neuro imaging. types of scan ct mri ct vs mri
TRANSCRIPT
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Neuro Imaging
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Types of scan
CT MRI
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CT vs MRI
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• CT – fast & easy to spot haemorrhage. Fresh blood on CT scan is white.
– Once bleed is ruled out more time for:
• DWI – best for ischaemic damage
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Right Anterior Cerebral Artery (ACA) infarct
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Left Posterior Cerebral Artery (PCA) infarct
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Left Middle Cerebral Artery (MCA) infarct
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Indications• Trauma: fractures,hemorrhage• Stroke: Initial evaluation• Hydrocephalus• Mass effect/ midline shift• Detect calcification
Advantages• Detect calcification• Quick, readily available• Better at evaluating the bony structures especially for fractures Disadvantages• Radiation• Not as good as MRI at evaluating the soft tissue structures
CT
Indications• Tumors• Stroke• Epilepsy• Demyelination• Infection• Cranial Nerve palsy• Chronic headache• Dementia
Advantages• Exquisite soft tissue contrast between
normal tissue and pathologic tissue.• Customize imaging technique to answer
specific questions.• No ionising radiation.• Ability to do functional MRI
Disadvantage• Higher cost, limited access• Difficult for unstable pts• Claustrophobia• Not as great for bony detail
MRI
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Corpus callosum
Mamillary body
Pituitary gland
Pons
Fourth ventricle
Medulla
Thalamus Fornix Superior sagittal sinus
Cerebellum
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Always remember to say left or right!
4. Caudate nucleus
5. Internal capsule
6. Putamen
7. Thalamus
8. Fornix
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Transverse sinusSuperior sagittal sinus
Inferior sagittal sinus
Straight sinus
Sigmoid sinus
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Circle of Willis
Internal carotid artery
Vertebral artery
Common carotid artery
Subclavian artery
Brachiocephalic trunk
Basilar arteryWhat level does the common carotid artery bifurcate?C4
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Anterior cerebral artery
Internal carotid artery
Middle cerebral artery
Posterior communicating artery
Posterior cerebral artery
Watershed infarct: Area supplied by Anterior cerebral and Middle cerebral artery (man in a barrel) OR Area supplied by the Middle cerebral artery and the Posterior cerebral artery.
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Intracranial bleeds:
Intra axial – Intraparenchymal, Intraventricular.
Extra axial – Extradural (Epidural), Subdural, subarachnoid.
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Intraparenchymal haemorrhage
In this case the bleed has spread into the lateral ventricles.
Usually in a hypertensive patient.The basal ganglia is particularly susceptible to hypertensive bleeds.
Risk factors?
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Intraventricular haemorrhage:
Third ventricle
Which ventricle is the bleeding occurring in?
More common in premature babies but can also be due to trauma.
Common presentation?
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Extradural haemorrhage:
Between the dura mater and the skull.
Lentiform (lens shape)
Shape?
Injury followed by a lucid interval before sudden onset of symptoms
Trauma (coup)
History?
Middle meningeal artery rupture
Most common cause?
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Subdural heamorrhage:
Between the dura mater and the arachnoid mater
Crescent shaped
Shape on a CT?
The elderly and alcoholics – Cerebral atrophy
Babies – Shaken baby syndrome
Who’s most at risk?
Slower onset of symptoms than for an extradural haematoma.
Trauma – Especially involving shearing forces(Contrecoup)
History?
Tearing of the bridging veins
Most commonly?
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Sub-arachnoid heamorrhage:
Sometimes a CT is delayed while other causes eg. Meningitis are ruled out.
What would you see on the CT?
Thunderclap headache
Trauma but sometimes spontaneously (aneurism)
History?
Between the arachnoid and pia mater.
Bleed that follows the contour of the brain
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Herniations
Midline shift
Sub falcine herniation
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Uncal hernation(transtentorial)
Tonsilar herniation
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Cushing’s triad
Raised ICP causes compression of the cerebral arterioles, leading to ischaemia. Sympathetic nervous system response causes vascular constriction and so a raised BP (in an effort to restore blood supply to the brain). This is then detected by baroreceptors which causes a decrease in heart rate medicated by the vagus nerve. The pressure on the brainstem leads to irregular breathing.
Irregular breathing
Low heart rate
Raised Blood pressure
Nervous system response to raised ICP. Indication of imminent brain herniation.