Computed tomographic-angiographic findings within the first five hours of cerebral infarction

Radiation exposure of computed tomography imaging for the assessment of acute stroke

Purpose

To assess suspected acute stroke, the computed tomography (CT) protocol contains a non-contrast CT (NCCT), a CT angiography (CTA), and a CT perfusion (CTP). Due to assumably high radiation doses of the complete protocol, the aim of this study is to examine radiation exposure and to establish diagnostic reference levels (DRLs).

Methods

In this retrospective study, dose data of 921 patients with initial CT imaging for suspected acute stroke and dose monitoring with a DICOM header–based tracking and monitoring software were analyzed. Between June 2017 and January 2020, 1655 CT scans were included, which were performed on three different modern multi-slice CT scanners, including 921 NCCT, 465 CTA, and 269 CTP scans. Radiation exposure was reported for CT dose index (CTDI_vol) and dose-length product (DLP). DRLs were set at the 75th percentile of dose distribution.

Results

DRLs were assessed for each step (CTDI_vol/DLP): NCCT 33.9 mGy/527.8 mGy cm and CTA 13.7 mGy/478.3 mGy cm. Radiation exposure of CTP was invariable and depended on CT device and its protocol settings with CTDI_vol 124.9–258.2 mGy and DLP 1852.6–3044.3 mGy cm.

Conclusion

Performing complementary CT techniques such as CTA and CTP for the assessment of acute stroke increases total radiation exposure. Hence, the revised DRLs for the complete protocol are required, where our local DRLs may help as benchmarks.

Multimodal imaging in acute ischemic stroke

OPINION STATEMENT

Recent years have seen the development of novel neuroimaging techniques whose roles in the management of acute stroke are sometimes confusing and controversial. This may be attributable in part to a focus on establishing simplified algorithms and terminology that omit consideration of the basic pathophysiology of cerebral ischemia and, consequently, of the full potential for optimizing patients' care based upon their individual imaging findings. This review begins by discussing cerebral hemodynamic physiology and of the effects of hemodynamic disturbances upon the brain. Particular attention will be paid to the hemodynamic measurements and markers of tissue injury that are provided by common clinical imaging techniques, with the goal of enabling greater confidence and flexibility in understanding the potential uses of these techniques in various clinical roles, which will be discussed in the remainder of the review.

The role of imaging in acute ischemic stroke

Neuroimaging has expanded beyond its traditional diagnostic role and become a critical tool in the evaluation and management of stroke. The objectives of imaging include prompt accurate diagnosis, treatment triage, prognosis prediction, and secondary preventative precautions. While capitalizing on the latest treatment options and expanding upon the "time is brain" doctrine, the ultimate goal of imaging is to maximize the number of treated patients and improve the outcome of one the most costly and morbid disease. A broad overview of comprehensive multimodal stroke imaging is presented here to affirm its utilization.

Xenon-enhanced computed tomography cerebral blood flow measurements in acute cerebral ischemia: Review of 56 cases

OBJECTIVE

Ischemic stroke must be diagnosed promptly if patients are to be treated with thrombolytic therapy. The diagnosis of acute cerebral ischemia, however, is usually based on clinical and computed tomography (CT) scan findings. CT scans are often normal in the first few hours after stroke. The purpose of this study was to determine whether Xenon-enhanced CT (XeCT) cerebral blood flow (CBF) studies could increase the sensitivity of stroke detection in the acute stage.

METHODS

CBF studies performed within 8 hours of symptom onset were evaluated in 56 patients who presented with hemispheric stroke symptoms. Mean CBF in the symptomatic vascular territory was calculated and compared with the corresponding contralateral area. CBF values below 18 mL/100g/min on 2 adjacent regions of interest were considered ischemic lesions. CT scans and angiograms were compared with the XeCt findings. Neurological condition on admission and discharge was evaluated by using National Institutes of Health Stroke Scale (NIHSS) scores.

RESULTS

The mean NIHSS score on admission was 12+/-5. Early CT scans were abnormal in 28 (50%) patients. There were 9 (16%) patients who had normal XeCT scans because of spontaneous reperfusion of the ischemic area. XeCT studies showed an ischemic lesion in 47 (84%) patients. In these patients, the mean CBF in the affected vascular territory was 16+/-8 mL/100g/min compared with 35+/-13 mL/100g/min in the contralateral specular territory (P<0.001). There were no false positive or negative XeCT studies, and the location of the perfusion defect corresponded with the CT and/or angiographic findings in all cases. Eight patients died (14%), and the 48 survivors (86%) had a mean NIHSS score of 9+/-6 on discharge.

CONCLUSIONS

CBF measurements were correlated with the CT and angiographic results and greatly assisted in the diagnosis of acute ischemic stroke. XeCT studies used for estimating the location and extent of cerebral ischemia may be important in the triage of patients for acute stroke therapy.

Imaging Stroke Evolution after Middle Cerebral Artery Occlusion in Non-human Primates

This article reviews imaging approaches applied to the study of stroke in nonhuman primates. We briefly survey the various surgical and minimally invasive experimental stroke models in nonhuman primates, followed by a summary of studies using computed tomography, positron emission tomography and magnetic resonance imaging and spectroscopy to monitor stroke from the hyperacute phase (within minutes of the onset of cerebral ischemia) to the chronic phase (1 month and beyond).

Mechanisms of ischemic stroke secondary to large artery atherosclerotic disease

Atherosclerotic occlusive disease of the cervical and intracranial arteries leads to ischemic stroke through two separate, but interrelated, mechanisms: local thrombosis or embolism from atherosclerotic plaque, and hemodynamic failure (low flow). In this article, the author discusses the evidence linking these two mechanisms with cerebral ischemia, and the evidence for the synergistic effects of thromboembolism and impaired hemodynamics. An understanding of these two mechanisms is important because these mechanisms provide the rationale for revascularization for patients who have atherosclerotic stenosis or occlusion. In addition, the biologic imaging of atherosclerotic plaques and hemodynamic assessment eventually will play an important role in stratifying patient risk and guiding physiologically based patient selection for intervention.

Improved early stroke detection: Wavelet-based perception enhancement of computerized tomography exams

Nonenhanced computerized tomography (CT) exams were used to detect acute stroke by notification of hypodense area. Infarction perception improvement by data denoising and local contrast enhancement in multi-scale domain was proposed. The wavelet-based image processing method enhanced the subtlest signs of hypodensity, which were often invisible in standard CT scan review. Thus improved detection efficiency of perceptual ischemic changes was investigated. Data processing became more effective by initial segmentation of brain tissue and extraction of regions susceptible to tissue density changes. The new method was experimentally verified. Sensitivity of stroke diagnosis increased to 56.3% in comparison to 12.5% of standard CT scan preview.

Progression of middle cerebral artery susceptibility sign on T2*-weighted images: its effect on recanalization and clinical outcome after thrombolysis

OBJECTIVE

The middle cerebral artery (MCA) "susceptibility sign" on T2*-weighted imaging has been reported to indicate acute thrombotic occlusion. We evaluated the serial progression of this susceptibility sign on follow-up MRI and its effect on recanalization and clinical outcome after intraarterial thrombolysis.

MATERIALS AND METHODS

Thirty-three acute ischemic stroke patients who were treated with intraarterial thrombolysis and underwent MRI within 6 hours of symptom onset were enrolled in this study. All study participants had either M1 or M2 occlusion on digital subtraction angiography before thrombolysis and underwent follow-up MRI 2-3 days after thrombolysis. Recanalization status was evaluated using the thrombolysis in myocardial infarction (TIMI) flow grade on digital subtraction angiography immediately after thrombolysis. The serial progression of the susceptibility sign on follow-up T2*-weighted imaging was compared with the MR angiographic findings. Baseline clinical parameters and clinical outcome were also reviewed.

RESULTS

A positive MCA susceptibility sign on the initial T2*-weighted imaging was detected in 16 (48%) of the 33 patients. The mean TIMI grade was higher in the patients with a positive sign on imaging than in those without the sign (2.3 vs 1.0, respectively; p < 0.005). In the risk factor analysis, a history of atrial fibrillation was significantly higher in the patients with the MCA susceptibility sign than in those with negative findings for the sign (13/16 [81%] vs 4/17 [24%], respectively). In 14 of the 16 patients with the positive sign, the sign disappeared on follow-up MRI, and that finding (i.e., disappearance of the sign) was well correlated with complete recanalization on follow-up MR angiography in 12 patients. Multivariate logistic regression analysis showed that this sign was not associated with a favorable functional outcome 30 days after thrombolytic treatment.

CONCLUSION

The MCA susceptibility sign can be indicative of acute thromboembolic occlusion and can be used to predict the immediate effectiveness of intraarterial thrombolysis. However, the appearance of this sign was not associated with a favorable clinical outcome after thrombolysis in our small series study.

Detection of BBB disruption and hemorrhage by Gd-DTPA enhanced MRI after embolic stroke in rat

Thrombolytic therapy with rtPA increases the risk of hemorrhagic transformation (HT) after cerebral ischemia. We employed contrast enhancement MRI with Gd-DTPA to detect HT in a rat model of embolic stroke treated with rtPA and a glycoprotein IIb/IIIa receptor antagonist, 7E3 F(ab')2, at 4 h after embolic stroke. Male Wistar rats were subjected to embolic stroke and treated with the combination of rtPA and 7E3 F(ab')2 (n=12) or with saline (n=10) at 4 h after onset of stroke. MRI studies were performed immediately and at 24 h after embolization using a 7-T system. Histological measurements were obtained at 48 h. With Gd-DTPA, T1WI images and permeability related MRI parameters (the blood-to-brain transfer constant, Ki, and the distribution volume of mobile protons, Vp) of 15 out of 18 animals showed hyperintensity regions in gross or microscopic HT areas at 24 h, confirmed histologically at 48 h post stroke. Contrast enhancement MRI detected six of seven (86%) animals with gross HT and nine of eleven (82%) animals with microscopic HT at 24 h after ischemia. Two of eighteen animals with HT, had MRI indices of hemorrhage at 3 h post stroke. However, compared to HT data measured histologically at 48 h in embolic stroke rats, the enhanced areas by Gd-DTPA at 24 h were larger, and the patterns (time, intensity and region) did not directly correlate to the subtypes of HT, i.e., gross or microscopic hemorrhage. Contrast enhancement MRI using Gd-DTPA provides a method to detect gross and microscopic HT after stroke in rats.

Diffusion-Weighted Imaging in Acute Stroke

Diffusion MR imaging has improved evaluation of acute ischemic stroke vastly. It is highly sensitive and specific in the detection of infarction at early time points when CT and conventional MR sequences are unreliable. The initial DWI lesion is believed to represent infarction core and usually progresses to infarction unless there is early reperfusion. The initial DWI lesion volume and ADC ratios correlate highly with final infarction volume and with acute and chronic neurologic assessment tests. ADC values may be useful in differentiating tissue destined to infarct from that potentially salvageable with reperfusion therapy. ADC values also may be useful for determining tissue at risk of HT after reperfusion therapy. DTI can quantify differences in the responses of gray versus white matter to ischemia. FA may be important in determining stroke onset time, and tractography provides early detection of wallerian degeneration that may be important in determining prognosis. Finally, DWI can determine which patients who have TIA are at risk for subsequent large vessel infarction and can differentiate stroke from stroke mimics. With improvements in MR software and hardware, diffusion MR undoubtedly will continue to improve the management of patients who have acute stroke.

Perfusion computed tomography: prediction of final infarct extent and stroke outcome

The Alberta Stroke Program Early Computed Tomography Score (ASPECTS) has not been previously applied to perfusion CT (CTP). Five raters assigned ASPECTS to baseline noncontrast CT (NCCT), CT angiography source images (CTA-SI), CTP source images (CTP-SI), and CTP maps of cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) from 37 consecutive patients with less than 6-hour anterior circulation ischemic stroke. Major reperfusion was identified on follow-up imaging. Mean baseline ASPECTS was compared with follow-up imaging ASPECTS. Rates of favorable outcome were compared for dichotomized baseline ASPECTS. In patients with major reperfusion, mean CBV and CTP-SI ASPECTS closely predicted final infarct ASPECTS. In patients without major reperfusion, mean CBF and MTT ASPECTS best predicted final infarct ASPECTS. There were significant increases in rates of favorable outcome for CTP-SI and CBV ASPECTS of greater than 6, versus less than or equal to 6, but not for other baseline CT modalities. ASPECTS applied to CTP is more accurate at identifying the extent of reversible and irreversible ischemia and at predicting final clinical outcome than NCCTor CTA-SI.

CT perfusion source images improve identification of early ischaemic change in hyperacute stroke

CT perfusion scanning produces dynamic contrast-enhanced brain images, but to generate and interpret the colour maps of cerebral perfusion from these source images requires specialist neuroimaging knowledge. We hypothesized that physicians without such training might still utilise the CT perfusion source images (CTPSI) to diagnose early ischaemic change. Fifteen patients had cerebral non-contrast CT (NCCT) and perfusion CT within 6 hours of hemispheric stroke onset. We tested 15 non-stroke clinicians and radiology trainees, plus three experts, in assessing the presence and extent of early ischaemic change on NCCT versus CTPSI. Day 5-7 CT or MRI was used as the gold standard. Agreement with follow-up imaging was poor for both detection, and extent of early ischaemic change on NCCT (kappa = 0.01-0.11). There was a marked improvement in agreement for both the presence and extent of early ischaemic change on CTPSI (kappa = 0.67-0.83). CTPSI were much more accurate than NCCT in identifying acute ischaemic change. 'Less expert' users accurately identified major early ischaemic change on acute CTPSI. These findings suggest that such physicians might utilise CTPSI to screen potential thrombolysis candidates.

The Hyperdense Cerebral Artery Sign on Head CT Scan

The hyperdense artery sign on noncontrast head CT is thought to be one of the earliest and most useful signs of intra-arterial clot and probable (clinical) stroke. It should be evaluated in the context of the clinical scenario. Rigorous criteria should be applied in order to reduce potential false positives. The hyperdense middle cerebral artery sign is the most studied version and correlates with patient outcome. Our data suggest that the density on noncontrast head CT is not likely to universally represent in situ clot.

Diffusion-Weighted Imaging in Acute Stroke

In magnetic resonance diffusion-weighted imaging (DWI), regions of the brain are depicted not only on the basis of physical properties, such as T2 relaxation and spin density, which influence image contrast in conventional MR imaging, but also by local characteristics of water molecule diffusion. The diffusion of water molecules is altered in a variety of disease processes, including ischemic stroke. The changes that occur in acute infarction enable DWI to detect very early ischemia. Also, because predictable progression of diffusion findings occurs during the evolution of ischemia, DWI enables more precise estimation of the time of stroke onset than does conventional imaging.

Frequency and risk factors for spontaneous hemorrhagic transformation of cerebral infarction

OBJECTIVE

Hemorrhagic transformation of cerebral infarction (HTI) occurs spontaneously but its frequency and risk factors are uncertain with mixed results in previous studies. We aimed to determine the overall frequency of and risk factors for HTI.

METHODS

We performed a systematic review according to Cochrane Collaboration methods of published reports of HTI with reliable, systematic follow-up with computed tomography or magnetic resonance imaging.

RESULTS

In all, 28 observational studies and 19 randomized controlled trials in stroke were identified that included follow-up imaging data. Problems with inconsistent definitions or small and biased patient populations limited detailed interpretation. The overall frequency of any HTI in untreated patients was 8.5% (95% confidence interval 7%-10%). Severe HTI (i.e., HTI accompanied by neurologic deterioration or parenchymal hematoma formation) occurred in 1.5% (95% confidence interval 0.8%-2.2%). The frequency of HTI increased markedly with increasing use of antithrombotic or thrombolytic drugs. Magnetic resonance imaging detected more HTI than did computed tomography. The published data were generally inadequate to undertake more detailed analysis of risk factors. However, in the 8 studies that did provide the information, HTI was associated with large infarcts, mass effect, hypodensity observed early after the stroke, and age older than 70 years, but not hypertension or cardioembolic stroke.

CONCLUSIONS

Severe HTI is uncommon in patients not receiving antithrombotic or thrombolytic agents. The methods used to assess the frequency of and risk factors for HTI, particularly a standard of definitions in future prospective studies, could be improved.

Acute Stroke Assessment with CT: Do We Need Multimodal Evaluation?

PURPOSE

To assess detection of stroke and prediction of extent of infarction with multimodal computed tomographic (CT) evaluation (unenhanced CT, perfusion CT, and CT angiography) in patients suspected of having acute stroke.

MATERIALS AND METHODS

Forty-four consecutive patients with a mean National Institutes of Health Stroke Scale score of 10.45 and suspected of having ischemic stroke of the anterior circulation were examined with multi-detector row CT within 8 hours (mean, 3.05 hours) of onset of symptoms. All evaluations were performed with the knowledge that acute stroke was suspected but without detailed clinical information. The extent of ischemia or final infarction on the baseline unenhanced CT scan and follow-up images was assessed with the Alberta Stroke Program Early CT score. Different perfusion maps and follow-up images were assessed to determine the percentage of the ischemia-affected hemisphere. Each component, as well as the multimodal CT evaluation, was compared with follow-up unenhanced CT scans or magnetic resonance images after a mean time of 2.32 days.

RESULTS

Multimodal CT revealed true-positive findings in 30 of 41 patients and true-negative findings in three, resulting in a sensitivity of 78.9%. Unenhanced CT, CT angiography, and perfusion CT showed sensitivities of 55.3%, 57.9%, and 76.3%, respectively. In eight patients, small infarctions (mean size, 1.47 cm) that were proved at follow-up were missed with all modalities at initial multimodal CT. With perfusion CT, four of these small infarctions were missed within the white matter of the section levels. Maps of cerebral blood flow showed the best correlation with the final size of infarction with an r(2) value of 0.71.

CONCLUSION

The presented multimodal CT evaluation improves detection rate and prediction of the final size of infarction in comparison with unenhanced CT, CT angiography, and perfusion CT alone.

Neuroimaging of stroke: a review

Advances in neuroimaging technology during the past 30 years have resulted in a virtual explosion in the amount of pathologic information that can be obtained in the clinical stroke setting. This neuroimaging revolution has led to a much better understanding of cerebrovascular and tissue pathology, creating a wide array of opportunities for acute treatment and secondary prevention. Advances include early and accurate detection of ischemic and infarcted tissue and the ability to reveal hypoperfused tissue at risk. Clinicians are increasingly able to noninvasively detect embolic and atherothrombotic intravascular lesions. Vascular lesions associated with stroke can be characterized through endovascular neuroimaging techniques and repaired by various means. In this article, we provide an overview and update on the various techniques used in the neuroimaging of stroke and intracranial hemorrhage, including computed tomography, magnetic resonance imaging, ultrasound, and catheter angiography. We outline the specific role of each modality in clinical practice.

Computed tomographic and transcranial Doppler sonographic findings in acute and subacute phases of middle cerebral artery strokes

PURPOSE

The aim of this study was to compare the sensitivities of visual and densitometric analyses of CT scans and transcranial Doppler sonograms (TCD) in detecting early changes in acute stroke.

METHODS

CT and TCD were each performed twice in 12 patients; first in the acute phase (within 28 hours of stroke onset), then in the subacute phase (mean +/- standard deviation, 6 +/- 3 days after onset) of a stroke. Hypodensity on the CT scans was evaluated visually, and the optical density of both the stroke region and the corresponding region on the unaffected side was measured. Measurement of flow parameters in the middle cerebral artery was carried out with TCD before or shortly (within 4 hours) after CT scanning.

RESULTS

In the acute phase, blood flow velocities were significantly lower on the affected side than they were on the unaffected side (means, 42 +/- 13 and 55 +/- 25 cm/second, respectively; p = 0.012). Marked asymmetry in flow velocity was found in 3 of the 4 patients who had normal CT scans in the acute phase. The asymmetry in flow velocity disappeared by the sixth day after the stroke. The resistance index did not correlate with the final infarct size.

CONCLUSIONS

In some patients, the use of TCD in acute stroke may show alterations that reflect tissue damage that is undetectable on CT. Therefore, CT and TCD should be considered complementary diagnostic tools in the acute phase of stroke.

CT and MRI in the diagnosis of acute stroke and their role in thrombolysis

Thrombolysis is an effective but potential deleterious therapy and should therefore be limited to patients with acute intracerebral vessel occlusion and salvageable tissue. MRI currently develops towards the new diagnostic standard for the selection of stroke patients eligible for acute thrombolytic treatment and acute stroke studies. Diffusion- and perfusion-weighed MRI provides diagnostic information not available from the neurological assessments or from CCT and conventional spin-echo MRI. As high-speed DWI and PWI protocols become standardized, a 15-minute integrated stroke protocol of employing echo-planar imaging (EPI) can be outinely performed in the setting of acute clinical stroke. The combination of these MR techniques is suitable to define tissue at risk of infarction that is potentially salvageable brain tissue (an estimate of the ischemic penumbra) and may respond to early recanalization even beyond 3 hours after stroke onset. The extension of the therapeutic window for thrombolytic therapy towards 6 hours in a subpopulation of acute stroke patients might open the way for the successful reperfusion therapy in more stroke patients.

Thrombolytic therapy for ischemic stroke--a review. Part II--Intra-arterial thrombolysis, vertebrobasilar stroke, phase IV trials, and stroke imaging

OBJECTIVE

Intra-arterial thrombolytic therapy for carotid and vertebrobasilar stroke may result in a more rapid clot lysis and higher recanalization rates than can be achieved with intravenous thrombolysis and thus may warrant the more invasive and time-consuming therapeutic approach. We present an overview of all hitherto completed trials of intra-arterial thrombolytic therapy for carotid and vertebrobasilar artery stroke including recommendations for therapy and a meta-analysis. Furthermore, new imaging techniques such as diffusion- and perfusion-weighted magnetic resonance imaging and their impact on patient selection are discussed. Finally, phase IV trials of thrombolysis in general and cost efficacy analyses are presented.

DATA SOURCES

We performed an extensive literature search not only to identify the larger and well-known randomized trials but also to identify smaller pilot studies and case series. Trials included in this review, among others, are the PROACT I and PROACT II studies and the Cochrane Library report.

CONCLUSION

Intra-arterial thrombolytic therapy of acute M1 and M2 occlusions with 9 mg/2 hrs pro-urokinase significantly improves outcome if administered within 6 hrs after stroke onset. Seven patients need to be treated to prevent one patient from death or dependence. Vertebrobasilar occlusion has a grim prognosis and intra-arterial thrombolytic therapy to date is the only life-saving therapy that has demonstrated benefit with regard to mortality and outcome, albeit not in a randomized trial. New magnetic resonance imaging techniques may facilitate and improve the selection of patients for thrombolytic therapy. Presently, thrombolytic therapy is still underutilized because of problems with clinical and time criteria, and lack of public and professional education to regard stroke as a treatable emergency. If applied more widely, thrombolytic therapy may result in profound cost savings in health care and reduction of long-term disability of stroke patients.

Early prediction of irreversible brain damage after ischemic stroke at CT

PURPOSE

To assess the capability of computed tomography (CT) in the prediction of irreversible ischemic brain damage and its association with the clinical course within 6 hours of stroke onset.

MATERIALS AND METHODS

Serial CT scans obtained within 6 hours of stroke onset, at 22-96 hours (median, 1 day), and at 2-36 days (median, 7 days) after symptom onset in 786 patients with ischemic stroke were prospectively studied, and follow-up CT scans were used as the reference. Clinical variables were assessed prospectively and independently of CT evaluation.

RESULTS

The specificity and positive predictive value of ischemic edema at baseline CT for brain infarcts were 85% (95% CI: 77%, 91%) and 96% (95% CI: 94%, 98%), respectively. Sensitivity and negative predictive values were 64% (95% CI: 60%, 67%) and 27% (95% CI: 23%, 32%), respectively. Patients without early CT findings were less severely affected (P<.001), developed smaller infarcts (P<.001), had fewer intracranial bleeding events (P<.001), and had a better clinical outcome at 90 days (P<.001) compared with patients with hypoattenuating brain tissue at early CT.

CONCLUSION

After ischemic stroke, x-ray hypoattenuation at CT is highly specific for irreversible ischemic brain damage if detection occurs within the first 6 hours. Patients without hypoattenuating brain tissue have a more favorable clinical course.

A rating system for prompt clinical diagnosis of ischemic stroke

BACKGROUND

When a CT scan is not available, an early accurate clinical diagnosis of ischemic stroke is essential to initiate prompt therapy. Our objective was to construct a clinical index that is easy to use when stroke patients are first evaluated at the hospital, to identify those who probably are experiencing an acute ischemic episode. The study was conducted at a university-affiliated medical referral center and two community general hospitals in Mexico.

METHODS

Clinical records were reviewed for 801 patients with sudden onset of a focal or global neurologic dysfunction, presumably of vascular origin lasting more than 24 h. Eligibility criteria for this study were admission to the hospital within the first 24 h after symptomatic onset, CT scan diagnosis between 24 and 72 h, and age >45 years. Ischemic stroke included cases of arterial brain infarction, while nonischemic stroke included subarachnoid or intraparenchymatous hemorrhage, mass lesion, venous infarction, and in cases without a CT scan evidence that could explain the clinical manifestations. Data excerpted for analysis were age, sex, history of diabetes mellitus or previous stroke/transient ischemic attack (TIA), time of onset of symptoms, presence of headache, vomiting, neck stiffness, hemiplegia, leukocytosis or atrial fibrillation, diastolic blood pressure, and Glasgow coma scale (GCS) rating. Two multivariable analyses were used: 1) step-wise multiple logistic regression (SMLR), and 2) conjunctive consolidation (CC).

RESULTS

After appropriate exclusions, the study proceeded with 83 ischemic and 42 nonischemic stroke patients. With SMLR, six variables were selected as predictive for ischemic stroke, including neck stiffness, diastolic blood pressure, previous history of stroke/TIA, hemiplegia, GCS, and atrial fibrillation. An appropriate sum of weighted ratings had a positive predictive value (PPV) of 100% for ischemic stroke. With consolidated categories, the PPV was 97% when patients had the following: no neck stiffness; no atrial fibrillation but history of stroke/TIA and GCS > or =12, or no neck stiffness but atrial fibrillation.

CONCLUSIONS

Among patients with acute stroke, clinical data can be used to identify a group with a high probability of ischemic stroke. There are slightly different results between both methods; while SMLR includes the four variables selected by CC, the latter included neither diastolic blood pressure nor hemiplegia/hemiparesia. However, CC results seem easier to understand and interpret than with SMLR.

Magnetic resonance imaging of cerebral hemorrhagic stroke

Despite a traditional perception of reliance on computed tomography and lack of acceptance of magnetic resonance imaging (MRI) for detecting acute hemorrhage, MRI appears to be used increasingly in hemorrhagic stroke. This review addresses the MRI findings of acute hemorrhagic stroke obtained using relatively new imaging techniques. These new techniques have resulted in more acute stroke patients undergoing MRI examination. New information about the frequency and appearance of hemorrhage is emerging: for example, approximately 15-26% of cases of acute cerebral infarctions appear to be complicated by intracerebral hemorrhage. The MRI appearances of hemorrhagic transformation of ischemic infarction, as well as acute hypertensive intracerebral hemorrhage, are discussed based on clinical, biochemical, and technical aspects.

The future of stroke treatment

The concept of the therapeutic window of opportunity in ischemic neuronal injury and understanding the necessity of well organized stroke services revolutionized the management of acute ischemic stroke during the last years of the second millennium. Thrombolysis with IV rt-PA within 3 hours from the onset of symptoms is an established therapy for selected patients. The challenge of stroke therapy at the outset of this millennium is how to translate basic pathophysiologic evidence of ischemic neuronal injury into novel neuroprotective therapies either independently or combined with thrombolysis. Great hopes are placed in identification of pivotal molecular events in ischemic brain tissue and design of effective pharmacological interventions to target them. Aggressive, invasive procedures are also being developed and therapies such as intra-arterial clot lysis, hemicraniectomy and mild hypothermia may improve the bleakest outcomes associated with the most severe forms of ischemic stroke, but their role must be rigorously evaluated. There is, however, no need to wait for future breakthroughs. The existing evidence strongly implies that good care of patients with stroke starts with organization of the entire stroke chain; from the prehospital scene, through the emergency room, to the stroke unit. Without structured stroke services no pharmacological or intervening therapy is likely to improve the outcome of the patient with a stroke.

Middle cerebral artery (MCA) susceptibility sign at susceptibility-based perfusion MR imaging: clinical importance and comparison with hyperdense MCA sign at CT

PURPOSE

To describe the radiologic findings of susceptibility changes in acute middle cerebral artery (MCA) thromboembolism detected with three-dimensional (3D) susceptibility-based perfusion magnetic resonance (MR) imaging and to compare the detectability and clinical value of this sign with those of the hyperdense MCA sign at computed tomography (CT).

MATERIALS AND METHODS

Twenty-three patients (mean age, 55 years) underwent CT and MR imaging within the first 6 hours after the onset of acute MCA stroke. The hyperdense MCA sign at CT and the presence of susceptibility changes in acute thromboembolism as depicted on T2*-weighted 3D perfusion MR images were assessed. The presence of each sign was correlated with clinical presentation.

RESULTS

The sensitivity of the hyperdense MCA sign at CT was 54% (negative predictive value, 71%) compared with 82% (negative predictive value, 86%) for the susceptibility changes at MR imaging. There were no false-positive CT or MR readings. The presence of the MCA susceptibility sign correlated positively with the initial clinical presentation (chi(2) = 7.987, P =.009, Spearman rho = 0.589). However, neither of the signs was a predictor for clinical outcome in cases of spontaneous MCA stroke.

CONCLUSION

In addition to the information traditionally provided with reconstructed perfusion parameter maps, 3D susceptibility-based perfusion MR images allow the identification of acute MCA thromboembolism with a sensitivity higher than that of CT.

Computed tomography findings in the first few hours of ischemic stroke: implications for the clinician

In order to evaluate the clinical usefulness of emergency computed tomography (CT) in acute ischemic stroke, we assessed whether CT findings within the first few hours of stroke onset reliably predict type, site and size of the index infarction, and risk of death or disability. For this reason we reviewed clinical and CT findings in a cohort of unselected consecutive patients referred to the stroke unit of a large urban hospital because of a presumed ischemic stroke in the anterior circulation (AC), and submitted to CT within 5 h from onset. Out of 158 total patients, emergency CT revealed parenchymal changes compatible with AC focal ischemia in 77 (49%) and a hyperdense middle cerebral artery (MCA) in 41 (26%). Parenchymal changes and hyperdense MCA predicted an AC territorial infarction respectively in 97% of cases (95% C.I. 93% to 100%) and in 95% of cases (95% C.I. 88% to 100%). Site and size of early changes coincided with those of final lesions in 79% of patients with cortical changes and in 95% of patients with cortico-subcortical changes, but only in 37% of patients with initial subcortical changes, the remainder of whom developed a cortico-subcortical infarction. At logistic regression parenchymal changes were the only independent predictor of an AC territorial infarction. Negative predictive power, however, was only 40% (95% C. I. 29% to 51%) for parenchymal changes, and 35% for hyperdense MCA (95% C.I. 26% to 44%). The odds for death or disability at 1 month associated with parenchymal changes were thrice as high as with negative CT, even after adjustment for clinical severity on admission. These results indicate that CT scan adds significantly to the prediction of outcome made on clinical grounds. The frequent development of a territorial infarction in patients with initially negative CT and the subsequent recruitment of the cortex in those initially exhibiting only subcortical changes suggest that the transition from ischemia to infarction often occurs after the first five h following stroke.

Neuroprotection in acute ischaemic stroke. II: Clinical potential

In the 4 years since our first article, there has been considerable progress in our understanding of the pathophysiology of acute ischaemic stroke, and the results of well-conducted trials have at last begun to change everyday clinical practice. The timing of the various processes of the ischaemic cascade and the potential time windows for different interventions are better understood. Furthermore, the importance of maintaining cerebral perfusion and optimizing systemic physiological and biochemical factors in order to prevent neurological deterioration ('progressing stroke') is increasingly being realized. Numerous antithrombotic and neuroprotective drugs have been evaluated in clinical trials, and while none has shown unequivocal benefits on its own, prospects for successful intervention are still good. This will probably involve different combinations of treatments targeted on different pathophysiological stroke types, so that the management of acute stroke will offer a considerable challenge to the stroke physicians of the future.

Assessment of brain tissue viability under clinical circumstances

The growing body of clinical and instrumental information that can be gathered from the earliest phases of stroke has radically modified the way in which neurologists tackle the treatment of stroke patients. It is now theoretically possible to tailor therapeutic choices on the basis of prognostic estimates made within a few hours of stroke onset, that is at a time when numerous options to limit the ischemic insult are still open. However, once many hours or even days have passed, all one can do is witness the effects of a natural course which by then is virtually unmodifiable. This applies not only to stroke patients being treated within the context of pharmacological trials, but also to those in daily clinical management, since some choices, such as when and how to treat brain oedema and give thrombolytics, may now be made earlier and more accurately than in the past. Emergency CT in particular discloses important indices of subsequent clinical evolution and outcome, thus adding to already well-known predictors such as age and severity of neurological status at hospital admission [20]. CT does have the aforementioned limitations regarding inter-observer agreement, which may, however, be minimised by an appropriate training of observers. Moreover it has intrinsic limitations regarding the visualisation of the actual brain tissue damage, since up to one fifth of patients with no or very limited early CT signs may present symptomatic hemorrhagic transformation after thrombolysis [23] and approximately one sixth of early deteriorating patients do not show early CT signs [52]. Other techniques, such as positron and single photon emission tomography and in particular MR imaging, which may shed light on tissue viability and perfusion as well as arterial patency simultaneously, might be able to provide more accurate information [19] Nevertheless, CT is still the most widely used tool in clinical centres which hospitalise stroke patients, and is unlikely to be routinely replaced by the other imaging devices in the foreseeable future. Consequently, there is an urgent need both for a general consensus on the identification criteria of early CT signs and for the widest possible awareness of knowledge regarding CT capabilities among neurologists [47], waiting for the wide applicability of newer technologies.

Prediction of cerebral infarct sizes by cerebral blood flow SPECT performed in the early acute stage

Cerebral infarct due to embolic stroke without recanalization was examined by cerebral blood flow (CBF) SPECT in the early acute stage, and the possibility of predicting the size it will reach in the later stages was evaluated. Twenty patients (67 +/- 13 years) were examined by CBF SPECT with 99mTc-ECD 4.5 +/- 3.1 hours after the onset of cardiogenic cerebral embolism. The ratio of the anteroposterior length of the cerebral hemisphere to that of the severe ischemic region, which was defined as an area of clear-cut severe reduction in CBF as observed by SPECT, was calculated. One week after the onset, the cerebral infarct was measured in the same manner by CT, and the relationship between the two measurements was evaluated. The CBF in the region of severe ischemia and the surrounding region was determined by the Patlak plot method, and the affected/non-affected (A/NA) ratio was calculated. In severe ischemic regions the CBF ranged from 1.7 ml/100 g/min to 20 ml/100 g/min (mean, 11 +/- 5 ml/100 g/min), whereas the A/NA ratio ranged from 4% to 45% (mean, 26 +/- 11%). On the other hand, the CBF in the surrounding regions ranged from 20 ml/100 g/min to 52 ml/100 g/min (mean, 34 +/- 8 ml/100 g/min) whereas the A/NA ratio ranged from 52% to 104% (mean, 77 +/- 11%). The coefficient of correlation between the infarct size predicted by SPECT and that measured by CT was r = 0.986, and the correlation equation was Y = 1.047X - 2.969. CBF SPECT performed in the early acute stage can be used to predict the size of cerebral infarct.

Carotid disease in acute stroke: A review

This article reviews the literature about carotid disease in acute stroke. Several conclusions are drawn. First, carotid disease is an important cause of ipsilateral cortical strokes, with significant ipsilateral disease found in about one fourth of patients. Second, the role of carotid disease in lacunar stroke is less certain but probably causes a small number of lacunar infarcts. Third, the majority of infarcts that occur with severe carotid stenosis or acute carotid occlusion are caused by cerebral emboli, whereas most infarcts with preexisting occlusion are probably caused by hemodynamic factors. Fourth, the optimal timing of carotid surgery in acute stroke is uncertain. Clinical trials of endarterectomy in acute stroke are now required.

Intravenous thrombolytic therapy in acute stroke

The article reviews the experimental basis of thrombolytic therapy, and summarizes the results of the recent trials of thrombolysis. Five large clinical trails have evaluated intravenous thrombolytic therapy for the treatment of hyperacute (< 6 h) stroke. Three of these studies were negative, one was equivocal, and one was strongly positive. The failure of demonstrate efficacy definitively in four of these trials may be related to a number of methodological factors, including the type and dose of drug administered, the timing of drug administered, and the method of patient selection for treatment. The NINDS recombinant tissue plasminogen activator (rt-PA) study showed that thrombolytic therapy can be of substantial benefit when administered within 3 h of stroke onset using strict patient selection criteria and rt-PA is now FDA approved for treatment of acute stroke. However, the risk of clinically significant bleeding is elevated. To achieve the favorable risk/benefit ratio demonstrated in the NINDS trial, patients must be screened by experienced clinicians for contraindications to thrombolysis and the acute computerized tomography (CT) brain scan must be carefully evaluated for radiographic features that increase the risk of cerebral hemorrhage. Guidelines for the use of rt-PA are provided, as well as insights into future thrombolytic treatment strategies.

Early CCT signs of supratentorial brain infarction: clinico-radiological correlations

Early signs of brain infarction can be detected by modern CCT technology even within the first 6 h after stroke. Little is known about the prognostic significance of early infarction signs in CCT. We prospectively evaluated clinical and CCT findings of 95 consecutive patients with an acute ischemia in the territory of the middle cerebral artery. All patients were admitted to our stroke unit within 6 h after stroke. In 55 patients CCT was performed within 3 h, and in 40 cases between 3 and 6 h. In all patients the clinical findings were assessed by the Scandinavian Stroke Scale (SSS). The disability due to stroke was evaluated after 4 weeks by use of the modified Rankin Scale. We could demonstrate the following early signs of cerebral infarction: focal hypodensity (23.2%), obscuration of basal ganglia (12.6%), focal brain swelling (22.1%), hyperdense middle cerebral artery sign (HMCA; 11.5%). In 3 patients early edema led to ventricular compression, in 1 patient to midline shift. The occurrence of early infarction signs did not depend on the etiology of ischemia but was significantly associated with a severe neurological deficit at admission and an unfavourable disability status 4 weeks after stroke. Focal brain swelling and HMCA were often followed by extensive infarction lesions on the follow-up CCT. In conclusion, early signs of hemispheric brain infarction visible on CCT scans performed within 6 h after stroke are correlated with severe stroke and an unfavourable functional outcome. However, a substantial part of our patients had a benign course of the disease in spite of early CCT pathology. Decisions on therapy in individual patients therefore should not depend on early CCT findings exclusively.

Carotid arterial dissection as a cause of severe brain infarction in young adults

OBJECTIVES

To investigate the occurrence of cervicocerebral arterial dissection in young adults, we examined the etiology of first-ever brain infarction and the timing of angiography.

METHODS

One hundred eighty-four subjects with first stroke aged 16 to 49 years, admitted to the Helsinki University Hospital between 1983 and 1990 were included. Seventy-eight percent of the angiographies were performed more than 1 week after the onset of stroke symptoms.

RESULTS

We identified 19 (10%) subjects with carotid arterial dissection and none with vertebral arterial dissection. Mortality attributed to ischemic stroke caused by carotid arterial dissection was high (26%). With longer time between onset of stroke symptoms and angiography, dissection was a rarer finding (P < .01), and there were more angiographies with no findings (P < .05). Trauma (P < .001) and headache (P < .05) preceded onset of stroke more frequently in these patients than in others.

CONCLUSIONS

Prompt imaging of the cervicocerebral arteries is indicated if the patient has preceding trauma or complains of headache and/or neck pain.

Detectability of cerebral hemisphere ischaemic infarcts by CT within 6 h of stroke

To determine how early and how reliably ischaemic brain infarcts can be detected on CT within 6 h of the onset of cerebral hemisphere strokes, 44 such studies were interpreted by an experienced neuroradiologist blinded to clinical signs, but aware that the cohort was a stroke population. He was asked to detect and localise an area of parenchymal low density and/or focal brain swelling. A follow-up study showing the definite infarct served as a reference in each case. In 38 patients areas of slightly low density were seen, and in 36 follow-up CT confirmed infarcts in the locations indicated. In 2 patients the reading was false positive. In 6 patients no low density focus could be detected. In these 8 patients examined by CT within 180 min of the stroke, no low density could be identified, even in retrospect with the knowledge of the findings on follow-up. Thus, 42 readings (95%) were true positive or true negative; 2 were false positive; and none was a false negative. CT within 6 h of the onset of symptoms has a mean sensitivity of 82% (36/44) for ischaemic cerebral hemisphere infarcts. By contrast, its sensitivity to ischaemic parenchymal low density is low during the initial 2 h. The early development of hemispheric infarcts can be detected reliably if the radiologist is familiar with the signs.

Thrombolysis acute ischemic stroke

Thrombolysis is an attractive but potentially dangerous they for cerebral ischemia: it is capable of dissolving an arterial thrombus, but can also transform a pale infarct into a hematoma and/or may cause severe oedema and herniation. The safety and efficacy of the treatment critically depend on the timing of intervention ad on patient selection. In recent studies on ischemic stroke, spontaneous hemorrhagic transformation of an infarct seems to be related to the size of the lesion, and can be reliably predicted as early as five hours from stroke onset by the presence of focal hypodensity in the CT scan. That is why in the European Co-operative Acute Stroke (ECASS), a randomised, double blind trial on intravenous rt-PA in hemispheric stroke, patients showing, on the admission CT scan, extended early hypodensity, involving more than one third of the territory of the middle cerebral artery, were excluded from the day. Other ongoing trials on thrombolytic agents are expected to provide further indications on how to identify those patients most likely to benefit and least likely to experience adverse effects from this treatment.

Acute neuroradiology: methods, indications and timing

The rapid development of radiological examination methods, technical innovations and creative and critical radiological research have dramatically changed the diagnostic approach with new indications and changed timing in the examination of patients with acute neurological lesions. The role of CT as the primary radiological examination method in these patients is well established, and is routinely used before the start of suitable treatment to detect or exclude intracranial haemorrhage, either traumatic or nontraumatic, or to detect other causes of acute onset of neurological disease, such as intracerebral tumours or subdural haematoma. The role of MRI still needs further confirmation. The sensitivity of MRI is superior to that of CT, especially in examination of the spinal cord. The main drawbacks of MRI are the problems in monitoring acutely ill patients, the unfamiliarity with the method, and capacity problems. Today, MRI is mainly used as a complement to CT, with the exception of spine injuries where MRI is the method of first choice. Also, the role of digital subtraction angiography is changing from diagnostic examinations towards endovascular therapeutic procedures. An experienced neuroradiologist has the key position in choosing and performing the most suitable examination method for each specific indication.

Clinical-radiographic correlations within the first five hours of cerebral infarction

Fifty patients, ages 54-79, with ischemic hemispheric strokes productive of hemiparesis, at a minimum, underwent standardized neurological evaluations, computed tomographic scanning and cerebral angiography (N = 38) or carotid ultrasound (N = 12) within 5 h of onset. A second scan was performed at 5-7 days. Clinical scores were not associated with a history of, or the presence of: hypertension, smoking or cardiac disease, including atrial fibrillation, nor with severe internal carotid artery stenosis or occlusion. Clinical scores were adversely affected by early scan abnormalities (especially mass effect), lesion size, intracranial arterial occlusions, elevated serum glucose levels and the subsequent development of hemorrhagic infarction. Glucose levels correlated with infarct size and the development of hemorrhagic infarction. Delayed intracranial arterial filling and collateral flow were associated with reduced infarct size but did not confer clinical protection. We believe that combining the initial glucose level and scan results has prognostic significance, and early angiography is valuable in characterizing infarct etiology and assessing clinical severity.