Imaging of Suspected Stroke in Children, From the AJR Special Series on Emergency Radiology.

Pediatric stroke encompasses different causes, clinical presentations, and associated conditions across ages. Although it is relatively uncommon, pediatric stroke presents with poor short- and long-term outcomes in many cases. Because of a wide range of overlapping presenting symptoms between pediatric stroke and other more common conditions, such as migraine and seizures, stroke diagnosis can be challenging or delayed in children. When combined with a comprehensive medical history and physical examination, neuroimaging plays a crucial role in diagnosing stroke and differentiating stroke mimics. This review highlights the current neuroimaging workup for diagnosing pediatric stroke in the emergency department, describes advantages and disadvantages of different imaging modalities, highlights disorders that predispose children to infarct or hemorrhage, and presents an overview of stroke mimics. Key differences in the initial approach to suspected stroke between children and adults are also discussed.

Third Ventricle Obstruction by Thalamic Intracerebral Hemorrhage Predicts Poor Functional Outcome Among Patients Treated with Alteplase in the CLEAR III Trial.

INTRODUCTION: The Clot Lysis: Evaluating Accelerated Resolution of IVH trial examined whether irrigating the ventricular system with alteplase improved functional outcomes in patients with small intracerebral hemorrhage (ICH) and large intraventricular hemorrhage (IVH). Thalamic ICH location was common and was associated with poor outcome. One possible explanation is thalamic ICH-associated mass effect obstructing the third ventricle. We hypothesized that patients with thalamic ICH obstructing the third ventricle would have worse functional outcomes compared to patients without obstructing lesions. METHODS: ICH obstruction of third ventricle was defined as third ventricle compression on 1 or more axial computed tomography slices visually impeding cerebral spinal fluid flow. If the third ventricle was casted with IVH, it was scored as such. Multivariable logistic regression analyses were used to determine whether obstruction of the third ventricle predicts poor functional outcomes defined as modified Rankin score (mRS) 4-6, higher mRS, and mortality at 180 days. Models were adjusted for thalamic ICH location, ICH volume, IVH volume, age, hydrocephalus, baseline Glasgow coma scale, and percentage of low cerebral perfusion pressures during treatment. RESULTS: Among saline-treated patients, obstruction of the third ventricle by IVH was a significant predictor of higher mRS at 180 days (OR 1.87, CI 1.01-3.47) and mortality at 180 days (OR 2.73, CI 1.27-5.87) while obstruction by ICH was not. In contrast, among alteplase-treated patients, obstruction by ICH was a significant predictor of mRS 4-6 (OR 3.20, CI 1.30-7.88) and higher mRS at 180 days (OR 2.33, CI 1.24-4.35), while obstruction by IVH was not. CONCLUSIONS: Poor outcomes were associated with mass-related obstruction of the third ventricle from thalamic ICH in alteplase-treated patients and from IVH in saline-treated patients. Once the ventricular system is cleared with alteplase, obstruction of cerebral spinal fluid flow from thalamic ICH might become important in functional recovery.

Quantitative Intracerebral Hemorrhage Localization.

BACKGROUND AND PURPOSE: The location of intracerebral hemorrhage (ICH) is currently described in a qualitative way; we provide a quantitative framework for estimating ICH engagement and its relevance to stroke outcomes. METHODS: We analyzed 111 patients with ICH from the Minimally Invasive Surgery Plus Recombinant-Tissue Plasminogen Activator for Intracerebral Evacuation (MISTIE) II clinical trial. We estimated ICH engagement at a population level using image registration of computed tomographic scans to a template and a previously labeled atlas. Predictive regions of National Institutes of Health Stroke Scale and Glasgow Coma Scale stroke severity scores, collected at enrollment, were estimated. RESULTS: The percent coverage of the ICH by these regions strongly outperformed the reader-labeled locations. The adjusted R(2) almost doubled from 0.129 (reader-labeled model) to 0.254 (quantitative location model) for National Institutes of Health Stroke Scale and more than tripled from 0.069 (reader-labeled model) to 0.214 (quantitative location model). A permutation test confirmed that the new predictive regions are more predictive than chance: P<0.001 for National Institutes of Health Stroke Scale and P<0.01 for Glasgow Coma Scale. CONCLUSIONS: Objective measures of ICH location and engagement using advanced computed tomographic imaging processing provide finer, objective, and more quantitative anatomic information than that provided by human readers. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00224770.

Accuracy of the ABC/2 Score for Intracerebral Hemorrhage: Systematic Review and Analysis of MISTIE, CLEAR-IVH, and CLEAR III.

BACKGROUND AND PURPOSE: The ABC/2 score estimates intracerebral hemorrhage (ICH) volume, yet validations have been limited by small samples and inappropriate outcome measures. We determined accuracy of the ABC/2 score calculated at a specialized reading center (RC-ABC) or local site (site-ABC) versus the reference-standard computed tomography-based planimetry (CTP). METHODS: In Minimally Invasive Surgery Plus Recombinant Tissue-Type Plasminogen Activator for Intracerebral Hemorrhage Evacuation-II (MISTIE-II), Clot Lysis Evaluation of Accelerated Resolution of Intraventricular Hemorrhage (CLEAR-IVH) and CLEAR-III trials. ICH volume was prospectively calculated by CTP, RC-ABC, and site-ABC. Agreement between CTP and ABC/2 was defined as an absolute difference up to 5 mL and relative difference within 20%. Determinants of ABC/2 accuracy were assessed by logistic regression. RESULTS: In 4369 scans from 507 patients, CTP was more strongly correlated with RC-ABC (r(2)=0.93) than with site-ABC (r(2)=0.87). Although RC-ABC overestimated CTP-based volume on average (RC-ABC, 15.2 cm(3); CTP, 12.7 cm3), agreement was reasonable when categorized into mild, moderate, and severe ICH (κ=0.75; P<0.001). This was consistent with overestimation of ICH volume in 6 of 8 previous studies. Agreement with CTP was greater for RC-ABC (84% within 5 mL; 48% of scans within 20%) than for site-ABC (81% within 5 mL; 41% within 20%). RC-ABC had moderate accuracy for detecting ≥5 mL change in CTP volume between consecutive scans (sensitivity, 0.76; specificity, 0.86) and was more accurate with smaller ICH, thalamic hemorrhage, and homogeneous clots. CONCLUSIONS: ABC/2 scores at local or central sites are sufficiently accurate to categorize ICH volume and assess eligibility for the CLEAR-III and MISTIE III studies and moderately accurate for change in ICH volume. However, accuracy decreases with large, irregular, or lobar clots. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: MISTIE-II NCT00224770; CLEAR-III NCT00784134.

Validated automatic brain extraction of head CT images.

BACKGROUND: X-ray computed tomography (CT) imaging of the brain is commonly used in diagnostic settings. Although CT scans are primarily used in clinical practice, they are increasingly used in research. A fundamental processing step in brain imaging research is brain extraction - the process of separating the brain tissue from all other tissues. Methods for brain extraction have either been 1) validated but not fully automated, or 2) fully automated and informally proposed, but never formally validated. AIM: To systematically analyze and validate the performance of FSL's brain extraction tool (BET) on head CT images of patients with intracranial hemorrhage. This was done by comparing the manual gold standard with the results of several versions of automatic brain extraction and by estimating the reliability of automated segmentation of longitudinal scans. The effects of the choice of BET parameters and data smoothing is studied and reported. METHODS: All images were thresholded using a 0-100 Hounsfield unit (HU) range. In one variant of the pipeline, data were smoothed using a 3-dimensional Gaussian kernel (σ=1mm(3)) and re-thresholded to 0-100HU; in the other, data were not smoothed. BET was applied using 1 of 3 fractional intensity (FI) thresholds: 0.01, 0.1, or 0.35 and any holes in the brain mask were filled. For validation against a manual segmentation, 36 images from patients with intracranial hemorrhage were selected from 19 different centers from the MISTIE (Minimally Invasive Surgery plus recombinant-tissue plasminogen activator for Intracerebral Evacuation) stroke trial. Intracranial masks of the brain were manually created by one expert CT reader. The resulting brain tissue masks were quantitatively compared to the manual segmentations using sensitivity, specificity, accuracy, and the Dice Similarity Index (DSI). Brain extraction performance across smoothing and FI thresholds was compared using the Wilcoxon signed-rank test. The intracranial volume (ICV) of each scan was estimated by multiplying the number of voxels in the brain mask by the dimensions of each voxel for that scan. From this, we calculated the ICV ratio comparing manual and automated segmentation: ICVautomated/ICVmanual. To estimate the performance in a large number of scans, brain masks were generated from the 6 BET pipelines for 1095 longitudinal scans from 129 patients. Failure rates were estimated from visual inspection. ICV of each scan was estimated and an intraclass correlation (ICC) was estimated using a one-way ANOVA. RESULTS: Smoothing images improves brain extraction results using BET for all measures except specificity (all p<0.01, uncorrected), irrespective of the FI threshold. Using an FI of 0.01 or 0.1 performed better than 0.35. Thus, all reported results refer only to smoothed data using an FI of 0.01 or 0.1. Using an FI of 0.01 had a higher median sensitivity (0.9901) than an FI of 0.1 (0.9884, median difference: 0.0014, p<0.001), accuracy (0.9971 vs. 0.9971; median difference: 0.0001, p<0.001), and DSI (0.9895 vs. 0.9894; median difference: 0.0004, p<0.001) and lower specificity (0.9981 vs. 0.9982; median difference: -0.0001, p<0.001). These measures are all very high indicating that a range of FI values may produce visually indistinguishable brain extractions. Using smoothed data and an FI of 0.01, the mean (SD) ICV ratio was 1.002 (0.008); the mean being close to 1 indicates the ICV estimates are similar for automated and manual segmentation. In the 1095 longitudinal scans, this pipeline had a low failure rate (5.2%) and the ICC estimate was high (0.929, 95% CI: 0.91, 0.945) for successfully extracted brains. CONCLUSION: BET performs well at brain extraction on thresholded, 1mm(3) smoothed CT images with an FI of 0.01 or 0.1. Smoothing before applying BET is an important step not previously discussed in the literature. Analysis code is provided.

Minimally invasive surgery plus recombinant tissue-type plasminogen activator for intracerebral hemorrhage evacuation decreases perihematomal edema.

BACKGROUND AND PURPOSE: Perihematomal edema (PHE) can worsen outcomes after intracerebral hemorrhage (ICH). Reports suggest that blood degradation products lead to PHE. We hypothesized that hematoma evacuation will reduce PHE volume and that treatment with recombinant tissue-type plasminogen activator (rt-PA) will not exacerbate it. METHODS: Minimally invasive surgery and rt-PA in ICH evacuation (MISTIE) phase II tested safety and efficacy of hematoma evacuation after ICH. We conducted a semiautomated, computerized volumetric analysis on computed tomography to assess impact of hematoma removal on PHE and effects of rt-PA on PHE. Volumetric analyses were performed on baseline stability and end of treatment scans. RESULTS: Seventy-nine surgical and 39 medical patients from minimally invasive surgery and rt-PA in ICH evacuation phase II (MISTIE II) were analyzed. Mean hematoma volume at end of treatment was 19.6±14.5 cm(3) for the surgical cohort and 40.7±13.9 cm(3) for the medical cohort (P<0.001). Edema volume at end of treatment was lower for the surgical cohort: 27.7±13.3 cm(3) than medical cohort: 41.7±14.6 cm(3) (P<0.001). Graded effect of clot removal on PHE was observed when patients with >65%, 20% to 65%, and <20% ICH removed were analyzed (P<0.001). Positive correlation between PHE reduction and percent of ICH removed was identified (ρ=0.658; P<0.001). In the surgical cohort, 69 patients underwent surgical aspiration and rt-PA, whereas 10 underwent surgical aspiration only. Both cohorts achieved similar clot reduction: surgical aspiration and rt-PA, 18.9±14.5 cm(3); and surgical aspiration only, 24.5±14.0 cm(3) (P=0.26). Edema at end of treatment in surgical aspiration and rt-PA was 28.1±13.8 cm(3) and 24.4±8.6 cm(3) in surgical aspiration only (P=0.41). CONCLUSIONS: Hematoma evacuation is associated with significant reduction in PHE. Furthermore, PHE does not seem to be exacerbated by rt-PA, making such neurotoxic effects unlikely when the drug is delivered to intracranial clot.

Cerebral small vessel disease modifies outcomes after minimally invasive surgery for intracerebral haemorrhage.

BACKGROUND: Minimally invasive surgery (MIS) for spontaneous supratentorial intracerebral haemorrhage (ICH) is controversial but may be beneficial if end-of-treatment (EOT) haematoma volume is reduced to ≤15 mL. We explored whether MRI findings of cerebral small vessel disease (CSVD) modify the effect of MIS on long-term outcomes. METHODS: Prespecified blinded subgroup analysis of 288 subjects with qualified imaging sequences from the phase 3 Minimally Invasive Surgery Plus Alteplase for Intracerebral Haemorrhage Evacuation (MISTIE) trial. We tested for heterogeneity in the effects of MIS and MIS+EOT volume ≤15 mL on the trial's primary outcome of good versus poor function at 1 year by the presence of single CSVD features and CSVD scores using multivariable models. RESULTS: Of 499 patients enrolled in MISTIE III, 288 patients had MRI, 149 (51.7%) randomised to MIS and 139 (48.3%) to standard medical care (SMC). Median (IQR) ICH volume was 42 (30-53) mL. In the full MRI cohort, there was no statistically significant heterogeneity in the effects of MIS versus SMC on 1-year outcomes by any specific CSVD feature or by CSVD scores (all Pinteraction >0.05). In 94 MIS patients with EOT ICH volume ≤15 mL, significant reduction in odds of poor outcome was found with cerebral amyloid angiopathy score <2 (OR, 0.14 (0.05-0.42); Pinteraction=0.006), absence of lacunes (OR, 0.37 (0.18-0.80); Pinteraction=0.02) and absence of severe white matter hyperintensities (WMHs) (OR, 0.22 (0.08-0.58); Pinteraction=0.03). CONCLUSIONS: Following successful haematoma reduction by MIS, we found significantly lower odds of poor functional outcome with lower total burden of CSVD in addition to absence of lacunes and severe WMHs. CSVD features may have utility for prognostication and patient selection in clinical trials of MIS.

Resolution of intraventricular hemorrhage varies by ventricular region and dose of intraventricular thrombolytic: the Clot Lysis: Evaluating Accelerated Resolution of IVH (CLEAR IVH) program.

BACKGROUND AND PURPOSE: The Clot Lysis: Evaluating Accelerated Resolution of IVH (CLEAR IVH) program is assessing the efficacy of intraventricular recombinant tissue-type plasminogen activator (rtPA) for spontaneous intraventricular hemorrhage (IVH). This subanalysis assesses the effect of dose of rtPA by region on clearance of IVH. METHODS: Sixty-four patients within 12 to 24 hours of spontaneous IVH were randomized to placebo or 0.3 mg, 1 mg, or 3 mg of rtPA twice daily through an extraventricular drain. Twelve subregions of the ventricles were scored from 0 to 4. Effect of dose on IVH clearance to 50% of baseline score was compared by survival analysis for all regions combined and by subregion. Models including ventricular region, dose, and baseline score were compared by Cox proportional hazards. RESULTS: IVH score reduced faster across all regions with increasing rtPA dose (clearance to 50%: log-rank P<0.0001; placebo-11.43 days, 95% CI, 5.68-17.18; 0.3 mg-3.19 days, 1.00-5.38; 1 mg-3.54 days, 0.45-6.64; 3 mg-2.59 days, 1.72-3.46). In the combined models, dose and baseline score were independently associated with reduction in IVH score, which was quickest in the midline ventricles, then the anterior half of the lateral ventricles and slowest in the posterior half of the lateral ventricles (clearance to 50%: P<0.0001; rtPA dose: hazard ratio, 1.47, 1.30-1.67; midline versus anterolateral hazard ratio, 1.71, 1.08-2.71; midline versus posterolateral hazard ratio, 4.05, 2.46-6.65; baseline score hazard ratio, 0.96, 0.91-1.01) with a significant interaction between dose and ventricular region (P=0.005). CONCLUSIONS: rtPA accelerates resolution of IVH. This effect is dose-dependent, is greatest in the midline ventricles, and least in the posterolateral ventricles.

PItcHPERFeCT: Primary Intracranial Hemorrhage Probability Estimation using Random Forests on CT.

INTRODUCTION: Intracerebral hemorrhage (ICH), where a blood vessel ruptures into areas of the brain, accounts for approximately 10-15% of all strokes. X-ray computed tomography (CT) scanning is largely used to assess the location and volume of these hemorrhages. Manual segmentation of the CT scan using planimetry by an expert reader is the gold standard for volume estimation, but is time-consuming and has within- and across-reader variability. We propose a fully automated segmentation approach using a random forest algorithm with features extracted from X-ray computed tomography (CT) scans. METHODS: The Minimally Invasive Surgery plus rt-PA in ICH Evacuation (MISTIE) trial was a multi-site Phase II clinical trial that tested the safety of hemorrhage removal using recombinant-tissue plasminogen activator (rt-PA). For this analysis, we use 112 baseline CT scans from patients enrolled in the MISTE trial, one CT scan per patient. ICH was manually segmented on these CT scans by expert readers. We derived a set of imaging predictors from each scan. Using 10 randomly-selected scans, we used a first-pass voxel selection procedure based on quantiles of a set of predictors and then built 4 models estimating the voxel-level probability of ICH. The models used were: 1) logistic regression, 2) logistic regression with a penalty on the model parameters using LASSO, 3) a generalized additive model (GAM) and 4) a random forest classifier. The remaining 102 scans were used for model validation.For each validation scan, the model predicted the probability of ICH at each voxel. These voxel-level probabilities were then thresholded to produce binary segmentations of the hemorrhage. These masks were compared to the manual segmentations using the Dice Similarity Index (DSI) and the correlation of hemorrhage volume of between the two segmentations. We tested equality of median DSI using the Kruskal-Wallis test across the 4 models. We tested equality of the median DSI from sets of 2 models using a Wilcoxon signed-rank test. RESULTS: All results presented are for the 102 scans in the validation set. The median DSI for each model was: 0.89 (logistic), 0.885 (LASSO), 0.88 (GAM), and 0.899 (random forest). Using the random forest results in a slightly higher median DSI compared to the other models. After Bonferroni correction, the hypothesis of equality of median DSI was rejected only when comparing the random forest DSI to the DSI from the logistic (p < 0.001), LASSO (p < 0.001), or GAM (p < 0.001) models. In practical terms the difference between the random forest and the logistic regression is quite small. The correlation (95% CI) between the volume from manual segmentation and the predicted volume was 0.93 (0.9,0.95) for the random forest model. These results indicate that random forest approach can achieve accurate segmentation of ICH in a population of patients from a variety of imaging centers. We provide an R package (https://github.com/muschellij2/ichseg) and a Shiny R application online (http://johnmuschelli.com/ich_segment_all.html) for implementing and testing the proposed approach.

Characterization of intraventricular and intracerebral hematomas in non-contrast CT.

Characterization of hematomas is essential in scan reading, manual delineation, and designing automatic segmentation algorithms. Our purpose is to characterize the distribution of intraventricular (IVH) and intracerebral hematomas (ICH) in NCCT scans, study their relationship to gray matter (GM), and to introduce a new tool for quantitative hematoma delineation. We used 289 serial retrospective scans of 51 patients. Hematomas were manually delineated in a two-stage process. Hematoma contours generated in the first stage were quantified and enhanced in the second stage. Delineation was based on new quantitative rules and hematoma profiling, and assisted by a dedicated tool superimposing quantitative information on scans with 3D hematoma display. The tool provides: density maps (40-85HU), contrast maps (8/15HU), mean horizontal/vertical contrasts for hematoma contours, and hematoma contours below a specified mean contrast (8HU). White matter (WM) and GM were segmented automatically. IVH/ICH on serial NCCT is characterized by 59.0HU mean, 60.0HU median, 11.6HU standard deviation, 23.9HU mean contrast, -0.99HU/day slope, and -0.24 skewness (changing over time from negative to positive). Its 0.1(st)-99.9(th) percentile range corresponds to 25-88HU range. WM and GM are highly correlated (R (2)=0.88; p<10(-10)) whereas the GM-GS correlation is weak (R (2)=0.14; p<10(-10)). The intersection point of mean GM-hematoma density distributions is at 55.6±5.8HU with the corresponding GM/hematoma percentiles of 88(th)/40(th). Objective characterization of IVH/ICH and stating the rules quantitatively will aid raters to delineate hematomas more robustly and facilitate designing algorithms for automatic hematoma segmentation. Our two-stage process is general and potentially applicable to delineate other pathologies on various modalities more robustly and quantitatively.