Flashcards in Session 9 - Stroke Deck (51)
What are the two main arteries that supply blood to the brain?
ICA and Vertebral arteries
What are the branches of the ICA in the skull?
o Ophthalmic Arteries
o Posterior Communicating Arteries
o Middle Cerebral Arteries
Lateral surfaces of the cerebral cortex
o Anterior Cerebral Arteries
Supplies medial surfaces of the frontal and parietal lobes
What does ICA travel through to reach the brain matter?
The carotid canal
How do the vertebral arteries enter the hollow of the skull?
Through the foramen magnum and joins to form the basilar artery, which supplies the cerebellum and brainstem
What does the basilar artery pair into/
Posterior cerebral arteries
What does the anterior cerebral artery supply?
Medial surfaces of the frontal and parietal lobes
What does the middle cerebral artery supply?
Lateral surfaces of cerebral cortex
What does the posterior cerebral artery do?
Inferior surface of the Brain
What is the circle of willis?
The Anterior and Posterior Cerebral Arteries are joined together through communicating branches to form the Circle of Willis at the base of the brain.
What is autoregulation in the brain?
A change in CPP causes an appropriate compensatory change in cerebral blood vessels. This means that CPP can fluctuate (within certain limits) without causing a significant change in cerebral blood flow.
o Decreased CPP causes cerebral vasodilation
o Increased CPP causes cerebral vasoconstriction
What is chemoregulation of the cerebral blood supply?
The build-up of metabolic by-products results in cerebral vasodilation
o Decreased extracellular pH
o Decreased pO2
o Increased pCO2
The opposite will cause cerebral vasoconstriction
o Increased extracellular pH
o Increased pO2
o Decreased pCO2
What is cerebral perfusion pressure?
Net pressure gradient causing cerebral blood flow to the brain
What is the equation for CPP
CPP=Mean Arterial Pressure-Intracranial Pressure
A stroke is a clinical syndrome of abrupt loss of focal brain function lasting over 24 hours (or causing death) that is due to either spontaneous haemorrhage into brain substance or inadequate blood supply to a part of the brain.
Name the two main types of stroke
How common is ischaemic stroke?
80-85% of strokes
What are the two main causes of ischaemic stroke
o Large vessel atheroma/embolism (e.g. ICA) – 75-80%
o Cardiac Embolism (Atrial Fibrillation) – 20%
What is the most common symptom of ischaemic stroke?
What is a haemorrhagic infarct?
o Thrombus occludes vessel, necroses distal tissue and then either a)dissolves and blood floods into area through necrotic capillaries (perhaps due to thrombolysis) or b) collateral circulation, which is insufficient to support metabolic needs of tissue floods area with blood
o Results in haemorrhagic (red) infarct
o Most common in embolus
How common are haemorrhagic strokes?
What is a primary haemorrhagic stroke?
No structural lesion
What is a secondary cause of haemorrhagic stroke?
Why would a young man present with haemorrhagic stroke?
What occurs in the frontal lobe?
What occurs in the parietal lobe?
- Inferior homonymus Quandrantopia
What occurs in the temporal lobe?
Taste and smell
- Superior homonymous quadrantanopie
What occurs in the occipital lobe?
Primary visual cortex
What happens in the cerebellum/brainstem?
Motor and sensory tracts
Cranial Nerve nuclei
Give some vascular risk factors for stroke?
Heavy alcohol intake
What are the inititial investigations in stroke?
o BM (check for hypoglycaemia)
o Haematological – FBC, INR
o ECG (check for AF)
o Brain imaging
What is a CT scan used for?
Will demonstrate haemorrhage immediately
Does not rule out ischaemic stroke (but may visualise an infarct)
CT superior for haemorrhage and bony anatomy, and can be done quickly
More sensitive to calcification in a lesion, which is useful in tumour diagnosis
Emergency patients undergo CT
What is an MRI used for?
due to infarction
MRI superior for white matter disease (?)
MRI better for long term detection of haemorrhage – sign disappear on CT after a few weeks, whereas indefinite on MRI
Non-emergency patients undergo MRI
What are the three constituents of the cranial cavity?
Brain, blood and CSF
What is normal intracranial pressure?
When does ICP reach 20mmHg normally?
Coughing and straining
What common pathologies cause raised ICP?
Haemorrhage, tumours, meningitis and cerebral infarction
What are three areas which can herniate in raised ICP?
o The Cingulate Gyrus
o The Uncus
o The Cerebellar Tonsils
What compartments make up the brain?
o Falx Cerebri – In the midline between the two cerebral hemispheres
o Tentorium Cerebelli – Lies on the superior face of the cerebellum
Name four types of herniation
o Subfalcine Herniation
o Central Herniation
o Uncal Herniation
o Tonsillar Herniation
What is the path of raised ICP?
1. Localising Signs
2. Decreasing levels of consciousness
4. Death (if untreated)
Give some causes of raised ICP
Coughing (Stop a patient coughing by intubating/ventilating them under anaesthesia as part of a protective plan)
Impaired venous drainage
o Cerebrospinal Fluid
Subarachnoid haemorrhage (Cerebral blood vessels are very sensitive to CO2 and will dilate, causing a rise in ICP)
Blockage in ventricular system (Ventricular shunt to treat)
Trauma – Extradural, subdural, intracerebral
How does direct head trauma cause raised ICP?
Head injuries are common and result in the brain being shaken inside the skull.
This causes direct injury to the brain resulting in oedema or haemorrhage due to the rupture of arteries or veins, producing extradural or subdural haematoma and consequent rise in intracranial pressure.
Outline the monro-kellie hypothesis for the sequence of events which stem from raised ICP and lead to brain herniation
o Any increase in Brain, Blood or CSF can cause an increase in ICP, and will usually have an impact on the other two unaffected constituents
o Small increases in ICP (<25mmHg) will cause displacement of the CSF in the spinal cord
o Once ICP reaches pressure of mean systemic BP, it will reduce Cranial perfusion pressure (CPP = BP – ICP)
o This will cause cushing’s reflex to kick, with the body increasing systemic blood pressure and cause dilation of cerebral blood vessels
o This raised ICP further, causing reduction in cerebral flow and perfusion
o This can result in a midline shift, in which one of the brain hemispheres is compressed by the other, potentially causing blockage of a ventricle and hydrocephalus (Further raised ICP!)
o Brainstem compression can then occur (see above for types)
Give some of the long term sequlae of head injury
o Neurological deficit
o Chronically raised pressure if the circulation of CSF has been impaired by scarring
How do you know if a head injury is serious?
o Mechanism of injury
How much force went through the brain
o Signs of brain injury
Change in consciousness
Knocked out/Amnesia – Quite a lot of force needed!
o Patter of change
Got better or worse since?
o Primary injury
o Secondary Injury
E.g. Hypoxia, hypotension, blood clot
Recognise and treat quickly
Outline the blood supply to the spinal cord
o Anterior Spinal Artery
Supplies anterior two thirds
o 2x Posterior Spinal Arteries (Paired)
Supplies posterior third
What is the anterior spinal artery forme dby?
The union of branches of the vertebral arteries
What special artery supplies the lower thoracic or upper lumbar segments of the spinal cord?
The artery of adamkiewicz
What is anterior spinal artery syndrome, and what are its causes?
Occlusion of the Anterior Spinal Artery is most common (95%). Causes include:
o Disease of the Aorta
Aneurysm, trauma, dissection, atherosclerosis
o Aortic Surgery
o Sickle cell disease
o Cardiac emboli
o Disc herniation, compressing vessels
What will you find on examination of a patient with anterior spinal syndrome?
o Spinal Shock initially
o Complete motor paralysis below the level of the lesion due to interruption of the Corticospinal Tract
o Loss of pain and temperature (Interruption of Anterior and Lateral Spinothalamic Tracts)
Fine touch and vibration preserved as Dorsal Column is supplied by the Posterior Spinal Artery
o Progress to Upper Motor Neurone signs with muscle atrophy
o Sensory level pattern of loss