CT INTERPRETATION COURSE

Transcription

1 CT INTERPRETATION COURSE Refresher Course ASTRACAT October 2012

2 Stroke is a Clinical Diagnosis A clinical syndrome characterised by rapidly developing clinical symptoms and/or signs of focal loss of cerebral function lasting more than 24 hours.

3 DEFINITIONS Stroke is classified into two major types Brain Ischaemia - due to thrombosis, embolism, or systemic hypoperfusion Brain Haemorrhage - due to intracerebral haemorrhage or subarachnoid haemorrhage A stroke is the acute neurologic injury that occurs as a result of one of these pathologic processes Approximately 80 percent of strokes are due to ischaemic cerebral infarction and 20 percent to brain haemorrhage iwt

4 What s the point of imaging? Exclude haemorrhage Determine the mechanism/cause Differentiate infarcted tissue from salvageable tissue Identify intravascular thrombi Patient selection for therapy Assess risk of complications Haemorrhagic transformation Hydrocephalus in posterior circulation infarction Assist with prognosis

5 CT is the best test in the acute/subacute phase It confidently detects or excludes haemorrhage Confirms the diagnosis in most cases Quick & patient friendly Easy to interpret Readily available

6 How to Recognise Haemorrhage on CT

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8 Dense white blob Only seen after blood clots Minimal oedema

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10 Complex haematoma White blob not homogeneous Thalamic haematoma

11 Complex haematoma Blob not homogeneous More white matter oedema

12 Unclotted blood same density as brain clotted blood white NB Normal white Matter in a young person NOT oedema

13 Beware the Resolving Haematoma

14 Acute

15 Fading, subacute ICH

16 CE CT on FU Without previous CT, could be taken for SOL

17 Final FU atrophy at haematoma site

18 Post contrast medium CT looks like SOL

19 Non contrast CT 2 weeks earlier

20 (Infarct) ischaemic oedema Haematoma

21 Normal Anatomy

22 CN Insular Ribbon Th LN Th = Thalamus

23 Insular Ribbon Int. Caps.

24 How to Recognise an Infarct Actually Ischaemic Oedema Dead infarct (core) indistinguishable from salvageable ischaemic oedema surrounding it (penumbra)

25 Low density Wedge shaped Grey & white matter Within known arterial vascular territory Proportionally little mass effect

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28 Subcortical infarct NB Grey matter not confined to the cortex CN Ant. LN Int. caps obliterated

29 Stroke oedema?

30 Stroke oedema?

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32 Stroke oedema?

33 This small haematoma caused the stroke Stroke oedema?

34 Stroke oedema? Complex SOL

35 Hyperdense MCA

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39 Dense ICA Plus fleck of Calcification in Vessel wall Dense MCA

40 More Subtle Examples of Early Infarction Basic neuroanatomy to support early diagnosis

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45 Insular Ribbon, BG & CN obliterated on Right. Normal on Left. Blue stars = Insula. Yellow star = BG CN

46 Reduced attenuation (low density) obliterates grey/white differentiation

47 Next day

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56 Ext caps CN LN

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58 Haemorrhagic Infarction and how to tell it from a primary intracerebral haemorrhage

59 Pt with SBE throwing off multiple emboli New H gic infarct Old Infarct Why?

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61 Plain CT haemorrhagic infarction

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64 ICH

65 Watershed Infarcts ie Border Zone

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67 Radiology Assistant

68 How to Recognise the Different Vascular Territories

69 Green = ACA Red = MCA Purple = PCA lat midline from top from below

70 Circle of Willis rarely a true circle

71 No circle at all No Post.Comm. Arteries Ant & Post circulation isolated iwt

72 Dominant Post Comm

73 ICA occlusion ACA & MCA infarcts

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76 MCA & PCA infarcts because of dominant Post Comm Art on Right

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79 Carotid Artery Dissection No infarct Circle of Willis protects brain

80 Polo Mint thrombus in arterial wall, end on Thrombus en face

81 C of W protects via Ant Comm No infarct

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83 How to Select Patients for thrombolysis? Clinical NIHSS Infarct size ASPECT Score Distinguishing dead tissue from living, but stunned, brain CT Perfusion iwt

84 How to Select Patients for thrombolysis? Clinical NIHSS Infarct size ASPECT Score Distinguishing dead tissue from living, but stunned, brain CT Perfusion iwt

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86 ASPECT Scoring System A = ACA; P = PCA; M = MCA MCA territory (10 points is Normal) Subtract one point for each: M1, M2, M3 M4, M5, M6 Caudate, Int Caps, LN, Insula

87 Level with foramina of Monro c ic LN In

88 M1 Sylvian fissure Level with 3 rd V M2 M3

89 M4 Level with top of Lat Vs M5 M6 (VRS)

90 ASPECTS iwt

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93 Examples from paper

94 How to Select Patients for thrombolysis? Clinical NIHSS Infarct size ASPECT Score Distinguishing dead tissue from living, but stunned, brain CT Perfusion iwt

95 Penumbra Unlike muscle, brain tissue exquisitely sensitive to ischaemia Absence of neuronal energy stores In complete absence of blood flow, available energy can sustain neuronal viability for 2-3 minutes In acute stroke, ischaemia incomplete Collateral blood supply from uninjured arterial & leptomeningeal territories Results in central infarcted tissue surrounded by peripheral stunned cells (penumbra)

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97 Imaging of the Penumbra CT MRI Discrepancy in perfusion parameters Mismatch between diffusion & perfusion parameters (DWI/PWI)

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100 Pericallosal artery Sigmoid (venous) sinus

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102 CTP CBV CBF MTT

103 Normal CT CTP perfusion defect CTA ICA dissection radiology assistant

104 Goals of Acute Stroke Imaging The Four Ps Parenchyma Assess early signs of acute stroke Rule out haemorrhage Pipes look for intravascular thrombus Extracranial circulation (neck) Intracranial circulation Perfusion Cerebral blood volume Cerebral blood flow Mean transit time Penumbra Tissue at risk

105 Conclusions Stroke is a clinical diagnosis CT is best and will suffice in majority MR for CT neg. stroke or for definitive diagnosis when suggested clinically eg dissection or where CT suggests alternative diagnosis eg SOL Advanced MR techniques best left to specialist units

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108 LancetNeurol November 2011

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