Lesions visualized by contrast-enhanced magnetic resonance imaging in transient ischemic attacks

Acute EEG Patterns Associated With Transient Ischemic Attack

BACKGROUND

Transient ischemic attack (TIA) is characterized by stroke-like neurologic signs and symptoms in the absence of demonstrable structural neuropathology. There is no test for TIA, with classification often reliant on subjective, retrospective report. Functional brain measures such as the electroencephalogram (EEG) may be helpful in objectively detecting and describing the pathophysiology of TIA, but this has not been adequately examined.

METHODS

EEG was obtained from a single electrode over the left frontal lobe during 3-minute resting-state and auditory oddball conditions administered to consecutive patients within 72 hours of admission to the acute stroke ward of a tertiary hospital. Separately, patients were classified by their treating team as having suffered either an ischemic stroke (n = 10) or a TIA (n = 10). Relative power of delta, theta, alpha, and beta EEG frequency bands were extracted for comparison between the 2 clinical groups and an existing normative sample of 10 healthy, age-, gender-, and education-matched older adults.

RESULTS

Analysis of variance with post hoc testing identified pronounced delta activity in stroke patients, while alpha and beta power were elevated in TIA patients. Both patient groups exhibited attenuated theta activity compared with healthy controls. Receiver operating characteristic curve analysis identified thresholds for each EEG frequency capable of distinguishing the 3 participant groups.

CONCLUSIONS

TIA, ischemic stroke, and healthy aging are each associated with distinct electrophysiological profiles. These preliminary findings suggest that acute EEG may be helpful in elucidating the pathophysiology and reversibility of TIA symptoms, and further exploration of the value of this unique functional brain data is encouraged.

Diffusion-weighted lesions in stroke patients with transient symptoms--where are they located?

BACKGROUND

MR diffusion-weighted imaging (DWI) has revolutionized neuroimaging and contributed to a tissue-based redefinition of transient ischemic attack (TIA). Stroke patients with DWI lesions may have neurological symptoms that resolve completely within 24 h, suggesting successful vessel recanalization. Prior studies of stroke patients with transient symptoms have not found any predilection for DWI lesions in any specific territory. Other studies have, however, reported an association between higher brain dysfunction and presence of DWI lesions in patients with transient ischemic symptoms, suggesting a high rate of cortical affection in these patients. We sought to see whether DWI location in stroke patients with transient symptoms <24 h differed from those with persistent symptoms ≥ 24 h. We hypothesized an association between transient symptoms <24 h and cortical DWI lesion localization due to a possible higher rate of vessel recanalization in patients with transient symptoms causing distal cortical infarctions.

METHODS

Ischemic stroke patients examined with DWI and admitted within 24 h after symptom onset between February 2006 and November 2013 were prospectively registered in a database (The Bergen NORSTROKE Registry). Based on neurological examination 24 h after admission, patients were classified as having either transient symptoms <24 h (DWI <24) or persistent symptoms ≥ 24 h (DWI ≥ 24). DWI lesions were classified into different groups depending on lesion location: cortical lesions, confined to the supratentorial cortex; large subcortical lesions, located in the hemispheric white matter, basal ganglia, internal capsule, thalamus or corona radiate with a diameter ≥ 15 mm; lacunar lesions, located in the same territory as large subcortical lesions with a diameter <15 mm; mixed cortical-subcortical lesions, located in both supratentorial cortex and subcortex; cerebellar lesions, confined to the cerebellum; brain stem lesions, confined to the brain stem; multiple locations, located in more than one of the above defined areas.

RESULTS

A total of 142 ischemic stroke patients had DWI <24 and 830 DWI ≥ 24. Cortical DWI location was more frequent in patients with DWI <24 (54.2% vs. 29.5%, p < 0.001), while proportions of mixed cortical-subcortical lesions (13.4% vs. 26.5%, p = 0.001) and lesions with multiple locations (5.6% vs. 11.1%, p = 0.048) were less frequent as compared to DWI ≥ 24. Cortical DWI location was independently associated with DWI <24 when adjusted for confounders in multiple regression analyses (OR 1.89, 95% CI 1.28-2.81, p = 0.001).

CONCLUSION

Cortical DWI location was independently associated with transient stroke symptoms <24 h. This may be explained by vessel recanalization, resulting in upstream transportation of remaining particles and distal cortical lesions.

Contrast-enhanced MR imaging in neuroimaging

MR imaging without and with gadolinium-based contrast agents (GBCAs) is an important imaging tool for defining normal anatomy and characteristics of lesions. GBCAs have been used in contrast-enhanced MR imaging in defining and characterizing lesions of the central nervous system for more than 20 years. The combination of unenhanced and GBCA-enhanced MR imaging is the clinical gold standard for the noninvasive detection and delineation of most intracranial and spinal lesions. MR imaging has a high predictive value that rules out neoplasm and most inflammatory and demyelinating processes of the central nervous system.

Evaluation and management of transient ischemic attack: an important component of stroke prevention

Stroke and transient ischemic attack (TIA) share similar risk factors and methods of evaluation and secondary prevention. As neurological symptoms resolve after TIA, however, there has been a widely held perception that urgent evaluation and treatment following TIA are unnecessary. In actual fact, it is becoming increasingly clear that the short-term stroke risk after TIA is very high. Recent studies have identified independent predictors that indicate which patients are at highest risk of recurrent ischemic events. These risk scores could enable physicians to target appropriate patients for urgent care. In this Review, we summarize the recent literature on stroke risk after TIA and risk stratification, and recently published guidelines on evaluation and treatment.

Systematic Review of Associations Between the Presence of Acute Ischemic Lesions on Diffusion-Weighted Imaging and Clinical Predictors of Early Stroke Risk After Transient Ischemic Attack

BACKGROUND AND PURPOSE

Early risk of stroke after a transient ischemic attack can be reliably predicted with risk scores based on clinical features of the patient and of the ischemic event, but it is unclear how these features correlate with findings on brain imaging.

METHODS

We performed a systematic review of the literature and identified all previous studies which reported patient characteristics and the nature of transient ischemic attack symptoms in relation to appearances on diffusion-weighted imaging (DWI). We then performed a meta-analysis of the associations between the components of the risk scores and positive DWI. Authors were contacted for additional unpublished data.

RESULTS

Nineteen studies were identified by the systematic review, and additional unpublished data were obtained from 11 of these studies. On meta-analysis, several components of the risk scores were associated with positive DWI, including symptom duration > or =60 minutes (13 studies, odds ratio [OR], 1.50; 95% CI, 1.16 to 1.96; P=0.004), dysphasia (9 studies, OR, 2.25; 95% CI, 1.57 to 3.22; P<0.001), dysarthria (8 studies, OR, 1.73; 95% CI, 1.11 to 2.68; P=0.03) and motor weakness (9 studies, OR, 2.20; 95% CI, 1.56 to 3.10; P<0.001). However patient age, sex, hypertension and diabetes were not associated with the presence of DWI lesions. From an etiologic perspective, atrial fibrillation (9 studies, OR, 2.75; 95% CI, 1.78 to 4.25; P<0.001) and ipsilateral > or =50% carotid stenosis (10 studies, OR, 1.93; 95% CI, 1.34 to 2.76; P=0.001) were associated with positive DWI.

CONCLUSIONS

Presence of acute ischemic lesions on DWI correlates with several clinical features known to predict stroke risk after transient ischemic attack. Large studies (sample size >1000) will therefore be required to determine the independent prognostic value of DWI and its interactions with these clinical characteristics.

Stroke Imaging at 3.0 T

Stroke is a devastating disease with a complex pathophysiology. It is a major cause of death and disability in North America. To fully characterize its extent and effects, one requires numerous specialized anatomical and functional MR techniques, specifically diffusion-weighted imaging, MR angiography, and perfusion-weighted imaging. The advent of 3.0 T clinical scanners has the potential to provide higher quality information in potentially less time compared with 1.5 T stroke-specific MR imaging protocols. This article gives a brief overview of stroke, presents the principles and clinical applications of the relevant MR techniques required for diagnostic stroke imaging at high field, and discusses the advantages, challenges, and limitations of 3.0 T imaging as they relate to stroke.

Diffusion-weighted MR imaging in transient ischaemic attacks

The purpose of this study was to determine frequency and the characteristics of diffusion-weighted imaging (DWI) abnormalities in patients with transient ischaemic attack (TIA). We analysed data of 98 consecutive patients (mean age: 60.6+/-15.4 years, 56 men) admitted between January 2003 and April 2004 for TIA. Age, gender, symptom type and duration, delay from onset to magnetic resonance imaging (MRI), probable or possible TIA and cause of TIA were compared in patients with (DWI+) and without (DWI-) lesions on DWI. Volume and apparent diffusion coefficient (ADC) values of DWI lesions were computed. DWI revealed ischaemic lesions in 34 patients (34.7%). Lesions were small (mean volume: 1.9 cm(3)+/-3.3), and ADC was moderately decreased (mean ADC ratio: 79.5%). The diagnosis of TIA was considered as probable in all DWI+ patients. A multiple logistic regression model demonstrated that TIA duration greater than or equal to 60 min (OR, 7.6; 95% CI, 2.3-25.7), aphasia (OR, 9.2; 95% CI, 2.7-31.4) and motor deficit (OR, 5.1; 95% CI, 1.5-17.8) were independent predictors of DWI lesions. Prolonged TIA duration, aphasia and motor deficits are associated with DWI lesions. More than half of TIA patients with symptoms lasting more than 60 min have DWI lesions.

Epidemiological impact in the United States of a tissue-based definition of transient ischemic attack

BACKGROUND AND PURPOSE

The traditional definition of transient ischemic attack (TIA), based on an arbitrary time criterion of symptom resolution within 24 hours, is problematic because a large number of patients with traditionally defined TIAs have a relevant cerebral infarction on brain imaging. The objective of this study was to characterize the epidemiological impact of adopting a tissue-based definition of TIA.

METHODS

Estimates of the annual US incidence of traditionally defined transient ischemic attacks were abstracted from the literature. Models were then constructed for determining the frequency of brain injury in traditionally defined TIAs, derived from recent human studies of MR diffusion-weighted imaging (DWI) in transient cerebral ischemia.

RESULTS

Traditionally defined US TIA annual incidence rates ranged from 37 to 107 per 100,000 per year. Across 5 series, the raw frequency of DWI positivity in traditionally defined TIAs was 44%. Adjusting for an overrepresentation of longer-duration TIAs in MR series yielded an expected frequency of diffusion MRI positivity of 33% in unselected, traditionally defined TIAs. Applying this model to the US population in the year 2000 showed that adopting a tissue-based definition of TIA would decrease the annual number of events classified as TIAs from 179,840 to 120,493 and increase events classified as strokes from 821,181 to 880,520.

CONCLUSIONS

Adopting a tissue-based definition of transient ischemic attack would reduce estimates of the annual incidence of TIA by 33% (sensitivity analysis range, 19% to 44%) and increase estimates of the annual incidence of stroke in the United States by 7% (range, 4% to 10%).