What are the 3 main mechanisms of cerebrovascular disorders?
What is hypoxia?
HYPOXIA is a reduction in either oxygen supply
or oxygen utilisation by the tissues
What mechanisms can deprive the brain of oxygen?
Low partial pressur eof oxygen, impaired oxygen carrying capacity (eg CO poisoning), toxins that interfere with oxygen
Ischaemia: Tissue hypoperfusion (transient or permanent), hypotension, vascular obstruction, or both.
What is a combination of hypoxia and ischaemia called?
Hypoxic Ischaemic Encephalopathy. The combined term is not recommended. A reduction in oxygen can occur along several points of oxygen delivery to the brain.
What is histotoxic hypoxia?
Inability of tissue to utilise oxygen.
What causes histotoxic hypoxia?
Environmental toxins such as cyanide and sulfide bind to brain receptors but cause severe hypotension due to heart failure resulting in brain necrosis.
What happens during carbon monoxide poisoning?
Oxygen on haemoglobin is displaced. This results in hypoxia that is irreversible.
Which parts of the brain are most affected by CO poisoning?
High iron content areas
What kind of syndrome is associated with low dose CO?
Amotivational state called psychic akinesia. This is seen more commonly in cases who survived attempted suicide in modern car.
What are the types of necrosis of brain tissue?
Selective neuronal necrosis
What does selective neuronal necrosis indicate in forensic findings?
The death must have happened after some time from the initial injury.
Why must hypoxia and ischaemia be distinguished?
To be able to predict outcome of a global insult and coma.
Medico-legal determine whether a respiratory arrest or a cardiorespiratory arrest has occured. The clinical outcome is vastly different if the heart has not stopped and the blood pressure has been maintained.
Causes of pure hypoxia include infections of tracheobronchial tree and short lived anaesthetic errors. Hypoxic coma can be followed by complete recovery.
What are the potential non-traumatic causes of subarachnoid haemorrhage?
Rupture of aneuryms
Arteriovenous malformations abnormal development of vessels
Mycotic (septic embolus that weakens the vessel wall where it lodges)
What layer is missing in blood vessels that get aneurysms?
Tunica media (all that remains is the tunica intima and adventitia)
Where do berry aneurysms occur most often?
90% of them occur in anterior circulation near major arterial branches. (20 - 30% of cases have multiple aneurysms)
What are the major symptoms of berry aneurysm rupture (subarachnoid haemorrhage)?
Very intense headaches and vomiting with lucid interval.
What conditions are aneurysms associated with?
Polycystic kidney disease
Coarctation of the aorta
What is the most common cause of mortality in people with subarachnoid haemorrhage?
Vasospasm which is a direct effect of the blood or blood products on the adventitia of the artery.
What are the symptoms of an aneurysm?
Prior to rupture usually asymptomatic unless large enough to press on
Aneurysmal rupture has a high mortality .
Neurosurgical and endovascular intervention is available.
There is a risk of re- bleeding.
Some do return to a normal life and others are partially or severely
disabled ( variable).