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

Individualized interpretation for the clinical significance of fluid-attenuated inversion recovery vessel hyperintensity in ischemic stroke and transient ischemic attack: A systematic narrative review

Fluid-attenuated inversion recovery (FLAIR) vessel hyperintensity（FVH）refers to the hyperintensity corresponding to the arteries in the subarachnoid space. It is caused by critically slowed blood flow and is commonly encountered in patients with large artery steno-occlusions. Quite a few studies have focused on the clinical significance of FLAIR vessel hyperintensity in terms of its relationship to the prognosis of transient ischemic attack (TIA), baseline severity or infarction volume, early neurological deterioration or infarction growth, and functional outcomes in acute ischemic stroke (AIS). However, inconsistent or conflicting findings were common in these studies and caused confusion in the clinical decision-making process guided by this imaging marker. Through reviewing the available studies on the etiologic mechanism of FVH and investigating findings on its clinical significance in AIS and TIA, this review aims to elucidate the key factors for interpreting the clinical significance of FVH individually.

Collaterals and Elusive Ischemic Penumbra

As alternative blood supply routes, collateral blood vessels can play a crucial role in determining patient outcomes in acute and chronic intracranial occlusive diseases. Studies have shown that increased collateral circulation can improve functional outcomes and reduce mortality, particularly in those who are not eligible for reperfusion therapy. This article aims to discuss the anatomy and physiology of collateral circulation, describe current imaging tools used to measure collateral circulation, and identify the factors that influence collateral status.

Proximal hyper-intense vessel sign on initial FLAIR MRI in hyper-acute middle cerebral artery ischemic stroke: a retrospective observational study

BACKGROUND

A hyper-intense vessel sign on fluid attenuated inversion recovery magnetic resonance imaging (FHV) represents slow blood flow in the cerebral arteries.

PURPOSE

To investigate the relationship between the proximal FHV (pFHV) on initial magnetic resonance imaging (MRI) and the status of the culprit vessel (stenosis, obstruction) in hyper-acute strokes affecting the territory of the middle cerebral artery (MCA).

MATERIAL AND METHODS

The study participants consisted of 105 patients presenting to the emergency department (ED) with acute MCA infarction within 4.5 h of onset of symptoms. Patients underwent brain MRI within 45 min of arrival at the ED and angiography within 2 h of arrival. Culprit vessel status and presence of a pFHV on initial MRI were investigated retrospectively.

RESULTS

The pFHV was observed in 71/105 (67.6%) patients who presented with a hyper-acute MCA infarction. All patients with hyper-acute MCA infarction caused by internal carotid artery (90.6% caused by M1 occlusion, 92.9% caused by M2 occlusion) showed a pFHV on initial MRI. After logistic regression analysis, the presence of a pFHV showed significant positive correlation with large vessel occlusion (adjusted odds ratio [OR] 34.533, 95% confidence interval [CI] 9.781-121.926; P < 0.001). A pFHV was not associated with severe large vessel stenosis.

CONCLUSION

A pFHV is independently representative of the acute occlusion of intervention-eligible proximal arteries within the territory of the MCA. If a patient with a hyper-acute MCA infarction shows a pFHV, aggressive flow augmentation strategies and early activation of intervention team should be warranted for best patient outcome.

Association of FLAIR vascular hyperintensity and acute MCA stroke outcome changes with the severity of leukoaraiosis

PURPOSE

The clinical significance of FLAIR vascular hyperintensity (FVH), a marker of collateral circulation in ischaemic stroke, remains controversial. We hypothesised that the association between FVH and outcomes varies with the severity of leukoaraiosis (LA), another marker of collaterals, and that their combined significance may vary with time.

METHODS

We included 459 consecutive patients with middle cerebral artery (MCA) stroke. Proximal and distal FVHs were distinguished based on location. LA was divided into two grades, according to Fazekas scores of 0-2 and 3-6. Symptom-to-MRI time was divided into two categories: ≤ 14 days and ≥ 15 days.

RESULTS

We found no difference in FVH proportion according to LA grade. Multivariate analysis revealed that LA and FVH status were independently associated with unfavourable outcomes (modified Rankin scale ≥ 2) in patients with symptom-to-MRI times ≤ 14 days (P = 0.008), but not in those with symptom-to-MRI times ≥15 days (P = 0.61). In the group with symptom-to-MRI times ≤14 days, patients with LA 3-6 and FVH(+) (OR, 3.044; 95% CI, 1.116-8.305) were more likely to have unfavourable clinical outcomes compared with patients with LA 0-2 and FVH(+) but not compared with those with LA 0-2 and FVH(-) or LA 3-6 and FVH(-). In addition, FVH location did not influence the relationship between FVH and outcomes.

CONCLUSIONS

The association between FVH and outcomes was influenced by the degree of LA in the acute but not in the subacute and chronic stages of MCA infarction. FVH predicts clinical outcomes independently only in those with more extensive LA.

A prediction model of brain edema after endovascular treatment in patients with acute ischemic stroke

BACKGROUND

Clinical tools predicting brain edema after reperfusion therapy in acute ischemic stroke are scarce. We aim to develop a nomogram model to predict brain edema within the first 24 h after endovascular treatment (EVT) in the anterior cerebral circulation.

METHODS

A total of 199 patients were retrospectively identified in a single-center stroke registry. Brain edema was measured by midline shift (MLS). The associations between MLS and early neurologic outcomes were described. A nomogram predicting MLS was developed and internally validated. The nomogram was also compared with an available model using the area under the receiver operating characteristic curve (AUC) and decision curve analyses.

RESULTS

Overall, 87 patients (43.7%) had MLS. The patients with MLS ≥ 6 mm showed progressive neurological deterioration according to repeated measures analysis of variance. Each millimeter increase in MLS was strongly correlated with the presence of in-hospital death or forgoing treatment (Spearman's rho = 0.429, P < .001). Patients with brain edema were less likely to have functional independence at 3 months (19.5% vs. 46.8%, P < .001). A nomogram model including 24-h CT ASPECT scores and cisternal effacement, hypertension and complete recanalization showed a C-index of 0.874. This tool exhibited a higher AUC and higher net benefit than the available model.

CONCLUSIONS

This study showed a profound association between MLS and early neurologic outcomes. A nomogram model was developed to predict patients at risk of brain edema after EVT in the anterior cerebral circulation.

The Association between FLAIR Vascular Hyperintensity and Stroke Outcome Varies with Time from Onset

BACKGROUND AND PURPOSE

FLAIR vascular hyperintensity has been recognized as a marker of collaterals in ischemic stroke, but the impact on outcome is still controversial. We hypothesized that the association between FLAIR vascular hyperintensity and outcome varies with time.

MATERIALS AND METHODS

We included 459 consecutive patients with middle cerebral artery stroke and divided them into 3 groups by symptom-to-MR imaging time (group 1, ≤7 days; group 2, 8-14 days; group 3, ≥15 days). The FLAIR vascular hyperintensity score, ranging from 0 to 3 points, was based on territory distributions of different MCA segments. The associations between FLAIR vascular hyperintensity and outcome with time were analyzed qualitatively and quantitatively.

RESULTS

No patients underwent MR imaging within 6 hours of onset. The proportion of FLAIR vascular hyperintensity (+) and severe stenosis or occlusion of MCA was not significantly dependent on time. In groups 1 and 2, FLAIR vascular hyperintensity (+) was significantly associated with larger lesions, the prevalence of flow injury, and unfavorable outcome (mRS ≥ 2). There were no such associations in group 3. Multiple logistic regressions demonstrated that FLAIR vascular hyperintensity (+) was an independent risk factor for unfavorable outcome in group 2. Infarction volume tended to increase with the increase of the distal FLAIR vascular hyperintensity score in groups 1 and 2, while declining in group 3.

CONCLUSIONS

FLAIR vascular hyperintensity is associated with unfavorable outcome within 6 hours to 14 days of onset, while the wider distribution of distal FLAIR vascular hyperintensity may be favorable beyond 14 days of onset in MCA infarction. Symptom-to-MR imaging time should be considered when assessing the prognostic value of FLAIR vascular hyperintensity.

Significance of Magnetic Resonance Imaging (MRI) T2 Hyperintense Endo-Vessels Sign in Progressive Posterior Circulation Infarction

Background

MRI FLAIR hyperintense vessels sign (FHVs) is a special imaging marker that plays a key role in acute infarction imaging and diagnosis. However, FHVs have not been studied in the context of progressive posterior circulation infarction (PPCI), and little is known about the association of hyperintense endo-vessels sign (HEVs) on transverse section MRI with infarction. Thus, our objective here was to investigate the clinical significance of transverse MRI T2 HEVs in patients with PPCI.

Material/Methods

In this retrospective, case-control study, we enrolled 100 consecutive posterior circulation infarction patients. All the patients underwent head MRI examinations on the onset day and the seventh day after admission. Neurologic deficits of the patients were assessed by the National Institutes of Health Stroke Scale (NIHSS) scores upon admission and after 7 days. Infarction volume on DWI was compared.

Results

HEVs were detected in 25 of 37 patients in the PPCI group (67.6%) and 22 of 63 patients in the NPPCI group (34.9%). Logistic regression analysis showed that the proportion of HEVs in the PPCI group was higher than in the NPPCI group (P=0.007). Among all the patients, HEVs were detected in 15 of 18 patients (83.3%) with occlusion of the vertebral artery or basilar artery, and 17 of 23 (73.9%) showed severe stenosis. The proportion of vertebrobasilar artery occlusions in the PPCI group was higher than in the NPPCI group (P<0.05). MRI DWI showed that 20 patients had cerebellum infarction among 23 vertebral artery HEVs patients, and 14 patients had brainstem infarction among 15 basilar artery HEVs patients. All of the 9 vertebral and basilar artery HEVs patients had brainstem infarction. The increase in NIHSS scores from baseline to 7 days was significantly greater in patients with HEVs than in patients without HEVs in the PPCI group (P=0.002). The expansion of the infarction size from baseline to 7 days was significantly larger in patients with HEVs than in patients without HEVs in the PPCI group (P=0.037).

Conclusions

HEVs are frequently detected in patients with vertebrobasilar artery territory infarction, and they can be considered as a special imaging marker for vertebral artery and basilar artery occlusion and severe stenosis. HEVs can indicate whether or not posterior circulation infarction progresses and they may be an independent risk factor of PPCI.

Timely Visualization of the Collaterals Formed during Acute Ischemic Stroke with Fe3 O4 Nanoparticle-based MR Imaging Probe

Ischemic stroke is one of the major leading causes for long-term disability and mortality. Collateral vessels provide an alternative pathway to protect the brain against ischemic injury after arterial occlusion. Aiming at visualizing the collaterals occurring during acute ischemic stroke, an integrin α_v β₃ -specific Fe₃ O₄ -Arg-Gly-Asp (RGD) nanoprobe is prepared for magnetic resonance imaging (MRI) of the collaterals. Rat models are constructed by occluding the middle cerebral artery for imaging studies of cerebral ischemia and ischemia-reperfusion on 7.0 Tesla MRI using susceptibility-weighted imaging sequence. To show the binding specificity to the collaterals, the imaging results acquired with the Fe₃ O₄ -RGD nanoprobe and the Fe₃ O₄ mother nanoparticles, respectively, are carefully compared. In addition, an RGD blocking experiment is also carried out to support the excellent binding specificity of the Fe₃ O₄ -RGD nanoprobe. Following the above experiments, cerebral ischemia-reperfusion studies show the collateral dynamics upon reperfusion, which is very important for the prognosis of various revascularization therapies in the clinic. The current study has, for the first time, enabled the direct observation of collaterals in a quasi-real time fashion and further disclosed that the antegrade flow upon reperfusion dominates the blood supply of primary ischemic tissue during the early stage of infarction, which is significantly meaningful for clinical treatment of stroke.

Infarct morphology assessment in patients with carotid artery/middle cerebral artery occlusion using fast fluid-attenuated inversion recovery (FLAIR) vascular hyperintensity (FVH)

We aim to evaluate the value of fast fluid-attenuated inversion recovery (FLAIR) vascular hyperintensity (FVH) in assessing infarct morphology in patients with symptomatic internal carotid artery (ICA) or middle cerebral artery (MCA) occlusions. Magnetic resonance (MR) diffusion-weighted imaging (DWI) FLAIR sequences, and carotid/cerebral magnetic resonance angiography of 102 patients with symptomatic ICA or MCA occlusions were evaluated. The location and score of FVH were determined using Olindo’s method; patients were classified as having Low or High FVHs based on FVH score, and either Distal or Proximal FVH based on FVH location. The differences between infarct morphologies were analyzed. FVH were detectable in 62 patients with High FVH and in 40 patients with Low FVHs based on the Olindo’s scale. There were no statistically significant differences in age, gender, hypertension, diabetes, hyperlipidemia, smoking history, and vascular occlusive site between High and Low FVHs patients, except for infarct morphology (P<0.01). Patients with Distal FVH presented with significant (P<0.01) perforating artery and border zone infarcts, whereas those with Proximal FVH had significant (P<0.01) large territorial infarcts. The scores and locations of FVH could be a predictive imaging marker for infarct morphology in patients with symptomatic ICA or MCA occlusion.

Collateral vessels on magnetic resonance angiography in endovascular-treated acute ischemic stroke patients associated with clinical outcomes

Purpose

Collateral vessels were considered to be related with outcome in endovascular-treated acute ischemic stroke patients. This study aimed to evaluate whether the collateral vessels on magnetic resonance angiography (MRA) could predict the clinical outcome.

Materials and Methods

Acute stroke patients with internal carotid artery or middle cerebral artery occlusion within 6 hours of symptom onset were included. All patients underwent MRI and received endovascular treatment. The collateral circulations at the Sylvian fissure and the leptomeningeal convexity were evaluated. The preoperative and postoperative infarct volume was measured. The clinical outcome was evaluated by mRS score at 3 months after stroke.

Results

Of 55 patients, Cases with insufficient collateral circulation at the Sylvian fissure and leptomeningeal convexity showed that the NIHSS score at arrival and preoperative infarct volume were significantly lower in mRS score of 0–2 (both P < 0.05) than mRS score of 3–6. Multivariate testing revealed age and collateral status at the leptomeningeal convexity were independent of the clinical outcome at 3 months after stroke (odds ratio (95% confidence interval): 1.094 (1.025–1.168); 9.542 (1.812–50.245) respectively). The change of infarct volume in the group with mRS score of 0–2 was smaller than that with mRS score of 3–6. While multivariate logistic models showed that postoperative infarct volume was non-significant in predicting the clinical outcome after stroke.

Conclusions

The extent of collateral circulation at the leptomeningeal convexity may be useful for predicting the functional recovery while the relationship between postoperative infarct volume and clinical outcome still requires for further study.

Cerebral collateral circulation in experimental ischemic stroke

Cerebral collateral circulation is a subsidiary vascular network, which is dynamically recruited after arterial occlusion, and represents a powerful determinant of ischemic stroke outcome. Although several methods may be used for assessing cerebral collaterals in the acute phase of ischemic stroke in humans and rodents, they are generally underutilized. Experimental stroke models may play a unique role in understanding the adaptive response of cerebral collaterals during ischemia and their potential for therapeutic modulation. The systematic assessment of collateral perfusion in experimental stroke models may be used as a “stratification factor” in multiple regression analysis of neuroprotection studies, in order to control the within-group variability. Exploring the modulatory mechanisms of cerebral collaterals in stroke models may promote the translational development of therapeutic strategies for increasing collateral flow and directly compare them in term of efficacy, safety and feasibility. Collateral therapeutics may have a role in the hyperacute (even pre-hospital) phase of ischemic stroke, prior to recanalization therapies.

Sulcal effacement with preserved gray-white junction: a sign of reversible ischemia

BACKGROUND AND PURPOSE

Sulcal effacement with preserved underlying gray-white matter junction (isolated sulcal effacement [ISE]) in acute ischemic stroke may not represent irreversible parenchymal injury. We aimed to evaluate the frequency and significance of ISE in patients with large vessel occlusion acute ischemic stroke.

METHODS

Consecutive acute ischemic stroke patients with middle cerebral artery M1 or internal carotid artery terminus occlusions who underwent computed tomography angiogram/perfusion followed by intra-arterial therapy were screened for ISE.

RESULTS

Out of the 568 patients who underwent intra-arterial therapy between March 2011 and September 2014, 108 fulfilled inclusion criteria. ISE was present in 8 (7.4%) patients (age 55.7±10.5 years, 6 female, baseline National Institutes of Health Stroke Scale 16.1±3.8, 5 middle cerebral artery-M1, and 3 internal carotid artery terminus occlusions). Computed tomography angiogram revealed engorged/dilated leptomeningeal vessels obliterating the sulci within the areas of effacement, whereas computed tomography perfusion indicated normal-to-increased cerebral blood volume and prolonged Tmax in all patients. Modified treatment in cerebral ischemia (mTICI) 2b-3 reperfusion was achieved in all patients. Follow-up imaging confirmed no infarct in the ISE area in all patients, and 5 (62%) had modified Rankin Scale 0 to 2 at 3 months.

CONCLUSIONS

Sulcal effacement with preserved gray-white delineation is occasionally visualized in patients with proximal occlusion strokes, relates to robust leptomeningeal collaterals, and indicates preserved underlying parenchyma. ISE should not be used to exclude patients from thrombectomy.

A novel magnetic resonance imaging approach to collateral flow imaging in ischemic stroke

OBJECTIVE

Dedicated magnetic resonance (MR) imaging (MRI) sequences for evaluation of collaterals can be generated using MR perfusion (MRP) source data. We compared a novel collateral flow imaging technique with digital subtraction angiography (DSA) for determining collateral circulation in acute stroke and evaluated the ability of MR-based collateral flow maps to predict outcomes after recanalization therapy.

METHODS

Consecutive patients who were candidates for endovascular treatment were enrolled. A collateral flow map derived from MRP source data was generated by manual or automatic postprocessing. Collateral grading based on the collateral flow map was performed and compared with grading based on DSA. Clinical and radiological outcomes were evaluated according to MR-based collateral grading and early reperfusion (ER) status.

RESULTS

There was good correlation between MRI-based and DSA-based collateral grades (weighted κ-coefficient = 0.70). Collateral status and achievement of ER were the 2 main determinants of a favorable functional outcome and neurological improvement, in addition to infarct growth. Regardless of achievement of ER, better collaterals were significantly associated with a lower modified Rankin score at day 90 (p < 0.001 for trend in both ER(-) and ER(+) ). Most symptomatic intracranial hemorrhages occurred in patients with a poor collateral grade and ER(+) , whereas no patient with excellent collaterals suffered symptomatic intracranial hemorrhage or died.

INTERPRETATION

MRI techniques to assess collaterals are rapidly being developed, and may provide insight into collateral perfusion. The combination of collateral images derived from pretreatment MRP source data and reperfusion status is a robust predictor of outcomes in acute ischemic stroke.

What is meant by "TICI"?

BACKGROUND

In 2003, Higashida et al proposed the Thrombolysis In Cerebral Infarction scale to evaluate angiographic intracranial flow. Our aim is to review how subsequently published studies define TICI.

MATERIALS AND METHODS

We used the ISI Web of Knowledge and SciVerse Scopus databases to search for "TICI" and "thrombolysis in cerebral infarction" and for articles that cited the original TICI paper from January 2004 through May 2012. Articles were categorized according to their definition of the TICI categories, typically grades 0-4, with grade 2 (partial reperfusion) subdivided into 2a and 2b, and rate of contrast entry to the perfused area. In addition, we catalogued the type of redefinitions of TICI subcategory 2 and additions of new categories.

RESULTS

Of 236 articles screened, 74 were included. Eight (11%) explicitly followed the TICI scale as originally defined. Thirty-seven (50%) cited Higashida but did not define their scale. Fifteen (21%) used and explained modified scales. Thirteen (18%) used the term TICI, but did not define the scale and did not cite Higashida. Eighteen (24%) specified a 2a subcategory. Nine defined grade 2a as <67% filling, 6 defined it as <50%, and 3 did not offer a percentage. Two studies added a 2c subcategory. Fifty-two (70%) used a cutoff level to define "successful reperfusion." Of these, 65% used TICI ≥2, 33% used TICI ≥2b, and 2% used TICI = 3.

CONCLUSIONS

There is substantial variability in the definition and/or application of the TICI scale in the literature. This variability could considerably impact our understanding of results of revascularization studies.

Fluid-attenuated inversion recovery hyperintense vessels in posterior cerebral artery infarction

Background

Fluid-attenuated inversion recovery hyperintense vessels (FHVs) are known to reflect stagnant or slow blood flow within the cerebral artery. FHVs are frequently observed in patients with acute cerebral infarction accompanied by arterial occlusion or significant stenosis of the anterior cerebral circulation. However, FHVs have not been studied in the context of posterior cerebral circulation. Thus, we investigated the prevalence of FHVs and its clinical significance in patients with acute posterior cerebral artery (PCA) territory infarction.

Methods

In this retrospective study, consecutive patients with PCA territory infarction who underwent MRI within 1 week after symptom onset were enrolled. Two neurologists who were blinded to the angiographic findings read the images and determined the presence of FHVs. Afterwards, FHVs were graded according to the extent (subtle or prominent) and location (proximal or distal) of the hyperintense vessels. Neurologic deficits of the patients were assessed by the National Institutes of Health Stroke Scale (NIHSS) upon admission and after 5 days. The clinical outcome between patient groups based on FHVs grading was compared using the NIHSS. Among the patients with PCA occlusion, infarction volume on the diffusion-weighted image was compared between the two groups with and without distal FHVs.

Results

FHVs were observed in 25 of the 87 patients (28.7%) with PCA territory infarction and in 65.7% of the 35 patients with significant arterial stenosis (10 patients) or occlusion (25 patients) in the posterior cerebral circulation. Among the 18 patients with PCA occlusion, the NIHSS score was significantly improved in patients with distal FHVs compared to the others (2.00 ± 2.18 vs. 0.56 ± 1.01, p = 0.04). The infarction volume was smaller in the distal FHV group than in the others (8.3 ± 8.7 vs. 16.8 ± 17.6 ml), but the difference was not statistically significant.

Conclusions

FHVs are detected in patients with PCA territory infarction, especially in those with an occlusive lesion in the PCA. FHVs can be used as an imaging marker of PCA occlusion. Although this study showed a better clinical improvement in patients with distal FHVs, further study is needed to elucidate the clinical meaning of FHVs in PCA infarction.