Intracranial atherosclerosis: Review of imaging features and advances in diagnostics.

Intracranial atherosclerotic disease is one of the leading causes of ischemic strokes and poses a moderate risk of recurrence. Diagnosis is currently limited to stenosis on luminal imaging, which likely underestimates the true prevalence of the disease. Detection of non-stenosing intracranial atherosclerosis is important in order to optimize secondary stroke prevention strategies. This review collates findings from the early seminal trials and the latest studies in advanced radiological techniques that characterize symptomatic intracranial atherosclerotic disease across various imaging modalities. While computed tomography angiography (CTA) and magnetic resonance angiography (MRA) comprise diagnostic mainstays in identifying stenotic changes secondary to atherosclerosis, emerging techniques such as high-resolution MRA, quantitative MRA, and computational fluid dynamics may reveal a myriad of other underlying pathophysiological mechanisms.

Lipid Levels and Short-Term Risk of Recurrent Brain Infarcts in Symptomatic Intracranial Stenosis.

OBJECTIVES: Hyperlipidemia is a strong risk factor for intracranial atherosclerotic disease (ICAD) and clinical stroke recurrence. We explored the effect of serum lipid levels on subclinical infarct recurrence in the Mechanisms of earlY Recurrence in Intracranial Atherosclerotic Disease (MYRIAD) study. MATERIALS AND METHODS: We included enrolled MYRIAD patients with lipid measurements and brain MRI at baseline and brain MRI at 6-8 weeks. Infarct recurrence was defined as new infarcts in the territory of the symptomatic artery on brain MRI at 6-8 weeks compared to baseline brain MRI. We assessed the association between baseline total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglyceride (TG) levels and recurrent infarct at 6-8 weeks using multivariable logistic regression. RESULTS: Among 74 patients (mean age 64.2±12.9 years, 59.5% were white, 60.8% men), 20 (27.0%) had new or recurrent infarcts. Mean HDL-C (37.2 vs. 43.9 mg/dL, P=0.037) was lower and TG (113.5 vs. 91.3 mg/dL, P=0.008) was higher while TC (199.8 vs. 174.3 mg/dL, P=0.061) and LDL-C (124.3 vs. 101.2 mg/dL, P=0.053) were nominally higher among those with recurrent infarcts than those without. LDL-C (adj. OR 1.022, 95% CI 1.004-1.040, P=0.015) and TG (adj. OR 1.009, 95% CI 1.001-1.016, P=0.021) were predictors of recurrent infarct at 6-8 weeks adjusting for other clinical and imaging factors. CONCLUSIONS: Baseline cholesterol markers can predict early infarct recurrence in patients with symptomatic ICAD. More intensive and rapid lipid lowering drugs may be required to reduce risk of early recurrence.

Intracranial atherosclerotic disease mechanistic subtypes drive hypoperfusion patterns.

BACKGROUND AND PURPOSE: In symptomatic intracranial atherosclerotic stenosis (ICAS), borderzone infarct pattern and perfusion mismatch are associated with increased risk of recurrent strokes, which may reflect the shared underlying mechanism of hypoperfusion distal to the intracranial atherosclerosis. Accordingly, we hypothesized a correlation between hypoperfusion volumes and ICAS infarct patterns based on the respective underlying mechanistic subtypes. METHODS: We conducted a retrospective analysis of consecutive symptomatic ICAS cases, acute strokes due to subocclusive (50%-99%) intracranial stenosis. The following mechanistic subtypes were assigned based on the infarct pattern on the diffusion-weighted imaging: Branch occlusive disease (BOD), internal borderzone (IBZ), and thromboembolic (TE). Perfusion parameters, obtained concurrently with the MRI, were studied in each group. RESULTS: A total of 42 patients (57% women, mean age 71 ± 13 years old) with symptomatic ICAS received MRI within 24 h of acute presentation. Fourteen IBZ, 11 BOD, and 17 TE patterns were identified. IBZ pattern yielded higher total Tmax > 4 s and Tmax > 6 s perfusion delay volumes, as well as corresponding Tmax  > 4 s and Tmax  > 6 s mismatch volume, compared to BOD. TE pattern exhibited greater median Tmax  > 6 s hypoperfusion delay in volume compared to BOD. In IBZ versus TE, the volume difference between Tmax > 4 s and Tmax > 6 s (Δ Tmax  > 4 s - Tmax  > 6 s) was substantially greater. CONCLUSION: ICAS infarct patterns, in keeping with their respective underlying mechanisms, may correlate with distinct perfusion profiles.

Predictors of Early Infarct Recurrence in Patients With Symptomatic Intracranial Atherosclerotic Disease.

BACKGROUND AND PURPOSE: While prior studies identified risk factors for recurrent stroke in patients with symptomatic intracranial atherosclerotic disease, few have assessed risk factors for early infarct recurrence. METHODS: We performed a post hoc analysis of the MYRIAD study (Mechanisms of Early Recurrence in Intracranial Atherosclerotic Disease) of intracranial atherosclerotic disease patients with recent (<21 days) stroke/transient ischemic attack, 50% to 99% stenosis and who underwent 6- to 8-week magnetic resonance imaging (MRI) per protocol. Infarct recurrence was defined as new infarcts in the territory of the symptomatic artery on brain MRI at 6 to 8 weeks compared to index brain MRI. Qualifying events and clinical and imaging outcomes were centrally ascertained by 2 independent reviewers. We assessed the association between baseline clinical and imaging variables and recurrent infarct in bivariate models and multivariable logistic regression to identify independent predictors of infarct recurrence. RESULTS: Of 105 enrolled patients in MYRIAD, 89 (84.8%) were included in this analysis (mean age, 64±12 years, 54 [60.7%] were male, and 53 [59.6%] were White). The median time from qualifying event to MRI was 51+16 days, on which 22 (24.7%) patients had new or recurrent infarcts. Younger age (57.7 versus 66.0 years; P<0.01), diabetes (32.6% versus 14.6%, P=0.05), index stroke (31.3% versus 4.6%, P=0.01), anterior circulation location of stenosis (29.7% versus 12.0%, P=0.08), number of diffusion-weighted imaging lesions (>1: 40.0%, 1: 26.9% versus 0: 4.4%, P<0.01), and borderzone infarct pattern (63.6% versus 25.0%, P=0.01) on baseline MRI were associated with new or recurrent infarcts. Age (adjusted odds ratio, 0.93 [95% CI, 0.89-0.98], P<0.01) and number of diffusion-weighted imaging lesions (adjusted odds ratio, 3.24 [95% CI, 1.36-7.71], P<0.01) were independently associated with recurrent infarct adjusting for hypertension, diabetes, and stenosis location (anterior versus posterior circulation). CONCLUSIONS: An index multi-infarct pattern is associated with early recurrent infarcts, a finding that might be explained by plaque instability and artery-to-artery embolism. Further investigation of plaque vulnerability in intracranial atherosclerotic disease is needed. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02121028.

Endothelial Shear Stress and Platelet FcγRIIa Expression in Intracranial Atherosclerotic Disease.

Intracranial atherosclerotic disease (ICAD) has been characterized by the degree of arterial stenosis and downstream hypoperfusion, yet microscopic derangements of endothelial shear stress at the luminal wall may be key determinants of plaque growth, vascular remodeling and thrombosis that culminate in recurrent stroke. Platelet interactions have similarly been a principal focus of treatment, however, the mechanistic basis of anti-platelet strategies is largely extrapolated rather than directly investigated in ICAD. Platelet FcγRIIa expression has been identified as a potent risk factor in cardiovascular disease, as elevated expression markedly increases the risk of recurrent events. Differential activation of the platelet FcγRIIa receptor may also explain the variable response of individual patients to anti-platelet medications. We review existing data on endothelial shear stress and potential interactions with the platelet FcγRIIa receptor that may alter the evolving impact of ICAD, based on local pathophysiology at the site of arterial stenosis. Current methods for quantification of endothelial shear stress and platelet activation are described, including tools that may be readily adapted to the clinical realm for further understanding of ICAD.

Impaired Distal Perfusion Predicts Length of Hospital Stay in Patients with Symptomatic Middle Cerebral Artery Stenosis.

BACKGROUND AND PURPOSE: Perfusion imaging can risk stratify patients with symptomatic intracranial stenosis. We aim to determine the association between perfusion delay and length of hospital stay (LOS) in symptomatic middle cerebral artery (MCA) stenosis patients. METHODS: This is a retrospective study of consecutive patients admitted to a comprehensive stroke center over 5 years with ischemic stroke or transient ischemic attack (TIA) within 7 days of symptom onset due to MCA stenosis (50-99%) and underwent perfusion imaging. Patients were divided into three groups: mismatch volume ≥ 15 cc based on T max > 6 second delay, T max 4-6 second delay, and <4 second delay. The outcome was LOS, both as a continuous variable and categorical (≥7 days [prolonged LOS] vs. <7 days). We used adjusted regression analyses to determine the association between perfusion categories and LOS. RESULTS: One hundred and seventy eight of 194 patients met the inclusion criteria. After adjusting for age and NIHSS, T max >6 second mismatch was associated with prolonged LOS (OR 2.94 95% CI 1.06-8.18; P = .039), but T max 4-6 second was not (OR 1.45 95% CI .46-4.58, P = .528). We found similar associations when LOS was a continuous variable for T max > 6 second (ß coefficient = 2.01, 95% CI .05-3.97, P = .044) and T max 4-6 second (ß coefficient = 1.24, 95% CI -.85 to 3.34, P = .244). CONCLUSION: In patients with symptomatic MCA stenosis, T max > 6 second perfusion delay is associated with prolonged LOS. Prospective studies are needed to validate our findings.

Infarct Recurrence in Intracranial Atherosclerosis: Results from the MyRIAD Study.

BACKGROUND: Intracranial atherosclerotic disease (ICAD) is a common cause of ischemic stroke with a high risk of clinical stroke recurrence. Multiple mechanisms may underlie cerebral ischemia in this condition. The study's objective is to discern the mechanisms of recurrent ischemia in ICAD through imaging biomarkers of impaired antegrade flow, poor distal perfusion, abnormal vasoreactivity, and artery-to-artery embolism. METHODS: This prospective multicenter observational study enrolled patients with recent (≤21 days) ischemic stroke or transient ischemic attack (TIA) caused by ICAD with 50-99% stenosis treated medically. We obtained baseline quantitative MRA (QMRA), perfusion MRI (PWI), transcranial Doppler vasoreactivity (VMR), and emboli detection studies (EDS). The primary outcome was ischemic stroke in the territory of the stenotic artery within 1 year of follow-up; secondary outcomes were TIA at 1 year and new infarcts in the territory on MRI at 6-8 weeks. RESULTS: Amongst 102 of 105 participants with clinical follow-up (mean 253±131 days), the primary outcome occurred in 8.8% (12.7/100 patient-years), while 5.9% (8.5/100 patient-years) had a TIA. A new infarct in the territory of the symptomatic artery was noted in 24.7% at 6-8 weeks. A low flow state on QMRA was noted in 25.5%, poor distal perfusion on PWI in 43.5%, impaired vasoreactivity on VMR in 67.5%, and microemboli on EDS in 39.0%. No significant association was identified between these imaging biomarkers and primary or secondary outcomes. CONCLUSIONS: Despite intensive medical management in ICAD, there is a high risk of clinical cerebrovascular events at 1 year and an even higher risk of new imaging-evident infarcts in the subacute period after index stroke. Hemodynamic and plaque instability biomarkers did not identify a higher risk group. Further work is needed to identify mechanisms of ischemic stroke and infarct recurrence and their consequence on long-term physical and cognitive outcomes. TRIAL REGISTRATION: ClinicalTrials.gov: NCT02121028.

Mechanisms of early Recurrence in Intracranial Atherosclerotic Disease (MyRIAD): Rationale and design.

RATIONALE: Intracranial atherosclerotic disease (ICAD) is the most common cause of ischemic stroke with the highest rate of recurrence, despite aggressive medical management. Diverse mechanisms may be responsible for ICAD-related cerebral ischemia, with potential therapeutic implications. Here we present the rationale, design and methods of the Mechanisms of Early Recurrence in Intracranial Atherosclerotic Disease (MyRIAD) study. The aim of MyRIAD is to determine the mechanisms of stroke in ICAD through physiologic imaging biomarkers that evaluate impaired antegrade flow, poor distal perfusion, abnormal vasoreactivity, artery to artery embolism, and their interaction. METHODS AND DESIGN: This is a prospective observational study of patients with recently symptomatic (<21 days) ICAD with 50-99% stenosis treated medically and monitored for up to 1 year. An estimated 110 participants are recruited at 10 sites to identify the association between the presence of each mechanism of ischemia and recurrent stroke. The primary outcome is ischemic stroke in the territory of the symptomatic artery. Secondary outcomes include new cerebral infarction on MRI at 6-8 weeks and recurrent TIA in the territory of the symptomatic artery. DISCUSSION: MyRIAD is positioned to define the role of specific mechanisms of recurrent ischemia in patients with symptomatic ICAD. This knowledge will allow the development and implementation of effective and specific treatments for this condition.

Poststroke Montreal Cognitive Assessment and Recurrent Stroke in Patients With Symptomatic Intracranial Atherosclerosis.

BACKGROUND AND PURPOSE: Cognitive impairment occurs in 20%-40% of stroke patients and is a predictor of long-term morbidity and mortality. In this study, we aim to determine the association between poststroke cognitive impairment and stroke recurrence risk, in patients with anterior versus posterior circulation intracranial stenosis. METHODS: This is a post-hoc analysis of the Stenting and Aggressive Medical Therapy for Preventing Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) trial. The primary predictor was poststroke cognitive function measured by Montreal Cognitive Assessment (MOCA) at 3-6 months and the primary outcome was recurrent ischemic stroke. We used univariate and multivariable cox-regression models to determine the associations between MOCA at 3-6 months and recurrent stroke. RESULTS: Of the 451 patients enrolled in SAMMPRIS, 393 patients met the inclusion criteria. The mean age of the sample (in years) was 59.5 ± 11.3, 62.6% (246 of 393) were men. Fifty patients (12.7%) had recurrent ischemic stroke during a mean follow up of 2.7 years. The 3-6 month MOCA score was performed on 351 patients. In prespecified multivariable models, there was an association between 3 and 6 month MOCA and recurrent stroke (hazard ratio [HR] per point increase .93 95% confidence interval [CI] .88-.99, P = .040). This effect was present in anterior circulation stenosis (adjusted HR per point increase .92 95% CI .85-0.99, P = .022) but not in posterior circulation artery stenosis (adjusted HR per point increase 1.00 95% .86-1.16, P = .983). CONCLUSIONS: Overall, we found weak associations and trends between MoCA at 3-6 months and stroke recurrence but more notable and stronger associations in certain subgroups. Since our study is underpowered, larger studies are needed to validate our findings and determine the mechanism(s) behind this association.

Imaging Patterns of Recurrent Infarction in the Mechanisms of Early Recurrence in Intracranial Atherosclerotic Disease (MyRIAD) Study.

Introduction: While much is known about recurrent clinical events in patients with intracranial atherosclerotic disease (ICAD), there is limited data on characteristics of recurrent infarcts. Methods: The NIH-funded MyRIAD prospective, observational study was designed to identify mechanisms of ischemia and predictors of recurrence in ICAD. Recurrent infarction was assessed on MRI at 6-8 weeks. We reviewed the DWI/ADC and FLAIR sequences in patients with recurrent stroke and characterized the number of infarcts, infarct location, size, and patterns based on whether they were borderzone (BZ), perforator (SC/P), cortical or territorial (C/T), and mixed. Temporal characteristics were delineated by ADC/FLAIR correlation. Results: Of the 89 patients with 6-8 weeks MRI, 22 (24.7%) had recurrent infarcts in the territory of the symptomatic artery. Recurrent infarcts were evident on DWI in 63.6% and single infarcts in 54.5%. The median recurrent infarct volume was 2.0 cm3 compared to median index infarct volumes of 2.5 cm3. A mixed infarct pattern was most common (40.9%), followed by borderzone (22.7%), cortical or territorial (27.3%), while only 9.1% were in a perforator artery distribution. Amongst those with a mixed pattern, 8/9 had a borderzone distribution infarct as part of their mixed infarct pattern. Conclusion: These findings provide novel data on the characteristics of early recurrent infarcts in patients with symptomatic ICAD.

A New Transcranial Doppler Scoring System for Evaluating Middle Cerebral Artery Stenosis.

BACKGROUND AND PURPOSE: Transcranial Doppler (TCD) criteria for cerebrovascular stenosis are only based on velocity with unsatisfactory positive predictive value (PPV) in previous studies. We refined a published scoring system that integrates several characteristics of TCD data in diagnosing middle cerebral artery (MCA) stenosis. METHODS: Using the TCD-digital subtraction angiography (DSA) database from Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis (SONIA) trial, velocity, spectrum pattern, diffuse ratio, and asymmetry ratio were assessed. The cutpoints were defined for each parameter and a point value was assigned to each category within that parameter. A summed score was calculated for each MCA. The accuracy was assessed for different cutpoints in predicting ≥50% MCA stenosis measured by DSA. Logistic regression and C-statistics were used for analysis. RESULTS: A total of 114 MCAs were included in vessel-based and 87 patients were included in patient-based analysis. Compared to the velocity-only cutpoints in SONIA, the score results in much improved PPV while negative predictive value (NPV) remains unchanged. The score based on mean velocity (score 0: <140 cm/s, score 3: ≥140 cm/s), spectrum pattern (score 0: no turbulence; score 1: mild turbulence; 2: significant turbulence), and asymmetry ratio (score 0: ratio <1.5, score 1: ratio 1.5-2; score 2: ratio ≥2.1) has the highest NPV while PPV remains favorable (PPV: 72% [95% CI 54-90%]; NPV: 84% [95% CI: 75-93%], area under curve [AUC]: .76 [95% CI: .66-.86]). CONCLUSIONS: The multiparameter scoring system incorporating several characteristics of TCD measures yielded higher PPV while maintaining high NPV compared with the single-parameter velocity criteria in diagnosing MCA ≥50% stenosis.

Flow limitation/obstruction with recovery breath (FLOW) event for improved scoring of mild obstructive sleep apnea without electroencephalography.

OBJECTIVE: Apnea/hypopnea index (AHI), especially without arousal criteria, does not adequately risk stratify patients with mild obstructive sleep apnea (OSA). We describe and test scoring reliability of an event, Flow Limitation/Obstruction With recovery breath (FLOW), representing obstructive airflow disruptions using only pressure transducer and snore signals available without electroencephalography. METHODS: The following process was used (i) Development of FLOW event definition, (ii) Training period and definition refinement, and (iii) Reliability testing on 10 100-epoch polysomnography (PSG) samples and two 100-sample tests. Twenty full-night in-laboratory baseline PSGs in OSA patients with AHI with ≥4% desaturations <15 were rescored for FLOW events, traditional hypopneas with desaturations, respiratory-related arousal (RRA) events (hypopneas with arousals and respiratory-effort related arousals) and non-respiratory arousals (NRA). RESULTS: Scoring of FLOW events in 100-epoch samples had good reliability with intraclass correlation (ICC) of 0.91. The overall kappa for presence of events on two sets of 100 sample events was 0.84 and 0.87 demonstrating good agreement. Moreover, 80% of RRA and 8% of NRA were concurrent with FLOW events. Furthermore, 56% of FLOW events were independent of RRA events. FLOW stratifies patients in traditional AHI categories with 50%/8% of AHI with ≥3% desaturations (AHI3) <5 and 12%/63% of AHI3 >5 in lowest/highest tertiles of AHI3 plus FLOW index. CONCLUSIONS: Scoring of FLOW after training is reliable. FLOW scores a high proportion of RRA and many currently unrepresented obstructive airflow disruptions. FLOW allows for stratification within the current normal-mild OSA category, which may better identify patients who will benefit from treatment.

To Treat or Not to Treat?

Background and Purpose- The 2015 updated US Food and Drug Administration alteplase package insert altered several contraindications. We thus explored clinical factors influencing alteplase treatment decisions for patients with minor stroke. Methods- An expert panel selected 7 factors to build a series of survey vignettes: National Institutes of Health Stroke Scale (NIHSS), NIHSS area of primary deficit, baseline functional status, previous ischemic stroke, previous intracerebral hemorrhage, recent anticoagulation, and temporal pattern of symptoms in first hour of care. We used a fractional factorial design (150 vignettes) to provide unconfounded estimates of the effect of all 7 main factors, plus first-order interactions for NIHSS. Surveys were emailed to national organizations of neurologists, emergency physicians, and colleagues. Physicians were randomized to 1 of 10 sets of 15 vignettes, presented randomly. Physicians reported the subjective likelihood of giving alteplase on a 0 to 5 scale; scale categories were anchored to 6 probabilities from 0% to 100%. A conjoint statistical analysis was applied. Results- Responses from 194 US physicians yielded 156 with complete vignette data: 74% male, mean age 46, 80% neurologists. Treatment mean probabilities for individual vignettes ranged from 6% to 95%. Treatment probability increased from 24% for NIHSS score =1 to 41% for NIHSS score =5. The conjoint model accounted for 25% of total observed response variance. In contrast, a model accounting for all possible interactions accounted for 30% variance. Four of the 7 factors accounted jointly for 58% of total relative importance within the conjoint model: previous intracerebral hemorrhage (18%), recent anticoagulation (17%), NIHSS (13%), and previous ischemic stroke (10%). Conclusions- Four main variables jointly account for only a small fraction (<15%) of the total variance related to deciding to treat with intravenous alteplase, reflecting high variability and complexity. Future studies should consider other variables, including physician characteristics.

Development of a high resolution MRI intracranial atherosclerosis imaging phantom.

BACKGROUND AND PURPOSE: Currently, there is neither a standard protocol for vessel wall MR imaging of intracranial atherosclerotic disease (ICAD) nor a gold standard phantom to compare MR sequences. In this study, a plaque phantom is developed and characterized that provides a platform for establishing a uniform imaging approach for ICAD. MATERIALS AND METHODS: A patient specific injection mold was 3D printed to construct a geometrically accurate ICAD phantom. Polyvinyl alcohol hydrogel was infused into the core shell mold to form the stenotic artery. The ICAD phantom incorporated materials mimicking a stenotic vessel and plaque components, including fibrous cap and lipid core. Two phantoms were scanned using high resolution cone beam CT and compared with four different 3 T MRI systems across eight different sites over a period of 18 months. Inter-phantom variability was assessed by lumen dimensions and contrast to noise ratio (CNR). RESULTS: Quantitative evaluation of the minimum lumen radius in the stenosis showed that the radius was on average 0.80 mm (95% CI 0.77 to 0.82 mm) in model 1 and 0.77 mm (95% CI 0.74 to 0.81 mm) in model 2. The highest CNRs were observed for comparisons between lipid and vessel wall. To evaluate manufacturing reproducibility, the CNR variability between the two models had an average absolute difference of 4.31 (95% CI 3.82 to 5.78). Variation in CNR between the images from the same scanner separated by 7 months was 2.5-6.2, showing reproducible phantom durability. CONCLUSIONS: A plaque phantom composed of a stenotic vessel wall and plaque components was successfully constructed for multicenter high resolution MRI standardization.

Management of Brain Arteriovenous Malformations: A Scientific Statement for Healthcare Professionals From the American Heart Association/American Stroke Association.

PURPOSE: The aim of this statement is to review the current data and to make suggestions for the diagnosis and management of both ruptured and unruptured brain arteriovenous malformations. METHODS: The writing group met in person and by teleconference to establish search terms and to discuss narrative text and suggestions. Authors performed their own literature searches of PubMed, Medline, or Embase, specific to their allocated section, through the end of January 2015. Prerelease review of the draft statement was performed by expert peer reviewers and by the members of the Stroke Council Scientific Oversight Committee and Stroke Council Leadership Committee. RESULTS: The focus of the scientific statement was subdivided into epidemiology; diagnosis; natural history; treatment, including the roles of surgery, stereotactic radiosurgery, and embolization; and management of ruptured and unruptured brain arteriovenous malformations. Areas requiring more evidence were identified. CONCLUSIONS: Brain arteriovenous malformations are a relatively uncommon but important cause of hemorrhagic stroke, especially in young adults. This statement describes the current knowledge of the natural history and treatment of patients with ruptured and unruptured brain arteriovenous malformations, suggestions for management, and implications for future research.

Principles of precision medicine in stroke.

The era of precision medicine has arrived and conveys tremendous potential, particularly for stroke neurology. The diagnosis of stroke, its underlying aetiology, theranostic strategies, recurrence risk and path to recovery are populated by a series of highly individualised questions. Moreover, the phenotypic complexity of a clinical diagnosis of stroke makes a simple genetic risk assessment only partially informative on an individual basis. The guiding principles of precision medicine in stroke underscore the need to identify, value, organise and analyse the multitude of variables obtained from each individual to generate a precise approach to optimise cerebrovascular health. Existing data may be leveraged with novel technologies, informatics and practical clinical paradigms to apply these principles in stroke and realise the promise of precision medicine. Importantly, precision medicine in stroke will only be realised once efforts to collect, value and synthesise the wealth of data collected in clinical trials and routine care starts. Stroke theranostics, the ultimate vision of synchronising tailored therapeutic strategies based on specific diagnostic data, demand cerebrovascular expertise on big data approaches to clinically relevant paradigms. This review considers such challenges and delineates the principles on a roadmap for rational application of precision medicine to stroke and cerebrovascular health.

Imaging of cerebrovascular disorders: precision medicine and the collaterome.

Imaging of stroke and neurovascular disorders has profoundly enhanced clinical practice and related research during the last 40 years since the introduction of computed tomography (CT) and magnetic resonance imaging (MRI) enabled mapping of the brain. We highlight recent advances in neurovascular imaging. We describe how the convergence of readily available data and new clinical trial paradigms will recast our methods for studying the neurovascular patient. The application of a precision medicine approach to the collaterome, a comprehensive synthesis of neurovascular pathophysiology, will entail novel methods for clinical trial randomization, collection of routine and clinical trial imaging results, data archiving, and analysis.

Hemodynamic Impact of Systolic Blood Pressure and Hematocrit Calculated by Computational Fluid Dynamics in Patients with Intracranial Atherosclerosis.

OBJECTIVE: Success in clinical trials of intracranial atherosclerosis (ICAS) is related to accurate identification of high-risk patients. Noninvasive computational fluid dynamics (CFD) of stenotic lesions may enhance therapeutic decision-making. We determined whether physiologic parameters change downstream cerebral hemodynamics in patients with ICAS. METHODS: Consecutive ICAS patients who underwent both CT angiography (CTA) and digital subtraction angiography were enrolled. CFD models were made using CTA source images. Inlet boundary conditions were defined using three ranges of systolic blood pressure (BP) (109.2, 158, and 225 mmHg) and hematocrit (27.3, 40.2, and 48.8). Ratios of pressure, shear strain rates (SSR), and flow velocity across the lesion were calculated using CFD simulations. A linear mixed model was used for the statistical analysis of repeated simulations. RESULTS: Among the 56 patients, 32 had moderate stenosis (50-69%) and 24 had severe stenosis (70-99%). A linear mixed model revealed that the ratio of pressure was predicted by systolic BP and stenosis group interaction (P = .036). These pressure decreases were associated with systolic BP (P < .001) and stenosis group (P < .001), but not with hematocrit (P = .337). Post-hoc analysis revealed that pressure decreases were more profound in the severe stenosis than the moderate stenosis group when comparing high and low systolic BP (P = .0108). Ratios of SSR and velocity were only associated in the stenosis group. CONCLUSIONS: Our study showed that systolic BP along with the degree of stenosis was associated with pressure decreases across stenotic lesions. Physiologic conditions may superimpose further changes in post-stenotic or downstream blood flow.

To treat or not to treat? Pilot survey for minor and rapidly improving stroke.

BACKGROUND AND PURPOSE: Minor strokes and rapidly improving stroke symptoms are frequent exclusions for intravenous tissue-type plasminogen activator. We explored factors influencing tissue-type plasminogen activator treatment decision for minor strokes/rapidly improving stroke symptoms. METHODS: A pilot survey, including 110 case scenarios, was completed by 17 clinicians from 2 academic medical centers. Respondents were asked whether they would treat each case with tissue-type plasminogen activator at 60 minutes after emergency department admission. Cases varied by (1) National Institutes of Health Stroke Scale score at treatment decision time, (2) symptom pattern over time (improvement or worsening and then improving), (3) type of neurological deficit (3 main domains: motor, visual/sensory/ataxia, and language/neglect), and (4) age/occupation (4 profiles). Logistic regression was used to predict probability of omission (pO). A binomial regression model was used to predict probability of treatment decision. RESULTS: Predicted probability of treatment decision was affected by National Institutes of Health Stroke Scale score (P<0.001) and age/occupation profiles (P<0.001) but not by symptom patterns (P=0.334). There were significant, albeit modest, main effects on probability of treatment decision for neurological domains. Responses were most likely omitted (P=0.027) for cases improvement pattern and language/neglect domain (pO=0.74; 95% confidence interval, 0.52-0.89) and with visual/sensory/ataxia domain (pO=0.74; confidence interval, 0.37-0.93) when compared with improvement pattern and motor domain (pO=0.17; confidence interval, 0.06-0.42) and to any worsening and then improving patterns (0.37