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Stage 2: Supporting Life > Neuroimaging > Flashcards

Neuroimaging Flashcards

1
Q

What are the HU units of water, white matter, grey matter, blood, contrast and bone?

A
  • Water = 0
  • White matter = 30
  • Grey matter = 45
  • Blood = 60-100
  • Contrast > 130
  • Bone > 400
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2
Q

What colour is air/water on CT?

A

Black

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3
Q

What colour is bone on CT?

A

White

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4
Q

What colour is associated with increasing HU?

A

White

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5
Q

What is the mnemonic for interpreting a head CT in an acute setting?

A 
Asymmetry 
Blood 
Brain 
CSF spaces 
Skull/Scalp
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6
Q

What asymmetry are you looking for in a head CT?

A

Differences between the right and left

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7
Q

How do you want to interpret blood in a head CT?

A

Look at location → parenchymal, CSF spaces, meningeal, vessel

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8
Q

What are you looking for in the brain of a CT?

A
  • Grey white matter differentiation of density
  • Hyperdensity = acute blood, tumour, bone, contrast, foreign body
  • Hypodensity = oedema, infarct, air, tumour
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9
Q

What are you looking for in the CSF spaces of a CT?

A
  • Cisternal spaces
  • Sulcal spaces
  • Ventricles
  • Assess their size and whether they have the normal density of CSF
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10
Q

What are you looking for in the skull/scalp of a CT?

A
  • Soft tissue swelling
  • Fractures
  • Adjust to bone windows
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11
Q

How might a subarachnoid haemorrhage present?

A

As a sudden onset very bad headache

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12
Q

Where does a subarachnoid haemorrhage occur?

A

Between the arachnoid membrane/space and brain itself, closest to the brain parenchyma

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13
Q

How might you see blood on a CT in a subarachnoid haemorrhage?

A

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

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14
Q

What are causes of a subarachnoid haemorrhage?

A
  • Rupture of an intracranial aneurysm e.g. MCA
  • Trauma
  • Haemorrhage from AVM (arteriovenous malformation)
  • Vascular malformation
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15
Q

What would you use to visualise an aneurysm?

A

CT angiogram

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16
Q

How would you treat an aneurysm?

A

Intra-arterial interventional treatment

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17
Q

What is an AVM?

A

An abnormal connection between an artery and vein with disrupts normal blood flow and oxygen circulation

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18
Q

How would an extradural haemorrhage present?

A

Confusion following a fall (trauma) with an associated fracture

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19
Q

What would you see on a CT of an extradural haemorrhage?

A
  • 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)
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20
Q

What is an extradural haemorrhage?

A

A lentiform/biconvex blood collection between the skull and dura → lenticular shape characteristic of extradural location

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21
Q

How are patients with an extradural haemorrhage treated?

A

Urgent haematoma evacuation

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22
Q

What happens as a result of an extradural haemorrhage?

A

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

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23
Q

What are symptoms of a rapidly increasing ICP resulting from an extradural haemorrhage?

A
  • Drowsiness
  • Neck stiffness
  • Papilloedema
  • Coma
  • Brain stem failure
  • Death
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24
Q

How might a brain abscess (from the middle ear) present?

A

Headache, earache, fever, previous infection

25
Q

What might you see on a CT of a space occupying lesion?

A
  • Low attenuation mass lesion within the left cerebellar hemisphere
  • After contrast administration demonstrate a slightly regular thin/thick walled ring enhancement
26
Q

What can a space occupying lesion lead to?

A
  • 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
27
Q

What are the two differentials for a ring enhancing lesion?

A

Abscess or tumour

28
Q

What would you need to consider in the case of an abscess?

A
  • Involvement of the adjacent sinus

- If there are multiple abscesses to think of a central cause e.g. infection of the valves (bacterial endocarditis)

29
Q

How do you treat a patient with an abscess?

A

Urgent surgical evacuation of the abscess

30
Q

How might a subdural haemorrhage present?

A
  • Increasing confusion after fall

- Fluctuating levels of consciousness

31
Q

How might a subdural haemorrhage present in contrast with an extradural haemorrhage and why?

A

Slower onset → the increased ICP and mass effect can develop and may present several days after the trauma

32
Q

What can occur as a complication of a subdural haemorrhage?

A

Obstructive hydrocephalus

33
Q

Why are the elderly at an increased risk of a subdural haemorrhage?

A

Due to wider subdural spaces bc of brain atrophy

34
Q

What might you see on a CT of someone with a subdural haemorrhage?

A

Crescentic/biconvex area of high density (blood) which increases over 3 days

35
Q

What shape of high density is characteristic of an extradural haemorrhage?

A

Lenticular

36
Q

What shape of high density is characteristic of a subdural haemorrhage?

A

Crescentic

37
Q

What happens to the blood density of the lesion in a subdural haemorrhage after 3 days?

A

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

38
Q

What is the typical presentation of meningitis?

A

Young person with confusion, headache, fever and neck stiffness

39
Q

What can you see on a CT of someone with viral or bacterial meningitis?

A

V little even after contrast administration → maybe some subtle loss of sulcal spaces due to early swelling

40
Q

How do you diagnose meningitis as the CT is not helpful?

A

Clinical and supported by positive lumbar puncture

41
Q

What is the presentation of someone with complicated bacterial meningitis?

A

Confusion, headache, fever

42
Q

What can you see on a CT of someone with complicated bacterial meningitis?

A

Several ring enhancing lesions after contrast administration → abscesses

43
Q

What 4 infections can you possibly use a CT to diagnose?

A

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

44
Q

How might someone with a hyperacute infarct present?

A

Acute loss of right limbs power and unable to speak

45
Q

What is the main thing you might see on a CT of someone with a hyperacute infarct?

A
  • 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
46
Q

What do 60% of patients with a hyperacute ischaemic stroke (infarct) at < 6 hours have?

A

A normal CT scan

47
Q

What are other further signs of a hyperacute ischaemic stroke (infarct at < 6 hours)?

A

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

48
Q

When is stroke easier to diagnose?

A

After 12h

49
Q

What would you see on a CT of a stroke after 12-24h?

A

1) Low density which confines to/occupies an arterial/vascular territory
2) Associated brain swelling in the same area

50
Q

What would you see in a CT scan of a stroke after 6h?

A

Low density with brain swelling in a vascular territory

51
Q

When may you see nothing on a CT during a stroke?

A

In the hyperacute phase

52
Q

Why would you carry out vascular imaging in stroke

A

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

53
Q

How might someone with a parenchymal haemorrhage present?

A

Collapse followed by seizures

54
Q

What might you see on a CT of someone with a parenchymal haemorrhage?

A

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

55
Q

What location is typical for a hypertensive bleed leading to parenchymal haemorrhage?

A

Basal ganglia

56
Q

What are the majority of intra-parenchymal haemorrhages caused by?

A

Hypertension

57
Q

What are other, rarer causes of intra-parenchymal haemorrhage?

A
  • Amyloid angiopathy
  • Vascular malformation
  • Drugs
58
Q

What are the 4 types of haemorrhage?

A

1) Subarachnoid
2) Subdural
3) Extradural
4) Parenchymal

59
Q

What are examples of 2 intracranial pathologies that are not ruled out by a normal CT?

A

Stroke and meningitis

Stage 2: Supporting Life (30 decks)

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