Experimental brain infarcts in cats. II. Ischemic brain edema

Alterations in brain fluid physiology during the early stages of development of ischaemic oedema

Oedema occurs when higher than normal amounts of solutes and water accumulate in tissues. In brain parenchymal tissue, vasogenic oedema arises from changes in blood-brain barrier permeability, e.g. in peritumoral oedema. Cytotoxic oedema arises from excess accumulation of solutes within cells, e.g. ischaemic oedema following stroke. This type of oedema is initiated when blood flow in the affected core region falls sufficiently to deprive brain cells of the ATP needed to maintain ion gradients. As a consequence, there is: depolarization of neurons; neural uptake of Na+ and Cl- and loss of K+; neuronal swelling; astrocytic uptake of Na+, K+ and anions; swelling of astrocytes; and reduction in ISF volume by fluid uptake into neurons and astrocytes. There is increased parenchymal solute content due to metabolic osmolyte production and solute influx from CSF and blood. The greatly increased [K+]isf triggers spreading depolarizations into the surrounding penumbra increasing metabolic load leading to increased size of the ischaemic core. Water enters the parenchyma primarily from blood, some passing into astrocyte endfeet via AQP4. In the medium term, e.g. after three hours, NaCl permeability and swelling rate increase with partial opening of tight junctions between blood-brain barrier endothelial cells and opening of SUR1-TPRM4 channels. Swelling is then driven by a Donnan-like effect. Longer term, there is gross failure of the blood-brain barrier. Oedema resolution is slower than its formation. Fluids without colloid, e.g. infused mock CSF, can be reabsorbed across the blood-brain barrier by a Starling-like mechanism whereas infused serum with its colloids must be removed by even slower extravascular means. Large scale oedema can increase intracranial pressure (ICP) sufficiently to cause fatal brain herniation. The potentially lethal increase in ICP can be avoided by craniectomy or by aspiration of the osmotically active infarcted region. However, the only satisfactory treatment resulting in retention of function is restoration of blood flow, providing this can be achieved relatively quickly. One important objective of current research is to find treatments that increase the time during which reperfusion is successful. Questions still to be resolved are discussed.

A novel fully automated method for measuring ASPECTS to improve stroke diagnosis: Comparison to traditional ASPECTS

BACKGROUND AND PURPOSE

To compare the accuracy of subjective Alberta Stroke Program Early CT Score (sASPECTS) evaluation and that of an automated prototype software (aASPECTS) on nonenhanced CT (NECT) in patients with early anterior territory stroke and controls using side-to-side quantification of hypoattenuated brain areas.

METHODS

We retrospectively analyzed the NECT scans of 42 consecutive patients with ischemic stroke before reperfusion and 42 controls using first sASPECTS and subsequently aASPECTS. We assessed the differences in Alberta Stroke Program Early CT Score (ASPECTS) and calculated the sensitivity and specificity of NECT with CT perfusion, whereas cerebral blood volume (CBV) served as the reference standard for brain infarction.

RESULTS

The clot was located in the middle cerebral artery (MCA) in 47.6% of cases and the internal carotid artery (ICA) in 28.6% of cases. Ten cases presented combined ICA and MCA occlusions. The stroke was right sided in 52.4% of cases and left sided in 47.6%. Reader-based NECT analysis yielded a median sASPECTS of 10. The median CBV-based ASPECTS was 7. Compared to the area of decreased CBV, sASPECTS yielded a sensitivity of 12.5% and specificity of 86.8%. The software prototype (aASPECTS) yielded an overall sensitivity of 65.5% and a specificity of 92.2%. The interreader agreement for ASPECTS evaluation of admission NECT and follow-up CT was almost perfect (κ = .93). The interreader agreement of the CBV color map evaluation was substantial (κ = .77).

CONCLUSIONS

aASPECTS of NECT can outperform sASPECTS for stroke detection.

Improved Visualization and Quantification of Net Water Uptake in Recent Small Subcortical Infarcts in the Thalamus Using Computed Tomography

Diagnosing recent small subcortical infarcts (RSSIs) via early computed tomography (CT) remains challenging. This study aimed to assess CT attenuation values (Hounsfield Units (HU)) and net water uptake (NWU) in RSSI and explore a postprocessing algorithm's potential to enhance thalamic RSSI detection. We examined non-contrast CT (NCCT) data from patients with confirmed thalamic RSSI on diffusion-weighted magnetic resonance imaging (DW-MRI) between January 2010 and October 2017. Co-registered DW-MRI and NCCT images enabled HU and NWU quantification in the infarct area compared to unaffected contralateral tissue. Results were categorized based on symptom onset to NCCT timing. Postprocessing using window optimization and frequency-selective non-linear blending (FSNLB) was applied, with interpretations by three blinded Neuroradiologists. The study included 34 patients (median age 70 years [IQR 63-76], 14 women). RSSI exhibited significantly reduced mean CT attenuation compared to unaffected thalamus (29.6 HU (±3.1) vs. 33.3 HU (±2.6); p < 0.01). Mean NWU in the infarct area increased from 6.4% (±7.2) at 0-6 h to 16.6% (±8.7) at 24-36 h post-symptom onset. Postprocessed NCCT using these HU values improved sensitivity for RSSI detection from 32% in unprocessed CT to 41% in FSNLB-optimized CT, with specificities ranging from 86% to 95%. In conclusion, CT attenuation values and NWU are discernible in thalamic RSSI up to 36 h post-symptom onset. Postprocessing techniques, particularly window optimization and FSNLB, moderately enhance RSSI detection.

Endovascular recanalization in patients with severely disabling non-acute ischemic stroke

BACKGROUND

It is unclear whether patients with severely disabling ischemic stroke (SDIS-that is, modified Rankin scale (mRS) scores of 3-5) benefit from non-acute endovascular recanalization (ER).

OBJECTIVE

To determine the effect of non-acute ER or medical treatment in severely disabled patients with non-acute ischemic stroke (mRS scores of 3-5).

METHODS

Between January 2018 and August 2021, non-acute patients with SDIS and large vessel occlusion were collected from two regional stroke centers. Patients who met the inclusion and exclusion criteria were assigned to two groups based on whether they underwent ER (ER group) or not (medical group). The primary functional outcome was the mRS score at 90 days. The primary safety outcomes were the recurrence of stroke and mortality.

RESULTS

Of the 325 patients with hypoperfusion cerebral infarction caused by large vessel occlusion, 63 met the inclusion criteria (32 patients in the ER group, 31 patients in the medical group). A favorable outcome (mRS score ≤2) occurred more often in the ER group than in the medical group (59.4% vs 22.6%, respectively; OR=0.12, 95% CI 0.02 to 0.58; P<0.01). There were no significant differences in new-onset ischemic stroke (6.3% vs 3.2%, respectively; P=1.000), symptomatic intracerebral hemorrhage (12.5% vs 0%, respectively; P=0.113), or mortality within 90 days (6.3% vs 6.5%, respectively; P=1.000) between the two groups. Preoperative mRS scores (OR=7.34, 95% CI 1.56 to 34.5; P=0.02) and ER (OR=0.12, 95% CI 0.02 to 0.58; P<0.01) were significantly associated with outcome.

CONCLUSION

Our data suggest that patients with SDIS (mRS score 3-5) with smaller infarct cores and better collateral circulation can benefit from non-acute ER, with no additional perioperative complications or mortality.

Reversible Ischemic Lesion Hypodensity in Acute Stroke CT Following Endovascular Reperfusion

BACKGROUND AND OBJECTIVES

In acute stroke, early ischemic lesion hypodensity in computed tomography (CT) is considered the imaging hallmark of brain infarction, representing a state of irreversible tissue damage with a continual increase of net water uptake. This dogma is however challenged by rare cases of apparently reversed early lesion hypodensity following complete reperfusion. The purpose of this study was to investigate the occurrence of reversible ischemic edema after endovascular treatment.

METHODS

184 acute ischemic anterior circulation stroke patients were included after consecutive screening. Ischemic brain edema was determined using quantitative lesion net water uptake (NWU) in admission-CT and follow-up CT based on CT-densitometry and ΔNWU was calculated as the difference. The association of edema progression to imaging and clinical parameters was investigated. Clinical outcome was assessed using modified Ranking Scale (mRS) scores at day 90.

RESULTS

27/184 patients (14.7%) showed edema arrest and 3 patients (1.6%) exhibited significant edema reversibility. Higher degree of recanalization (odds ratio (OR): 2.96, 95%CI: 1.46-6.01, p<0.01) and shorter time from imaging to recanalization (OR/hour: 0.32, 95%CI: 0.18-0.54, p<0.0001) were significantly associated with edema arrest or reversibility. Clinical outcome was significantly better in patients without edema progression (median mRS 2 versus mRS 5, p=0.004).

DISCUSSION

Albeit rare, lesion hypodensity considered to be representative of early infarct in acute stroke CT may be reversible following complete recanalization. Arrest of edema progression of acute brain infarct lesions may occur after successful rapid vessel recanalization, resulting in improved functional outcome. Future research is needed to investigate conditions where early revascularization may halt or even reverse vasogenic edema of ischemic tissue.

[A case of epileptic seizure that required differentiation from hyper-acute ischemic stroke: usefulness of comparing DWI and FLAIR]

A 60-year-old man developed aphasia and transient right upper limb paresis in the presence of chronic subdural hematoma and was transferred to our hospital at an early stage. Cranial MRI within an hour after onset showed diffusion-weighted image (DWI) hyperintensity in the left parietal, temporal, and insular cortex and the pulvinar, and decreased apparent diffusion coefficient (ADC) in the left parietal cortex and pulvinar, suggesting a differential diagnosis of hyper-acute ischemic stroke. However, the distribution and timing of the MRI abnormalities were considered to be atypical for hyper-acute ischemic stroke. The area with both DWI hyperintensity and decreased ADC included the cerebral cortex adjacent to the hematoma and the ipsilateral pulvinar, and fluid-attenuated inversion recovery (FLAIR) hyperintensity co-existed with DWI hyperintensity within only an hour from onset. Furthermore, FLAIR images showed infiltration of the hematoma content into the subarachnoid space, which might have triggered the attack. These findings collectively led us to diagnose an epileptic seizure. The present case suggests that the distribution and timing of MRI abnormalities are essential to differentiate epileptic seizures from hyper-acute ischemic stroke.

Rapid Apparent Diffusion Coefficient Evolution After Early Revascularization

Background and Purpose- In this era of endovascular therapy (EVT) with early, complete recanalization and reperfusion, we have observed an even more rapid apparent diffusion coefficient (ADC) normalization within the acute ischemic lesion compared with the natural history or IV-tPA-treated patient. In this study, we aimed to evaluate the effect of revascularization on ADC evolution within the core lesion in the first 24 hours in acute ischemic stroke patients. Methods- This retrospective study included anterior circulation acute ischemic stroke patients treated with EVT with or without intravenous tPA (IVT) from 2015 to 2017 compared with a consecutive cohort of IVT-only patients treated before 2015. Diffusion-weighted imaging and ADC maps were used to quantify baseline core lesions. Median ADC value change and core reversal were determined at 24 hours. Diffusion-weighted imaging lesion growth was measured at 24 hours and 5 days. Good clinical outcome was defined as modified Rankin Scale score of 0 to 2 at 90 days. Results- Twenty-five patients (50%) received IVT while the other 25 patients received EVT (50%) with or without IVT. Between these patient groups, there were no differences in age, sex, baseline National Institutes of Health Stroke Scale, interhospital transfer, or IVT rates. Thirty-two patients (64%) revascularized with 69% receiving EVT. There was a significant increase in median ADC value of the core lesion at 24 hours in patients who revascularized compared with further ADC reduction in nonrevascularization patients. Revascularization patients had a significantly higher rate of good clinical outcome at 90 days, 63% versus 9% (P=0.003). Core reversal at 24 hours was significantly higher in revascularization patients, 69% versus 22% (P=0.002). Conclusions- ADC evolution in acute ischemic stroke patients with early, complete revascularization, now more commonly seen with EVT, is strikingly different from our historical understanding. The early ADC normalization we have observed in this setting may include a component of secondary injury and serve as a potential imaging biomarker for the development of future adjunctive therapies. Clinical Trial Registration- URL: https://www.clinicaltrials.gov. Unique identifier: NCT00009243.

Subacute Infarct Volume With Edema Correction in Computed Tomography Is Equivalent to Final Infarct Volume After Ischemic Stroke: Improving the Comparability of Infarct Imaging Endpoints in Clinical Trials

OBJECTIVES

Final infarct volume is regularly used as an end point of tissue outcome in stroke trials; however, the reported volumes are most commonly derived from early follow-up imaging. Those volumes are significantly impaired by ischemic edema, which causes an overestimation of the true final lesion volume. As net water uptake within ischemic brain can be quantified densitometrically in computed tomography (CT) as recently described, we hypothesized that the final lesion volume can be better estimated by correcting the lesion volume in early follow-up for the corresponding proportion of edema.

MATERIALS AND METHODS

After retrospective consecutive screening of the local registry, 20 patients with acute middle cerebral artery large vessel occlusion met the inclusion criteria with early and late follow-up CT; the latter acquired at least 4 weeks after admission. In early follow-up imaging 24 hours after onset, the proportion of edema contributing to the infarct lesion was calculated by quantifying the total volume of ischemic net water uptake. Edema volume was then subtracted from the total lesion volume to obtain edema-corrected lesion volumes. Finally, these corrected lesion volumes were compared with the final lesion volume on late follow-up serving as ground truth.

RESULTS

The median lesion volume in the early follow-up was 115.1 mL (range, 21.9-539.9 mL) and significantly exceeded the median final lesion volume in the late follow-up CT, which was 86.6 mL (range, 11.2-399.0 mL; p < 0.001). The calculated mean proportion of edema within the early lesion volume was 25.8% (±5.9%; range, 11.1%-35.9%. The median edema-corrected lesion volume measured after 24 hours was 87.1 mL (range, 18.2-376.3 mL). The estimation of final lesion volume in the early follow-up CT was therefore improved by a mean of 31.4% (±2.1%) when correcting for the proportion of edema and did not differ significantly from the true final infarct volume (p = 0.2).

CONCLUSIONS

Edema-corrected volumes of early follow-up infarct lesion in CT were in close agreement with the actual final infarct volumes. Computed tomography-based edema correction of subacute infarct lesions improves the estimation of final tissue outcome. This could especially improve the comparability of imaging end points and facilitate patient recruitment in clinical trials.

Computed Tomography-Based Imaging of Voxel-Wise Lesion Water Uptake in Ischemic Brain: Relationship Between Density and Direct Volumetry

OBJECTIVES

Net water uptake per volume of brain tissue may be calculated by computed tomography (CT) density, and this imaging biomarker has recently been investigated as a predictor of lesion age in acute stroke. However, the hypothesis that measurements of CT density may be used to quantify net water uptake per volume of infarct lesion has not been validated by direct volumetric measurements so far. The purpose of this study was to (1) develop a theoretical relationship between CT density reduction and net water uptake per volume of ischemic lesions and (2) confirm this relationship by quantitative in vitro and in vivo CT image analysis using direct volumetric measurements.

MATERIALS AND METHODS

We developed a theoretical rationale for a linear relationship between net water uptake per volume of ischemic lesions and CT attenuation. The derived relationship between water uptake and CT density was tested in vitro in a set of increasingly diluted iodine solutions with successive CT measurements. Furthermore, the consistency of this relationship was evaluated using human in vivo CT images in a retrospective multicentric cohort. In 50 edematous infarct lesions, net water uptake was determined by direct measurement of the volumetric difference between the ischemic and normal hemisphere and was correlated with net water uptake calculated by ischemic density measurements.

RESULTS

With regard to in vitro data, water uptake by density measurement was equivalent to direct volumetric measurement (r = 0.99, P < 0.0001; mean ± SD difference, -0.29% ± 0.39%, not different from 0, P < 0.0001). In the study cohort, the mean ± SD uptake of water within infarct measured by volumetry was 44.7 ± 26.8 mL and the mean percent water uptake per lesion volume was 22.7% ± 7.4%. This was equivalent to percent water uptake obtained from density measurements: 21.4% ± 6.4%. The mean difference between percent water uptake by direct volumetry and percent water uptake by CT density was -1.79% ± 3.40%, which was not significantly different from 0 (P < 0.0001).

CONCLUSIONS

Volume of water uptake in infarct lesions can be calculated quantitatively by relative CT density measurements. Voxel-wise imaging of water uptake depicts lesion pathophysiology and could serve as a quantitative imaging biomarker of acute infarct lesions.

In patients with suspected acute stroke, CT perfusion-based cerebral blood flow maps cannot substitute for DWI in measuring the ischemic core

Background

Neuroimaging may guide acute stroke treatment by measuring the volume of brain tissue in the irreversibly injured “ischemic core.” The most widely accepted core volume measurement technique is diffusion-weighted MRI (DWI). However, some claim that measuring regional cerebral blood flow (CBF) with CT perfusion imaging (CTP), and labeling tissue below some threshold as the core, provides equivalent estimates. We tested whether any threshold allows reliable substitution of CBF for DWI.

Methods

58 patients with suspected stroke underwent DWI and CTP within six hours of symptom onset. A neuroradiologist outlined DWI lesions. In CBF maps, core pixels were defined by thresholds ranging from 0%-100% of normal, in 1% increments. Replicating prior studies, we used receiver operating characteristic (ROC) curves to select thresholds that optimized sensitivity and specificity in predicting DWI-positive pixels, first using only pixels on the side of the brain where infarction was clinically suspected (“unilateral” method), then including both sides (“bilateral”). We quantified each method and threshold’s accuracy in estimating DWI volumes, using sums of squared errors (SSE). For the 23 patients with follow-up studies, we assessed whether CBF-derived volumes inaccurately exceeded follow-up infarct volumes.

Results

The areas under the ROC curves were 0.89 (unilateral) and 0.90 (bilateral). Various metrics selected optimum CBF thresholds ranging from 29%-32%, with sensitivities of 0.79–0.81, and specificities of 0.83–0.85. However, for the unilateral and bilateral methods respectively, volume estimates derived from all CBF thresholds above 28% and 22% were less accurate than disregarding imaging and presuming every patient’s core volume to be zero. The unilateral method with a 30% threshold, which recent clinical trials have employed, produced a mean core overestimation of 65 mL (range: –82–191), and exceeded follow-up volumes for 83% of patients, by up to 191 mL.

Conclusion

CTP-derived CBF maps cannot substitute for DWI in measuring the ischemic core.

Spreading depolarization is not an epiphenomenon but the principal mechanism of the cytotoxic edema in various gray matter structures of the brain during stroke

Spreading depolarization (SD) is a phenomenon of various cerebral gray matter structures that only occurs under pathological conditions. In the present paper, we summarize the evidence from several decades of research that SD and cytotoxic edema in these structures are largely overlapping terms. SD/cytotoxic edema is a toxic state that - albeit initially reversible - leads eventually to cellular death when it is persistent. Both hemorrhagic and ischemic stroke are among the most prominent causes of SD/cytotoxic edema. SD/cytotoxic edema is the principal mechanism that mediates neuronal death in these conditions. This applies to gray matter structures in both the ischemic core and the penumbra. SD/cytotoxic edema is often a single terminal event in the core whereas, in the penumbra, a cluster of repetitive prolonged SDs is typical. SD/cytotoxic edema also propagates widely into healthy surrounding tissue as short-lasting, relatively harmless events so that regional electrocorticographic monitoring affords even remote detection of ischemic zones. Ischemia cannot only cause SD/cytotoxic edema but it can also be its consequence through inverse neurovascular coupling. Under this condition, ischemia does not start simultaneously in different regions but spreads in the tissue driven by SD/cytotoxic edema-induced microvascular constriction (= spreading ischemia). Spreading ischemia prolongs SD/cytotoxic edema. Thus, it increases the likelihood for the transition from SD/cytotoxic edema into cellular death. Vasogenic edema is the other major type of cerebral edema with relevance to ischemic stroke. It results from opening of the blood-brain barrier. SD/cytotoxic edema and vasogenic edema are distinct processes with important mutual interactions. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Imaging of cerebral ischemic edema and neuronal death

PURPOSE

In acute cerebral ischemia, the assessment of irreversible injury is crucial for treatment decisions and the patient's prognosis. There is still uncertainty how imaging can safely differentiate reversible from irreversible ischemic brain tissue in the acute phase of stroke.

METHODS

We have searched PubMed and Google Scholar for experimental and clinical papers describing the pathology and pathophysiology of cerebral ischemia under controlled conditions.

RESULTS

Within the first 6 h of stroke onset, ischemic cell injury is subtle and hard to recognize under the microscope. Functional impairment is obvious, but can be induced by ischemic blood flow allowing recovery with flow restoration. The critical cerebral blood flow (CBF) threshold for irreversible injury is ~15 ml/100 g × min. Below this threshold, ischemic brain tissue takes up water in case of any residual capillary flow (ionic edema). Because tissue water content is linearly related to X-ray attenuation, computed tomography (CT) can detect and measure ionic edema and, thus, determine ischemic brain infarction. In contrast, diffusion-weighted magnetic resonance imaging (DWI) detects cytotoxic edema that develops at higher thresholds of ischemic CBF and is thus highly sensitive for milder levels of brain ischemia, but not specific for irreversible brain tissue injury.

CONCLUSION

CT and MRI are complimentary in the detection of ischemic stroke pathology and are valuable for treatment decisions.

A case of acute acquired obstructive hydrocephalus in a cat with suspected ischaemic cerebellar infarct

Case summary

A case of acquired acute obstructive hydrocephalus that developed as a complication of an ischaemic infarct in the vascular territory of the rostral cerebellar artery is described in an adult domestic shorthair cat. The clinical findings, diagnostic investigations, treatment and prognosis are reported. MRI findings are described in detail.

Relevance and novel information

This is the first report of obstructive hydrocephalus as a complication of an ischaemic infarct in the region of the rostral cerebellar artery in a cat. MRI findings are described in detail with regard to the recognition of the early signs of obstructive hydrocephalus. A brief review of the literature is included, as this complication has been frequently reported in humans.

Regulation of mRNA following brain ischemia and reperfusion

There is growing appreciation that mRNA regulation plays important roles in disease and injury. mRNA regulation and ribonomics occur in brain ischemia and reperfusion (I/R) following stroke and cardiac arrest and resuscitation. It was recognized over 40 years ago that translation arrest (TA) accompanies brain I/R and is now recognized as part of the intrinsic stress responses triggered in neurons. However, neuron death correlates to a prolonged TA in cells fated to undergo delayed neuronal death (DND). Dysfunction of mRNA regulatory processes in cells fated to DND prevents them from translating stress-induced mRNAs such as heat shock proteins. The morphological and biochemical studies of mRNA regulation in postischemic neurons are discussed in the context of the large variety of molecular damage induced by ischemic injury. Open issues and areas of future investigation are highlighted. A sober look at the molecular complexity of ischemia-induced neuronal injury suggests that a network framework will assist in making sense of this complexity. The ribonomic network sits between the gene network and the various protein and metabolic networks. Thus, targeting the ribonomic network may prove more effective at neuroprotection than targeting specific molecular pathways, for which all efforts have failed to the present time to stop DND in stroke and after cardiac arrest. WIREs RNA 2017, 8:e1415. doi: 10.1002/wrna.1415 For further resources related to this article, please visit the WIREs website.

Ex-Vivo Characterization of Bioimpedance Spectroscopy of Normal, Ischemic and Hemorrhagic Rabbit Brain Tissue at Frequencies from 10 Hz to 1 MHz

Stroke is a severe cerebrovascular disease and is the second greatest cause of death worldwide. Because diagnostic tools (CT and MRI) to detect acute stroke cannot be used until the patient reaches the hospital setting, a portable diagnostic tool is urgently needed. Because biological tissues have different impedance spectra under normal physiological conditions and different pathological states, multi-frequency electrical impedance tomography (MFEIT) can potentially detect stroke. Accurate impedance spectra of normal brain tissue (gray and white matter) and stroke lesions (ischemic and hemorrhagic tissue) are important elements when studying stroke detection with MFEIT. To our knowledge, no study has comprehensively measured the impedance spectra of normal brain tissue and stroke lesions for the whole frequency range of 1 MHz within as short as possible an ex vivo time and using the same animal model. In this study, we established intracerebral hemorrhage and ischemic models in rabbits, then measured and analyzed the impedance spectra of normal brain tissue and stroke lesions ex vivo within 15 min after animal death at 10 Hz to 1 MHz. The results showed that the impedance spectra of stroke lesions significantly differed from those of normal brain tissue; the ratio of change in impedance of ischemic and hemorrhagic tissue with regard to frequency was distinct; and tissue type could be discriminated according to its impedance spectra. These findings further confirm the feasibility of detecting stroke with MFEIT and provide data supporting further study of MFEIT to detect stroke.

Early Head CT Findings Are Associated With Outcomes After Pediatric Out-of-Hospital Cardiac Arrest

OBJECTIVES

Head CT after out-of-hospital cardiac arrest is often obtained to evaluate intracranial pathology. Among children admitted to the PICU following pediatric out-of-hospital cardiac arrest, we hypothesized that loss of gray-white matter differentiation and basilar cistern and sulcal effacement are associated with mortality and unfavorable neurologic outcome.

DESIGN

Retrospective, cohort study.

SETTING

Single, tertiary-care center PICU.

PATIENTS

Seventy-eight patients less than 18 years old who survived out-of-hospital cardiac arrest to PICU admission and had a head CT within 24 hours of return of spontaneous circulation were evaluated from July 2005 through May 2012.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Median time to head CT from return of spontaneous circulation was 3.3 hours (1.0, 6.0). Median patient age was 2.3 years (0.4, 9.5). Thirty-nine patients (50%) survived, of whom 29 (74%) had favorable neurologic outcome. Nonsurvivors were more likely than survivors to have 1) loss of gray-white matter differentiation (Hounsfield unit ratios, 0.96 [0.88, 1.07] vs 1.1 [1.07, 1.2]; p < 0.001), 2) basilar cistern effacement (93% vs 7%; p = 0.001; positive predictive value, 94%; negative predictive value, 59%), and 3) sulcal effacement (100% vs 0%; p ≤ 0.001; positive predictive value, 100%; negative predictive value, 68%). All patients with poor gray-white matter differentiation or sulcal effacement had unfavorable neurologic outcomes. Only one patient with basilar cistern effacement had favorable outcome.

CONCLUSIONS

Loss of gray-white matter differentiation and basilar cistern effacement and sulcal effacement are associated with poor outcome after pediatric out-of-hospital cardiac arrest. Select patients may have favorable outcomes despite these findings.

Clinical utility of arterial spin-labeling as a confirmatory test for suspected brain death

Diagnosis of brain death is made on the basis of 3 essential findings: coma, absence of brain stem reflexes, and apnea. Although confirmatory tests are not mandatory in most situations, additional testing may be necessary to declare brain death in patients in whom results of specific components of clinical testing cannot be reliably evaluated. Recently, arterial spin-labeling has been incorporated as part of MR imaging to evaluate cerebral perfusion. Advantages of arterial spin-labeling include being completely noninvasive and providing information about absolute CBF. We retrospectively reviewed arterial spin-labeling findings according to the following modified criteria based on previously established confirmatory tests to determine brain death: 1) extremely decreased perfusion in the whole brain, 2) bright vessel signal intensity around the entry of the carotid artery to the skull, 3) patent external carotid circulation, and 4) "hollow skull sign" in a series of 5 patients. Arterial spin-labeling findings satisfied the criteria for brain death in all patients. Arterial spin-labeling imaging has the potential to be a completely noninvasive confirmatory test to provide additional information to assist in the diagnosis of brain death.

Automated brain computed tomographic densitometry of early ischemic changes in acute stroke

The Alberta Stroke Program Early CT score (ASPECTS) scoring method is frequently used for quantifying early ischemic changes (EICs) in patients with acute ischemic stroke in clinical studies. Varying interobserver agreement has been reported, however, with limited agreement. Therefore, our goal was to develop and evaluate an automated brain densitometric method. It divides CT scans of the brain into ASPECTS regions using atlas-based segmentation. EICs are quantified by comparing the brain density between contralateral sides. This method was optimized and validated using CT data from 10 and 63 patients, respectively. The automated method was validated against manual ASPECTS, stroke severity at baseline and clinical outcome after 7 to 10 days (NIH Stroke Scale, NIHSS) and 3 months (modified Rankin Scale). Manual and automated ASPECTS showed similar and statistically significant correlations with baseline NIHSS ([Formula: see text] and [Formula: see text], respectively) and with follow-up mRS ([Formula: see text] and [Formula: see text]), except for the follow-up NIHSS. Agreement between automated and consensus ASPECTS reading was similar to the interobserver agreement of manual ASPECTS (differences [Formula: see text] point in 73% of cases). The automated ASPECTS method could, therefore, be used as a supplementary tool to assist manual scoring.

Enalapril attenuates ischaemic brain oedema and protects the blood-brain barrier in rats via an anti-oxidant action

1. In the present study, we investigated the effects of postischaemic angiotensin-converting enzyme (ACE) inhibition with enalapril on vasogenic oedema formation and blood-brain barrier (BBB) integrity following transient focal cerebral ischaemia in rats. 2. Cerebral ischaemia was induced by 60 min occlusion of the right middle cerebral artery, followed by 24 h reperfusion. Vehicle and a non-hypotensive dose of enalapril (0.03 mg/kg) were administered at the beginning of the reperfusion period. A neurological deficit score (NDS) was determined for all rats at the end of the reperfusion period. Then, brain oedema formation was investigated using the wet-dry weight method and BBB permeability was evaluated on the basis of extravasation of Evans blue (EB) dye. In addition, oxidative stress was assessed by measuring reduced glutathione (GSH) and malondialdehyde (MDA) in brain homogenates. 3. Inhibition of ACE by enalapril significantly reduced NDS and decreased brain oedema formation (P < 0.05 for both). Disruption of the BBB following ischaemia resulted in considerable leakage of EB dye into the brain parenchyma of the ipsilateral hemispheres of vehicle-treated rats. Enalapril significantly (P < 0.05) decreased EB extravasation into the lesioned hemisphere. Enalapril also augmented anti-oxidant activity in ischaemic brain tissue by increasing GSH concentrations and significantly (P < 0.05) attenuating the increased MDA levels in response to ischaemia. 4. In conclusion, inhibition of ACE with a non-hypotensive dose of enalapril may protect BBB function and attenuate oedema formation via anti-oxidant actions.

Non-invasive diagnostic biomarkers for estimating the onset time of permanent cerebral ischemia

The treatments for ischemic stroke can only be administered in a narrow time-window. However, the ischemia onset time is unknown in ~30% of stroke patients (wake-up strokes). The objective of this study was to determine whether MR spectra of ischemic brains might allow the precise estimation of cerebral ischemia onset time. We modeled ischemic stroke in male ICR-CD1 mice using a permanent middle cerebral artery filament occlusion model with laser Doppler control of the regional cerebral blood flow. Mice were then subjected to repeated MRS measurements of ipsilateral striatum at 14.1 T. A striking initial increase in γ-aminobutyric acid (GABA) and no increase in glutamine were observed. A steady decline was observed for taurine (Tau), N-acetyl-aspartate (NAA) and similarly for the sum of NAA+Tau+glutamate that mimicked an exponential function. The estimation of the time of onset of permanent ischemia within 6 hours in a blinded experiment with mice showed an accuracy of 33±10 minutes. A plot of GABA, Tau, and neuronal marker concentrations against the ratio of acetate/NAA allowed precise separation of mice whose ischemia onset lay within arbitrarily chosen time-windows. We conclude that (1)H-MRS has the potential to detect the clinically relevant time of onset of ischemic stroke.

Antagonists of the Vasopressin V1 Receptor and of the β(1)-Adrenoceptor Inhibit Cytotoxic Brain Edema in Stroke by Effects on Astrocytes - but the Mechanisms Differ

Brain edema is a serious complication in ischemic stroke because even relatively small changes in brain volume can compromise cerebral blood flow or result in compression of vital brain structures on account of the fixed volume of the rigid skull. Literature data indicate that administration of either antagonists of the V1 vasopressin (AVP) receptor or the β1-adrenergic receptor are able to reduce edema or infarct size when administered after the onset of ischemia, a key advantage for possible clinical use. The present review discusses possible mechanisms, focusing on the role of NKCC1, an astrocytic cotransporter of Na(+), K(+), 2Cl(-) and water and its activation by highly increased extracellular K(+) concentrations in the development of cytotoxic cell swelling. However, it also mentions that due to a 3/2 ratio between Na(+) release and K(+) uptake by the Na(+),K(+)-ATPase driving NKCC1 brain extracellular fluid can become hypertonic, which may facilitate water entry across the blood-brain barrier, essential for development of edema. It shows that brain edema does not develop until during reperfusion, which can be explained by lack of metabolic energy during ischemia. V1 antagonists are likely to protect against cytotoxic edema formation by inhibiting AVP enhancement of NKCC1-mediated uptake of ions and water, whereas β1-adrenergic antagonists prevent edema formation because β1-adrenergic stimulation alone is responsible for stimulation of the Na(+),K(+)-ATPase driving NKCC1, first and foremost due to decrease in extracellular Ca(2+) concentration. Inhibition of NKCC1 also has adverse effects, e.g. on memory and the treatment should probably be of shortest possible duration.

Wake-up stroke: clinical characteristics, imaging findings, and treatment option - an update

About 25% of all strokes occur during sleep, i.e., without knowledge of exact time of symptom onset. According to licensing criteria, this large group of patients is excluded from treatment with received tissue-plasminogen activator, the only specific stroke treatment proven effective in large randomized trials. This paper reviews clinical and imaging characteristics of wake-up stroke and gives an update on treatment options for these patients. From clinical and imaging studies, there is evidence suggesting that many wake-up strokes occur close to awakening and thus, patients might be within the approved time-window of thrombolysis when presenting to the emergency department. Several imaging approaches are suggested to identify wake-up stroke patients likely to benefit from thrombolysis, including non-contrast CT, CT-perfusion, penumbral MRI, and the recent concept of diffusion weighted imaging-fluid attenuated inversion recovery (DWI-FLAIR). A number of small case series and observational studies report results of thrombolysis in wake-up stroke, and no safety concerns have occurred, while conclusions on efficacy cannot be drawn from these studies. To this end, there are ongoing clinical trials enrolling wake-up stroke patients based on imaging findings, i.e., the DWI-FLAIR-mismatch (WAKE-UP) or penumbral imaging (EXTEND). The results of these trials will provide evidence to guide thrombolysis in wake-up stroke and thus, expand treatment options for this large group of stroke patients.

Attenuation of focal cerebral ischemic injury following post-ischemic inhibition of angiotensin converting enzyme (ACE) activity in normotensive rat

BACKGROUND

Central renin angiotensin system has an important role on the cerebral microcirculation and metabolism. Our previous work showed that inhibition of angiotensin converting enzyme (ACE) activity prior to induction of ischemia protected the brain from severe ischemia/reperfusion (I/R) injuries. This study evaluated the impacts of post-ischemic inhibition of ACE, enalapril, on brain infarction in normotensive rats.

METHODS

Rats were anesthetized with chloral hydrate (400 mg/kg). Focal cerebral ischemia was induced by 60-min intraluminal occlusion of right middle cerebral artery (MCA). Intraperitoneal injection of enalapril (0.03 or 0.1 mg/kg) was done after MCA reopening (reperfusion). Neurological deficit score (NDS) was evaluated after 24 h and the animals randomly assigned for the assessments of infarction, absolute brain water content (ABWC) and index of brain edema.

RESULTS

Severe impaired motor functions (NDS = 2.78 ± 0.28), massive infarction (cortex = 214 ± 19 mm3, striatum = 86 ± 5 mm3) and edema (ABWC = 83.1 ± 0.46%) were observed in non-treated ischemic rats. Non-hypotensive dose of enalapril (0.03 mg/kg) significantly reduced NDS (1.5 ± 0.22), infarction (cortex = 102 ± 16 mm3, striatum = 38 ± 5 mm3) and edema (ABWC = 80.9 ± 0.81%). Enalapril at dose of 0.1 mg/kg significantly lowered arterial pressure could not improve NDS (2.0 ± 0.45) and reduce infarction (cortex = 166 ± 26 mm3, striatum = 71 ± 11 mm3).

CONCLUSION

Post-ischemic ACE inhibition in the normotensive rats without affecting arterial pressure protects the brain from reperfusion injuries; however, this beneficial action is masked by hypotension.

Correlated sodium and potassium imbalances within the ischemic core in experimental stroke: a 23Na MRI and histochemical imaging study

This study addresses the spatial relation between local Na(+) and K(+) imbalances in the ischemic core in a rat model of focal ischemic stroke. Quantitative [Na(+)] and [K(+)] brain maps were obtained by (23)Na MRI and histochemical K(+) staining, respectively, and calibrated by emission flame photometry of the micropunch brain samples. Stroke location was verified by diffusion MRI, by changes in tissue surface reflectivity and by immunohistochemistry with microtubule-associated protein 2 antibody. Na(+) and K(+) distribution within the ischemic core was inhomogeneous, with the maximum [Na(+)] increase and [K(+)] decrease typically observed in peripheral regions of the ischemic core. The pattern of the [K(+)] decrease matched the maximum rate of [Na(+)] increase ('slope'). Some residual mismatch between the sites of maximum Na(+) and K(+) imbalances was attributed to the different channels and pathways involved in transport of the two ions. A linear regression of the [Na(+)]br vs. [K(+)]br in the samples of ischemic brain indicates that for each K(+) equivalent leaving ischemic tissue, 0.8±0.1 Eq, on average, of Na(+) enter the tissue. Better understanding of the mechanistic link between the Na(+) influx and K(+) egress would validate the (23)Na MRI slope as a candidate biomarker and a complementary tool for assessing ischemic damage and treatment planning.

Measurement of brain edema by noninvasive cerebral electrical impedance in patients with massive hemispheric cerebral infarction

BACKGROUND

Malignant cerebral infarction often occurs in patients with massive cerebral infarction. Monitoring brain edema is therefore helpful to make correct clinical decisions. Our previous studies have confirmed that cerebral electrical impedance (CEI) can sensitively reflect the brain edema after stroke.

METHODS

The CEI was measured consecutively by a noninvasive brain edema monitor in 69 patients with massive hemispheric cerebral infarction (MHCI). The results of the CEI were converted into the perturbation index (PI). The characteristics of dynamic changes of the CEI after MHCI were analyzed. Receiver-operating characteristics analysis was used to calculate predictive values for PI and other known parameters including NIHSS score and infarct volume.

RESULTS

(1) The overall rate of positive CEI was 88.4% (61/69) in all patients with MHCI. (2) The PI on the infarct side increased significantly within 24 h after stroke onset and reached a peak level 3-5 days after stroke onset (p < 0.01). (3) Age, NIHSS score at admission, infarct volume, and the PI at 24 h after stroke onset were significantly different between the malignant and nonmalignant groups. The best predictor of a malignant MHCI was the PI at 24 h after stroke onset with a cut-off value of 10.02 (90.9% sensitivity, 87.2% specificity, 76.9% positive predictive value, 95.3% negative predictive value).

CONCLUSIONS

The noninvasive CEI can sensitively reflect the brain edema in patients with MHCI. Monitoring the CEI may help to predict malignant MHCI and guide treatment decisions.

Time Dependence of Reliability of Noncontrast Computed Tomography in Comparison to Computed Tomography Angiography Source Image in Acute Ischemic Stroke

There is no consensus on how the reliability and predictive ability of noncontrast computed tomography (NCCT) and computed tomography angiography source image (CTASI) change over time from acute ischemic stroke onset. We hypothesized that the reliability for detecting early ischemic changes (EIC) would be lower in early time periods and that changes identified on CTASI would be more reliable across examiners than changes identified on NCCT. To address this, we compared the relationships between CTASI, NCCT, and final infarct in patients with initial computed tomography (CT) imaging at different time points after stroke onset. Patients with acute ischemic stroke with proximal anterior circulation occlusions (internal carotid artery, middle carotid artery M1, proximal M2) from Calgary CT Angiography (CTA) database were studied. The cohort was categorized in four groups based on time from stroke onset to baseline NCCT/CTA: 0–90 mins ( n = 69), 91–180 mins ( n = 88), 181–360 mins ( n = 46), and >360 mins ( n = 58). Median scores of NCCT-Alberta Stroke Program Early CT Score (ASPECTS), CTASI ASPECTS, and follow-up ASPECTS among different time categories were compared. To determine reliability, a subsample of NCCT brain and CTASI were interpreted at separate sessions weeks apart by two neuroradiologists and two stroke neurologists in random order. Median and mean ASPECTS ratings on NCCT and CTASI were higher than final ASPECTS in each time category ( P < 0·001 for all comparisons). CTASI ASPECTS was lower than NCCT ASPECTS in each time category, and differences were significant at 0–90 mins and 91–180 mins ( P < 0·001). The least agreement among readers was in detection of EIC on NCCT brain in the ultra-early phase (<90 mins) [intraclass correlation coefficient (ICC) = 0·48. By contrast, there was excellent agreement on EIC on CTASI regardless of time period (ICC = 0·87–0·96). Using ASPECTS methodology, CTASI is more reliable than NCCT at predicting final infarct extent particularly in the early time windows.

Sodium MRI and the assessment of irreversible tissue damage during hyper-acute stroke

Sodium MRI (sMRI) has undergone a tremendous amount of technical development during the last two decades that makes it a suitable tool for the study of human pathology in the acute setting within the constraints of a clinical environment. The salient role of the sodium ion during impaired ATP production during the course of brain ischemia makes sMRI an ideal tool for the study of ischemic tissue viability during stroke. In this paper, the current limitations of conventional MRI for the determination of tissue viability during evolving brain ischemia are discussed. This discussion is followed by a summary of the known findings about the dynamics of tissue sodium changes during brain ischemia. A mechanistic model for the explanation of these findings is presented together with the technical requirements for its investigation using clinical MRI scanners. An illustration of the salient features of the technique is also presented using a nonhuman primate model of reversible middle cerebral artery occlusion.

ASPECTS and other neuroimaging scores in the triage and prediction of outcome in acute stroke patients

Information obtained from brain imaging is now summarized in the form of various neuroimaging scores to help physicians in making therapeutic decisions and determining prognosis. The Alberta Stroke Program Early CT Score (ASPECTS) was devised to quantify the extent of early ischemic changes in the middle cerebral artery territory on noncontrast computed tomography. With its systematic approach, the score is simple, reliable, and a strong predictor of functional outcome. This review summarizes ASPECTS and other neuroimaging scores developed for risk prognostication and risk stratification with treatment in patients with acute ischemic stroke.

Sulcal effacement on fluid attenuation inversion recovery magnetic resonance imaging in hyperacute stroke: association with collateral flow and clinical outcomes

BACKGROUND AND PURPOSE

The clinical significance of sulcal effacement has been widely investigated in CT studies, but the results are controversial. In this study, we evaluated the presence of perisylvian sulcal effacement (PSE) on fluid attenuation inversion recovery MRI and hypothesized that PSE may be related to collateral flow status together with hyperintense vessels on fluid attenuation inversion recovery in hyperacute stroke. In addition, we investigated whether an association between PSE and clinical outcome could be found in these patients.

METHODS

Consecutive patients with acute middle cerebral artery infarcts within 6 hours of symptom onset were included. All patients had internal carotid artery or middle cerebral artery occlusion and underwent MRI including FLAIR. The presence of PSE and hyperintense vessels on fluid attenuation inversion recovery and the collateral status and occurrence of early recanalization (ER) on conventional angiography were evaluated.

RESULTS

Of 139 patients, 79 (56.8%) had PSE. Multivariate testing revealed PSE was independently associated with collateral status. The association between hyperintense vessels and collaterals was different depending on PSE. Compared to PSE-positive and ER-negative patients, PSE-negative and ER-negative patients (odds ratio, 4.11; 95% confidence interval, 1.12-15.17) and PSE-negative and ER-positive patients (odds ratio, 34.62; 95% confidence interval, 5.75-208.60), but not PSE-positive and ER-positive patients, were more likely to experience favorable clinical outcomes (modified Rankin Scale score ≤ 2 at 3 months).

CONCLUSIONS

PSE is independently associated with collateral status in patients with acute middle cerebral artery stroke. Moreover, PSE in conjunction with recanalization status can predict clinical outcomes in these patients.

K⁺ dynamics in ischemic rat brain in vivo by ⁸⁷Rb MRI at 7 T

The aims of the present study were as follows: (i) to perform the first (87)Rb MRI in live rats with focal ischemic stroke; and (ii) to test the hypothesis that K(+) egress from the brain in this model is quantifiable in individual animals by high-field (7-T) K/Rb substitution MRI. Rats preloaded with dietary Rb(+) (resulting in Rb/(K + Rb) replacement ratios of 0.1-0.2 in the brain) were subjected to permanent occlusion of the middle cerebral artery, and (87)Rb MRI was implemented with 13-min temporal resolution using a dedicated RF coil and a spiral ultrashort-TE sequence (TR/TE = 3/0.07 ms). The ischemic core was localized by apparent diffusion coefficient mapping, by microtubule-associated protein-2 immunohistochemistry and by changes in surface reflectivity. [K], [Na] and [Rb] were determined independently in the micropunched samples by post-mortem flame photometry. Both techniques were generally in agreement in the nonischemic cortex; however, the MRI-assessed [K(+) + Rb(+)] drop in ischemic brain was less pronounced (average efflux rate of 4.8 ± 0.2 nEq/mm(3) /h versus 10 ± 1 nEq/mm(3)/h by flame photometry; p < 0.0001). The use of higher field gradients for better spatial resolution, and hence more accurate quantification, is suggested.

Correlation between CT and diffusion-weighted imaging of acute cerebral ischemia in a rat model

BACKGROUND AND PURPOSE

The quantitative temporal relationship between changes in CT attenuation, ADC value, and DWI signal intensity of acute ischemic tissue has not yet been determined in an animal model. This study was performed to determine the temporal relationship between CT attenuation, ADC value, and DWI signal intensity in acute cerebral ischemia.

MATERIALS AND METHODS

CT and DWI were performed at 1, 3, 5, 7, and 9 hours after left MCA occlusion in 11 rats. Mean values for CT attenuation, ADC, and DWI signal intensity were determined for the ischemic hemisphere and contralateral normal hemisphere. Temporal changes in each mean value and the relationship between CT attenuation and ADC value and DWI signal intensity were evaluated.

RESULTS

The decrease of CT attenuation and the increase of DWI signal intensity occurred gradually after MCA occlusion, while ADC value decreased rapidly at 1 hour. Although correlation was significant between time and rCT or rDWI (P<.01, respectively), no correlation between time and rADC was found (P=.33). There was a significant linear correlation between rCT and rDWI (r=0.497, P<.01), but no significant correlation between rCT and rADC (P=.509) was found.

CONCLUSIONS

The temporal change in CT attenuation was different from that in ADC value with no significant linear correlation between CT attenuation and ADC value for acute cerebral ischemia. However, rCT and rDWI showed a modest correlation.

Cardiac arrest-induced regional blood-brain barrier breakdown, edema formation and brain pathology: a light and electron microscopic study on a new model for neurodegeneration and neuroprotection in porcine brain

Brief cardiac arrest and survival is often associated with marked neurological alterations related to cognitive and sensory motor functions. However, detail studies using selective vulnerability of brain after cardiac arrest in animal models are still lacking. We examined selective vulnerability of five brain regions in our well-established cardiac arrest model in pigs. Using light and electron microscopic techniques in combinations with immunohistochemistry, we observed that 5, 30, 60 and 180 min after cardiac arrest results in progressive neuronal damage that was most marked in the thalamus followed by cortex, hippocampus, hypothalamus and the brain stem. The neuronal damages are largely evident in the areas showing leakage of serum albumin in the neuropil. Furthermore, a tight correlation was seen between neuronal damage and increase in brain water content and Na(+) indicating vasogenic edema formation after cardiac arrest. Damage to myelinated fibers and loss of myelin as seen using Luxol fast blue and myelin basic protein (MBP) immunoreactivity is clearly evident in the brain areas exhibiting neuronal damage. Upregulation of GFAP positive astrocytes closely corresponds with neuronal damages in different brain areas after cardiac arrest. At the ultrastructural level, perivascular edema together with neuronal, glial and endothelia cell damages is frequent in the brain areas showing albumin leakage. Damage to both pre- and post-synaptic membrane is also common. Treatment with methylene blue, an antioxidant markedly reduced neuronal damage, leakage of albumin, overexpression of GFAP and damage to myelin following cardiac arrest. Taken together, these observations suggest that (a) cardiac arrest is capable to induce selective neuronal, glial and myelin damage in different parts of the pig brain, and (b) antioxidant methylene blue is capable to induce neuroprotection by reducing BBB disruption. These observations strongly suggest that the model could be used to explore new therapeutic agents to enhance neurorepair following cardiac arrest-induced brain damage for therapeutic purposes.

The use of MR-detectable reporter molecules and ions to evaluate diffusion in normal and ischemic brain

As a result of the technical challenges associated with distinguishing the MR signals arising from intracellular and extracellular water, a variety of endogenous and exogenous MR-detectable molecules and ions have been employed as compartment-specific reporters of water motion. Although these reporter molecules and ions do not have the same apparent diffusion coefficients (ADCs) as water, their ADCs are assumed to be directly related to the ADC of the water in which they are solvated. This approach has been used to probe motion in the intra- and extracellular space of cultured cells and intact tissue. Despite potential interpretative challenges with the use of reporter molecules or ions and the wide variety used, the following conclusions are consistent considering all studies: (i) the apparent free diffusive motion in the intracellular space is approximately one-half of that in dilute aqueous solution; (ii) ADCs for intracellular and extracellular water are similar; (iii) the intracellular ADC decreases in association with brain injury. These findings provide support for the hypothesis that the overall brain water ADC decrease that accompanies brain injury is driven primarily by a decrease in the ADC of intracellular water. We review the studies supporting these conclusions, and interpret them in the context of explaining the decrease in overall brain water ADC that accompanies brain injury.

Visualization of the ischemic core on native human brain slices by potassium staining method

The potassium staining method is based on the formation of potassium cobaltnitrite crystals after the treatment by sodium cobaltnitrite of brain tissue. The degree of staining correlates with the distinct potassium content of infracted and non-infarcted brain areas. The aim of the present study was to prove that potassium staining technique is a reliable method for localization of ischemic core on native whole hemisphere cryosections of stroke patients. Furthermore, potassium stained sections have been compared with appropriate postmortem MRI images of respective brains. Brains of stroke patients were removed within 24h after death and postmortem MRI scanning was performed. Horizontal cryosections of frozen brains were taken and potassium staining was performed. Using the stained whole hemisphere sections as "map" tissue sampling has been made in order to determine water and potassium content. Potassium content of infarcted samples was significantly decreased in comparison with intact regions (0.7346+/-0.2142 mg/L and 1.928+/-0.447 mg/L, respectively, p<0.01) (mean values+/-SD). Water content of affected areas (expressed in percents) has been found to be above non-infarcted regions (81.657%+/-4.07 and 72.96%+/-6.37, respectively, p<0.01). According to our results the potassium staining method of human whole hemisphere brain sections reliably differentiates focal ischemic areas from intact brain regions. In conclusion, the postmortem examination of ischemic brain could be started with making the potassium map of infarcted whole hemisphere cryosections providing guidance for targeted tissue sampling and base of comparison for further examinations.

Assessment of the effects of cellular tissue properties on ADC measurements by numerical simulation of water diffusion

The apparent diffusion coefficient (ADC), as measured by diffusion-weighted MRI, has proven useful in the diagnosis and evaluation of ischemic stroke. The ADC of tissue water is reduced by 30-50% following ischemia and provides excellent contrast between normal and affected tissue. Despite its clinical utility, there is no consensus on the biophysical mechanism underlying the reduction in ADC. In this work, a numerical simulation of water diffusion is used to predict the effects of cellular tissue properties on experimentally measured ADC. The model indicates that the biophysical mechanisms responsible for changes in ADC postischemia depend upon the time over which diffusion is measured. At short diffusion times, the ADC is dependent upon the intrinsic intracellular diffusivity, while at longer, clinically relevant diffusion times, the ADC is highly dependent upon the cell volume fraction. The model also predicts that at clinically relevant diffusion times, the 30-50% drop in ADC after ischemia can be accounted for by cell swelling alone when intracellular T(2) is allowed to be shorter than extracellular T(2).