Prediction of malignant middle cerebral artery infarction by early perfusion- and diffusion-weighted magnetic resonance imaging

Hemicraniectomy for space-occupying supratentorial ischemic stroke

Space-occupying, malignant hemispheric infarction is one of the most devastating forms of ischemic stroke. Until recently, there was no proven treatment. In 2007, results from randomized, controlled trials provided evidence for the benefit of early hemicraniectomy. This paper provides an overview on the current treatment options for malignant ischemic brain infarction, with a focus on hemicraniectomy. We also discuss major unsolved problems and open questions regarding the disease. Finally, we give a perspective on future clinical studies in this field of stroke.

Accuracy of perfusion-CT in predicting malignant middle cerebral artery brain infarction

BACKGROUND

We performed a prospective study on patients with middle cerebral artery(MCA) ischemic stroke to evaluate the accuracy of perfusion-CT imaging(PCT) to predict the development of malignant brain infarction (MBI).

METHODS

106 patients(women 37 %, mean age 65 years)underwent native cranial computed tomography (CCT), CT angiography(CTA) and PCT after a median of 2 h after stroke onset. We assessed the patency of the MCA and the area of tissue ischemia (AIT)according to cerebral blood flow(CBF), cerebral blood volume (CBV) and time-to-peak (TTP)maps. Optimum sensitivity, specificity,positive (PPV) and negative predictive values (NPV) were calculated for the end-point MBI (= midline shift > 5 mm or decompressive surgery) by means of receiver operating characteristics(ROC).

RESULTS

20 patients (19 %)developed a MBI. In these patients,a larger AIT was found in all perfusion maps as compared to the remaining patients (p < 0.001). All perfusion maps had a very high NPV (95.4-98.4 %), a high sensitivity (85-95 %) and specificity (71.6-77.9 %) and only a moderate PPV (44-47.4 %). Best prediction was found for CBF maps with AIT of > 27.9 % of the hemisphere.

CONCLUSION

PCT allows the discrimination of patients without a relevant risk for MBI from those having a 50 % risk of MBI development. Due to the high sensitivity and specificity, PCT is a reliable tool in detecting MBI. Because of PCT's better availability, it is the method of choice at present for an early risk stratification of acute stroke patients.

Pathophysiology of ischaemic stroke: insights from imaging, and implications for therapy and drug discovery

Preventing death and limiting handicap from ischaemic stroke are major goals that can be achieved only if the pathophysiology of infarct expansion is properly understood. Primate studies showed that following occlusion of the middle cerebral artery (MCA)--the most frequent and prototypical stroke, local tissue fate depends on the severity of hypoperfusion and duration of occlusion, with a fraction of the MCA territory being initially in a 'penumbral' state. Physiological quantitative PET imaging has translated this knowledge in man and revealed the presence of considerable pathophysiological heterogeneity from patient to patient, largely unpredictable from elapsed time since onset or clinical deficit. While these observations underpinned key trials of thrombolysis, they also indicate that only patients who are likely to benefit should be exposed to its risks. Accordingly, imaging-based diagnosis is rapidly becoming an essential component of stroke assessment, replacing the clock by individually customized management. Diffusion- and perfusion-weighted MR (DWI-PWI) and CT-based perfusion imaging are increasingly being used to implement this, and are undergoing formal validation against PET. Beyond thrombolysis per se, knowledge of the individual pathophysiology also guides management of variables like blood pressure, blood glucose and oxygen saturation, which can otherwise precipitate the penumbra into the core, and the oligaemic tissue into the penumbra. We propose that future therapeutic trials use physiological imaging to select the patient category that best matches the drug's presumed mode of action, rather than lumping together patients with entirely different pathophysiological patterns in so-called 'large trials', which have all failed so far.

Stellenwert der Revaskularisation eines akuten Karotisverschlusses

BACKGROUND AND PURPOSE

We examined indications for emergent revascularisation of acutely occluded internal carotid artery (ICA) using current diagnostic methods.

MATERIAL AND METHODS

From 1997 to 2006 we prospectively followed 34 consecutive patients undergoing emergency revascularisation due to acute extracranial ICA occlusion and acute ischaemic stroke within 72 h after symptom onset (mean 25) and within 36 h after admission (mean 16). Exclusion criteria were occlusion of the intracranial ICA or ipsilateral middle cerebral artery (MCA), ischaemic infarction of more than one third of the MCA perfusion area, or reduced level of consciousness. All patients underwent duplex sonography, cerebral CT, and/or MRI and angiography (MRA and/or DSA). We performed endarterectomy and thrombectomy of the ICA.

RESULTS

Confirmed by postoperative duplex sonography at discharge, ICA revascularisation was successful in 30 (88%) of 34 cases. Postoperative intracranial haemorrhage was detected in two patients (6%) and perioperative reinfarction in one (3%). Compared to the preoperative status, 20 patients (59%) showed signs of clinical improvement by at least one point on the Rankin scale, ten patients (29%) remained stable, and two patients (6%) had deteriorated. The 30-day mortality was 6% (two patients).

CONCLUSION

After careful diagnostic workup, revascularisation of acute extracranial ICA occlusion is feasible with low morbidity and mortality.

Midline-shift corresponds to the amount of brain edema early after hemispheric stroke--an MRI study in rats

Vasogenic brain edema formation is a serious complication in hemispheric stroke. Its space-occupying effect can lead to midline-shift (MLS), cerebral herniation, and death. Clinical studies indicate that quantification of MLS can predict cerebral herniation and subsequent death at early time-points, even before clinical deterioration becomes apparent. The present experimental study was designed to determine the relation between MLS, absolute edema volume, lesion size, and clinical findings in a rat stroke model. Middle cerebral artery-occlusion was performed in 24 rats using the suture technique. Clinical evaluation and magnetic resonance imaging (MRI) (Bruker PharmaScan 7.0T) was performed 24 hours later. Lesion volume, the volume-increase within the affected hemisphere (%HEV), and MLS were quantified on T2-weighted images. The absolute increase of hemispheric water content (DeltaH2O) was determined in a subgroup using the wet-dry method (n=12). MLS correlated significantly with the total amount of brain edema (magnetic resonance imaging study: r=0.82; P<0.01; wet-dry analysis r=0.80; P<0.01). MLS correlated only moderately with T2-lesion volume (r=0.55; P<0.01). No significant correlation could be detected between MLS and clinical scores (r=0.26; P>0.05). MLS thus quantitatively reflects the amount of vasogenic brain edema within the affected hemisphere at early time-points. MLS quantification can be regarded as an easily assessable and valid global quantitative parameter for brain edema and thus might facilitate the surgical and nonsurgical management of edema in acute stroke patients.

[Imaging of acute stroke]

Acute stroke patients represent an important diagnostic and therapeutic challenge. Patients with brain damage in the ischemic, but not yet infarcted, phase have the greatest potential for recovery. Here we review the most commonly employed diagnostic tools that are currently used before stroke therapy. While computed tomography is pertinent to differentiate ischemic from hemorrhagic stroke, this technique cannot be used as an etiological screening too. The ischemic origin of symptoms can be confirmed with magnetic resonance imaging which also contributes to for therapeutic decision making, prognosis assessment and etiological screening.

Hemicraniectomy and durotomy for malignant middle cerebral artery infarction

Decompressive surgery with hemicraniectomy and durotomy for malignant MCA infarction remains a salvage procedure but can be associated with reasonable clinical outcomes in highly selected patients. This selection of patients appropriate for intervention is of the utmost importance, but exact criteria remain to be defined; older age and increased numbers of associated medical comorbidities seem to define a group of patients who would not derive long term benefit, however. The determination as to whether or not surgery is equally beneficial for dominant or nondominant hemispheric infarction is hampered by lack of good comparative data, but selected case series suggest that some patients who have dominant hemispheric infarction achieve a reasonable degree of independence. Although a well-defined principle of stroke practice is that "time is brain," there are no clear data as to when intervention should be done, as there are some patients who have large MCA infarction and who may not progress to cerebral herniation. Clinicians managing the growing population of patient status post hemicraniectomy should also be aware of this process of the syndrome of the trephined and the potential for resolution that may prompt earlier cranial reconstruction. At present, the decision to proceed with this aggressive intervention of hemicraniectomy and durotomy for large ischemic infarction remains a case-by-case individualized approach, based on patient and family preferences and clinicians' subjective perspective as to patients' potential for clinical recovery.

Prospective evaluation of malignant middle cerebral artery infarction with blood–brain barrier imaging using Tc-99m DTPA SPECT

BACKGROUND

Malignant middle cerebral artery (MMCA) infarction is associated with severe brain edema which may lead to a rapid deterioration of consciousness, increase of intracranial pressure, brain midline shift and finally, herniation. We examined the correlation between the degree of the blood-brain barrier (BBB) permeability and MMCA.

METHODS

Twenty-five consecutive patients (17 men and 8 women, mean age 62.1+/-10.1) were included in the study. Each patient had a daily clinical examination, and the neurological deficits were scored using NIHSS score. A CT without contrast material was performed in all patients. (99m)Tc-DTPA SPECT was performed at 36 h after the stroke. A quantitative index of BBB breakdown (disruption index) was calculated.

RESULTS

The mean volume of stroke was 138+/-87 cm(3). The mean DTPA disruption index was 6.6+/-4.6 (range 1.0-21.0). The mean NIHSS score was 14+/-4 (p=0.2). Five of 25 patients had brain herniation as evidenced on brain CT. The volume of stroke was only marginally elevated in patients with herniation (p=0.062). All patients showed significant, inverse correlation between NIHSS score and DTPA uptake (r=-0.43, p=0.033). There was a significant correlation between the extent of DTPA distribution (more than one vascular territory) and the occurrence of herniation (p<0.001).

CONCLUSIONS

DTPA-SPECT imaging is a reliable complementary predictive tool in patients with an MCA stroke. The specific pattern found on DTPA SPECT, compatible with diffuse BBB disruption, may be of value in predicting "malignant MCA."

Imaging of acute stroke

Thrombolytic therapy has led to a higher proportion of patients presenting to hospital early, and this, with parallel developments in imaging technology, has greatly improved the understanding of acute stroke pathophysiology. Additionally, MRI, including diffusion-weighted imaging (DWI) and gradient echo, or T2*, imaging is important in understanding basic structural information--such as distinguishing acute ischaemia from haemorrhage. It has also greatly increased sensitivity in the diagnosis of acute cerebral ischaemia. The pathophysiology of the ischaemic penumbra can now be assessed with CT or MRI-based perfusion imaging techniques, which are widely available and clinically applicable. Pathophysiological information from CT or MRI increasingly helps clinical trial design, may allow targeted therapy in individual patients, and may extend the time scale for reperfusion therapy.

Neuroprotection in malignant MCA infarction

Massive unilateral hemispheric infarction often develops progressive postischemic edema that leads to a malignant course of stroke with mortality of up to 80% with conventional medical therapies. Hypothermia and decompressive hemicraniectomy have shown neuroprotective effects in several animal models of focal transient and permanent MCA occlusion by reducing infarct size and improving neurological outcome. Our aim in this paper was to review the possible mechanisms of both therapies as well as the optimal time window and duration of application of each treatment in animal model and in human malignant MCA infarction reported in the literature.

Xenon CT cerebral blood flow in acute stroke

Acute stroke therapy is evolving rapidly as research moves toward extending the time window for treatment so that more patients can benefit. As physiology-based imaging increasingly is used in patient selection, it is becoming evident that rigid time windows are not applicable to individual patients. Xenon CT has an important role in acute stroke therapeutic intervention as a quantitative, reproducible, rapid, and safe modality, which can provide valuable physiologic data that can optimize patient triage and aid in management.

Comparative overview of brain perfusion imaging techniques

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Xenon-enhanced Computed Tomography (XeCT), Dynamic Perfusion-computed Tomography (PCT), Magnetic Resonance Imaging Dynamic Susceptibility Contrast (DSC), Arterial Spin-Labeling (ASL), and Doppler Ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow (CBF) or volume (CBV). All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks. This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview, established by consensus among specialists of the various techniques. For clinicians, this paper should offers a clearer picture of the pros and cons of currently available brain perfusion imaging techniques, and assist them in choosing the proper method in every specific clinical setting.

Rodent models of focal stroke: size, mechanism, and purpose

Rodent stroke models provide the experimental backbone for the in vivo determination of the mechanisms of cell death and neural repair, and for the initial testing of neuroprotective compounds. Less than 10 rodent models of focal stroke are routinely used in experimental study. These vary widely in their ability to model the human disease, and in their application to the study of cell death or neural repair. Many rodent focal stroke models produce large infarcts that more closely resemble malignant and fatal human infarction than the average sized human stroke. This review focuses on the mechanisms of ischemic damage in rat and mouse stroke models, the relative size of stroke generated in each model, and the purpose with which focal stroke models are applied to the study of ischemic cell death and to neural repair after stroke.

Safety and Therapeutical Benefit of Hemicraniectomy Combined with Mild Hypothermia in Comparison with Hemicraniectomy Alone in Patients with Malignant Ischemic Stroke

INTRODUCTION

Both for hemicraniectomy and for hypothermia, several reports describe a beneficial effect in patients with malignant supratentorial cerebral ischemia. We compared the safety and the clinical outcome in patients with a malignant supratentorial infarction who were treated with hemicraniectomy alone (HA) or received a combination therapy with hemicraniectomy and hypothermia of 35 degrees C (HH), respectively.

METHODS

In a prospective and randomized study, 25 consecutive patients were treated after an ischemic infarction of more than two thirds of one hemisphere by HA (n=13 patients) or the HH combination therapy (n=12 patients). Safety parameters were compared between both treatment groups, the clinical outcome was assessed during treatment and after 6 months.

RESULTS

Age, cranial CT or MRI findings, initial National institutes of Health Stroke Scale Score (NIHSSS) and level of consciousness were not significantly different between both groups. Hemicraniectomy was performed within 15+/- 6 h after the ischemic event. Hypothermia was induced immediately after surgery. Overall mortality was 12% (2/13 vs. 1/12 in the two groups), but none of these 3 patients died due to treatment-related complications. There were no severe side effects of hypothermia. Duration of need for intensive care or for mechanical ventilation and infectious status did not differ significantly between both groups, but the need for catecholamine application was increased in the HH group. The clinical outcome showed a tendency for a better outcome in the HH compared with the HA group with respect to status after 6 months, as assessed by the NIHSSS (10+/-1 vs. 11+/-3, p<0.08).

DISCUSSION

The present study suggests that a combined therapy of mild hypothermia and hemicraniectomy in malignant brain infarction does not imply additional risks by side effects and improves functional outcome as compared with hemicraniectomy alone.

The Swedish Malignant Middle cerebral artery Infarction Study: long-term results from a prospective study of hemicraniectomy combined with standardized neurointensive care

OBJECTIVES

Hemicraniectomy in patients with malignant middle cerebral artery (mMCA) infarct may be life-saving. The long-term prognosis is unknown.

METHODS

Patients with mMCA infarct treated with hemicraniectomy between 1998 and 2002 at three hospitals were included. The criterion for surgical intervention was if the patients deteriorated from awake to being responding to painful stimuli only. All patients were followed for at least 1 year. Outcome was defined as alive/dead, walkers/non-walkers or modified Rankin Scale (mRS) score <or=2.

RESULTS

Thirty patients were included (median age at stroke onset 49 years, range 17-67 years). Fourteen patients had mMCA infarct on the left side and 16 patients on the right side. Fourteen patients had pupil dilatation before surgery. Hemicraniectomy was performed at a median of 52 h (range 13-235 h) after stroke onset. Nine patients died within 1 month after surgery because of cerebral herniation (n = 6), myocardial infarction (n = 1) or intensive care complications (n = 2). No further deaths occurred during follow-up, which was at median 3.4 years after surgery. Status for the 21 survivors at the last follow-up was: mRS 2 or less (n = 6) and mRS 3-5 (n = 15). The oldest patient with mRS 2 or less was 53 years at stroke onset. Thirteen patients (43%) could walk without substantial aid.

CONCLUSION

The long-term survival after mMCA infarction treated with hemicraniectomy seems to be favourable if the patient survives the acute phase. The outcome as measured with mRS may be better among younger patients.

Magnetic Resonance Imaging and Clinical Patterns of Patients with ‘Spectacular Shrinking Deficit’ after Acute Middle Cerebral Artery Stroke

BACKGROUND

Rapid resolution of neurological deficits after severe middle cerebral artery (MCA) stroke has been coined spectacular shrinking deficit (SSD). We studied clinical and MRI patterns in patients with SSD.

METHODS

Patients with acute MCA stroke <6 h were examined by stroke MRI (perfusion- and diffusion-weighted imaging (PWI, DWI), MR angiography (MRA)) at admission, day 1 and day 7. SSD was defined as a > or =8-point-reduction of neurological deficit in the National Institute of Health Stroke Scale (NIHSS) to a score of < or =4 within 24 h. PWI and DWI lesion volumes were measured on ADC (ADC < 80%) and time to peak maps (TTP > +4 s). Recanalization was assessed by MRA after 24 h. Final infarct volumes were defined on T2 weighted images at day seven. Outcome was assessed after 90 days using modified Rankin Scale (mRS) and Barthel Index (BI).

RESULTS

SSD was present in 14 of 104 patients. Initial DWI and PWI lesion volumes were smaller in SSD patients - ADC < 80%: 8.9 (4.3-20.5) vs. 30 (0-266.7) ml; TTP > +4 s: 91.6 (29.7-205.8) vs. 131.5 (0-311.5) ml. Early recanalization was associated with SSD resulted in smaller final infarct volumes (11.9 (2.4-25.9) vs. 47.7 (1.2-288.5)). All SSD patients were independent at day 90 (mRS 0 (0-2); BI 100).

CONCLUSION

The clinical syndrome of SSD is reflected by a typical MRI pattern with small initial DWI and PWI lesion volumes, timely recanalization and small final infarct volumes.

Treatment of massive cerebral infarction

Stroke is the third leading cause of death in the United States, with a person dying every 3 minutes of a stroke. Massive ischemic stroke accounts for 10% to 20% of ischemic strokes, has traditionally been associated with a high mortality and morbidity, and requires a unique management strategy. Recent advances in management, fueled by an increased understanding of the pathophysiology, may help decrease mortality and improve outcomes. Rapid access to reperfusion therapies remains the most critical element of stroke care and the cornerstone of therapy. This article focuses on newer therapies, including osmotic therapy, hypothermia, maintained normothermia, strict glycemic control, induced hypertension, and hemicraniectomy, all of which show promise for reducing mortality and improving functional outcome. These interventions have become integrated into neurologic intensive care units around the world. They are complicated, require a high level of expertise, and carry a significant learning curve. In order for these new management techniques to be effective, an expedited, aggressive, meticulous, and potentially prolonged medical management approach is needed. To accomplish this there is a growing need for focused specialists in the areas of neurointensive care and stroke.

Comparative overview of brain perfusion imaging techniques

BACKGROUND AND PURPOSE

Numerous imaging techniques have been developed and applied to evaluate brain hemodynamics. Among these are positron emission tomography, single photon emission computed tomography, Xenon-enhanced computed tomography, dynamic perfusion computed tomography, MRI dynamic susceptibility contrast, arterial spin labeling, and Doppler ultrasound. These techniques give similar information about brain hemodynamics in the form of parameters such as cerebral blood flow or cerebral blood volume. All of them are used to characterize the same types of pathological conditions. However, each technique has its own advantages and drawbacks.

SUMMARY OF REVIEW

This article addresses the main imaging techniques dedicated to brain hemodynamics. It represents a comparative overview established by consensus among specialists of the various techniques.

CONCLUSIONS

For clinicians, this article should offer a clearer picture of the pros and cons of currently available brain perfusion imaging techniques and assist them in choosing the proper method for every specific clinical setting.

The prediction of malignant cerebral infarction by molecular brain barrier disruption markers

BACKGROUND AND PURPOSE

Space-occupying brain edema is a life-threatening complication in patients with large hemispheric stroke. The aim of the study was to determine whether molecular markers of endothelial damage may help to predict secondary brain edema and, secondly, to identify patients who could benefit from aggressive therapies such as decompressive hemicraniectomy or hypothermia.

METHODS

We studied 40 consecutive patients with malignant middle cerebral artery (MCA) infarction and 35 controls with massive MCA infarctions <70 years of age and matched by stroke severity on admission. Cranial computed tomography (CT) was performed at entry and repeated between days 4 and 7, or earlier if there was neurological worsening. Malignant MCA (m-MCA) infarction was diagnosed when follow-up CT detected a more than two-thirds space-occupying MCA infarction with midline shift, compression of the basal cisterns, and neurological deterioration. Plasma concentrations of glutamate, glycine, gamma-aminobutyric acid, interleukin-6 (IL-6), IL-10, tumor necrosis factor-alpha, matrix metalloproteinase-9 (MMP-9), and cellular-fibronectin (c-Fn) were determined in blood samples obtained at admission.

RESULTS

Mean time from stroke onset to blood sampling was 6.3+/-4.8 in m-MCA and 7.7+/-6.0 hours in the control group (P=0.63). Baseline characteristics were comparable in both groups. c-Fn and MMP-9 levels were significantly higher in patients with m-MCA than in controls (all P<0.001). c-Fn >16.6 microg/mL had the highest sensitivity (90%), specificity (100%), and negative and positive predictive values (89% and 100%, respectively) for the prediction of m-MCA infarction.

CONCLUSIONS

A plasma c-Fn concentration >16.6 microg/mL at admission is associated with the development of m-MCA infarction with high sensitivity and specificity, suggesting that c-Fn might be useful in therapeutic decision making.

Extending the Time Window for Thrombolysis: Evidence from Acute Stroke Trials

Data from intravenous tissue plasminogen activator studies have shown rapidly diminishing clinical benefit beyond 3 hours when noncontrast CT is used for treatment triage. Newer trials, such as the Desmoteplase in Acute Ischemic Stroke trial, have now successfully pushed the time window out to 9 hours using the concept of penumbral imaging and treatment of the perfusion-diffusion mismatch. Advanced imaging with CT or MR imaging protocols is providing a means for rational physiologic selection and outcomes assessment in stroke treatment.

Semiquantitative analysis of ultrasonic cerebral perfusion imaging

The bolus kinetic in ultrasonic cerebral perfusion imaging is the most favored data acquisition and processing technique. However, there has not yet been convincing evidence for the potential to (semi-) quantitatively describe perfusion. Aim of this study was to determine the intraindividual range of relevant perfusion parameters to describe individual physiological cutoff scores. In 20 healthy volunteers, cerebral perfusion was evaluated using the bilateral approach with phase inversion harmonic imaging and the bolus kinetic. Relevant parameters (time-to-peak intensity, TPI; peak width, PW) were derived in 14 regions-of-interest in both hemispheres. The median and quartile deviation (QD) of these values were individually calculated. Within the 20 individuals, the mean QD of TPI was 0.68 s, and there was no case in which any TPI exceeded the mean more than 2 s. With PW, the mean QD was 1.2 s, and the mean was not exceeded by more than 6 s. Intraindividual perfusion parameters, especially TPI, show a considerable small range. Thus, the bolus kinetic derives reliable semiquantitative information once intraindividual comparison can be accomplished. We therefore propose that bilateral examination with the unaffected hemisphere as referential region should be performed in acute stroke. Future studies have to evaluate the potential of this approach of discriminating ischemia and hypoperfusion in the affected hemisphere.

Reduction of Diffusion-Weighted MRI Lesion Volume After Early Moderate Hypothermia in Ischemic Stroke

Background— Large areas of restricted diffusion in the middle cerebral artery (MCA) territory are highly predictive of severe and potentially space-occupying MCA stroke. A reduction of diffusion-weighted MRI (DWI) lesions occurs in 20% to 40% of acute stroke patients with early reperfusion.

Methods— We report of a patient with a severe stroke syndrome who was treated with early moderate hypothermia but not thrombolysis.

Results— The initially large DWI deficit of the whole MCA territory contrasted to the relatively small final lesion restricted to the basal ganglia on MRI and computed tomography scan.

Conclusion— This case describes an unexpected reduction of a DWI lesion after early moderate hypothermia and spontaneous recanalization 3 days after stroke onset. We discuss potential reasons for the unexpected DWI lesion reduction.

Unenhanced CT and Acute Stroke Physiology

Unenhanced CT remains the most widely used imaging technique and is the standard of care for acute stroke evaluation. Early ischemic signs (EIS) within the first 3 to 6 hours of symptom onset (eg, parenchymal hypodensity, sulcal effacement, and dense vessel) have been advocated as a triage tool for thrombolytic therapy. Recent studies have challenged the relevance of these EIS within 3 hours of stroke onset, with advanced MR and CT methods increasingly competing with unenhanced CT as the primary imaging modality for acute ischemia. Nonetheless, the insights regarding acute stroke physiology provided by studying the CT evolution of early ischemic signs continue to be valuable for the informed interpretation of all stroke images. It is these insights that comprise the topic of this article.

Which time-to-peak threshold best identifies penumbral flow? A comparison of perfusion-weighted magnetic resonance imaging and positron emission tomography in acute ischemic stroke

BACKGROUND AND PURPOSE

In acute ischemic stroke, the hypoperfused but viable tissue is the main therapeutic target. In clinical routine, time-to-peak (TTP) maps are frequently used to estimate the hemodynamic compromise and to calculate the mismatch volume. We evaluated the accuracy of TTP maps to identify penumbral flow by comparison with positron emission tomography (PET).

METHODS

Magnetic resonance imaging (MRI) and PET were performed in 11 patients with acute ischemic stroke (median 8 hours after stroke onset, 60 minutes between MRI and PET imaging). The volumes defined by increasing TTP thresholds (relative TTP delay of >2, >4, >6, >8, and >10 seconds) were compared with the volume of hypoperfusion (<20 mL/100 g per min) assessed by 15O-water PET. In a volumetric analysis, each threshold's sensitivity, specificity, and predictive values were calculated.

RESULTS

The median hypoperfusion volume was 34.5 cm3. Low TTP thresholds included large parts of the hypoperfused but also large parts of normoperfused tissue (median sensitivity/specificity: 93%/60% for TTP >2) and vice versa (50%/91% for TTP >10). TTP >4 seconds best identifies hypoperfusion (84%/77%). The positive predictive values increased with the size of hypoperfusion.

CONCLUSIONS

This first comparison of quantitative PET-CBF with TTP maps in acute ischemic human stroke indicates that the TTP threshold is crucial to reliably identify the tissue at risk; TTP >4 seconds best identifies penumbral flow; and TTP maps overestimate the extent of true hemodynamic compromise depending on the size of ischemia. Only if methodological restrictions are kept in mind, relative TTP maps are suitable to estimate the mismatch volume.

Serum S100B predicts a malignant course of infarction in patients with acute middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Early predictors of infarct volume may improve therapeutic decisions in patients with acute cerebral ischemia. We investigated whether measurements of serum astroglial protein S100B can predict a malignant course of infarction in acute middle cerebral artery (MCA) occlusion.

METHODS

We included 51 patients (24 women, mean age 69.1+/-12.4 years) admitted within 6 hours after stroke symptom onset caused by proximal MCA occlusion, as shown by magnetic resonance angiography (n=39), intra-arterial angiography (n=4), or transcranial duplex sonography (n=8). Blood samples were drawn at hospital admission and 8, 12, 16, 20, and 24 hours after symptom onset. Serum S100B concentrations were determined using a fully automated immunoluminometric assay. A malignant course of infarction was defined as the occurrence of clinical signs of cerebral herniation within the first 7 days of treatment or the clinical decision to perform decompressive hemicraniectomy caused by critical space-occupying swelling as detected by repeated neuroimaging.

RESULTS

Sixteen patients developed malignant infarction (31%). Beginning with the 12-hour value, mean S100B serum concentrations were significantly higher in patients with a malignant course compared with those without (12 hours 1.23+/-1.24 versus 0.29+/-0.45 microg/L; 16 hours 1.80+/-1.65 versus 0.38+/-0.53 microg/L; 20 hours 1.90+/-1.53 versus 0.44+/-0.48 microg/L; and 24 hours 2.41+/-1.59 versus 0.57+/-0.66 microg/L; all P<0.001). A 12-hour S100B value >0.35 microg/L predicted malignant infarction with 0.75 sensitivity and 0.80 specificity. A 24-hour value >1.03 microg/L provided 0.94 sensitivity and 0.83 specificity.

CONCLUSIONS

The serum marker S100B can predict a malignant course of infarction in proximal MCA occlusion. This finding may improve the identification and monitoring of patients at particularly high risk for herniation.

Delayed post-ischemic albumin treatment neither improves nor worsens the outcome of transient focal cerebral ischemia in rats

Human albumin therapy within the first 4 h is highly neuroprotective in focal ischemia, but it is unknown whether delayed albumin therapy is deleterious. Rats received 2 h middle cerebral artery suture-occlusion. Human albumin (25%, 2.5 mg/kg; n=12) or vehicle (0.9% saline, 5 ml/kg; n=9) were administered at 19 h. Neurological status was evaluated daily, and histopathology and brain swelling were quantified at 3 days. Delayed albumin treatment, while ineffective, failed to show adverse effects.

Application of new MR techniques in pediatric patients

Pediatric neuroradiology is a fascinating and challenging field because there are normal changes associated with normal development and unique and unusual pathologies that occur in this population. The numerous new MR techniques first applied in the adult population are appropriate for use in the pediatric population, often with minimal modification of parameters. These new techniques will undoubtedly contribute significantly to use of pediatric neuroimaging, but the adult experience is not always directly transferable. The pediatric brain, particularly the immature brain is different in structure, has predilection for different types of disease processes, and may react differently to insults than the adult brain. As a result, the role of these techniques needs to be evaluated in the context of the pediatric brain and common pediatric disease processes.

Imaging the ischaemic penumbra

PURPOSE OF REVIEW

Imaging the penumbra is essential, not only to identify patients who might benefit from thrombolysis, but also to further understanding of the ischaemic process, thereby potentially revealing new opportunities for therapeutic intervention. Here we review recent imaging studies of the acute stroke process.

RECENT FINDINGS

Perfusion-computed tomography and computed tomography angiography enable assessment of the haemodynamic status and site of occlusion, leading to their promising use in guiding thrombolysis. The magnetic resonance concept of the diffusion-perfusion 'mismatch' being representative of penumbra appears to be an oversimplification. The mapping of simple variables such as time-to-peak might not directly reveal true penumbral perfusion levels. Also, lesions seen with diffusion-weighted imaging may be reversible as a result of early reperfusion. This reversal with subsequent normalization may represent selective neuronal damage. Late secondary injury, as indicated by the reappearance of the diffusion-weighted imaging lesion, has recently been documented; the mechanisms are unknown but form potential targets for future therapies. Despite these caveats, diffusion-weighted imaging-perfusion-weighted imaging remains the most useful approach to map the pathophysiology of stroke in the clinical setting. Acute/subacute flumazenil positron emission tomography studies are being used as markers of neuronal integrity to help shed further light on infarction thresholds, and potentially document selective neuronal loss. F-labelled fluoromisonidazole positron emission tomography imaging of brain hypoxia documents the temporal and spatial progression of the penumbra.

SUMMARY

The goal of understanding the complex process that is acute ischaemia in stroke, and subsequently the development of therapeutic strategies, continues to be advanced by imaging the penumbra in novel ways.