Pattern of collaterals, type of infarcts, and haemodynamic impairment in carotid artery occlusion

An Illustrative Case of Bilateral Internal Carotid Artery Occlusion Concomitant with Aneurysm of the Obstructed ICA Reconstituted via Collaterals: Emphasizing the Role of Rescue Collaterals in Decision-Making

In patients with bilateral internal carotid artery (ICA) obstruction, the basilar and ophthalmic arteries become the most critical arteries for brain perfusion, and the location of aneurysm formation may be associated with increased wall shear stress induced by compromised carotid circulation. Consideration of collateral routes may have an impact on therapeutic decisions for patients undergoing extracranial to intracranial (EC-IC) bypass and aneurysm surgery. We report a rare case of a young woman with bilateral ICA occlusion simultaneous with dissecting aneurysm of the obstructed ICA reconstituted via collaterals, emphasizing the functional value of collaterals and therapeutic strategy. We present a young woman with angiographic evidence of cerebrovascular early atherosclerotic disease. A young patient was found to have bilateral ICA occlusion and dissecting aneurysm of the obstructed ICA. A large fusiform aneurysm was clipped. Then, an anastomosis was performed from the left superficial temporal to the M3 segment of the middle cerebral artery. The patient's postoperative course was uneventful, and she was discharged to rehabilitation with no residual sequelae. This case illustrates a rare case of bilateral ICA occlusions, presented with robust collaterals, and dissecting aneurysm of the obstructed ICA reconstituted via collaterals. We also demonstrate excellent surgical clipping of a challenging ICA aneurysm and cerebral bypass surgery.

Effect of the addition of 123I-iomazenil single-photon emission computed tomography to brain perfusion single-photon emission computed tomography on the detection accuracy of misery perfusion in adult patients with ischemic moyamoya disease

OBJECTIVE

The present prospective study aimed to determine whether the addition of ¹²³I-iomazenil (IMZ) single-photon emission computed tomography (SPECT) to brain perfusion SPECT could improve the detection accuracy of misery perfusion on positron emission tomography (PET) in adult patients with ischemic moyamoya disease (MMD).

METHODS

Oxygen extraction fraction (OEF) and brain perfusion were assessed using ¹⁵O gas PET and N-isopropyl-p-[¹²³I]-iodoamphetamine (IMP) SPECT, respectively, in 137 patients. IMZ SPECT was also performed. Regions of interest (ROIs) were automatically placed in the five middle cerebral artery (MCA) territories ipsilateral to the symptomatic cerebral hemisphere and in the contralateral posterior cerebral artery territory using a three-dimensional stereotaxic ROI template. The radioactive count of the MCA ROI to the contralateral posterior cerebral artery ROI was calculated on IMP SPECT (relative SPECT-IMP uptake) and IMZ SPECT (relative SPECT-IMZ uptake). The relative SPECT-IMZ uptake to the relative SPECT-IMP uptake was also calculated (relative SPECT-IMZ/IMP uptake). Of the five MCA ROIs in the symptomatic cerebral hemisphere in each patient, the ROI with the highest PET-OEF value (one ROI per patient) was selected for analysis.

RESULTS

Significant correlations were observed between the PET-OEF and relative SPECT-IMP uptake (correlation coefficient, - 0.683) and relative SPECT-IMZ/IMP uptake (correlation coefficient, 0.875). The area under the receiver operating characteristic curve for detecting misery perfusion (PET-OEF > 51.3%) was significantly greater for the relative SPECT-IMZ/IMP uptake than for the relative SPECT-IMP uptake (difference between areas, 0.080; p = 0.0004). The sensitivity, specificity, and positive- and negative-predictive values for the relative SPECT-IMZ/IMP uptake for detecting misery perfusion were 100%, 92%, 81%, and 100%, respectively. The specificity and positive-predictive value were significantly greater for the relative SPECT-IMZ/IMP uptake than for the relative SPECT-IMP uptake.

CONCLUSIONS

The addition of IMZ SPECT to brain perfusion SPECT improves the detection accuracy of misery perfusion on PET in adult patients with ischemic MMD.

Non-association of stroke risk with intracranial hemodynamic steal in patients with symptomatic internal carotid artery occlusions

OBJECTIVES

Paradoxical intracranial hemodynamic steal (IHS) is known in patients having persistent proximal arterial occlusions and is linked with early neurological worsening. However, stroke risk specific to symptomatic internal carotid artery occlusions (SICAO) having paradoxical IHS is unknown. Therefore, we aimed to investigate the association of paradoxical IHS in SICAO patients with stroke recurrence during a one-year follow-up.

MATERIALS AND METHODS

We prospectively enrolled adult patients having SICAO with a recent history of ischemic events. Steal magnitude (SM) to classify patients in IHS and non-IHS categories was evaluated by a breath-holding test using bilateral transcranial doppler (TCD). Patients were prescribed optimal medical therapy and followed up for one year for any ischemic stroke/TIA/cardiovascular death.

RESULTS

36 SICAO patients, mean age of 56 years, were assessed using TCD at median 22.5 days (Interquartile range, IQR= 9-42), and 11 (30.6%) had paradoxical IHS with median SM 12% (IQR= 6%-18%). On follow-up, 7 (19.4%) patients had event recurrence and its association with IHS was non-significant (IHS vs non-IHS, 18.2% vs 20%; Log-rank statistics=0.006; P=0.940). On Cox regression analysis, event recurrence was independently associated with the presence of significant contralateral stenosis only (regression coefficient= 2.237; P= 0.012; 95% CI= 1.63-53.89).

CONCLUSIONS

IHS prevalence among SICAO is high. However, paradoxical IHS was not associated with an increased risk of stroke in SICAO. Therefore, the presence of paradoxical IHS in SICAO may be considered a transit state and does not necessarily imply an increased risk of stroke.

Internal carotid artery patency after mechanical thrombectomy for stroke due to occlusive dissection: Impact on outcome

Introduction:

Internal carotid artery dissection (ICAD) is a rare cause of acute ischemic stroke with large vessel occlusion (AIS-LVO). We aimed investigating the impact on outcome of internal carotid artery (ICA) patency after mechanical thrombectomy (MT) for AIS-LVO due to occlusive ICAD.

Patients and methods:

We included consecutive patients with AIS-LVO due to occlusive ICAD treated with MT from January 2015 to December 2020 in three European stroke centers. We excluded patients with unsuccessful intracranial reperfusion after MT (modified Thrombolysis in Cerebral Infarction (mTICI) score < 2b). We compared 3-month favorable clinical outcome rate, defined as a modified Rankin scale (mRS) score ⩽2, according to ICA status (patency vs occlusion) at the end of MT and at 24-h follow-up imaging, using univariate and multivariable models.

Results:

Among 70 included patients, ICA was patent in 54/70 (77%) at the end of MT, and in 36/66 (54.5%) patients with 24-h follow-up imaging. Among patients with ICA patency at the end of MT, 32% presented ICA occlusion at 24-h control imaging. Favorable 3-month outcome occurred in 41/54 (76%) patients with ICA patency post-MT and in 9/16 (56%) patients with occluded ICA post-MT ( p = 0.21). Rates of favorable outcome were significantly higher in patients with 24-h ICA patency compared to patients with 24-h ICA occlusion (32/36 [89%] vs 15/30 [50%]), with an adjusted odds ratio of 4.67 (95% CI: 1.26–17.25).

Discussion and conclusion:

Obtaining sustained (24-h) ICA patency after MT could be a therapeutic target for improving functional outcome in patients with AIS-LVO due to ICAD.

Therapeutic Management of Ocular Ischemia in Takayasu's Arteritis: A Case-Based Systematic Review

Background

Takayasu’s arteritis (TA) is a rare, chronic granulomatous large-vessel vasculitis that can lead to ocular ischemia. Ocular outcomes after therapeutic management in TA remain largely unknown. We herein conduct a case-based systematic review to address the current treatment options in this particular cohort.

Methods

PubMed, Medline, and EMBASE databases were searched pertaining to ocular outcomes after systemic treatment in TA. Studies reporting ocular examinations before and after treatment in TA patients with ocular ischemia were included. Clinical characteristics, therapies, ocular outcomes, and complications were recorded.

Results

A 29-year-old woman with newly diagnosed TA showed dramatic regression of Takayasu’s retinopathy (TR) following balloon angioplasty. Optical coherence tomography angiography (OCTA) was used as a novel strategy for subsequent follow-up. A total of 117 eyes of 66 patients with a median age of 27 years were included for systematic review. TR was the most common ocular manifestation. Oral steroids were prescribed in nearly all patients (n = 65), followed by the use of methotrexate and antiplatelet therapy. Of the patients, 65.8% and 34.2% underwent open surgery and endovascular procedure, respectively. The median follow-up period was 12 weeks (interquartile range 8–33.5). Surgical therapy showed better ocular improvement (including visual and imaging responses) in both acute and chronic vision loss, along with fewer complications than medical therapy alone. In the surgical group, the visual prognosis was significantly better in patients with initial visual acuity better than 20/200 (p = 0.03) and those who underwent surgery before stage III TR (p = 0.01). Ocular outcomes were equivalent in the two surgical approaches.

Conclusion

Clinicians should be familiar with ophthalmic manifestations of this potentially treatable complication in TA. Compared with medical therapy alone, surgical intervention might be a better choice for both acute and chronic vision loss. Surgery is best recommended before the onset of irreversible ischemia to the globe. A combined regimen (oral steroids, immunosuppressants, and antiplatelet drugs) might be effective for those with surgical contradictions or reluctance to an invasive procedure. Physicians should be aware of the importance of ocular examinations, including OCTA, during the diagnosis and follow-up in TA.

Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

Endovascular Treatment of Acute Ischemic Stroke

PURPOSE OF REVIEW

This article reviews the actual indications for mechanical thrombectomy in patients with acute ischemic stroke and how the opportunities for endovascular therapy can be expanded by using the concept of clinical-imaging or perfusion-imaging mismatch (as a surrogate for salvageable tissue) rather than time of ischemia.

RECENT FINDINGS

Six randomized controlled trials undoubtedly confirmed the benefits of using endovascular thrombectomy on the clinical outcome of patients with stroke with large vessel occlusion within 6 hours from symptom onset compared with those receiving only standard medical care. In a meta-analysis of individual patient data, the number needed to treat with endovascular thrombectomy to reduce disability by at least one level on the modified Rankin Scale for one patient was 2.6. Recently, the concept of "tissue window" versus time window has proved useful for selecting patients for mechanical thrombectomy up to 24 hours from symptom onset. The DAWN (DWI or CTP Assessment With Clinical Mismatch in the Triage of Wake-Up and Late Presenting Strokes Undergoing Neurointervention) trial included patients at a median of 12.5 hours from onset and showed the largest effect in functional outcome ever described in any acute stroke treatment trial (35.5% increase in functional independence). In DEFUSE 3 (Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution 3), patients treated with mechanical thrombectomy at a median of 11 hours after onset had a 28% increase in functional independence and an additional 20% absolute reduction in death or severe disability.

SUMMARY

For patients with acute ischemic stroke and a large vessel occlusion in the proximal anterior circulation who can be treated within 6 hours of stroke symptom onset, mechanical thrombectomy with a second-generation stent retriever or a catheter aspiration device should be indicated regardless of whether the patient received treatment with intravenous (IV) recombinant tissue plasminogen activator (rtPA) in patients with limited signs of early ischemic changes on neuroimaging. Two clinical trials completely disrupted the time window concept in acute ischemic stroke, showing excellent clinical outcomes in patients treated up to 24 hours from symptom onset. Time of ischemia is, on average, a good biomarker for tissue viability; however, the window of opportunity for treatment varies across different individuals because of a range of compensatory mechanisms. Adjusting time to the adequacy of collateral flow leads to the concept of tissue window, a paradigm shift in stroke reperfusion therapy.

Semiautomatic cerebrovascular territory mapping based on dynamic ASL MR angiography without vessel-encoded labeling

PURPOSE

Characterizing vessel territories can provide crucial information for evaluation of cerebrovascular disorders. In this study, we present a novel postprocessing pipeline for vascular territorial imaging of cerebral arteries based on a noncontrast enhanced time-resolved 4D magnetic resonance angiography (MRA).

METHODS

Eight healthy participants, 1 Moyamoya patient, and 1 arteriovenous malformations patient were recruited. Territorial segmentation and relative blood flow rate calculations of cerebral arteries including left and right middle cerebral arteries and left and right posterior cerebral arteries were carried out based on the 4D MRA-derived arterial arrival time maps of intracranial vessels.

RESULTS

Among healthy young subjects, the average relative blood flow rate values corresponding to left and right middle cerebral arteries and left and right posterior cerebral arteries were 35.9 ± 5.9%, 32.9 ± 7.5%, 15.4 ± 3.8%, and 15.9 ± 2.5%, respectively. Excellent agreement was observed between relative blood flow rate values obtained from the proposed 4D MRA-based method and reference 2D phase contrast MRI. Abnormal cerebral circulations were visualized and quantified on both patients using the developed technique.

CONCLUSION

The vascular territorial imaging technique developed in this study allowed for the generation of territorial maps with user-defined level of details within a clinically feasible scan time, and as such may provide useful information to assess cerebral circulation balance in different pathologies.

Bilateral retinal artery occlusions with carotid artery occlusions-ocular and cerebral hemodynamic changes

Purpose

To introduce a case of bilateral retinal artery occlusions with carotid occlusions to achieve a fuller understanding of hemodynamic flow changes and the origin of emboli.

Observations

A 58-year-old male presented with binocular vision loss. Fundus examination revealed bilateral retinal whitening with multiple emboli. Cherry red spot was surrounded and shaped by white edematous ischemic retina. FAG showed retinal refilling but not to the macula and choroidal background. Carotid arteriography and color Doppler images demonstrated bilateral carotid occlusions. CT angiography showed compensatory flows perfused from vertebral arteries for the brain. Orbital color Doppler images revealed bilateral reversed ophthalmic flows indicating another compensatory flow arising from external carotid/ophthalmic collaterals to both eyes.

Conclusions and Importance

Reversed ophthalmic flow indicates the presence of external carotid/ophthalmic collaterals as the source of ocular blood supply and the origin of emboli. In this case, all the embolic, hemodynamic, and serotonin mechanisms may be responsible for the pathogenesis. RAO with multiple emboli is an important sign warning critical flow changes of carotid occlusions.

Retinal arterial occlusion with multiple retinal emboli and carotid artery occlusion disease. Haemodynamic changes and pathways of embolism

Objective

To introduce a special subgroup, retinal artery occlusion (RAO) with multiple emboli, which is highly associated with ipsilateral carotid artery occlusion disease (CAOD).

Methods and analysis

This is a cohort study. Cases of RAO with multiple retinal emboli were consecutively enrolled. All patients underwent at least one of the carotid/cerebral evaluations: carotid arteriography, orbital/carotid colour Doppler ultrasonography and CT angiography to demonstrate haemodynamic changes and to discuss possible mechanisms and pathways of the emboli.

Results

Among 208 RAO eyes, 12 eyes (5.7%) in 11 patients had multiple emboli were recruited in this study. Eleven eyes (91.6%) had ipsilateral carotid plaques and atherosclerosis with high-grade stenosis; among them, five were total carotid occlusion. Haemodynamic changes were found in nine patients with RAO (81.8%) with carotid stenosis 60% or greater. Most compensatory intracranial circulations were re-established via the circle of Willi with antegrade ophthalmic flows, but the direction of ophthalmic flow reversed in three eyes indicating the recruitment of external collaterals. Two cases underwent carotid stent successfully.

Conclusion

RAOs with multiple emboli are rare but highly associated with severe CAOD with haemodynamic flow changes, warning critical condition in carotid/cerebral circulations. Either direct embolism from the carotid or cardiac lesions or indirect embolism via the collateral pathways is the mechanism of pathogenesis. Immediate action should start to manage these patients to prevent further deterioration.

Multiparametric flow analysis using four-dimensional flow magnetic resonance imaging can detect cerebral hemodynamic impairment in patients with internal carotid artery stenosis

PURPOSE

MRI-based risk stratification should be established to identify patients with internal carotid artery stenosis (ICS) who require further PET or SPECT evaluation. This study assessed whether multiparametric flow analysis using time-resolved 3D phase-contrast (4D flow) MRI can detect cerebral hemodynamic impairment in patients with ICS.

METHODS

This retrospective study analyzed 26 consecutive patients with unilateral ICS (21 men; mean age, 71 years) who underwent 4D flow MRI and acetazolamide-stress brain perfusion SPECT. Collateral flow via the Willis ring was visually evaluated. Temporal mean flow volume rate (Net), pulsatile flow volume (ΔV), and pulsatility index (PI) at the middle cerebral artery were measured. Cerebral vascular reserve (CVR) was calculated from the SPECT dataset. Patients were assigned to the misery perfusion group if the CVR was < 10% and to the nonmisery perfusion group if the CVR was ≥ 10%. Parameters showing a significant difference in both groups were statistically evaluated.

RESULTS

Affected side ΔV, ratio of affected to contralateral side Net (rNet), and ratio of affected to contralateral side ΔV were significantly correlated to CVR (p = 0.030, p = 0.010, p = 0.015, respectively). Absence of retrograde flow at the posterior communicating artery was observed in the misery perfusion group (p = 0.020). Combined cut-off values of the affected side ΔV (0.18 ml) and rNet (0.64) showed a sensitivity and specificity of 100% and 77.8%, respectively.

CONCLUSION

Multiparametric flow analysis using 4D flow MRI can detect misery perfusion by comprehensively assessing blood flow data, including blood flow volume, pulsation, and collateral flow.

Collateral Circulation in Moyamoya Disease: A New Grading System

Background and Purpose- Predicting the risk of stroke and determining intervention indications are highly important for patients with Moyamoya disease (MMD). Here, we evaluated a novel MMD grading system based on collateral circulation and Suzuki stage to evaluate symptoms and predict prognosis. Methods- In total, 301 idiopathic MMD patients were retrospectively analyzed between 2014 and 2016. A collateral circulation grading system with scores ranging from 1 to 12 was established: the anatomic extent of pial collateral blood flow from posterior cerebral artery to middle cerebral artery and anterior cerebral artery was scored from 1 to 6; perforator collateral and internal cerebral artery flow were scored as 6 to 1, which corresponded to Suzuki stages 1 to 6. Dynamic susceptibility contrast-magnetic resonance imaging was used to evaluate hemodynamic status. We assessed the association between the grading system and clinical characteristics. Results- We analyzed 364 symptomatic hemispheres of 301 patients (146 males, 28±16 years). Ischemic patients who presented with infarction were more likely to score <8 points (P<0.001), whereas those with ischemia symptoms (transient ischemic attack and headache) were more likely to score >8 points. Hemorrhagic patients who presented with intraparenchymal hemorrhage were more likely to score <8 points, whereas those who presented with intraventricular hemorrhage were more likely to score >8 points (P<0.001). According to dynamic susceptibility contrast-magnetic resonance imaging, lower scores were correlated with more severe time to peak delay (P<0.001) and worse relative cerebral blood volume ratio (P=0.016) and cerebral flow ratio (P=0.002). Encephaloduroarteriosynangiosis was performed in 348 symptomatic hemispheres. Patients who had collateral scores <4 points were more likely to have a postoperative stroke and a worse prognosis during the follow-up. Conclusions- This new MMD collateral grading system correlated well with clinical symptoms, hemodynamic status, and therapeutic prognosis and may facilitate risk stratification and prognosis predictions in patients with MMD.

Genetic and Environmental Contributions to Variation in the Posterior Communicating Collaterals of the Circle of Willis

Variation in blood flow mediated by the posterior communicating collateral arteries (PComs) contributes to variation in the severity of tissue injury in obstructive disease. Evidence in animals and humans indicates that differences in the extent of PComs, i.e., their anatomic lumen diameter and whether they are present bilaterally, unilaterally, or absent, are a major factor. These differences arise during development since they are present at birth. However, the causal mechanisms are unknown. We used angiography after maximal dilation to examine involvement of genetic, environmental, and stochastic factors. The extent of PComs varied widely among seven genetically diverse strains of mice. Like pial collaterals in the microcirculation, aging and hypertension reduced PCom diameter, while in contrast, obesity, hyperlipidemia, metabolic syndrome, and diabetes mellitus had no effect. Naturally occurring intrauterine growth restriction had no effect on extent of PCom or pial collaterals in the adult. The number and diameter of PComs evidenced much larger apparent stochastic-dependent variation than pial collaterals. In addition, both PComs underwent flow-mediated outward remodeling after unilateral permanent MCA occlusion that varied with genetic background and was greater on the ipsilesional side. These findings indicate that variation in the number and diameter of PCom collateral arteries arises from stochastic factors and naturally occurring genetic variants that differ from those that cause variation in pial collateral arterioles. Environmental factors also contribute: aging and hypertension reduce PCom diameter. Our results suggest possible sources of variation of PComs in humans and provide information relevant when studying mouse models of occlusive cerebrovascular disease.

Hemodynamic mechanisms underlying elevated oxygen extraction fraction (OEF) in moyamoya and sickle cell anemia patients

Moyamoya is a bilateral, complex cerebrovascular condition characterized by progressive non-atherosclerotic intracranial stenosis and collateral vessel formation. Moyamoya treatment focuses on restoring cerebral blood flow (CBF) through surgical revascularization, however stratifying patients for revascularization requires abilities to quantify how well parenchyma is compensating for arterial steno-occlusion. Globally elevated oxygen extraction fraction (OEF) secondary to CBF reduction may serve as a biomarker for tissue health in moyamoya patients, as suggested in patients with sickle cell anemia (SCA) and reduced oxygen carrying capacity. Here, OEF was measured (TRUST-MRI) to test the hypothesis that OEF is globally elevated in patients with moyamoya (n = 18) and SCA (n = 18) relative to age-matched controls (n = 43). Mechanisms underlying the hypothesized OEF increases were evaluated by performing sequential CBF-weighted, cerebrovascular reactivity (CVR)-weighted, and structural MRI. Patients were stratified by treatment and non-parametric tests applied to compare study variables (significance: two-sided P < 0.05). OEF was significantly elevated in moyamoya participants (interquartile range = 0.38-0.45) compared to controls (interquartile range = 0.29-0.38), similar to participants with SCA (interquartile range = 0.37-0.45). CBF was inversely correlated with OEF in moyamoya participants. Elevated OEF was only weakly related to reductions in CVR, consistent with basal CBF level, rather than vascular reserve capacity, being most closely associated with OEF.

Accuracy of brain perfusion single-photon emission computed tomography for detecting misery perfusion in adult patients with symptomatic ischemic moyamoya disease

OBJECTIVE

The purpose of the present study was to determine how accurately relative cerebral blood flow (RCBF) and relative cerebrovascular reactivity (RCVR) to acetazolamide assessed using brain perfusion single-photon emission computed tomography (SPECT) detected misery perfusion identified on positron emission tomography (PET) in adult patients with ischemic moyamoya disease (MMD).

METHODS

Oxygen extraction fraction (OEF), RCBF, and RCVR were assessed using ¹⁵O gas PET and N-isopropyl-p-[¹²³I]-iodoamphetamine SPECT without and with acetazolamide challenge, respectively, in 45 patients. Regions of interest (ROIs) were automatically placed in the five middle cerebral artery (MCA) territories in the symptomatic cerebral hemisphere and in the ipsilateral cerebellar hemisphere using a three-dimensional stereotaxic ROI template. For RCBF and RCVR to acetazolamide, the ratio of the MCA ROI to cerebellar ROI was calculated. Of the five MCA ROIs in the symptomatic cerebral hemisphere in each patient, the ROI with the highest and lowest OEF value (two ROIs per patient) was selected for analyses.

RESULTS

A significant square or linear correlation was observed between the OEF and RCBF (correlation coefficient, 0.780) or RCVR (correlation coefficient, - 0.345), respectively. The area under the receiver operating characteristic curve for detecting misery perfusion (OEF > 51.3%) was significantly greater for the RCBF than for the RCVR (difference between areas, 0.221; p < 0.0001). Sensitivity, specificity, and positive- and negative-predictive values for the RCBF for detecting misery perfusion were 100, 91, 67, and 100%, respectively. The specificity and positive-predictive value did not differ between the combination of the RCBF and RCVR and the CBF ratio alone.

CONCLUSIONS

RCBF assessed using brain perfusion SPECT detects misery perfusion with high sensitivity, a high negative-predictive value, and a low positive-predictive value in adult patients with ischemic MMD. The accuracy of RCVR to acetazolamide assessed using brain perfusion SPECT is lower than that of RCBF.

MR Imaging of Individual Perfusion Reorganization Using Superselective Pseudocontinuous Arterial Spin-Labeling in Patients with Complex Extracranial Steno-Occlusive Disease

BACKGROUND AND PURPOSE

Patients with multiple stenoses or occlusions of the extracranial arteries require an individualized diagnostic approach. We evaluated the feasibility and clinical utility of a novel MR imaging technique for regional perfusion imaging in this patient group.

MATERIALS AND METHODS

Superselective pseudocontinuous arterial spin-labeling with a circular labeling spot enabling selective vessel labeling was added to routine imaging in a prospective pilot study in 50 patients (10 women, 70.05 ± 10.55 years of age) with extracranial steno-occlusive disease. Thirty-three had infarct lesions. DSC-MR imaging was performed in 16/50 (32%), and cerebral DSA, in 12/50 patients (24%). Vascular anatomy and the distribution of vessel stenoses and occlusions were defined on sonography and TOF-MRA. Stenoses were classified according to the NASCET criteria. Infarct lesions and perfusion deficits were defined on FLAIR and DSC-MR imaging, respectively. Individual perfusion patterns were defined on the superselective pseudocontinuous arterial spin-labeling maps and were correlated with vascular anatomy and infarct lesion localization.

RESULTS

The superselective pseudocontinuous arterial spin-labeling imaging sequence could be readily applied by trained technicians, and the additional scan time of 12.7 minutes was well-tolerated by patients. The detected vessel occlusions/stenoses and perfusion patterns corresponded between cerebral DSA and superselective pseudocontinuous arterial spin-labeling maps in all cases. Perfusion deficits on DSC-CBF maps significantly correlated with those on superselective pseudocontinuous arterial spin-labeling maps (Pearson r = 0.9593, P < .01). Individual collateral recruitment patterns were not predictable from the vascular anatomy in 71% of our patients.

CONCLUSIONS

Superselective pseudocontinuous arterial spin-labeling is a robust technique for regional brain perfusion imaging, suitable for the noninvasive diagnostics of individual perfusion patterns in patients with complex cerebrovascular disease.

4D Flow MR Imaging of Ophthalmic Artery Flow in Patients with Internal Carotid Artery Stenosis

Background and Purpose:

To assess the clinical feasibility of time-resolved 3D phase contrast (4D Flow) MRI assessment of the ophthalmic artery (OphA) flow in patients with internal carotid artery stenosis (ICS).

Materials and Methods:

Twenty-one consecutive patients with unilateral ICS were recruited. 4D Flow MRI and acetazolamide-stress brain perfusion single photon emission computed tomography (SPECT) were performed. The flow direction on the affected-side OphA was categorized into native flow (anterograde or unclear) and non-native flow (retrograde flow) based on 4D Flow MRI. In the affected-side middle cerebral artery (MCA) territory, the ratio of rest cerebral blood flow to normal control (RCBF_MCA) and cerebral vascular reserve (CVR_MCA) were calculated from SPECT dataset. High-risk patients were defined based on the previous large cohort study (RCBF_MCA < 80% and CVR_MCA < 10%).

Results:

Eleven patients had native OphA flow (4 anterograde, 7 unclear) and the remaining 10 had non-native OphA flow. RCBF_MCA and CVR_MCA each were significantly lower in non-native flow group (84.9 ± 18.9% vs. 69.8 ± 7.3%, P < 0.05; 36.4 ± 20.6% vs. 17.0 ± 15.0%, P < 0.05). Four patients in the non-native flow group and none in the native flow group were confirmed as high-risk (Sensitivity/Specificity, 1.00/0.65).

Conclusion:

The 6 min standard 4D Flow MRI assessment of OphA in patients with ICS can predict intracranial hemodynamic impairment.

Hemodynamic contribution of transdural collateral flow in adult patients with moyamoya disease

To evaluate the hemodynamic contributions of collateral flow in adult patients with moyamoya disease, neurological deterioration or fluctuation during admission, Suzuki grade, various collateral routes, lesion volume, cerebral blood flow (CBF), and their associations were analyzed. Thirty patients (60 cerebral hemispheres, mean age 45 ± 25 years, and 73.3 % female) who were diagnosed with moyamoya disease or syndrome were enrolled over 3 years. Moyamoya stages from each hemisphere were stratified according to the Suzuki's criteria through six-vessel angiography into internal carotid arteries (ICAs), external carotid arteries (ECAs), and vertebral arteries (VAs). Collateral routes were categorized into the circle of Willis, leptomeningeal, and transdural. The volume of ipsilateral infarction was analyzed by magnetic resonance imaging. CBF volume was measured using color-coded duplex sonography. Suzuki's grade was inversely correlated with flow volume of the ICAs (p < 0.001), whereas no association was found with that of the ECAs (p = 0.445) or VAs (p = 0.096). Among hemispheres with ≥ grade 3 (n = 36), patients with transdural ECA collateral flow had less neurological deterioration or fluctuation (0.0 vs. 30.8 %, p = 0.047), smaller lesion volume (2.4 ± 3.6 vs. 27.6 ± 59.3 mL, p = 0.041), lower ICA flow (88.4 ± 45.9 vs. 146.2 ± 121.7 mL/min, p = 0.022), higher ECA flow (205.7 ± 77.7 vs. 135.9 ± 52.7 mL/min, p = 0.046), and a higher ECA/ICA flow volume ratio (31.8 ± 92.8 vs. 1.7 ± 1.9, p = 0.024). Our results suggest that ICA flow volume is inversely correlated with Suzuki grade, and that transdural ECA collaterals appear to be an important detour in adult patients with advanced stage moyamoya disease, suggesting a protector against an impending ischemic attack.

Bypass surgery for the prevention of ischemic stroke: current indications and techniques

INTRODUCTION

Although most ischemic strokes are thromboembolic in origin and their management is endovascular or medical, some are haemodynamic in origin and their management may be surgical. We reviewed bypass indications, patient selection and surgical techniques used in our current practice.

METHODS

Extracranial-intracranial (EC-iC) bypass with superior temporal artery-to-middle cerebral artery (STA-MCA) bypass, high-flow interposition grafts and reconstructive techniques were used to treat patients with symptomatic ischemia.

RESULTS

During a 13-year period, 152 bypasses were performed for ischemia in 129 patients. Specific diagnoses included: (1) internal carotid artery (iCA) occlusion (58 bypasses); (2) MCA occlusion and, rarely, high-grade MCA stenosis (22 bypasses); (3) vertebrobasilar atherosclerotic steno-occlusive disease (2 bypasses); (4) moyamoya disease (65 bypasses); and (5) ischemic complications after aneurysm treatment (5 bypasses). of the 152 bypasses, 137 were conventional STA-MCA bypasses. fourteen patients had high-flow bypasses that included 4 "double-barrel" STA-MCA bypasses, 6 bypasses with interposition grafts to the cervical carotid artery, 2 subclavian artery-to-MCA bypasses, 1 MCA-to-posterior cerebral artery (PCA) bypass and 1 aorto-carotid bypass. The bypass patency rate was 96.1%.

CONCLUSIONS

Bypass surgery for the prevention of ischemic stroke is safe and elegant techniques have been developed. Patients with athero-occlusive disease, ischemic symptoms and haemodynamic insufficiency have significant risk of stroke if managed medically or left untreated. However, surgical intervention lacks supporting evidence from the recent Carotid occlusion Surgery Study (CoSS). Patients will be caught in a difficult position between a dismal natural history and an unproven surgical intervention. Clinicians must individualise their management until additional data are published or further consensus develops.

Endovascular Management of Long-Segmental Petrocavernous Internal Carotid Artery (Carotid S) Occlusion

Background and Purpose

Long-segmental thrombotic occlusion of the distal internal carotid artery (ICA) sparing the cervical segment proximally and the supraclinoid segment distally, which could be termed ’Carotid S occlusion’, has an unusual clinical presentation. However, endovascular management of this lesion is challenging. The purpose of our study is to report our endovascular treatment clinical experience of the disease.

Methods

From March 2008 to June 2013, we could identify 14 patients (average age: 62.1, median age: 62, range: 50-79) with ‘Carotid S occlusion’, who underwent endovascular recanalization procedures. Patient’s clinical presentations were collected and the imaging findings also analyzed. The technical success rate, 24-hour and follow-up imaging outcome, and the clinical outcome using the 90-day mRS (modified Rankin scale) score were evaluated.

Results

Patients presented with gradually progressing (n = 8), fluctuating (n = 3), transient ischemic attack (n = 2) and stationary (n = 1) symptoms. DWI showed internal and external border-zone lesions in six patients, only internal ICA border-zone lesions in three patients, and only external border-zone lesions in two patients. Underlying distal ICA stenosis was noted in 12 patients. The technical success rate was 92.8% (13/14). Luminal patency was noted in all patients (100%) after 24 hours and in nine of 10 (90%) on long-term follow-up (median: 6.5, average: 15.1, range: 1-39 months). A 90-day, good functional outcome (mRS ≤ 2) was noted in 13 of 14 patients (92.8%).

Conclusions

‘Carotid S occlusion’ usually presented with border-zone infarction and endovascular management of the lesions was feasible. A relatively successful clinical outcome could be achieved after successful revascularization.

Leptomeningeal enhancement on magnetic resonance imaging as a predictor of hemodynamic insufficiency

OBJECTIVE

The objective of this study was to evaluate the value of leptomeningeal enhancement on magnetic resonance imaging in relation to relative cerebral blood flow (rCBF) and cerebrovascular reserve.

METHODS

A retrospective analysis was performed for 31 patients with internal carotid artery or proximal middle cerebral artery occlusion without primary collateral flow, who underwent enhanced T1-weighted magnetic resonance imaging and acetazolamide-challenged perfusion computed tomography. They were graded into 3 groups in leptomeningeal enhancement on T1-weighted imaging. The rCBF and the percentage change of cerebral blood flow were obtained in the ipsilateral middle cerebral artery territory.

RESULTS

The mean percentage changes of CBF were -13.7%, 6.9%, and 23.8% in prominent (n = 11), mild (n = 11), and equivalent (n = 9) increased enhancements, respectively. The degree of leptomeningeal enhancement was significantly reverse-correlated with percentage change of CBF (P < 0.001), whereas the rCBFs were not significantly different.

CONCLUSIONS

The reverse correlation between leptomeningeal enhancement and cerebrovascular reserve suggests that increased enhancement may indicate impaired primary collaterals and hemodynamic insufficiency. Therefore, leptomeningeal enhancement degree can be used as an indicator of hemodynamic state in stroke.

Collaterals: an important determinant of prolonged ischemic penumbra versus rapid cerebral infarction?

Intravenous tissue plasminogen activator is the mainstay for the treatment of acute ischemic stroke in patients presenting within 4.5 h of symptom onset. Studies have demonstrated that treating patients early leads to improved long-term outcomes. MR imaging currently allows quantification of the ischemic penumbra in order to better identify individuals most likely to benefit from intervention, irrespective of “time last seen normal.” Its increasing use in clinical practice has demonstrated individual differences in rate of infarction. One explanation for this variability is a difference in collateral blood flow. We report two cases that highlight the individual variability of infarction rate, and discuss potential underlying mechanisms that may influence treatment decisions and outcomes.

Cerebrovascular collaterals correlate with disease severity in adult North American patients with Moyamoya disease

BACKGROUND AND PURPOSE

Cerebrovascular collaterals have been increasingly recognized as predictive of clinical outcomes in Moyamoya disease in Asia. The aim of this study was to characterize collaterals in North American adult patients with Moyamoya disease and to assess whether similar correlations are valid.

MATERIALS AND METHODS

Patients with Moyamoya disease (n = 39; mean age, 43.5 ±10.6 years) and age- and sex-matched control subjects (n = 33; mean age, 44.3 ± 12.0 years) were graded via angiography. Clinical symptoms of stroke or hemorrhage were graded separately by imaging. Correlations between collateralization and disease severity, measured by the modified Suzuki score, were evaluated in patients with Moyamoya disease by fitting a regression model with clustered ordinal multinomial responses.

RESULTS

The presence of leptomeningeal collaterals (P = .008), dilation of the anterior choroidal artery (P = .01), and the posterior communicating artery/ICA ratio (P = .004) all correlated significantly with disease severity. The presence of infarct or hemorrhage and posterior steno-occlusive disease did not correlate significantly with the modified Suzuki score (P = .1). Anterior choroidal artery changes were not specific for hemorrhage. Patients with Moyamoya disease were statistically more likely than controls to have higher posterior communicating artery/ICA ratios and a greater incidence of leptomeningeal collaterals.

CONCLUSIONS

As with Moyamoya disease in Asian patients, the presence of cerebrovascular collaterals correlated with the modified Suzuki score for disease severity in North American patients with Moyamoya disease. However, anterior choroidal artery changes, which correlated with increased rates of hemorrhage in Asian studies, were not specific to hemorrhage in North Americans.

Carotid artery stenting improves cerebral hemodynamics regardless of the flow direction of ophthalmic artery

We enrolled 221 patients with elective carotid artery stenting (CAS). Patients with contralateral carotid stenosis exceeding 50%, insufficient vertebral artery (VA) flows, or angioplasty at subclavian artery were excluded. All patients underwent serial cerebral ultrasound studies. Of the 116 included patients, the direction of ophthalmic artery (OA) flow was forward in 74 patients while reversed in 42. The reversed flow group had worse ipsilateral stenosis, higher hemoglobin, and cardiac output. After CAS, the reversed flow group had an immediate recovery of ipsilateral internal carotid artery flow volume (FV; P < .0001), time average velocity (TAV) of middle cerebral artery (P = .02), and normalization of OA flow. The forward flow group had gradual decrement in TAV of contralateral anterior cerebral artery (P = .01) and total FV of VA (P = .001). Our results suggest CAS improves cerebral hemodynamics through different ways regardless of the direction of OA flow.

Combination of blood flow asymmetry in the cerebral and cerebellar hemispheres on brain perfusion SPECT predicts 5-year outcome in patients with symptomatic unilateral major cerebral artery occlusion

BACKGROUND AND OBJECTIVE

Misery perfusion increases the risk of stroke recurrence in patients with symptomatic major cerebral artery occlusion. The ratio of brain perfusion contralateral-to-affected asymmetry in the cerebellar hemisphere to brain perfusion affected-to-contralateral asymmetry in the cerebral hemisphere (CblPR/CbrPR) indicates affected-to-contralateral asymmetry of oxygen extraction fraction (OEF) in the cerebral hemisphere. The purpose of the present study was to determine whether the CblPR/CbrPR on brain perfusion single-photon emission computed tomography (SPECT) predicts 5-year outcomes in patients with symptomatic unilateral occlusion of the middle cerebral artery (MCA) or internal carotid artery (ICA).

METHODS

Brain perfusion was assessed using N-isopropyl-p-[123I]-iodoamphetamine (123I-IMP) SPECT in 70 patients. A region of interest (ROI) was manually placed in the bilateral MCA territories and in the bilateral cerebellar hemispheres, and the CblPR/CbrPR was calculated. All patients were prospectively followed for 5 years. The primary end points were stroke recurrence or death.

RESULTS

A total of 17 patients exhibited the primary end points, 11 of whom experienced subsequent ipsilateral strokes. Multivariate analysis revealed that only high CblPR/CbrPR was significantly associated with the development of the primary end point or subsequent ipsilateral strokes (95% confidential limits [CIs], 1.130-3.145; P  =  0.0114 or 95% CIs, 2.558-5.140; P  =  0.0045, respectively). The CblPR/CbrPR provided 65% (11/17) or 91% (10/11) sensitivity and 88% (47/53) or 88% (52/59) specificity in predicting the primary end point or subsequent ipsilateral strokes, respectively.

CONCLUSIONS

The CblPR/CbrPR on brain perfusion SPECT predicts 5-year outcomes in patients with symptomatic unilateral occlusion of the MCA or ICA.

Clinical significance of STA-MCA double anastomosis for hemodynamic compromise in post-JET/COSS era

BACKGROUND

Even after the recent randomized clinical trials JET and COSS, it is still unclear that impaired cerebrovascular reactivity (CVR) to acetazolamide and oxygen extraction fraction (OEF) can identify the candidates for superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis. This prospective study was aimed to evaluate the benefits of STA-MCA "double" anastomosis on long-term outcome in patients with reduced cerebral blood flow (CBF) and CVR (Type 3 ischemia) and elevated OEF attributable to occlusive carotid diseases.

METHODS

This study included 49 patients with reduced CBF and CVR on SPECT in the ipsilateral MCA area. Using (15)O-gas PET, OEF was also measured in all patients. STA-MCA double anastomosis was recommended to the patients with Type 3 and elevated OEF. Those with Type 3 but normal OEF were medically treated.

RESULTS

Of 36 patients with Type 3 and elevated OEF, 25 consented to surgery. No perioperative morbidity or mortality were noted. The other 11 patients with Type 3 and elevated OEF were medically treated. Annual incidence of ipsilateral stroke was 0.7% and 6.5% in surgically and medically treated patients with Type 3 and elevated OEF, respectively (P = 0.0188). None of patients with Type 3 but normal OEF developed ipsilateral stroke during follow-up periods. STA-MCA "double" anastomosis significantly decreased OEF.

CONCLUSIONS

STA-MCA "double" anastomosis may still have the potential to reduce the risk of recurrent ipsilateral stroke in hemodynamically compromised patients. Further studies would be essential to advance diagnosis, surgical procedures, and perioperative managements to bring out maximal effects of bypass surgery.

A comprehensive study of the anatomical variations of the circle of willis in adult human brains

BACKGROUND

Cerebrovascular diseases such as stroke, aneurysms and arterio-venous malformations are very much prevalent in our country. Circle of Willis, as an anastomotic polygon at the base of the brain forms an important collateral network to maintain adequate cerebral perfusion. Changes in the normal morphology of the circle may condition the appearance and severity of symptoms of cerebrovascular disorders, such as aneurysms, infarctions and other vascular anomalies. A possible link between abnormalities of the circle of Willis and the mentally ill patients has been observed.

AIM AND OBJECTIVES

The aim of the present study is to have an intimate knowledge of the variations in the cerebral arterial circle and to clarify the clinical importance of these variations in certain forms of cerebrovascular diseases. So an attempt was made to analyse the anatomical variations of the circle in a random population.

MATERIAL AND METHODS

The work was based on fifty adult brains from persons died of diverse causes. The materials were obtained during routine autopsy studies. The base of the brain including the brain stem with intact arterial circle was preserved in 10% formalin for 10 days. The circle of Willis and its major branches were carefully dissected under water using a magnifying lens. The variations were recorded and photographed.

RESULTS

Majority of the circles (52%) showed anomalies. Hypoplasia was the most frequent anomaly and was found in 24% of the brains. Accessory vessels in the form of duplications/triplications of anterior communicating artery were seen in 12% of the circles. The embryonic origin of the posterior cerebral artery from the internal carotid persisted in 10% of the circles. An incomplete circle due to the absence of one or other posterior communicating artery was found in 6% of the specimens.Variations are more frequent in posterior half of the circle.

CONCLUSION

The anatomical variations of the circle of Willis were probably genetically determined, develop in early embryonic stage and persist in post natal life. The amplitude of neck movements, racial, environmental and hemodynamic factors may also modify these variations. These anomalies may alter the occurrence, severity of symptoms, treatment options and recovery from certain cerebrovascular disorders viz., stroke and aneurysms. A detailed knowledge of the vascular variants is useful to surgeons in planning their shunt operations, choice of the patients and also keeps away inadvertent vascular traumas during surgeries.

Detection of misery perfusion in the cerebral hemisphere with chronic unilateral major cerebral artery steno-occlusive disease using crossed cerebellar hypoperfusion: comparison of brain SPECT and PET imaging

PURPOSE

In patients with unilateral internal carotid or middle cerebral artery (ICA or MCA) occlusive disease, the degree of crossed cerebellar hypoperfusion that is evident within a few months after the onset of stroke may reflect cerebral metabolic rate of oxygen in the affected cerebral hemisphere relative to that in the contralateral cerebral hemisphere. The aim of the present study was to determine whether the ratio of blood flow asymmetry in the cerebellar hemisphere to blood flow asymmetry in the cerebral hemisphere on positron emission tomography (PET) and single photon emission computed tomography (SPECT) correlates with oxygen extraction fraction (OEF) asymmetry in the cerebral hemisphere on PET in patients with chronic unilateral ICA or MCA occlusive disease and whether this blood flow ratio on SPECT detects misery perfusion in the affected cerebral hemisphere in such patients.

METHODS

Brain blood flow and OEF were assessed using (15)O-PET and N-isopropyl-p-[(123)I]iodoamphetamine ((123)I-IMP) SPECT, respectively. All images were anatomically standardized using SPM2. A region of interest (ROI) was automatically placed in the bilateral MCA territories and in the bilateral cerebellar hemispheres using a three-dimensional stereotaxic ROI template, and affected-to-contralateral asymmetry in the MCA territory or contralateral-to-affected asymmetry in the cerebellar hemisphere was calculated. Sixty-three patients with reduced blood flow in the affected cerebral hemisphere on (123)I-IMP SPECT were enrolled in this study.

RESULTS

A significant correlation was observed between MCA ROI asymmetry of PET OEF and the ratio of cerebellar hemisphere asymmetry of blood flow to MCA ROI asymmetry of blood flow on PET (r = 0.381, p = 0.0019) or SPECT (r = 0.459, p = 0.0001). The correlation coefficient was higher when reanalyzed in a subgroup of 43 patients undergoing a PET study within 3 months after the last ischemic event (r = 0.541, p = 0.0001 for PET; r = 0.609, p < 0.0001 for SPECT). The blood flow ratio on brain perfusion SPECT in all patients provided 100 % sensitivity and 58 % specificity, with 43 % positive and 100 % negative predictive values for detecting abnormally elevated MCA ROI asymmetry of PET OEF.

CONCLUSION

The ratio of blood flow asymmetry in the cerebellar hemisphere to blood flow asymmetry in the cerebral hemisphere on PET and SPECT correlates with PET OEF asymmetry in the cerebral hemisphere, and this blood flow ratio on SPECT detects misery perfusion in the affected cerebral hemisphere.

Reversal of ophthalmic artery flow as a predictor of intracranial hemodynamic compromise: implication for prognosis of severe carotid stenosis

BACKGROUND AND PURPOSE

High-grade cervical carotid stenosis (70-99%) or occlusion often accompanies reversed ophthalmic artery flow (ROAF), but its potential clinical significances remain poor understood. This study assessed ROAF and the related variables caused by carotid hemodynamic compromise in patients with unilateral severe cervical carotid stenosis.

METHODS

The study consisted of 200 patients diagnosed as unilateral high-grade cervical carotid stenosis/occlusion using ultrasonography. The hemodynamic parameters of 152 patients, excluding 48 with cervical carotid occlusion, were compared based on the presence of ROAF. Out of 200 patients, 159 underwent brain magnetic resonance imaging and were analysed for risk factors impacting functional outcomes including ROAF.

RESULTS

The patients (n = 48) with internal carotid artery occlusion had significantly higher incidence (62.5%) of ROAF compared with that of 25.0% in those patients (n = 152) with unilateral high-grade carotid stenosis (P < 0.001). In ROAF patients (n = 38) with the unilateral high-grade stenosis, a significant retrobulbar arteries hemodynamic difference was observed between the stenotic and non-stenotic vessels. The patients (n = 159) with history of stroke (P = 0.035), ROAF (P = 0.023) and intracranial stenosis (P < 0.001) exhibited significantly higher incidence of poor functional outcome compared with the corresponding control groups. In the same patients (n = 159), those with both cervical and intracranial stenosis showed sevenfold higher risk (OR, 7.60; 95% CI, 3.44-16.81) for ROAF than those with only cervical stenosis.

CONCLUSIONS

ROAF may result from intracranial hemodynamic compromise. Patients with unilateral high-grade cervical carotid stenosis/occlusion in combination with intracranial stenosis appear to be a significant risk factor for poor functional outcome and increased incidence of ROAF.

Quantitative assessment of external carotid artery territory supply with modified vessel-encoded arterial spin-labeling

BACKGROUND AND PURPOSE

In patients with carotid stenosis or occlusion, cerebral blood could be supplied through collateral pathways to improve regional blood flow and protect against ischemic events. The contribution of collaterals from the ICA can be assessed by depiction of vascular perfusion territories with ASL. However, so far there is no method available to evaluate the collateral perfusion territory from the ECA in MR imaging. In this study, we present a new labeling scheme based on VE-ASL to quantitatively assess the perfusion territory of the ECA.

MATERIALS AND METHODS

A new labeling approach with a Hadamard encoding scheme was developed to label major arteries, especially the ECA. Twelve healthy subjects with normal cerebrovascular anatomy were examined to demonstrate their perfusion territories. Eight patients with carotid artery stenosis or occlusion were assessed before and after surgery to show changes of their collateral blood supply.

RESULTS

The proposed method enables assessment of the perfusion territories of the ECA. Good agreement was found between the vascular territories and normal cerebrovascular anatomy in healthy subjects. For the patients with carotid stenosis or occlusion, our noninvasive results provided information on collateral flow comparable with that from DSA. Their collateral flows from the ECA, moreover, could be quantitatively estimated pre- and postoperatively.

CONCLUSIONS

The modified approach has been validated by the consistency of collateral perfusion territories with cerebrovascular anatomy, and quantitative assessment of collaterals proved useful for assisting in evaluating therapeutic interventions.

Systematic review of methods for assessing leptomeningeal collateral flow

BACKGROUND AND PURPOSE

The importance of LMF in the outcome after acute ischemic stroke is increasingly recognized, but imaging presents a wide range of options for identification of collaterals and there is no single system for grading collateral flow. The aim of this study was to systematically review the literature on the available methods for measuring LMF adequacy.

MATERIALS AND METHODS

We performed a systematic review of Ovid, MEDLINE, and Embase databases for studies in which flow in the leptomeningeal collateral vessels was evaluated. Imaging technique, grading scale, and reliability assessment for collateral flow measurement were recorded.

RESULTS

We found 81 publications describing 63 methods for grading collateral flow on the basis of conventional angiography (n = 41), CT (n = 7), MR imaging (n = 9), and transcranial Doppler (n = 6). Inter- and/or intraobserver agreement was assessed in only 8 publications.

CONCLUSIONS

There is inconsistency in how LMF is graded, with a variety of grading scales and imaging modalities being used. Consistency in evaluating collateral flow at baseline is required for the impact of collateral flow to be fully appreciated.

Bypass for the prevention of ischemic stroke

OBJECTIVE

Although most ischemic strokes are thromboembolic in origin and their management is endovascular or medical, some are hemodynamic in origin and their management may be surgical. Extracranial-intracranial bypass with superficial temporal artery-to-middle cerebral artery (MCA) bypass, high-flow interposition grafts, and reconstructive techniques have been developed. Clinical indications and efficacy are controversial, and this review examines current practices.

METHODS

Bypass surgery is indicated for patients with athero-occlusive disease that results in chronic, low cerebral blood flow accompanied by episodes of ischemic symptoms. Specific diagnoses include: (1) internal carotid artery occlusion; (2) MCA occlusion and, rarely, high-grade MCA stenosis; (3) vertebrobasilar atherosclerotic steno-occlusive disease; (4) vasculitis resulting in severe occlusive disease; and (5) moyamoya disease.

RESULTS

Discouraging results from the Extracranial-Intracranial Bypass Trial demonstrated the importance of selecting surgical patients based on objective measures of hemodynamic insufficiency. Two such tests are xenon-enhanced computed tomography with acetazolamide challenge and positron emission tomography with measurement of oxygen extraction fraction. Perfusion computed tomography may be another, more practical test. Surgical series, systematic reviews of the literature, and two new randomized clinical trials that use these diagnostic techniques reveal contradictory results. Although they demonstrate that bypass surgery has a morbidity rate of less than 5% and a patency rate of more than 95%, they have not proven a clear benefit.

CONCLUSIONS

Patients with athero-occlusive disease and symptoms of hemodynamic insufficiency have significant risk of stroke if left untreated or managed medically. On the other hand, surgical intervention lacks supporting evidence. Clinicians must individualize their management recommendations until additional data are published or further consensus develops.

Cerebral hemodynamics and cognitive impairment: baseline data from the RECON trial

OBJECTIVE

To determine whether unihemispheral hemodynamic failure is independently associated with cognitive impairment among participants in the National Institute of Neurological Disorders and Stroke-sponsored, multicenter, randomized clinical trial, Randomized Evaluation of Carotid Occlusion and Neurocognition (RECON).

METHODS

Forty-three patients were randomized into RECON after recent symptomatic carotid artery occlusion and asymmetrically increased oxygen extraction fraction (OEF) by PET (OEF ratio >1.13), indicating stage II hemodynamic failure on the side of occlusion. The PET-positive patients were compared with 28 RECON-enrolled patients who met all clinical and radiographic inclusion/exclusion criteria but had no OEF asymmetry. A multivariable regression compared patients with PET OEF >1.13 or ≤1.13, stratifying by TIA vs. stroke as the qualifying event. The dependent variable was a composite neurocognitive score derived from averaging age-normalized z scores on a test battery that included global and internal carotid artery (ICA) side-relevant hemisphere-specific tests.

RESULTS

There were no differences in demographic, clinical, or radiologic characteristics between the PET-positive and PET-negative patients except for PET OEF asymmetry. The unadjusted average neurocognitive z score was -1.45 for the PET-positive and -1.25 for the PET-negative patients, indicating cognitive impairment in both groups but no difference between them (p = 0.641). After adjustment for age, education, side of occlusion, depression, and previous stroke, there was a significant difference between PET-positive and PET-negative patients among those with TIA as a qualifying event (average z score = -1.41 vs. -0.76, p = 0.040). Older age and right ICA side were also significant in this model.

CONCLUSION

Hemodynamic failure is independently associated with cognitive impairment in patients with carotid occlusion. This finding establishes the physiologic parameter upon which the extracranial-intracranial bypass will be tested.

Quantitative perfusion computed tomography measurements of cerebral hemodynamics: correlation with digital subtraction angiography identified primary and secondary cerebral collaterals in internal carotid artery occlusive disease

BACKGROUND

The aim of the present study was to assess hemodynamic variations in symptomatic unilateral internal carotid artery occlusion (ICAO) patients with primary collateral flow via circle of Willis or secondary collateral flow via ophthalmic artery and/or leptomeningeal collaterals.

METHODS

Thirty-eight patients with a symptomatic unilateral ICAO were enrolled in the study. Based on digital subtraction angiography (DSA) findings, patients were classified into 2 groups: primary collateral (n = 14) and secondary collateral (n = 24) groups. Collateral flow hemodynamics were investigated with perfusion computed tomography (PCT) by measuring the cerebral blood flow (CBF), cerebral blood volume (CBV) and time to peak (TTP) in the hemispheres ipsilateral and contralateral to ICAO. Based on the measurements, the ipsilateral to contralateral ratio for each parameter was calculated and compared.

RESULTS

Irrespective of the collateral patterns, ipsilateral CBF was not significantly different from that of the contralateral hemisphere (P = 0.285); ipsilateral CBV and TTP was significantly increased compared with those of the contralateral hemisphere (P=0.000 and P = 0.000 for CBV and TTP, respectively). Furthermore, patients with secondary collaterals had significantly larger ipsilateral-to-contralateral ratios for both CBV (rCBV, P = 0.0197) and TTP (rTTP, P = 0.000) than those of patients with only primary collaterals. These two groups showed no difference in ipsilateral-to-contralateral ratio for CBF (rCBF, P = 0.312).

CONCLUSION

Patients with symptomatic unilateral ICAO in our study were in an autoregulatory vasodilatation status. Moreover, secondary collaterals in ICAO patients were correlated with ipsilateral CBV and delayed TTP that suggested severe hemodynamic impairment, presumably increasing the risk of ischemic events.

Reperfusion phenomenon masking acute and subacute infarcts at dynamic perfusion CT: confirmation by fusion of CT and diffusion-weighted MR images

OBJECTIVE

The purpose of this study was to evaluate cerebral blood flow, cerebral blood volume, mean transit time, time to peak, and delay in a selected sample of patients with visually normal or increased cerebral blood volume to facilitate detection of a postischemic CT perfusion hyperperfusion-reperfusion phenomenon that may mask subacute and acute infarcts.

MATERIALS AND METHODS

Ten patients were included who had visually normal or elevated cerebral blood volume in infarcts larger than 1.5 cm confirmed on diffusion-weighted MR images within 48 hours of perfusion CT. The cases were selected from 371 perfusion CT studies of stroke patients (99 associated with positive diffusion-weighted imaging findings) reviewed over 2.5 years on a 64-MDCT scanner. The perfusion CT images were fused to the diffusion-weighted images for measurement of cerebral blood volume, cerebral blood flow, mean transit time, time to peak, and delay in each infarct versus the contralateral hemisphere. Two neuroradiologists reviewed the images in consensus.

RESULTS

The mean time between symptom onset and perfusion CT was 3.9 days. Infarcts were in the middle cerebral artery (n = 7) and posterior cerebral artery (n = 3) distributions. Significant differences versus the contralateral finding were found in cerebral blood volume (p = 0.016; mean increase, 30.0%), mean transit time (p = 0.007; mean increase, 38.1%), time to peak (p = 0.005; mean increase, 17.7%), and delay (p = 0.030; mean increase, 124.9%). The difference in cerebral blood flow (p = 0.785; mean increase, 1.8%) was not statistically significant. Infarcts became enhanced on the dynamic perfusion CT images of eight of 10 patients and on the contrast-enhanced T1-weighted MR images of six of nine patients.

CONCLUSION

Visual inspection of cerebral blood volume and cerebral blood flow maps alone is insufficient in the evaluation of infarcts. Mean transit time, time to peak, and delay maps also should be reviewed with dynamic source images to prevent misinterpretation of findings as false-negative. This phenomenon is unlikely to occur hyperacutely (< 8 hours after onset).

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.