April 2001 Imaging Modalities in Acute Stroke: Time is Brain Jeremiah Scharf, Harvard Medical School, MS IV Beth Israel-Deaconess Medical Center Department of Radiology
Stroke - Definition and Statistics http://www.swmed.edu/stars/resources/stroke.html Acute, vascular injury to CNS <24 hrs = TIA >24 hrs = stroke (CVA) Affects 600,000 people/ yr (that is 1 stroke per minute!) Is #3 cause of mortality in adults Is #1 cause of disability 2
Types of Stroke Hemorrhagic (20%) usually hypertensive hemorrhage Ischemic (80%) Thrombotic (40%) intracerebral atherosclerosis Embolic (60%) Cardiac embolus (thrombus, tumor, septic embolus) artery-to-artery (mainly carotid thrombus) Paradoxical embolus (thrombus, fat, air) 3
Risk Factors for Stroke Atherosclerosis risk factors Family history of CVA, TIA, or MI Hypertension Smoking Diabetes Hypercholesterolemia Previous CVA, TIA, or MI Atrial fibrillation 4
Our Patient - BF 86 yo F w/ Hx of HTN, CAD s/p MI, and high cholesterol presented to PCP for routine visit Felt funny -> began seizing In ED, unresponsive, L. sided hemiplegia eyes deviated to the right 5
Differential Diagnosis Many CNS diseases can mimic ischemic stroke Hemorrhage Mass lesion (tumor, abscess, AVM) Seizure (Todd s paralysis) Hemiplegic migraine MS flare Venous infarct 6
Goals of Imaging in Acute Stroke 1. Rule in or out other disease processes 2. Define location, extent and age of infarct 3. Do so as rapidly as possible TIME IS BRAIN 7
Cerebrovascular Anatomy Posterior Circulation Anterior Circulation 8 MGH Handbook of Neurology
Anatomy of the Anterior Circulation Anterior cerebral artery Middle cerebral artery Internal carotid artery Anterior cerebral artery Middle cerebral artery Internal carotid artery MGH Handbook of Neurology High Yield Neuroscience 9
Vascular territories in the brain 10 MGH Handbook of Neurology
Imaging Modalities in Acute Stroke CT without contrast Conventional MRI Diffusion-Weighted and Perfusion MRI MRA Ultrasound 11
CT Imaging in Acute Stroke - 1 Initial test of choice Best modality for detecting hemorrhage Identifies mass lesions (tumor, abscess, AVM) Fast and readily available = Crucial for stroke triage (rule in/out other diseases) Patient #2 - LL BIDMC 12
CT Imaging in Acute Stroke - 2 HOWEVER, CT is poor at detecting acute infarcts Only 40% sensitivity <24 h Our Patient Film Findings for our patient, BF: Normal Initial Head CT 2 hours post stroke BIDMC 13 Patient #1 BF; 1-2 hrs post stroke
Our patient BF: CT#2 8 hours later As time passes, classic signs of stroke appear: Loss of gray-white matter differentiation Normal G/W diff. Sulcal effacement Normal sulci BIDMC Patient #1 BF; 8 hrs post stroke 14
Our patient BF CT#3-2 days later Complete loss of gray-white matter differentiation? hemorrhagic transformation Sulcal effacement BIDMC Patient #1 BF; 48 hrs post stroke 15
Therefore, other imaging modalities are used to detect strokes < 6 hours! 16
Imaging Modalities in Acute Stroke CT without contrast Conventional MRI Diffusion-Weighted and Perfusion MRI MRA Ultrasound 17
T1 Conventional MR Imaging in Stroke Slight incr. detection rate over CT in early stroke Our Patient T2 T2 hyperintensity visible at 12-24 hrs (80% +) represents edema BIDMC T1 imaging basics CSF is dark Soft tissue is bright Good for mass lesions May see absent flow voids = arterial occlusion T2 imaging basics 18 BIDMC CSF is bright Soft tissue is dark Good for edema (bright)
Conventional MR Imaging in Stroke Our patient, BF, underwent an MRI study immediately following her initial CT, 2 hours after her stroke Film Findings: Normal Initial MRI:? Absent R. MCA Flow Void (suggestive of MCA occlusion) T2 image BIDMC 19 Patient BF; 2 hrs post stroke
Our patient BF - MRI #2 :30 hours later At 30 hrs., classic MR signs of infarct are present Film Findings: T2 hyperintensity in temporal lobe, MCA distribution T2 image BIDMC Patient BF; 30 hrs post stroke 20
Conclusions - Conventional MR Imaging in Acute Stroke Conventional MRI can detect acute infarcts slightly earlier than CT Nonetheless, additional techniques are still needed for early stroke detection 21
Imaging Modalities in Acute Stroke CT without contrast Conventional MRI Diffusion-Weighted and Perfusion MRI MRA Ultrasound 22
Diffusion Weighted MRI Imaging (DWI) Osmotic pump failure is 1 st event in ischemia Fluid shift extracellular->intracellular Water in cells now can t diffuse! Detected as decreased diffusion coefficient (ADC) Increased restriction of diffusion (DWI) Detects change within 30 minutes of onset of stroke Beats T2 signal by 3-6 hours!!! 23 Schaefer et al. Radiology 217:331-345, 2000
Our Patient had a DWI MRI immediately following the initial routine MRI 24
DWI in BF at 2 hours post-stroke In our patient, DWI sequences were performed during her initial MRI A faint increase in DWI signal was observed in the temporal and insular cortex. Indicated early ischemia in MCA territory Led to treatment with IV thrombolytic therapy (t-pa) Patient BF; 2 hrs post stroke BIDMC 25
That s good, but could we predict how bad her stroke might get? 26
Imaging the Penumbra: the Holy Grail of Stroke Diagnostics DWI is thought to show the area currently infarcting. But is there an area at risk where blood flow is reduced but cells haven t died yet? Imaging this region (the penumbra) = goal of MR perfusion imaging Uses gadolinium for contrast Changes magnetic properties of perfused tissue vs. non-perfused Measures decreased flow in penumbra! -increased mean-transit-time (MTT) of blood flow to penumbra 27 http://www.swmed.edu/stars/resources/stroke.html
Correlation of Perfusion Imaging with Infarct Progression MTT = area of low/ slow blood flow DWI Early (2h): =small area of injury = area at risk for stroke extension Baird AE and Warach S. J. Cereb. Blood Flow Metab. 18(6): 583-609, 1998. Late (29h): =larger area of injury (correlates w/ 2h MTT) 28
Progression of Infarct in BF: DWI at 30 hrs post-stroke normal DWI normal brain serial, axial sections demonstrating extent of infarct at 30 hours BIDMC 29
DWI in 3D - 2 normal DWI normal brain BIDMC 30
DWI in 3D - 3 increased DWI injured brain BIDMC 31
DWI in 3D - 4 increased DWI injured brain BIDMC 32
DWI in 3D - 5 increased DWI injured brain BIDMC 33
DWI in 3D - 6 increased DWI injured brain BIDMC 34
DWI in 3D - 7 increased DWI injured brain BIDMC 35
DWI in 3D - 8 increased DWI injured brain BIDMC 36
DWI in 3D - 9 increased DWI injured brain BIDMC 37
DWI in 3D - 10 increased DWI injured brain BIDMC 38
DWI in 3D - 11 increased DWI injured brain BIDMC 39
DWI in 3D - 12 increased DWI injured brain BIDMC 40
DWI in 3D - 13 increased DWI injured brain BIDMC 41
Summary Extent of infarct our patient R. MCA territory R. PCA territory (complete) BIDMC MGH Handbook of Neurology 42
Imaging Modalities in Acute Stroke CT without contrast Conventional MRI Diffusion-Weighted and Perfusion MRI MRA Ultrasound 43
MRA/Angiography of occluded MCA our patient R. MCA companion patient L. MCA our patient R. MCA BIDMC Patient BF; R. MCA occlusion BIDMC Patient BF; R. MCA occlusion Bahn et al. JMRI 6:833-845, 1996 L. MCA occlusion -literature 44
Imaging Modalities in Acute Stroke CT without contrast Conventional MRI Diffusion-Weighted and Perfusion MRI MRA Ultrasound 45
Ultrasound in Stroke Has a primary role in working up cause of stroke Echocardiography TEE for LA/LV thrombus Bubble echo study for PFO (paradoxical embolus) Carotid Ultrasound Evaluates patency of carotids and degree of stenosis Transcranial Doppler Ultrasound Evaluates patency of intracranial arteries (MCA) 46
Summary I Patient Course BF was given t-pa within 3 hours of onset 30% increase in recovery over controls (31% t-pa vs. 20% placebo = minimal/ no disability @ 3 mos.) 6-fold increased risk of bleeding (6% vs. 1%?) Symptoms of stroke did not improve considerably Intubated in ICU for 1 week Transferred to floor with residual weakness Discharged to rehabilitation facility after 10 days 47
Summary II Timing of stroke detection in our patient Imaging Modality CT without contrast Time of post-stroke imaging 2h 8h 30h - + + Conventional MRI - ND + DWI MRI + ND + MRA + ND + + = evidence of acute stroke; - = no evidence of acute stroke; ND = not determined 48
Summary III Imaging in Stroke Acute Stroke (<6 hours) CT (without contrast!!) Excellent for ruling out hemorrhage, other diseases Poor in defining early infarcts Conventional MRI (T1,T2) Bad for hemorrhage, fair for early infarcts Diffusion-Weighted and Perfusion MRI Excellent for defining early infarcts (1-2 hrs) and for estimating areas at risk 49
Summary IV - Imaging in Stroke Sub-acute Stroke (>6 hours) CT (without contrast) Excellent in defining late infarcts (>24 h) sulcal effacement, loss of gray-white differentiation Conventional MRI (T1,T2) Better than CT at 6-24h; Same as CT in infarcts > 24h T2 hyperintensity is most indicative of injury Ultrasound Critical for workup of origin of stroke (TEE, TCD, Carotid Doppler) 50
Summary V - Imaging in Stroke In the near future, there will hopefully be effective treatments for acute stroke. Patients will need to come to the ER at first sign of brain attack. Patients will need to be imaged by multiple modalities rapidly. Remember... TIME IS BRAIN 51
References AHA Website: http://www.americanheart.org/statistics/stroke.html Bahn MM, Oser AB, Cross DT. CT and MRI of Stroke. JMRI 6:833-845, 1996. Baird AE and Warach S. Magnetic Resonance Imaging in Acute Stroke. J. Cereb. Blood Flow Metab. 18(6): 583-609, 1998. Beauchamp NJ, Barker PB, Yang PY, vanzijl PCM. Imaging of Acute Cerebral Ischemia. Radiology 212:307-324, 1999. Culebras A et al. AHA Scientific Statement: Practice Guidelines for the Use of Imaging in Transient Ischemic Attacks and Acute Stroke. Stroke. 28:1480-1497, 1997. Flaherty AW. MGH Handbook of Neurology. Lippincott Williams and Wilkins 2000. Fix J. High-Yield Anatomy. Lippincott Williams & Wilkins. Philadelphia. 2000. Lev MH, Farkas J, Gemmete JJ, Hossain ST, Hunter GJ, Kroshetz WJ, Gonzalez RG. Acute Stroke: Improved Nonenhanced CT Detection Benefits of Soft-Copy Interpretation by Using Variable Window Width and Center Level Settings. Radiology 213: 150-155, 1999. Petrella JR and Provenzale JM. MR Perfusion Imaging of the Brain. AJR 175:207-219, 2000. Schaefer PW, Grant PE, Gonzalez RG. Diffusion Weighted MR Imaging of the Brain. Radiology 217:331-345, 2000 Simon RP, Aminoff MJ, Greenberg DA. Clinical Neurology. Appleton & Lange: Connecticut, 1999. UT Southwestern STARS Website: http://www.swmed.edu/stars/resources/stroke.html 52
Acknowledgments Andru Bageac and Daniel Saurborn - for help with case identification Beverlee Turner -for help with Power point and PACS Gillian Lieberman -for her enthusiasm in teaching medical students My classmates -for enduring this talk 53