from local sites - ears, eyes, sinuses
List differences in CSF appearance in pyogenic (acute bacterial) meningitis versus viral meningitis
viral meningitis
- the infection may be self-limiting.
- The CSF has normal glucose
- may contain lymphocytes & thus have a slight increase in proteins.
bacterial meningitis
- the CSF is often purelent, cloudy or turbid
- increased protein
- reduced or absent glucose.
- Neutrophils are present in bacterial meningitis and there may be puss.
In basic terms, this is because bacteria are usually extracellular thus metabolising in the CSF and will attract an acute response, whereas viral infections are intracellular.
List age-related diseases of the CNS
Parkinson’s disease
Alzheimers disease
Dementia
Examples of space occupying lesions (SOLs)
Tumours, haematomas, oedema/swelling (diffuse or localised), abscesses, hydrocephalus, aneurysm etc
