The role of imaging in the management of cerebral and ocular ischaemia

Alterations in Functional Network Topology Within Normal Hemispheres Contralateral to Anterior Circulation Steno-Occlusive Disease: A Resting-State BOLD Study

The purpose of this study was to assess spatially remote effects of hemodynamic impairment on functional network topology contralateral to unilateral anterior circulation steno-occlusive disease (SOD) using resting-state blood oxygen level-dependent (BOLD) imaging, and to investigate the relationships between network connectivity and cerebrovascular reactivity (CVR), a measure of hemodynamic stress. Twenty patients with unilateral, chronic anterior circulation SOD and 20 age-matched healthy controls underwent resting-state BOLD imaging. Five-minute standardized baseline BOLD acquisition was followed by acetazolamide infusion to measure CVR. The BOLD baseline was used to analyze network connectivity contralateral to the diseased hemispheres of SOD patients. Compared to healthy controls, reduced network degree (z-score = −1.158 ± 1.217, P < 0.001, false discovery rate (FDR) corrected), local efficiency (z-score = −1.213 ± 1.120, P < 0.001, FDR corrected), global efficiency (z-score = −1.346 ± 1.119, P < 0.001, FDR corrected), and enhanced modularity (z-score = 1.000 ± 1.205, P = 0.002, FDR corrected) were observed in the contralateral, normal hemispheres of SOD patients. Network degree (P = 0.089, FDR corrected; P = 0.027, uncorrected) and nodal efficiency (P = 0.089, FDR corrected; P = 0.045, uncorrected) showed a trend toward a positive association with CVR. The results indicate remote abnormalities in functional connectivity contralateral to the diseased hemispheres in patients with unilateral SOD, despite the absence of macrovascular disease or demonstrable hemodynamic impairment. The clinical impact of remote functional disruptions requires dedicated investigation but may portend far reaching consequence for even putatively unilateral cerebrovascular disease.

Acetazolamide-augmented dynamic BOLD (aczBOLD) imaging for assessing cerebrovascular reactivity in chronic steno-occlusive disease of the anterior circulation: An initial experience

The purpose of this study was to measure cerebrovascular reactivity (CVR) in chronic steno-occlusive disease using a novel approach that couples BOLD imaging with acetazolamide (ACZ) vasoreactivity (aczBOLD), to evaluate dynamic effects of ACZ on BOLD and to establish the relationship between aczBOLD and dynamic susceptibility contrast (DSC) perfusion MRI. Eighteen patients with unilateral chronic steno-occlusive disease of the anterior circulation underwent a 20-min aczBOLD imaging protocol, with ACZ infusion starting at 5 min of scan initiation. AczBOLD reactivity was calculated on a voxel-by-voxel basis to generate CVR maps for subsequent quantitative analyses. Reduced CVR was observed in the diseased vs. the normal hemisphere both by qualitative and quantitative assessment (gray matter (GM): 4.13% ± 1.16% vs. 4.90% ± 0.98%, P = 0.002; white matter (WM): 2.83% ± 1.23% vs. 3.50% ± 0.94%, P = 0.005). In all cases BOLD signal began increasing immediately following ACZ infusion, approaching a plateau at ~ 8.5 min after infusion, with the tissue volume of reduced augmentation increasing progressively with time, peaking at 2.60 min (time range above 95% of the maximum value: 0–4.43 min) for the GM and 1.80 min (time range above 95% of the maximum value: 1.40–3.53 min) for the WM. In the diseased hemisphere, aczBOLD CVR significantly correlated with baseline DSC time-to-maximum of the residue function (T_max) (P = 0.008 for the WM) and normalized cerebral blood flow (P = 0.003 for the GM, and P = 0.001 for the WM). AczBOLD provides a novel, safe, easily implementable approach to CVR measurement in the routine clinical environments. Further studies can establish quantitative thresholds from aczBOLD towards identification of patients at heightened risk of recurrent ischemia and cognitive decline.

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A method coupling BOLD with ACZ challenge (aczBOLD) for CVR assessment was proposed.

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Compromised CVR was detected in patients with cerebrovascular disease.

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Dynamic effects of ACZ on BOLD were characterized.

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CVR correlated with baseline dynamic susceptibility contrast perfusion MRI.

The evolution of cerebral revascularization surgery

Among the relatively few surgeons to be awarded the Nobel Prize was Alexis Carrel, a French surgeon and pioneer in revascularization surgery at the turn of the 20th century. The authors trace the humble beginnings of cerebral revascularization surgery through to the major developments that helped shape the modern practice of cerebral bypass surgery. They discuss the cornerstone studies in the development of this technique, including the Extracranial/Intracranial Bypass Study initiated in 1977. Recent innovations, including modern techniques to monitor cerebral blood flow, microanastomosis techniques, and ongoing trials that play an important role in the evolution of this field are also evaluated.

Intracranial pathology of the visual pathway

Intracranial pathologies involving the visual pathway are manifold. Aligning to anatomy, the most frequent and/or most important extrinsic and intrinsic intracranial lesions are presented. Clinical symptoms and imaging characteristics of lesions of the sellar region are demonstrated in different imaging modalities. The extrinsic lesions mainly consist of pituitary adenomas, meningeomas, craniopharyngeomas and chordomas. In (asymptomatic and symptomatic) aneurysms, different neurological symptoms depend on the location of aneurysms of the circle of Willis. Intrinsic tumors as astrocytoma of any grade, ependymoma and primary CNS-lymphoma require the main pathology in the course of the visual pathway. Vascular and demyelinating diseases complete this overview of intracranial lesions.

Hyperintense middle cerebral artery sign using MRI

AIM

To assess whether the presence of the hyperintense middle cerebral artery (MCA) sign, detected using magnetic resonance imaging (MRI), has any prognostic value in subacute infarction. The results were also compared with computed tomography (CT).

MATERIALS AND METHODS

Twenty-five consecutive patients with suspected subacute ischaemic stroke (6-48 h after onset of symptoms) underwent MRI and CT assessment. The incidence of intraluminal thrombus demonstrated by conventional T1 and T2-weighted images was assessed. The results were correlated with National Institutes of Health Stroke Scale (NIHSS).

RESULTS

Hyperintense MCA was identifiable on T1-weighted images in 77.8% patients, on T2-weighted images in 61.1% patients, and in 38.9% patients using CT. Patients with intraluminal thrombus identified by MRI had more severe stroke (mean NIHSS of 12.2+/-8.0 versus 4+/-3.2 respectively, p=0.003).

CONCLUSIONS

The presence of hyperintense MCA by MRI is associated with higher NIHSS and may therefore have a prognostic value.

Comparison of Doppler ultrasound, magnetic resonance angiographic techniques and catheter angiography in evaluation of carotid stenosis

AIM

To compare the accuracy of ultrasound and two magnetic resonance (MR) angiographic techniques with catheter angiography in assessing atherosclerosis at the carotid bifurcation.

MATERIALS AND METHODS

Forty patients with symptomatic carotid stenosis were studied by Doppler ultrasound, time-of-flight MR angiography, contrast-enhanced MR angiography and conventional catheter angiography. The degree of stenosis found on ultrasound and MR angiography was compared with the results of catheter angiography. Four different assessment methods were conducted for the MR angiographic data. Kappa, sensitivity and specificity (with confidence intervals) values were calculated for the US and MR angiography results compared to catheter angiography.

RESULTS

Catheter angiography showed 12 internal carotid artery occlusions (15%), 34 severe (44%), 12 moderate (15%) and 20 mild stenoses (26%), using NASCET criteria. Ultrasound showed 65% sensitivity and 95% specificity in detecting surgically amenable lesions, whilst the MR angiographic techniques had sensitivities varying from 82-100%, and specificities from 95-100%.A moderate kappa value was calculated for the US data, whilst all MR techniques were found to show very good agreement with catheter angiography.

CONCLUSION

This data suggests that MR angiography is more accurate than Doppler ultrasound in defining surgical lesions and has comparable accuracy to catheter angiography. The use of contrast-enhanced MR angiography is useful in certain situations but is not essential in all cases.

STAR MR angiography for rapid detection of vascular abnormalities in patients with acute cerebrovascular disease

BACKGROUND AND PURPOSE

We undertook to investigate the usefulness of signal targeting with alternating radiofrequency magnetic resonance angiography (STAR MRA) in the diagnosis of acute cerebrovascular disease. The potential advantage of the technique is that angiographic images can be acquired in less than 1 minute.

METHODS

We studied 19 patients (11 men and 8 women, ranging in age from 36 to 84 years [mean age, 66 years]) presenting with signs and symptoms of acute stroke. Patients underwent STAR MRA and three-dimensional fast imaging with steady-state precession (3D FISP) MRA. The MRAs were analyzed as to image quality and vascular abnormalities in the vascular territory of stroke as defined by diffusion-weighted imaging abnormalities and compared using a Wilcoxon signed-rank test.

RESULTS

STAR MRAs had slightly inferior image quality compared with 3D FISP MRA (P < .05). STAR MRA and 3D FISP MRA agreed in 18 of 19 cases regarding vascular abnormalities in the territory of the infarct (occlusion, n = 8; stenosis, n = 4; no abnormality, n = 6). In one patient, the techniques disagreed, when 3D FISP MRA was normal and STAR MRA demonstrated a vessel occlusion in the vascular territory of a stroke as defined by diffusion-weighted imaging abnormalities (P > .05).

CONCLUSIONS

Despite slightly inferior image quality compared with 3D FISP MRA, STAR MRA is comparable with 3D FISP MRA in depicting abnormalities in the proximal parts of the cerebral arteries corresponding to ischemic regions on diffusion-weighted imaging, in a strikingly shorter acquisition time. Further studies are necessary to confirm that the smaller branches are better shown by using longer inversion times.

Computed tomographic brain scans and antiplatelet therapy after stroke: a study of the quality of care in Dutch hospitals

BACKGROUND AND PURPOSE

We sought to develop a measure ("quality weight" that indicates the severity of a deviation from optimal care with respect to secondary prevention with antiplatelet treatment after stroke. We also sought to estimate the effects that efforts to improve the quality of secondary prevention may have on health outcome and healthcare costs in the Netherlands.

METHODS

First, we developed quality weights with decision analysis techniques. These quality weights express the excess risk of vascular events in the first 2 years after stroke compared with the optimal strategy (CT brain scan in all patients and aspirin in case of cerebral infarction). Second, these weights were applied in a follow-up study of 738 stroke patients older than 45 years. The number of stroke patients admitted to a hospital in 1991 in the Netherlands was used to estimate nationwide effects. We used data from 23 neurological departments and from the Information Center for Health Care in the Netherlands.

RESULTS

The 2-year excess risk of fatal and nonfatal vascular events caused by omitting CT brain scan and giving aspirin to all patients is rather small (on average, 0.6%). The 2-year excess risk caused by not giving aspirin to a patient with cerebral infarction is much higher (4.1%). The follow-up study indicated that only 6% of the admitted patients had not been evaluated with a CT brain scan and that 14% of the patients with cerebral infarction proven by CT scan did not get antiplatelet treatment at discharge. Efforts to improve the quality of secondary prevention after stroke may prevent 74 vascular events annually in the Netherlands at an expense of 6200 Dutch guilders per prevented event (1 Dutch guilder=0.53 US dollar, 1991).

CONCLUSIONS

Efforts to improve the quality of secondary prevention with antiplatelet treatment might reduce the number of new vascular events within the first 2 years after stoke by approximately 3%. The total costs related to the extra diagnostic and therapeutic activities are approximately 0.2% of the total annual hospital costs for acute stroke patients in teh Netherlands (250 million Dutch guilders).

Stenoses of the first segment of the vertebral artery: difficulties in angiographic diagnosis

Pathology at the origin of the vertebral artery may be the cause of incapacitating vertebrobasilar insufficiency (VBI). Preoperative diagnosis is made primarily on angiographic criteria. We compared intraoperative and angiographic findings in 30 patients and found important diagnostic discrepancies in patients with a caudal, ventral or dorsal origin of the vertebral artery. In their angiograms, vessel superimposition led us to over look 3 ostial stenoses and 10 stenoses due to kinking. Angiographic assessment of patients with VBI can be difficult. Adequate visualisation of the origin of the vertebral artery is mandatory for accurate diagnosis.

Cost-effective investigation of patients with suspected transient ischaemic attacks

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