Time to Reset the Definition of Successful Revascularization in Endovascular Treatment of Acute Ischemic Stroke.

BACKGROUND: A 2013 consensus statement recommended the use of the modified Treatment In Cerebral Ischemia (mTICI) scale to evaluate angiographic revascularization after endovascular treatment (EVT) of acute ischemic stroke due to its higher inter-rater agreement and capacity of clinical outcome prediction. The current definition of successful revascularization includes the achievement of grades mTICI 2b or 3. However, mTICI 2b grade encompasses a large heterogeneity of revascularization states, and prior studies suggested that the magnitude of benefit derived from mTICI 2b and mTICI 3 does not seem to be equivalent. In a way to restrain the referred heterogeneity, Goyal et al. [J Neurointerv Surg 2014; 6: 83-86] proposed a revised mTICI scale that includes a 2c grade (rTICI). METHODS: Retrospective analysis of prospectively collected data from consecutive cases of EVT for anterior circulation large-vessel occlusion, performed between January 2015 and July 2017. Patients with mTICI 2b or 3 grades were reclassified according to the rTICI scale, and the outcomes between the 3 revascularization grades (rTICI 2b, 2c, 3) compared. RESULTS: Our study population of 226 patients (64 rTICI 2b, 30 rTICI 2c, 132 rTICI 3) has a mean age of 71 years, 48.2% males, median baseline NIHSS of 16 (13-19) and ASPECTS of 8 (7-9). The 3 revascularization grades are represented by homogeneous populations. Logistic regression analysis showed statistically significant higher rates of functional independence at 3 months (65.9 vs. 50.0%; adjusted OR 0.39, 95% CI 0.18-0.86), with lower rates of mortality (8.3 vs. 15.6%; adjusted OR 3.54, 95% CI 1.14-10.97) and intracranial hemorrhage (ICH) in rTICI 3 than 2b groups. When comparing rTICI 3 with 2c groups, there were only statistically significant differences in the total ICH rate (8.3 vs. 26.7%; adjusted OR 7.08, 95% CI 1.80-27.82) but not in symptomatic ICH. CONCLUSIONS: These results corroborate the scarce prior findings suggesting that patients with rTICI 2c grade should be reported separately, since they have similar outcomes to rTICI 3, and better than rTICI 2b patients. Therefore, we suggest resetting the angiographic revascularization endpoint to perfect revascularization (rTICI 2c or 3 grades), a target that neurointerventionalists should strive to achieve.

Picking the good apples: statistics versus good judgment in choosing stent operators for a multicenter clinical trial.

BACKGROUND AND PURPOSE: The Carotid Revascularization Endarterectomy Versus Stenting Trial was completed with a low stroke and death rate. A lead-in series of patients receiving carotid artery stenting was used to select the physician-operators for the study, where performance was evaluated by complication rates and by peer review of cases. Herein, we assess the potential contribution of statistical evaluation of complication rates. METHODS: The ability to discriminate between stent operators who can successfully meet the published guideline of <3% combined rate of stroke and death is calculated under the binomial distribution, based on a small consecutive case series (n=24 patients). RESULTS: A criterion of ≤2 stroke or death events among the 24 patients (<8% event rate) was required of operators. Setting such a high criterion, however, ensures an inability to exclude operators who cannot meet the criteria. In fact, if a good operator is defined as having a 2% event rate and a poor operator as a 6% event rate, even a series of 240 patients would (on average) still exclude 5.4% of the good operators and include 4.6% of the poor operators. CONCLUSIONS: The low periprocedural event rates in the trial suggest success in separating skillful operators from less skillful. However, it seems unlikely that statistical assessment of event rates in the lead-in contributed to successful selection, but rather successful selection was more likely because of peer review of subjective and other factors including patient volume and technical approaches. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT00004732.

Predictors of functional dependence despite successful revascularization in large-vessel occlusion strokes.

BACKGROUND AND PURPOSE: High revascularization rates in large-vessel occlusion strokes treated by mechanical thrombectomy are not always associated with good clinical outcomes. We evaluated predictors of functional dependence despite successful revascularization among patients with acute ischemic stroke treated with thrombectomy. METHODS: We analyzed the pooled data from the Multi Mechanical Embolus Removal in Cerebral Ischemia (MERCI), Thrombectomy Revascularization of Large Vessel Occlusions in Acute Ischemic Stroke (TREVO), and TREVO 2 trials. Successful revascularization was defined as thrombolysis in cerebral infarction score 2b or 3. Functional dependence was defined as a score of 3 to 6 on the modified Rankin Scale at 3 months. We assessed relationship of demographic, clinical, angiographic characteristics, and hemorrhage with functional dependence despite successful revascularization. RESULTS: Two hundred and twenty-eight patients with successful revascularization had clinical outcome follow-up. The rates of functional dependence with endovascular success were 48.6% for Trevo thrombectomy and 58.0% for Merci thrombectomy. Age (odds ratio, 1.04; 95% confidence interval, 1.02-1.06 per 1-year increase), National Institutes of Health Stroke Scale score (odds ratio, 1.08; 95% confidence interval, 1.02-1.15 per 1-point increase), and symptom onset to endovascular treatment time (odds ratio, 1.11; 95% confidence interval, 1.01-1.22 per 30-minute delay) were predictors of functional dependence despite successful revascularization. Symptom onset to reperfusion time beyond 5 hours was associated with functional dependence. All subjects with symptomatic intracranial hemorrhage had functional dependence. CONCLUSIONS: One half of patients with successful mechanical thrombectomy do not have good outcomes. Age, severe neurological deficits, and delayed endovascular treatment were associated with functional dependence despite successful revascularization. Our data support efforts to minimize delays to endovascular therapy in patients with acute ischemic stroke to improve outcomes. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT00318071, NCT01088672, and NCT01270867.

Multisociety consensus quality improvement guidelines for intraarterial catheter-directed treatment of acute ischemic stroke, from the American Society of Neuroradiology, Canadian Interventional Radiology Association, Cardiovascular and Interventional Radiological Society of Europe, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, European Society of Minimally Invasive Neurological Therapy, and Society of Vascular and Interventional Neurology.

PURPOSE: In this international multispecialty document, quality benchmarks for processes of care and clinical outcomes are defined. It is intended that these benchmarks be used in a quality assurance program to assess and improve processes and outcomes in acute stroke revascularization. MATERIALS AND METHODS: Members of the writing group were appointed by the American Society of Neuroradiology, Canadian Interventional Radiology Association, Cardiovascular and Interventional Radiological Society of Europe, Society of Cardiac Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, European Society of Minimally Invasive Neurological Therapy, and Society of Vascular and Interventional Neurology. The writing group reviewed the relevant literature from 1986 through February 2012 to create an evidence table summarizing processes and outcomes of care. Performance metrics and thresholds were then created by consensus. The guideline was approved by the sponsoring societies. It is intended that this guideline be fully updated in 3 years. RESULTS: In this international multispecialty document, quality benchmarks for processes of care and clinical outcomes are defined. These include process measures of time to imaging, arterial puncture, and revascularization and measures of clinical outcome up to 90 days. CONCLUSIONS: Quality improvement guidelines are provided for endovascular acute ischemic stroke revascularization procedures.

Computed tomography perfusion-based selection of patients for endovascular recanalization.

Intravenous and intraarterial recombinant tissue plasminogen activator remains underutilized in the treatment of acute ischemic stroke, largely due to strict adherence to the concept of the therapeutic time window for administration. Recent efforts to expand the number of patients eligible for thrombolysis have been mirrored by an evolution in endovascular recanalization technology and techniques. As a result, there is a growing need to establish efficient and reliable means by which to select candidates for endovascular intervention beyond the traditional criteria of time from symptom onset. Perfusion imaging techniques, particularly CT perfusion used in combination with CT angiography, represent an increasingly recognized means by which to identify those patients who stand to benefit most from endovascular recanalization. Additionally, CT perfusion and CT angiography appear to provide sufficient data by which to exclude patients in whom there is little chance of neurological recovery or a substantial risk of postprocedure symptomatic intracranial hemorrhage. The authors review the current literature as it pertains to the limitations of time-based selection of patients for intervention, the increasing utilization of endovascular therapy, and the development of a CT perfusion-based selection of acute stroke patients for endovascular recanalization. Future endeavors must prospectively evaluate the utility and safety of CT perfusion-based selection of candidates for endovascular intervention.

The adverse effects of flow-diverter stent-like devices on the flow pattern of saccular intracranial aneurysm models: computational fluid dynamics study.

BACKGROUND: Stent deployment across the aneurysmal neck has been established as one of the endovascular methods to treat intracranial aneurysms with or without coils. OBJECTIVE: The purpose is to study the possible adverse effects of deployment of the new flow-diverter stent-like devices (FD) on the flow characteristics of saccular aneurysm models. METHODS: Numerical simulations of the blood flow patterns in the artificial models of three aneurysms were studied. One model was designed without an FD stent, the second model with one FD stent, and the third model with two stents. Numerical simulation for incompressible laminar blood flow was conducted in the three artificial cerebral aneurysm models by means of computational fluid dynamics. RESULTS: There was a noticeable increase in the values of the circumferential pressure distributed on the walls of the aneurysm after stent deployment; this led to an increase the tension of the aneurysm surface and was considered to be an adverse effect. This pressure increase was further aggravated by the deployment of another stent. However, there is a beneficial effect of using FD stents, translating into the reduction of the flow velocity inside the aneurysm and wall shear stress at the inflow zone. This reduction decreases further with the deployment of another stent. CONCLUSION: Aneurysms become tenser after the deployment of one flow-diverter stent and (more tense still) after after the deployment of another stent. This principle should be kept in mind when choosing which group of aneurysms is the best candidate for such a treatment strategy. This study recommends deploying several FD stents during endovascular procedures until complete arrest of the blood flow occurs during the procedure; otherwise, the aneurysm may become tenser and dangerous if a slow blood flow jet still exists inside it at the end of the procedure.

Validation and Application for the Berlin Grading System of Moyamoya Disease in Adult Patients.

BACKGROUND: Traditional moyamoya disease (MMD) classification relies on morphological digital subtraction angiography (DSA) assessment, which do not reflect hemodynamic status, clinical symptoms, or surgical treatment outcome. OBJECTIVE: To (1) validate the new Berlin MMD preoperative symptomatology grading system and (2) determine the clinical application of the grading system in predicting radiological and clinical outcomes after surgical revascularization. METHODS: Ninety-six MMD patients (192 hemispheres) with all 3 investigations (DSA, magnetic resonance imaging [MRI], Xenon-CT) performed preoperatively at our institution (2007-2013) were included. Two clinicians independently graded the imaging findings according to the proposed criteria. Patients' modified Rankin Score (mRS) scores (preoperative, postoperative, last follow-up), postoperative infarct (radiological, clinical) were collected and statistical correlations performed. RESULTS: One hundred fifty-seven direct superficial temporal artery-middle cerebral artery bypasses were performed on 96 patients (66 female, mean age 41 yr, mean follow-up 4.3 yr). DSA, MRI, and cerebrovascular reserve capacity were independent factors associated hemispheric symptomatology (when analyzed individually or in the combined grading system). Mild (grade I), moderate (grade II), severe (grade III) were graded in 45, 71, and 76 hemispheres respectively; of which, clinical symptoms were found in 33% of grade I, 92% of grade II, 100% of grade III hemispheres (P < .0001). Two percent of grade I, 11% of grade II, 20% of grade III hemispheres showed postoperative radiological diffusion weighted image-positive ischemic changes or hemorrhage on MRI (P = .018). Clinical postoperative stroke was observed in 1.4% of grade II, 6.6% of grade III hemispheres (P = .077). The grading system also correlated well to dichotomized mRS postoperative outcome. CONCLUSION: The Berlin MMD grading system is able to stratify preoperative hemispheric symptomatology. Furthermore, it correlated with postoperative new ischemic changes on MRI, and showed a strong trend in predicting clinical postoperative stroke.

Assessing reperfusion and recanalization as markers of clinical outcomes after intravenous thrombolysis in the echoplanar imaging thrombolytic evaluation trial (EPITHET).

BACKGROUND AND PURPOSE: Reperfusion and recanalization have both been used as surrogate markers of clinical outcome in trials of stroke thrombolysis. We aimed to prove that the beneficial impact of recanalization with intravenous tissue plasminogen activator on clinical outcomes is attributable to reperfusion in the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET). METHODS: EPITHET was a prospective, randomized, placebo-controlled trial of intravenous tissue plasminogen activator in the 3- to 6-hour window. Reperfusion was defined as >90% reduction in magnetic resonance perfusion-weighted imaging lesion volume and recanalization as improvement of MR angiographic Thrombolysis In Myocardial Infarction grading by > or =2 points from baseline to Day 3 to 5. RESULTS: At Day 3 to 5, reperfusion and recanalization with intravenous tissue plasminogen activator were strongly correlated. Reperfusion was associated with improved clinical outcome independent of whether recanalization occurred. In contrast, recanalization was not associated with clinical outcome when reperfusion was included as a covariate in regression analyses. CONCLUSIONS: Reperfusion is a surrogate marker of clinical outcomes independent of recanalization based on the criteria applied in EPITHET. The impact of recanalization on clinical outcomes was attributable to reperfusion.

Reporting standards for angioplasty and stent-assisted angioplasty for intracranial atherosclerosis.

BACKGROUND AND PURPOSE: Intracranial cerebral atherosclerosis causes ischemic stroke in a significant number of patients. Technological advances over the past 10 years have enabled endovascular treatment of intracranial atherosclerotic stenosis. The number of patients treated with angioplasty or stent-assisted angioplasty for this condition is increasing. Given the lack of universally accepted definitions, the goal of this document is to provide consensus recommendations for reporting standards, terminology, and written definitions when reporting clinical and radiological evaluation, technique, and outcome of endovascular treatment using angioplasty or stent-assisted angioplasty for stenotic and occlusive intracranial atherosclerosis. SUMMARY OF REPORT: This article was written under the auspices of Joint Writing Group of the Technology Assessment Committee, Society of NeuroInterventional Surgery, Society of Interventional Radiology; Joint Section on Cerebrovascular Neurosurgery of the American Association of Neurological Surgeons and Congress of Neurological Surgeons; and the Section of Stroke and Interventional Neurology of the American Academy of Neurology. A computerized search of the National Library of Medicine database of literature (PubMed) from January 1997 to December 2007 was conducted with the goal to identify published endovascular cerebrovascular interventional data in stenotic intracranial atherosclerosis that could be used as benchmarks for quality assessment. We sought to identify those risk adjustment variables that affect the likelihood of success and complications. This document offers the rationale for different clinical and technical considerations that may be important during the design of clinical trials for endovascular treatment of intracranial stenotic and occlusive atherosclerosis. Included in this guidance document are suggestions for uniform reporting standards for such trials. These definitions and standards are primarily intended for research purposes; however, they should also be helpful in clinical practice and applicable to all publications. CONCLUSIONS: In summary, the definitions proposed represent recommendations for constructing useful research data sets. The intent is to facilitate production of scientifically rigorous results capable of reliable comparisons between and among similar studies. In some cases, the definitions contained here are recommended by consensus of a panel of experts in this writing group for consistency in reporting and publication. These definitions should allow different groups to publish results that are directly comparable.

Graft selection in cerebral revascularization.

Cerebral revascularization constitutes an important treatment modality in the management of complex aneurysms, carotid occlusion, tumor, and moyamoya disease. Graft selection is a critical step in the planning of revascularization surgery, and depends on an understanding of graft and regional hemodynamics, accessibility, and patency rates. The goal of this review is to highlight some of these properties.

Giant serpentine aneurysms.

Segal and McLaurin first described giant serpentine aneurysms, based on their distinct angiographic features, in 1977. These lesions are >or= 25 mm, partially thrombosed aneurysms with a patent, serpiginous vascular channel that courses through the aneurysm. There is a separate inflow and outflow of the aneurysm, of which the outflow channel supplies brain parenchyma in the territory of the parent vessel. Given the large size, unique neck, and dependent distal vessels, these aneurysms pose a technical challenge in treatment. Initial management has included surgical obliteration, but as endovascular techniques have evolved, treatment options too have expanded. In this review the authors attempt to summarize the existing body of literature on this rare entity and describe some of their institutional management strategies.

The Identification of Factors That Influence the Quality of Bypass Anastomosis and an Evaluation of the Usefulness of an Experimental Practical Scale in This Regard.

BACKGROUND: Several factors associated with interrupted and continuous suturing techniques affect the quality of bypass anastomosis. It is difficult to determine the impact of these factors during surgery. The primary objective of this study was to evaluate factors with the potential to influence the quality of bypass anastomosis using either interrupted or continuous suturing. A secondary objective was to evaluate the usefulness of a practical scale when comparing interrupted and continuous suturing techniques to improve bypass anastomosis. METHODS: Interrupted (n = 100) and continuous (n = 100) suturing techniques were used in 200 end-to-side bypasses to a depth of 3 cm and were assessed by 5 neurosurgeons. RESULTS: Vessel closing time (P < 0.001), stitch distribution (P < 0.001), intima-intima attachment (P < 0.001), and size of the orifice (P < 0.001) had a significant impact on the quality of the bypass regardless of the suturing technique used. The suturing technique used (interrupted or continuous) and positioning of the recipient vessel (vertical or horizontal) did not significantly influence the quality of anastomosis. Using multivariate analysis, the highest statistical significance with regard to bypass quality was attributed to the large size of the orifice and intimal attachment. CONCLUSIONS: There were advantages and disadvantages to both suturing techniques. The scale was a practical way to measure and improve performance.

Redefining 'success': a systematic review and meta-analysis comparing outcomes between incomplete and complete revascularization.

BACKGROUND: Conventionally, 'successful' endovascular thrombectomy (EVT) had been defined as achieving revascularization of thrombolysis in cerebral infarction (TICI)-2B or greater, rather than as 'complete' (TICI-3) versus 'incomplete' (TICI-2B) revascularization. PURPOSE: We performed a systematic review and meta-analysis of studies comparing clinical outcomes between patients with TICI-2B and TICI-3 revascularization. METHODS: Multiple databases were searched for relevant publications between January 2003 and March 2018. Studies comparing outcomes between the TICI-2B and the TICI-3 group of acute ischemic stroke (AIS) patients treated with EVT were included. Random effects meta-analysis was performed to evaluate outcomes among TICI-2B and TICI-3 groups. The following outcomes were assessed: good neurologic outcome (modified Rankin Scale (mRS)≤2 at day 90), mortality, and intracerebral hemorrhage (ICH). RESULTS: Twenty-one studies comprising 2747 patients were identified. Patients with TICI-2B revascularization had mRS≤2 at day 90 rates of 46% (391/847) compared with 66% (522/791) for TICI-3 patients (OR 0.46, 95% CI 0.37 to 0.57). Mortality rates were significantly higher in the TICI-2B group (78/570, 14%) than in the TICI-3 group (55/709, 8%) (OR 2.00, 95% CI 1.38 to 2.91). The ICH rates were also significantly higher in the TICI-2B group as compared with the TICI-3 group (31% [134/439] vs. 22% [108/490]; OR 2.20, 95% CI 1.47 to 3.30). CONCLUSIONS: Differences in all major outcome measures were markedly better in patients with complete versus incomplete but still 'successful' revascularization using prior thresholds, with ORs in the order of those seen in recent definitive trials comparing EVT to an intravenous tissue plasminogen activator.

Moyamoya disease: current concepts and future perspectives.

Moyamoya disease is an uncommon cerebrovascular disease that is characterised by progressive stenosis of the terminal portion of the internal carotid artery and its main branches. The disease is associated with the development of dilated, fragile collateral vessels at the base of the brain, which are termed moyamoya vessels. The incidence of moyamoya disease is high in east Asia, and familial forms account for about 15% of patients with this disease. Moyamoya disease has several unique clinical features, which include two peaks of age distribution at 5 years and at about 40 years. Most paediatric patients have ischaemic attacks, whereas adult patients can have ischaemic attacks, intracranial bleeding, or both. Extracranial-intracranial arterial bypass, including anastomosis of the superficial temporal artery to the middle cerebral artery and indirect bypass, can help prevent further ischaemic attacks, although the beneficial effect on haemorrhagic stroke is still not clear. In this Review, we summarise the epidemiology, aetiology, clinical features, diagnosis, surgical treatment, and outcomes of moyamoya disease. Recent updates and future perspectives for moyamoya disease will also be discussed.

Radiographic and clinical predictors of hemodynamic insufficiency in patients with athero-occlusive disease.

INTRODUCTION: Recent studies have shown that patients with increased oxygen extraction fraction (OEF) as measured by positron emission tomography (PET) have a substantially increased risk of stroke as a result of hemodynamic insufficiency. These patients appear to be ideal candidates for extracranial (EC)-intracranial (IC) bypass. The feasibility of this screening protocol, however, is controversial given PET's limited availability and high expense. A better understanding of the clinical factors that identify patients with potential hemodynamic insufficiency would streamline screening and improve cost-efficiency. METHODS: We performed a MEDLINE (1985-2007) database search for studies identifying clinical and radiographic predictors of hemodynamic failure and increased OEF on PET. We used the following key words, singly and in combination: "EC-IC bypass," "hemodynamic failure," and "misery perfusion." Additional studies were identified manually by scrutinizing references from manuscripts, major neurosurgical journals and texts, and personal files. Each study was reviewed for methodology, clinical criteria, and correlation with subsequent PET findings and stroke rates. A consensus was determined regarding the predictive value of each marker. RESULTS: Our literature search revealed 5 clinical and radiographic markers that have been used to identify patients with hemodynamic failure: orthostatic limb shaking, blurry vision on exposure to heat, leptomeningeal and ophthalmic collateral circulation on angiography, watershed infarction, and impaired vasodilatory response to acetazolamide. Orthostatic limb shaking is a rare finding but is predictive of hemodynamic failure and is associated with increased stroke risk. Blurry vision on exposure to heat is not predictive of increased stroke risk. Leptomeningeal and ophthalmic collateral circulation is a sensitive but not specific marker. Watershed infarction is highly sensitive and impaired vasodilatory response to acetazolamide is associated with increased OEF but may not be interchangeable. CONCLUSIONS: Orthostatic limb shaking, watershed infarction, collateral circulation, and impaired vasoreactivity to acetazolamide in patients with athero-occlusive disease may predict hemodynamic failure, increased OEF on PET, and high stroke rates. Recognition of these predictive markers may improve patient selection for surgical intervention, as such individuals appear to benefit from EC-IC bypass.

Usefulness of catheter angiography in the evaluation of common carotid artery origin occlusion.

Currently, catheter angiography is seldom used to evaluate occlusive cervical carotid disease after stroke. Despite the use of a variety of noninvasive tests, only cerebral angiography could document both carotid bifurcation patency and anterograde flow of the internal carotid artery intracranially in two patients with common carotid artery origin occlusion. These findings significantly influenced each patient's treatment. Common carotid artery origin occlusion represents one potential indication for catheter angiography.

Aneurysmal Subarachnoid Hemorrhage and Vasospasm.

Aneurysmal subarachnoid hemorrhage is potentially fatal and is associated with poor outcomes in many patients. Advances in neurosurgical and medical management of ruptured aneurysms have improved mortality rates in patients with aneurysmal subarachnoid hemorrhage. Surgical and endovascular interventions, such as external ventricular drain placement, aneurysm clipping, and endovascular coiling, have been developed over the past few decades. Patients with aneurysmal subarachnoid hemorrhage are also at risk for cerebral vasospasm and delayed cerebral ischemia. This article describes the diagnosis and treatment of aneurysmal subarachnoid hemorrhage, vasospasm, and cerebral ischemia. Concurrent medical considerations and ideas for future neuroinflammatory vasospasm research are also discussed.

Guidelines for evaluation and management of cerebral collateral circulation in ischaemic stroke 2017.

Collateral circulation plays a vital role in sustaining blood flow to the ischaemic areas in acute, subacute or chronic phases after an ischaemic stroke or transient ischaemic attack. Good collateral circulation has shown protective effects towards a favourable functional outcome and a lower risk of recurrence in stroke attributed to different aetiologies or undergoing medical or endovascular treatment. Over the past decade, the importance of collateral circulation has attracted more attention and is becoming a hot spot for research. However, the diversity in imaging methods and criteria to evaluate collateral circulation has hindered comparisons of findings from different cohorts and further studies in exploring the clinical relevance of collateral circulation and possible methods to enhance collateral flow. The statement is aimed to update currently available evidence and provide evidence-based recommendations regarding grading methods for collateral circulation, its significance in patients with stroke and methods under investigation to improve collateral flow.

Flow-assisted surgical technique in cerebrovascular surgery.

BACKGROUND: Cerebrovascular surgery is a technically challenging subspecialty of neurosurgery. A flow-based approach to cerebrovascular surgery can help to optimize neurosurgical interventions. METHODS: Direct intraoperative flow measurements can be made using a quantitative ultrasonic microvascular flow probe. In this article, we review the applications and utility of the FAST in aneurysm and EC-IC bypass surgery. RESULTS: In aneurysm surgery, flow measurements provide a quick and repeatable method to assess vessel patency and avoid complications related to vascular compromise. In bypass for flow augmentation in the setting of ischemia, flow measurements assess bypass patency and can assess the physiologic success of the bypass strategy. In bypass for flow replacement in the setting of planned vessel sacrifice, flow measurements can measure the flow deficit resulting from the vessel occlusion, assess the adequacy of in situ donor vessels, and confirm the ultimate adequacy of the bypass at the completion of surgery. CONCLUSIONS: The FAST strategy provides a useful approach to optimizing decision making and outcomes during cerebrovascular surgery.