CT INTERPRETATION COURSE Refresher Course ASTRACAT October 2012
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.
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
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
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
How to Recognise Haemorrhage on CT
Dense white blob Only seen after blood clots Minimal oedema
Complex haematoma White blob not homogeneous Thalamic haematoma
Complex haematoma Blob not homogeneous More white matter oedema
Unclotted blood same density as brain clotted blood white NB Normal white Matter in a young person NOT oedema
Beware the Resolving Haematoma
Acute
Fading, subacute ICH
CE CT on FU Without previous CT, could be taken for SOL
Final FU atrophy at haematoma site
Post contrast medium CT looks like SOL
Non contrast CT 2 weeks earlier
(Infarct) ischaemic oedema Haematoma
Normal Anatomy
CN Insular Ribbon Th LN Th = Thalamus
Insular Ribbon Int. Caps.
How to Recognise an Infarct Actually Ischaemic Oedema Dead infarct (core) indistinguishable from salvageable ischaemic oedema surrounding it (penumbra)
Low density Wedge shaped Grey & white matter Within known arterial vascular territory Proportionally little mass effect
Subcortical infarct NB Grey matter not confined to the cortex CN Ant. LN Int. caps obliterated
Stroke oedema?
Stroke oedema?
Stroke oedema?
This small haematoma caused the stroke Stroke oedema?
Stroke oedema? Complex SOL
Hyperdense MCA
Dense ICA Plus fleck of Calcification in Vessel wall Dense MCA
More Subtle Examples of Early Infarction Basic neuroanatomy to support early diagnosis
Insular Ribbon, BG & CN obliterated on Right. Normal on Left. Blue stars = Insula. Yellow star = BG CN
Reduced attenuation (low density) obliterates grey/white differentiation
Next day
Ext caps CN LN
Haemorrhagic Infarction and how to tell it from a primary intracerebral haemorrhage
Pt with SBE throwing off multiple emboli New H gic infarct Old Infarct Why?
Plain CT haemorrhagic infarction
ICH
Watershed Infarcts ie Border Zone
Radiology Assistant
How to Recognise the Different Vascular Territories
Green = ACA Red = MCA Purple = PCA lat midline from top from below
Circle of Willis rarely a true circle
No circle at all No Post.Comm. Arteries Ant & Post circulation isolated iwt
Dominant Post Comm
ICA occlusion ACA & MCA infarcts
iwt
MCA & PCA infarcts because of dominant Post Comm Art on Right
iwt
iwt
Carotid Artery Dissection No infarct Circle of Willis protects brain
Polo Mint thrombus in arterial wall, end on Thrombus en face
C of W protects via Ant Comm No infarct
How to Select Patients for thrombolysis? Clinical NIHSS Infarct size ASPECT Score Distinguishing dead tissue from living, but stunned, brain CT Perfusion iwt
How to Select Patients for thrombolysis? Clinical NIHSS Infarct size ASPECT Score Distinguishing dead tissue from living, but stunned, brain CT Perfusion iwt
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
Level with foramina of Monro c ic LN In
M1 Sylvian fissure Level with 3 rd V M2 M3
M4 Level with top of Lat Vs M5 M6 (VRS)
ASPECTS iwt
iwt
iwt
Examples from paper
How to Select Patients for thrombolysis? Clinical NIHSS Infarct size ASPECT Score Distinguishing dead tissue from living, but stunned, brain CT Perfusion iwt
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)
Imaging of the Penumbra CT MRI Discrepancy in perfusion parameters Mismatch between diffusion & perfusion parameters (DWI/PWI)
Pericallosal artery Sigmoid (venous) sinus
CTP CBV CBF MTT
Normal CT CTP perfusion defect CTA ICA dissection radiology assistant
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
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
LancetNeurol November 2011