STROKE - IMAGING Dr RAJASEKHAR REDDY 2nd Yr P.G. RADIODIAGNOSIS KIMS,Narkatpalli.
STROKE Describes a clinical event that consists of sudden onset of neurological symptoms Types Infarction - occlusion of cerebral arteries and veins(85%) Hemorrhage intraparenchymal, subarachnoid Infarction without occlusion of cerebral arteries or veins may also occur-severe sustained hypotension,toxic,anoxic insult
Imaging manifestations of ischemia -infarction These vary with time Acute (upto-24hrs) Subacute early,late ( 1-7 days. ) Chronic (after 3 weeks )
CT Hyperacute (<12hrs) 50 to 60 % normal Hyperdense middle cerebral artery Obscuration of lentiform nuclei Insular- ribbon sign Acute(12 to 24hrs) Low density basal ganglia Loss of grey white interface Sulcal effacement (gyral swelling)
CT axial plain Hyperdense MCA low density basal ganglia
Subacute early (1 to 3 days) Wedge shaped low density area involving both grey and white matter Hemorrhagic transformation may occur Increasing mass effect brain herniation ventricular trapping(raised Intra Cranial Tension) If extensive can result in life threateningmalignant brain edema in cases of Internal Carotid Artery Occlusion,ICA dissection.
CT axial plain SubAcute infarct
Subacute late (4 to 7 days) Gyral enhancement Mass effect,edema persist Chronic Encephalomalacic changes,volume loss Calcification rare
MRI Diffusion weighted sequence is sensitive in acute infarcts Hyperacute :- Immediate Absence of normal flow void <12 hrs- gyral edema, sulcal effacement, loss of grey white interface In hyperacute diffusion restriction is seen with low ADC values (decrease to 30 to 40% below normal) 12 to 24hrs : Hyperintensity on T2 Meningeal enhancement, mass effect Intravascular contrast enhancement.
coronal T1W E+ axial
DIFFUSION WEIGHTED IMAGING PRINCIPLE IN Acute stroke Due to alteration of homeostasis results in excess intracellular water accumulation - cytotoxic edema - with an overall decreased rate of water molecular diffusion within the affected tissue Showing diffusion restriction which appers bright.
Subacute infarct on MRI Late subacute Gs effect resolves T2 fogging Hemorrhagic changes Chronic Enc Hemorrhagic residua Wallerian degener T2W axial TIW E+axial
C.T ANGIOGRAPHY C.T Angiography -widely available technique for assesement of both the intracranial and extracranial circulation. C.T Angiographic demonstration of a significant thrombus can guide appropriate therapy in the form of intra arterial or mechanical thrombolysis. Furthermore,identification of the carotid disease and visualisation of the aortic arch can provide clues to the cause of the ishemic event and guidance for the I.R
Similar findings can be obtained by MR Angiography. Like CT Angio MR Angio is useful for detection of intravascular occlusion due to thrombus and for evaluating the carotid bifurcation in patients with acute stroke. Time of Flight MR and contrast enhanced MR angio commonly used to evaluate intra cranial and extracranial circulation
C.T PERFUSION IMAGING Used in the assesement of ischemic penumbra This is done by measuring, -cerebral blood volume -cerebral blood flow Mean Transit Time - time difference between arterial and venous (inflow and outflow )
ARTERIAL
VENOUS
The evaluation of the Brain perfusion is based on the central volume principle which is Cerebral Blood Flow= Cerebral Blood Volume /Mean Transition Time. Both the arterial and venous Region of Interest are optimally chosen in large vessels that course in a direction nearly perpendicular to the plane of C.T acquisition. Arterial ROI Is typically either of two A.C.A or unaffected M.C.A, Venous ROI is placed over the superior sagittal sinus, transverse sinus.
Comparision of DWI and PWI - The lesion appears smaller on DWI Than on the Perfusion Weighted Images.This is typically observed in large vessel strokes. -The lesion appears same size on DWI and PWI when the tissue is irreversibly infarcted and there is no penumbra.
The lesion appears larger on DWI than on PW Images or the lesion seen only on DW Images but not on Perfusion Weighted images. These findings are usually associated with early reperfusion of ischemic tissue.
TAKE HOME MESSAGE In case of suspected infarct C.T is the modality of choice to rule out Haemorrhage & to find early signs of infarction. However it should be followed by DWI of brain to early visualisation of acute infarct (about 30 min ) Further advanced imaging modalities like CT/MR Angiography for localisation of Vascular Pathology. Perfusion study is done to look for Penumbra (salvagable brain parenchyma ) & planning of interventions.
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