CT INTERPRETATION COURSE

Transcription

1 CT INTERPRETATION COURSE Introductory Lecture on Basic Principles ASTRACAT 2012 Part One

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 Pathophysiology of stroke An infarcted brain is pale initially. Within hours to days, the gray matter becomes congested with engorged, dilated blood vessels and minute petechial hemorrhages. When an embolus blocking a major vessel migrates, lyses, or disperses within minutes to days, recirculation into the infarcted area can cause a haemorrhagic infarction A primary intracerebral haemorrhage damages the brain directly at the site of the haemorrhage and by compressing the surrounding tissue Thrombosis generally refers to local in situ obstruction of an artery Embolism refers to particles of debris originating elsewhere that block arterial access to a particular brain region iwt

5 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

6 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

7 How to Recognise Haemorrhage on CT

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9 Dense white blob Only seen after blood clots Minimal oedema

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11 Complex haematoma White blob not homogeneous Thalamic haematoma

12 Complex haematoma Blob not homogeneous More white matter oedema

13 Venous haemorrhage SSS thrombosis

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

15 Acute on chronic SDH Old Old & New Mixed Newly clotted blood

16 Blood clot/fluid level anticoagulants ( complex haematoma)

17 Beware the Resolving Haematoma

18 Acute

19 Fading, subacute ICH

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

21 Final FU atrophy at haematoma site

22 Post contrast medium CT looks like SOL

23 Non contrast CT 2 weeks earlier

24 (Infarct) ischaemic oedema Haematoma

25 Normal Anatomy

26 Optic tract Substantia nigra Red nucleus

27 CN Insular Ribbon Th LN Th = Thalamus

28 Insular Ribbon Int. Caps.

29 Rostrum, corpus callosum Insular Ribbon ic ic ic Splenium, corpus callosum

30 Head of caudate Lentiform Internal Capsule Optic radiation

31 Insular ribbon

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

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

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

37 Same rules apply to MRI

38 Stroke oedema?

39 Stroke oedema?

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41 Stroke oedema?

42 This small haematoma caused the stroke Stroke oedema?

43 Stroke oedema? Complex SOL

44 Stroke? MRI Same rules

45 Hyperdense MCA

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

50 Hyperdense MCA with Fragmentation

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

53 CN Insular Ribbon LN

54 Insular Ribbon Int. Caps.

55 Rostrum, corpus callosum Insular Ribbon ic ic ic Splenium, corpus callosum

56 Head of caudate Lentiform Internal Capsule Optic radiation

57 Insular ribbon

58 Insular Ribbon & BG signs

59 Early Infarction & FU (Insular ribbon & BG signs)

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

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

66 Next day

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69 Insular Ribbon Int. Caps.

70 Rostrum, corpus callosum Insular Ribbon ic ic ic Splenium, corpus callosum

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77 Ext caps CN LN

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79 Day 1

80 Day 2

81 Day 4

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

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

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87 Plain CT haemorrhagic infarction

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90 ICH

91 Contrast Enhancement in Infarction Luxury perfusion and the blood brain barrier

92 Plain CT CE CT

93 NC CE

94 NC CE

95 CE CE

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97 Special Infarcts or unusual consequences

98 BG (Pallidal) Infarction CO Poisoning

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100 Bilateral BG/Ext Caps Infarction

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102 Post Cardiac Arrest Infarction Cortical Mantle

103 Post Arrest Plain CT

104 Post CE Acute Cortical Laminar Necrosis

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106 Acute Occlusion ICA > ACA/MCA Infarction > Malignant Oedema > Herniation > Venous Congestion & Haemorrhage

107 Raised ICP with h age often mistaken for SAH

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109 Normal CT Then Effect of Sudden Rise in ICP

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111 Intradural venous congestion over tent looks like SAH

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113 Watershed Infarcts ie Border Zone

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115 Radiology Assistant

116 How to Recognise the Different Vascular Territories

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

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119 Circle of Willis rarely a true circle

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

121 Dominant Post Comm

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123 ICA occlusion ACA & MCA infarcts

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

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129 Carotid Artery Dissection No infarct Circle of Willis protects brain

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

132 C of W protects No infarct

133 C of W protects via Ant Comm No infarct

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135 Vascular Territories (contd) - PCA

136 PCA

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

140 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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142 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

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144 Level with foramina of Monro c ic LN In

145 M1 Sylvian fissure Level with 3 rd V M2 M3

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

147 ASPECTS iwt

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150 Examples from paper

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

155 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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157 Imaging of the Penumbra CT MRI Discrepancy in perfusion parameters Mismatch between diffusion & perfusion parameters (DWI/PWI)

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160 CT Perfusion Imaging CBF = CBV/MTT CBV = area under parenchymal curve/area under arterial curve MTT calculated from time difference between arterial inflow & venous outflow + time to peak enhancement Penumbra -v-dead tissue

161 Pericallosal artery Sigmoid (venous) sinus

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163 CTP CBV CBF MTT

164 Normal CT CTP perfusion defect CTA ICA dissection radiology assistant

165 CTA

166 Normal CTA

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169 Hypodensity Right Insula CTA

170 Taken from Radiographics, October 2006 iwt

171 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

172 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

173 DDX of Arterial Infarction

174 Not all Infarction is Arterial Venous Infarction

175 Venous sinus thrombosis Low incidence [<1 in 10,000 persons] Risks factors Tissue damage and stasis Haematological disorders Malignancies Collagen vascular disorders Pregnancy Medications

176 Venous sinus thrombosis CT brain shows non-arterial distribution infarcts in the white matter and/or cortical white matter junction, often associated with haemorrhage Empty delta sign on contrast-enhanced CT scan Occasionally, the cortical veins can be seen with fresh thrombus within.

177 MR and MR Venography Advantages sensitive to blood and parenchymal changes Cortical vein thrombosis and sinus thrombosis can be identified with multiple appropriate sequences Disadvantages Difficult to recognise thrombus in first few days on conventional MRI Flow and susceptibility artefacts and saturation effects in TOF can make interpretation difficult Difficult in unwell patients Contraindications to MRI Expensive and availability

178 CT Venogram Advantages Can be added as an adjunct to unenhanced CT - Non invasive Not expensive, reliable and easy to interpret Fast acquisition reduces motion artefacts Monitoring of critically ill patients is easier. Can differentiate slow flow from thrombus, which is a problem with MRI. Disadvantages Radiation (Mean effective dose <2.2 msv) Contrast media flow dynamics not seen as well as in DSA Metallic artefacts may impair visualisation of venous structures Contraindicated in pregnancy

179 Normal CTV Anatomy For interest only

180 Normal radiological cerebral venous anatomy

181 Normal radiological cerebral venous anatomy

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183 Deep veins

184 Outflow tracts

185 Normal Variants Asymmetric transverse sinus

186 Venous thrombosis Empty Delta Sign (SSS = sup sag sinus & TS = transverse sinus)

187 Venous sinus thrombosis Arrows point to Empty Delta Sign

188 Example: Plain T1W MRI Bilat. Parasagittal H age Thrombus in SSS

189 MRV showing non-filling of SSS and SS