Neuroimaging Flashcards
What are the HU units of water, white matter, grey matter, blood, contrast and bone?
- Water = 0
- White matter = 30
- Grey matter = 45
- Blood = 60-100
- Contrast > 130
- Bone > 400
What colour is air/water on CT?
Black
What colour is bone on CT?
White
What colour is associated with increasing HU?
White
What is the mnemonic for interpreting a head CT in an acute setting?
Asymmetry Blood Brain CSF spaces Skull/Scalp
What asymmetry are you looking for in a head CT?
Differences between the right and left
How do you want to interpret blood in a head CT?
Look at location → parenchymal, CSF spaces, meningeal, vessel
What are you looking for in the brain of a CT?
- Grey white matter differentiation of density
- Hyperdensity = acute blood, tumour, bone, contrast, foreign body
- Hypodensity = oedema, infarct, air, tumour
What are you looking for in the CSF spaces of a CT?
- Cisternal spaces
- Sulcal spaces
- Ventricles
- Assess their size and whether they have the normal density of CSF
What are you looking for in the skull/scalp of a CT?
- Soft tissue swelling
- Fractures
- Adjust to bone windows
How might a subarachnoid haemorrhage present?
As a sudden onset very bad headache
Where does a subarachnoid haemorrhage occur?
Between the arachnoid membrane/space and brain itself, closest to the brain parenchyma
How might you see blood on a CT in a subarachnoid haemorrhage?
1) Hyperdensities of ~80HU which follow the Sylvian fissures and quadrigeminal cistern, intrahemispheric fissure and within the third ventricle
2) Blood within the suprasellar cistern at the circle of willis level and within the fourth ventricle
What are causes of a subarachnoid haemorrhage?
- Rupture of an intracranial aneurysm e.g. MCA
- Trauma
- Haemorrhage from AVM (arteriovenous malformation)
- Vascular malformation
What would you use to visualise an aneurysm?
CT angiogram
How would you treat an aneurysm?
Intra-arterial interventional treatment
What is an AVM?
An abnormal connection between an artery and vein with disrupts normal blood flow and oxygen circulation
How would an extradural haemorrhage present?
Confusion following a fall (trauma) with an associated fracture
What would you see on a CT of an extradural haemorrhage?
- Crescentic high density (of blood - 80) lesion which pushes away from the brain parenchyma
- Line through bone, showing a fracture with associated dense soft tissue swelling (haematoma of scalp)
What is an extradural haemorrhage?
A lentiform/biconvex blood collection between the skull and dura → lenticular shape characteristic of extradural location
How are patients with an extradural haemorrhage treated?
Urgent haematoma evacuation
What happens as a result of an extradural haemorrhage?
1) Rapidly developing mass effect with shift of the brain on the other side
2) This causes a midline shift compression of parenchyma and ventricles
3) This leads to a rapidly increasing ICP
What are symptoms of a rapidly increasing ICP resulting from an extradural haemorrhage?
- Drowsiness
- Neck stiffness
- Papilloedema
- Coma
- Brain stem failure
- Death
How might a brain abscess (from the middle ear) present?
Headache, earache, fever, previous infection
What might you see on a CT of a space occupying lesion?
- Low attenuation mass lesion within the left cerebellar hemisphere
- After contrast administration demonstrate a slightly regular thin/thick walled ring enhancement
What can a space occupying lesion lead to?
- The surrounding oedema can cause compression of the 4th ventricle and upstream dilation of ventricles incl. temporal horns of lateral ventricles
- This can lead to obstructive hydrocephalus
What are the two differentials for a ring enhancing lesion?
Abscess or tumour
What would you need to consider in the case of an abscess?
- Involvement of the adjacent sinus
- If there are multiple abscesses to think of a central cause e.g. infection of the valves (bacterial endocarditis)
How do you treat a patient with an abscess?
Urgent surgical evacuation of the abscess
How might a subdural haemorrhage present?
- Increasing confusion after fall
- Fluctuating levels of consciousness
How might a subdural haemorrhage present in contrast with an extradural haemorrhage and why?
Slower onset → the increased ICP and mass effect can develop and may present several days after the trauma
What can occur as a complication of a subdural haemorrhage?
Obstructive hydrocephalus
Why are the elderly at an increased risk of a subdural haemorrhage?
Due to wider subdural spaces bc of brain atrophy
What might you see on a CT of someone with a subdural haemorrhage?
Crescentic/biconvex area of high density (blood) which increases over 3 days
What shape of high density is characteristic of an extradural haemorrhage?
Lenticular
What shape of high density is characteristic of a subdural haemorrhage?
Crescentic
What happens to the blood density of the lesion in a subdural haemorrhage after 3 days?
1) After first 3 days it starts to become of lower density as the clot retracts and gets decomposed
2) Therefore, it becomes difficult to diagnose as it becomes the same density of the brain parenchyma
3) Eventually they become the same density as CSF (black) in the chronic phase
What is the typical presentation of meningitis?
Young person with confusion, headache, fever and neck stiffness
What can you see on a CT of someone with viral or bacterial meningitis?
V little even after contrast administration → maybe some subtle loss of sulcal spaces due to early swelling
How do you diagnose meningitis as the CT is not helpful?
Clinical and supported by positive lumbar puncture
What is the presentation of someone with complicated bacterial meningitis?
Confusion, headache, fever
What can you see on a CT of someone with complicated bacterial meningitis?
Several ring enhancing lesions after contrast administration → abscesses
What 4 infections can you possibly use a CT to diagnose?
1) Meningitis
2) Pyogenic abscess
3) TB meningitis → tuberculoma (enhancing mass lesion) and thick meningeal enhancement
4) In immunosuppressed patients should consider opportunistic infections e.g. toxoplasma/cryptococcus
How might someone with a hyperacute infarct present?
Acute loss of right limbs power and unable to speak
What is the main thing you might see on a CT of someone with a hyperacute infarct?
- Loss of grey white differentiation involving the left caudate head and lentiform nucleus obscuration
- This reflects subtle early changes caused by oedema within the grey matter which brings its density down to that of white matter, making in indistinguishable
What do 60% of patients with a hyperacute ischaemic stroke (infarct) at < 6 hours have?
A normal CT scan
What are other further signs of a hyperacute ischaemic stroke (infarct at < 6 hours)?
1) Insular ribbon sign → loss of high density associated with the insular cortex
2) Hyperdense vessel sign → linear density along the RMCA artery when compared with the LMCA, representing a clot in the artery
3) Sulcal effacement → loss of the ribbons of the cortex within the right hemisphere and a bit of swelling when compared with the left
When is stroke easier to diagnose?
After 12h
What would you see on a CT of a stroke after 12-24h?
1) Low density which confines to/occupies an arterial/vascular territory
2) Associated brain swelling in the same area
What would you see in a CT scan of a stroke after 6h?
Low density with brain swelling in a vascular territory
When may you see nothing on a CT during a stroke?
In the hyperacute phase
Why would you carry out vascular imaging in stroke
To identify the critical narrowing e.g. narrowing of carotid artery in the neck or vessel occlusion → these may then be treated with interventional clot retrieval
How might someone with a parenchymal haemorrhage present?
Collapse followed by seizures
What might you see on a CT of someone with a parenchymal haemorrhage?
A central high density area which occupies the region of the deep grey nuclei which is the density of acute blood, located in the brain parenchyma itself
What location is typical for a hypertensive bleed leading to parenchymal haemorrhage?
Basal ganglia
What are the majority of intra-parenchymal haemorrhages caused by?
Hypertension
What are other, rarer causes of intra-parenchymal haemorrhage?
- Amyloid angiopathy
- Vascular malformation
- Drugs
What are the 4 types of haemorrhage?
1) Subarachnoid
2) Subdural
3) Extradural
4) Parenchymal
What are examples of 2 intracranial pathologies that are not ruled out by a normal CT?
Stroke and meningitis
