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CT scan findings in Acute CVA

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CT and MRI Findings in Acute CVA:

CT and MRI F indings in Acute CVA By Dr Shashidhar Patil SR MICU, SJMCH, Bangalore

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Stroke, or cerebrovascular accident (CVA), is a clinical term that describes a sudden loss of neurologic function persisting for more than 24 hours that is caused by an interruption of the blood supply to the brain. It is the third leading cause of death in the United States and the second most common cause of death worldwide, with considerable disability among survivors. C erebrovascular A ccident

Etiology:

Etiology The etiologies of stroke are varied but can broadly be categorized into  ischemic   or hemorrhagic  infarctions. Approximately 80-87% of strokes are from ischemic infarction due to thrombotic or embolic cerebrovascular occlusion. Hemorrhagic infarctions comprise most of the remainder of strokes with a smaller number due to aneurysmal  subarachnoid hemorrhage

What is a CT (or CAT) scan?:

What is a CT (or CAT) scan? CT stands for “computed tomography” - this is a complex machine that uses x-rays to create three-dimensional images of the body

What is bright/dark on CT?:

What is bright/dark on CT? The more dense the tissue, the brighter it looks on CT Any calcified structure (like the skull) appears bright New hemorrhage in the brain is also bright Water (or CSF) looks dark on CT

Noncontrast CT:

Noncontrast CT On noncontrast CT scan, early findings (within 6 hours) include subtle loss of gray-white differentiation corresponding to increased water content from early cytotoxic edema .   Loss of definition of cortex and obscuration of deep gray matter structures may exist . In middle cerebral artery infarction, obscuration of lateral margins of the insula, (the insular ribbon sign) and loss of density of the basal ganglia nuclei, such as the lentiform nucleus (vanishing basal ganglia sign), may exist

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Noncontrast CT was obtained to evaluate this 64-year-old male who awoke with aphasia and right-sided weakness . Loss of the normal gray-white differentiation between the normally denser insular cortex and the less attenuating subinsular white matter is seen; this is consistent with loss of the " insular ribbon ."

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Follow-up noncontrast CT scan obtained approximately 12 hours after the initial study in the same patient demonstrates further evolution of the infarction, which is now extensive and spans most of the left middle cerebral artery (MCA) territory.

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Noncontrast CT scanning was performed to evaluate this 70-year-old female with a history of acute onset of right-hand weakness and aphasia. Loss of gray-white differentiation in the left insular cortex and in the immediately adjacent cortical and subcortical portions of the left temporal operculum is seen; this is strongly suggestive of an acute infarction .

Hyperattenuation of vessels may be seen (dense vessel sign or dot sign); these are believed to represent acute thrombus or embolus and has been described in the MCA, basilar artery, and venous sinuses:

Hyperattenuation of vessels may be seen (dense vessel sign or dot sign); these are believed to represent acute thrombus or embolus and has been described in the MCA, basilar artery, and venous sinuses H yperdense appearance of the right MCA with subtle loss of gray-white differentiation of the anterior right temporal lobe.  The left middle cerebral artery (MCA) trunk appears highly attenuated ( the dense MCA sign ), suspicious for acute thrombosis or embolism.

Dense basilar artery: Axial noncontrast CT scan demonstrates a hyperdense basilar artery in a patient with pontine infarction who was later found to have basilar artery thrombosis. Other large vessels besides the middle cerebral artery (MCA) can produce a dense vessel sign when occluded.:

Dense basilar artery: Axial noncontrast CT scan demonstrates a hyperdense basilar artery in a patient with pontine infarction who was later found to have basilar artery thrombosis. Other large vessels besides the middle cerebral artery (MCA) can produce a dense vessel sign when occluded.

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After approximately 12-24 hours, a more well-defined area of hypodensity , which may have associated mass effect with sulcal or ventricular effacement, may be seen. The hypodensity is usually irreversible and is felt to correlate with minimum final infarct size . Mass effect typically peaks by about 5 days post ictus and disappears over the next several weeks . In roughly one half of cases, the infarct may change from hypodense to isodense . This has been termed the "fogging effect" on CT and is usually seen 2-3 weeks post ictus during the subacute phase of infarction and should resolve on subsequent imaging . IV contrast may make the infarct more conspicuous. The phenomenon is believed to be due to influx of lipid-laden macrophages, decreased water content, proliferation of capillaries, reperfusion, and petechial hemorrhage

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CT fogging effect : Axial noncontrast CT scan demonstrates focal low density, loss of gray-white differentiation, and mild sulcal effacement in the right parietal region (left image, arrow) in a 62-year-old female presenting with acute stroke. A follow-up noncontrast CT scan obtained 10 days later demonstrates diminished sulcal effacement and isodensity with a near-normal appearance (middle image), thought to be secondary to the CT "fogging effect" that may be seen during the evolution of an infarct. The axial diffusion-weighted image (right) confirms the right parietal infarct .

After approximately 6-8 weeks, a well-defined cavity may be seen, corresponding to encephalomalacia. Evidence of volume loss, such as ex-vacuo dilatation of the adjacent ventricle, may exist. Cortical laminar necrosis may be seen in chronic infarcts with gyriform cortical calcification :

After approximately 6-8 weeks, a well-defined cavity may be seen, corresponding to encephalomalacia . Evidence of volume loss, such as ex- vacuo dilatation of the adjacent ventricle, may exist. Cortical laminar necrosis may be seen in chronic infarcts with gyriform cortical calcification  Evidence of parenchymal volume loss with ex- vacuo dilatation of the right lateral ventricle is present, indicating chronicity infarction.   a well-defined area of volume loss in the right temporal lobe with a low-density appearance consistent with encephalomalacia . No mass effect exists

Contrast-enhanced CT:

Contrast-enhanced CT Contrast enhancement following brain infarction is typically seen in about two thirds of cases, usually during the second or third week post ictus. Common patterns of enhancement include patchy, gyriform , ring-like, and homogenous. Earlier contrast enhancement corresponds to infarcts with larger volume and mass effect and is secondary to disruption of the blood-brain barrier with increased vascular permeability and/or reperfusion from recanalization or collateral circulation. Early contrast enhancement portends an increased risk of hemorrhagic transformation.

CT angiography:

CT angiography The most important purpose of CTA in acute stroke is to detect vessel thrombosis or occlusion. CTA source images should always be assessed, in addition to multiplanar reconstruction (MRP) and maximum intensity projection (MIP) images . Proper interpretation requires attention to luminal enhancement to assess vessel patency, intimal flaps to exclude dissection, filling defects and vessel wall calcifications to assess stenosis, and occlusions and focal outpouchings suggestive of aneurysm or pseudoaneurysm

Images of the circle of Willis from a CTA in a 70-year-old female with acute onset right-sided weakness. A high-grade stenosis of the distal left middle cerebral artery (MCA) trunk (red circles) is seen, with filling of the remainder of the MCA territory via an anterior branch near the bifurcation.:

I mages of the circle of Willis from a CTA in a 70-year-old female with acute onset right-sided weakness. A high-grade stenosis of the distal left middle cerebral artery (MCA) trunk (red circles) is seen, with filling of the remainder of the MCA territory via an anterior branch near the bifurcation.

CTA source data can also be useful to assess for areas of hypoperfusion and poor enhancement that may correspond to areas of greatest ischemia.there is diminished enhancement involving the caudate head, lentiform nucleus, and capsular regions. High density noted centrally in this poorly enhancing region represents an area of hemorrhagic transformation.:

CTA source data can also be useful to assess for areas of hypoperfusion and poor enhancement that may correspond to areas of greatest ischemia.there is diminished enhancement involving the caudate head, lentiform nucleus, and capsular regions. High density noted centrally in this poorly enhancing region represents an area of hemorrhagic transformation .

CT angiography:

CT angiography CTA has been demonstrated to be highly reliable for the detection or exclusion of large intracranial vessels, such as the ICA and MCA trunk up to the M2 segment and basilar arteries . Using modern multidetector CT with voxel sizes well below 1 mm and postprocessing tools, CTA is highly accurate in measuring vessel diameters adjacent to stenosis and is superior for grading of intracranial stenosis compared with 3D TOF MRA technique . CTA has the advantage over MRA and DSA of detecting mural calcifications in relation to stenosis . In addition to vascular occlusions, CTA source images are able to demonstrate hypoperfused brain parenchyma in acute stroke similar to DWI images.

CT perfusion:

CT perfusion Perfusion maps can usually be compared visually to qualitatively look for areas of gross or subtle asymmetry. Quantitative CBF values can also be examined with thresholds for ischemic and infarcted tissue in mind. A low CBV abnormality best correlates with the infarct core . The mismatch between abnormal CBV and abnormal CBF estimates the penumbra

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After selecting the appropriate arterial and venous input functions, the computer software is able to generate perfusion maps of different parameters (CBF = cerebral blood flow, CBV = cerebral blood Volume, MTT = mean transit time, TTP = time to peak enhancement). Regions of interest can then be placed over these maps for quantitative information. In this patient with occlusion of the distal left MCA trunk, elevated MTT and diminished CBF exists in the left basal ganglia, insular and opercular regions. The CBV is mildly increased in this same region, which is believed to be due to autoregulatory vasodilation in response to ischemia.

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