Cerebral infarction in patients with transient ischemic attacks

Factors Associated with Cognitive Decline in Transient Ischemic Attack Patients

Chronic cerebrovascular disease and large ischemic stroke are both associated with cognitive impairment. Much less is known about the acute cognitive sequelae of transient ischemic attack (TIA). Although often overlooked, there is increasing evidence that cognitive impairment does occur following TIA. In some patients, cognitive changes persist after resolution of focal neurological deficits, but the temporal profile of these symptoms is unknown. In addition, clinical and imaging correlates of cognitive impairment after TIA have not been systematically studied. This under-studied and recognized problem has significant implications for TIA patient management. In this review, we summarize the evidence currently available and identify future research priorities.

Head Computed Tomography Findings Predict Short-Term Stroke Risk After Transient Ischemic Attack

Background and Purpose— Current guidelines recommend the use of head CT in the evaluation of patients with transient ischemic attack (TIA), but data supporting its value are sparse.

Methods— Patients who presented to 1 of 16 emergency departments of a large Northern California health maintenance organization and received a diagnosis of TIA from November 1997 through February 1998 were enrolled and followed up for 90 days. Clinical, demographic, and outcome data were obtained from computerized databases and medical records. Physicians blinded to patient characteristics and outcomes abstracted head CT findings from radiology reports. Abstracted findings included evidence of old or new infarct, periventricular white-matter disease, cerebral atrophy, cerebral vascular calcification, and nonischemic lesions.

Results— Head CT was performed in 67% of eligible patients (n=322) diagnosed with TIA. Evidence of a new infarct was seen on head CT in 13 patients (4%). A nonischemic cause of TIA symptoms was found in 4 patients (1.2%). During follow-up, 10.9% of TIA patients experienced subsequent stroke. After adjustment for confounders, risk for stroke during follow-up was significantly higher in those with a new infarct on head CT compared with others with TIA (odds ratio, 4.06; 95% confidence interval, 1.16 to 14.14; P =0.028). Old infarction, periventricular white-matter disease, cerebral atrophy, and cerebral vascular calcification were not predictors of subsequent risk of stroke.

Conclusions— Evidence of a new infarct on head CT in patients presenting with TIA is associated with increased short-term risk for stroke. Head CT appears to have prognostic value in patients with TIA and, for this reason alone, may be justified in their evaluation.

Hemodynamic and metabolic changes in transient ischemic attack patients: a magnetic resonance angiography and (1)H-magnetic resonance spectroscopy study performed within 3 days of onset of a transient ischemic attack

BACKGROUND AND PURPOSE

We investigated whether patients with transient ischemic attack (TIA) have systemic low flow to the brain or an abnormal intracranial flow distribution caused by an abnormal anatomy of the circle of Willis. Furthermore, we investigated whether metabolic changes were present in the brain.

METHODS

Forty-four patients with clinically diagnosed TIA were prospectively included in our study. Clinical and neurological data were compiled. MR imaging; quantitative flow measurements of the internal carotid, middle cerebral, and basilar arteries; MR angiography of the circle of Willis; and (1)H-MR spectroscopy were performed in all patients within 3 days of onset of symptoms.

RESULTS

Compared with control subjects, TIA patients did not have altered flow volume in any of the arteries and had normal flow distribution through the circle of Willis. In TIA patients, the N-acetylaspartate (NAA)/choline ratio in noninfarcted regions was significantly decreased in the symptomatic hemisphere (1.73+/-0.16) compared with the asymptomatic hemisphere (1.84+/-0.19, P<0.05) and control subjects (1.90+/-0.17, P<0.001). In the symptomatic hemisphere, the lactate/NAA ratio was significantly increased (0.04+/-0.08) compared with control subjects (0.00+/-0.01, P<0.05). Patients with a history of prior TIA had a significantly decreased NAA/choline ratio in both the symptomatic (P<0.05) and asymptomatic (P<0.05) hemispheres compared with TIA patients without a prior TIA.

CONCLUSIONS

TIA patients have neurological deficits that are transient; however, metabolic damage to the brain is present up to 3 days after the onset of the symptoms. These metabolic changes are not restricted to the symptomatic hemisphere or to areas close to ischemic lesions.

Prevalence and associations of MRI-demonstrated brain infarcts in elderly subjects with a history of transient ischemic attack. The Cardiovascular Health Study

BACKGROUND AND PURPOSE

MRI is more sensitive than CT, but the significance of brain abnormalities seen on MR images obtained in older subjects with transient ischemic attack (TIA) is not clear. We studied the prevalence and risk factors associated with MRI-demonstrated infarcts in elderly subjects with a history of TIA.

METHODS

Participants of the Cardiovascular Health Study, aged 65 years or more and without prior stroke, were studied with brain MRI (n=3456). The prevalence of brain infarcts (>/=3 mm) on MRI was determined in subjects with and without TIA. The cardiovascular risk factors and clinical and subclinical cardiovascular disease associated with MRI infarcts were studied in subjects with TIA.

RESULTS

Subjects with TIA (n=100) had a higher prevalence of MRI infarcts than subjects without TIA (46% versus 28%; P<0.001). The unadjusted odds ratio for having MRI infarcts in subjects with TIA was 2.20 (95% CI, 1.47 to 3.30) and remained significantly elevated after adjustments for risk factors and cerebrovascular disease (odds ratio, 1.86; 95% CI, 1.23 to 2.83). In subjects with TIA, diastolic blood pressure (P=0.01) and internal carotid artery intima-media thickness (P=0.01) were the only factors predictive of the presence of MRI infarcts by stepwise logistic regression analysis.

CONCLUSIONS

MRI infarcts are imaging manifestations of clinically important cerebrovascular disease in subjects with a history of TIA, given their increased prevalence and positive association with increased diastolic blood pressure and internal carotid artery intima-media thickness.

Cigarette smoking and other risk factors for silent cerebral infarction in the general population

BACKGROUND AND PURPOSE

Silent cerebral infarctions (SCIs) have a prevalence between 10% and 40% in the transient ischemic attack population and have been associated with increased mortality and morbidity; however, little is known about the prevalence and risk factors for SCI in the general population. This report focuses on the role of cigarette smoking and other risk factors for SCI in the general population.

METHODS

MRI scans were performed on 1737 participants selected from the general population as part of the Atherosclerosis Risk in Communities Study. Smoking status and other major cerebrovascular risk factors were assessed, and associations between smoking status and SCIs were established with the use of ANCOVA.

RESULTS

Overall, the prevalence of SCI in this population aged 55 to 70 years was 11%. Cigarette smoking had an ordered association (P=0.029) with the presence of SCI, with the odds ratio (OR) of nonsmoking participants exposed to environmental tobacco smoke being 1.06 (95% confidence interval [CI], 0.64 to 1.75) times as great as for nonsmokers not exposed; the OR of past smokers was 1.16 (95% CI, 0.74 to 1.83) times greater, and the OR of current smokers was 1.88 (95% CI, 1.13 to 3.13) times greater. An increased prevalence was also noted among black, older, and hypertensive participants.

CONCLUSIONS

This report is among the first to examine the risk factors for SCI in the general population and finds a relatively high overall prevalence (11%). There is an ordered relationship between increasing exposure to cigarette smoke and the presence of SCI that parallels the relationship between smoking and carotid atherosclerosis. The magnitude of the association with smoking is substantial compared with the effect of hypertension and other traditional cerebrovascular risk factors. The reduction in prevalence of SCI between current and past smokers and the trend that increased pack-years of smoking is related to increased prevalence of SCI are both additional arguments for smoking avoidance and cessation.

HMG-CoA reductase inhibitor therapy and stroke risk reduction: an analysis of clinical trials data

Although associations of cholesterol and coronary heart disease (CHD) are well accepted, the association between cholesterol and stroke has been a subject of some confusion. Epidemiologic evidence suggests no association between plasma concentrations of cholesterol and stroke, and earlier clinical trials were also negative. Two early meta-analyses of clinical trials designed to evaluate the effects of cholesterol lowering on CHD concluded that cholesterol lowering had no effect. More recently newer, more potent and better tolerated agents (HMG-CoA reductase inhibitors, reductase inhibitors) have become available and have been tested for their efficacy in reducing cholesterol and CHD in both primary prevention and secondary prevention trials. Meta-analyses of these trials, in contrast to the earlier trials, reveal a powerful statistically significant effect to reduce stroke as well as CHD in secondary prevention (30%); the direction of the effect is the same in trials of primary prevention or trials that randomized patients with and without CHD (mixed primary and secondary prevention trials) where the risk reductions for stroke, although not reaching statistical significance are 11 and 30%, respectively. An important difference in the newer analysis is the availability of several trials of secondary prevention in which low density lipoprotein cholesterol was lowered 25-30% and in which CHD event reduction was similarly reduced by 30%. Mechanisms for stroke reduction likely involve retardation of plaque progression in the intracranial and extracranial carotid arteries, plaque stabilization, and, in addition, stroke may be reduced partly as a consequence of CHD reduction.

Persisting perfusion defect in transient ischemic attacks: a new clinically useful subgroup?

BACKGROUND AND PURPOSE

Cerebral infarction and prolonged regional hypoperfusion have been described in patients with transient ischemic attacks (TIAs). The aim of this study was to compare the sensitivity of single-photon emission CT (SPECT) with that of brain CT and to evaluate the clinical significance of differentiation of TIA patients with or without focal hypoperfusion.

METHODS

From a hospital-based population, we studied the SPECT and CT findings in 76 consecutive patients, without a stroke history, who presented with TIA in the carotid artery territory. The recorded variables were the time of SPECT, imaging (<36 or > or = 36 hours), clinical presentation, history of previous TIA(s), duration of the presenting attack (<2 or > or = 2 hours), vascular risk factors, and etiology. We used both visual and semiquantitative analyses for the SPECT evaluation. Acetazolamide challenge was not performed.

RESULTS

The overall SPECT sensitivity was 36% (27/76). When brain CT and SPECT were performed in the same patients, the SPECT sensitivity was significantly higher than that of CT (19/59 [32%] versus 8/59 [14%]; P=.007). The SPECT sensitivity was not dependent on the time of investigation, duration of attacks, history of TIA(s), or the clinical presentation. The vascular risk and etiologic factors were not significantly different between the patients with or without prolonged focal hypoperfusion. Logistic regression did not identify any variable to discriminate the two groups.

CONCLUSIONS

Despite its better sensitivity compared with CT, SPECT performed without the acetazolamide test provides no additional clinically useful information on the vascular risk factors and etiology in TIA patients.

Silent cerebral infarction in a community-based autopsy series in Japan. The Hisayama Study

BACKGROUND AND PURPOSE

The purpose of this study was to assess the prevalence and characteristics of silent cerebral infarction in a population-based consecutive autopsy series of residents of Hisayama, Kyushu, Japan.

METHODS

Autopsy records, cerebral pathological findings, and clinical charts of 966 Hisayama residents recorded during the 26 years from 1961 to 1987 were examined (autopsy rate, 82.4%). The subjects were divided into three groups: those with both clinically apparent strokes and pathologically verified cerebral infarcts (stroke group), those having pathological evidence of cerebral infarction in the brain but without clinical stroke episodes (silent infarction group), and those with neither infarction nor stroke episode (noninfarction group). Risk factors and brain pathology in the three groups were compared.

RESULTS

Silent cerebral infarction was found in 12.9% of the 966 subjects who had undergone autopsy, and its frequency increased with age. The subjects with silent infarcts were older, had higher systolic or diastolic blood pressure, and had atrial fibrillation more frequently than subjects in the noninfarction group. There were no significant differences in the locations of infarcts between the stroke and silent infarction groups, although infarcts tended to be located in the deeper area of the brain in the latter. The number and size of infarcts were smaller in the silent infarction group than in the stroke group.

CONCLUSIONS

Diastolic blood pressure and atrial fibrillation appear to be strong predictors of silent cerebral infarction in the Japanese general population. Stroke becomes clinically apparent as infarct volume increases.

Silent brain infarcts in 755 consecutive patients with a first-ever supratentorial ischemic stroke. Relationship with index-stroke subtype, vascular risk factors, and mortality

BACKGROUND AND PURPOSE

We wanted to establish independent associations of various clinical variables, computed tomographic (CT) scan features, presenting stroke subtypes, and outcome with the presence of silent infarcts on CT.

METHODS

We studied 755 consecutive patients in a prospective registration of patients with first-ever supratentorial atherothrombotic, cardioembolic, or lacunar stroke or stroke of undetermined cause by multiple logistic regression analysis.

RESULTS

Two hundred six patients (27%) with a first symptomatic territorial or small deep ischemic stroke had one or more silent infarcts on CT. Of all silent lesions, 169 (82%) were small and deep. Silent infarcts were significantly more strongly associated with a lacunar than atherothrombotic (odds ratio [OR], 1.59; 95% confidence interval [CI], 1.02 to 2.47; P = .039) or cardioembolic (OR, 1.89; 95% CI, 1.2 to 2.99; P = .005) index stroke. Silent territorial lesions were more strongly associated with cardioembolic than with lacunar stroke but not with atherothrombotic stroke. In this respect, no differences were found between the atherothrombotic and undetermined-cause group. Advanced age and hypertension were the only risk factors that were significantly associated with silent infarcts (OR, 1.76; 95% CI, 1.14 to 2.71; P = .011; and OR, 1.58; 95% CI, 1.13 to 2.21; P = .007; respectively), mainly because of a strong independent association of these risk factors with silent small deep infarcts (OR, 1.75; 95% CI, 1.10 to 2.79; P = .018; and OR, 1.57; 95% CI, 1.09 to 2.24; P = .014; respectively). A cardioembolic source or atrial fibrillation in specific was not independently associated with any type or number of silent infarcts. Significant carotid stenosis (diameter reduction > 50%) was not significantly associated with any type of silent lesion. Initial severe handicap (Rankin Scale score > 3), 30-day case fatality rate, and 1-year mortality were not affected by the presence of silent infarcts.

CONCLUSIONS

The strong association of silent small deep lesions with first symptomatic small deep infarcts suggests a common underlying mechanism (presumably small-vessel vasculopathy), whereas cardiogenic embolism and large-vessel thromboembolism are the most likely causes in both silent and first symptomatic territorial infarcts. Single or multiple silent infarcts do not predict a cardioembolic stroke mechanism in first symptomatic supratentorial brain infarcts. As silent infarcts do not predict the cause of carotid embolic stroke in first symptomatic brain infarcts, their presence should not influence the decision on carotid surgery. Silent infarcts do not affect the degree of initial handicap, 30-day case fatality, or 1-year mortality. The significance of silent infarcts for predicting possible future cognitive decline and risk of recurrent stroke deserves further study.

Silent infarction on a second CT scan in 91 patients without manifest stroke in the Dutch TIA trial

The frequency of silent infarction is an important issue because it is a marker of vascular disease. We studied the occurrence of silent infarction in a sample of patients from the Dutch TIA trial, in which patients were randomized between 30 and 283 mg of aspirin. A total of 91 patients with TIA or non-disabling ischemic stroke and who did not suffer a stroke during a period of one to four years (mean 32 months) underwent CT scanning both on entry and at the end of the study. A cardiac source of embolism was an exclusion criterion for the trial. We found only one patient with a possibly silent infarction; in four patients a previously detected symptomatic infarct on CT was no longer visible. The rarity of silent infarction in this study may have several explanations; (1) the relatively short period of follow-up, (2) the selection of patients (no cardiac source of embolism), (3) the clinical monitoring at four monthly intervals aimed at detection of focal ischemia, (4) the use of aspirin. Given these circumstances, silent infarction is an infrequent problem.

Baseline silent cerebral infarction in the Asymptomatic Carotid Atherosclerosis Study

BACKGROUND AND PURPOSE

In a group of patients with high-grade asymptomatic carotid artery stenosis, we prospectively determined the prevalence and radiological characteristics of clinically asymptomatic brain infarction evident on computed tomography. Risk factors and extent of carotid disease were also determined.

METHODS

Patients randomized into the Asymptomatic Carotid Atherosclerosis Study (ACAS) underwent a neurological history, a detailed stroke/transient ischemic attack questionnaire, and a detailed neurological examination. Computed tomography scans were examined by standardized criteria developed as part of a quality-control program supervised by a neuroradiologist. The presence, location, and size of all cerebral infarctions evident by computed tomography were determined.

RESULTS

Among 1132 patients, 848 had no history of stroke or transient ischemic attack. One hundred twenty-six patients (15%) had a silent infarct; 95 (11%) had one, 24 (3%) had two, and 7 (1%) had three or more infarcts. The infarct size was small and deep for 117 patients (72%), less than one-half lobe for 45 (28%), and one-half to less than one lobe for 1 (0.5%). The silent infarcts were evenly distributed ipsilaterally and contralaterally to the study artery but were significantly more frequent in the right hemisphere (P < .05). Factors associated with silent infarction were abnormal gait (P < .001), abnormal deep tendon reflexes or plantar responses (P = .038), but not degree of carotid stenosis. Silent infarction was less frequent among this totally asymptomatic cohort (15%) compared with those with transient ischemic attacks (34/139, 25%; P < .001).

CONCLUSIONS

Silent infarction in the setting of asymptomatic carotid stenosis is not uncommon, but silent infarctions are rarely sizable. The clinical significance of silent cerebral infarction in patients with asymptomatic carotid artery stenosis has yet to be established.

The prognosis of hospital-referred transient ischaemic attacks

A cohort of 469 hospital-referred patients with transient ischaemic attacks (TIA) of the brain (66%) or eye (34%) due to presumed atheromatous thromboembolism, lipohyalinosis or cardiogenic embolism, without prior stroke, was assembled between 1976-86. Follow up was prospective and complete until the patients death or the end of 1986. During a mean period of follow up of 4.1 years there were 82 deaths (58 vascular, 24 non-vascular), 63 first-ever strokes and 58 patients with coronary events. A coronary event accounted for 51% of deaths whilst stroke was the cause in 12%. The average risk of death over the first five years after TIA was 4.5% per year. The risk of stroke was 6.6% in the first year and 3.4% per year on average over the first five years. Stroke occurred in the same vascular territory as the initial TIA in about two-thirds of cases, and was of lacunar type in one fifth of these strokes. The average risk of a coronary event over the first five years after TIA was 3.1% per year, similar to that of stroke. However, the risk of a coronary event, and also death, was fairly constant each year after a TIA, in contrast to the risk of stroke which was highest in the first year. The average risk of stroke, myocardial infarction or vascular death over the first five years after TIA was 6.5% per year and the average risk of stroke, myocardial infarction or death from any cause was 7.5% per year. The prognosis of this cohort of hospital-referred TIA patients was better than that of TIA patients in the same community who presented to the Oxfordshire Community Stroke Project (OCSP), and reflected the impact of referral bias. The hospital-referred patients were younger, assessed at a later date after their last TIA, and comprised a greater proportion of patients who had had a TIA of the eye (amaurosis fugax), which had a better prognosis than TIA of the brain. Knowledge of the prognosis of different populations of TIA patients not only enhances understanding and interpretation of previous studies but is also required for optimal patient management and the planning of treatment trials.

High frequency of asymptomatic visual field defects in subjects with transient ischaemic attacks or minor strokes

The hypothesis that asymptomatic visual field defects can be found in patients with carotid transient ischaemic attacks (TIA) or minor strokes was tested. Twenty-two consecutive male patients with TIA and 18 patients with minor strokes from the carotid artery territory were examined by perimetry, cerebral computerised tomography and regional cerebral blood flow. Asymptomatic visual field defects were found in many TIA and minor stroke patients, 29% (5/17) and 57% (8/14), respectively (NS). Eighty-five per cent (11/13) of the scotomas were solely or predominantly located in the upper part of the visual field (P = 0.008 for absolute defects and P = 0.03 for relative defects). We conclude that both carotid territory TIA and minor stroke patients have a high frequency of asymptomatic visual field defects, predominantly located in the upper part of the visual field.

Cerebral infarction verified by cranial computed tomography and prognosis for survival following transient ischemic attack

Of 564 consecutive patients with transient ischemic attack, 350 (62%) had cranial computed tomography performed. Except for date of admission and smoking history, there were few differences between the patients evaluated with computed tomography and the 214 who were not. Cerebral infarcts were found in 59 (17%) of the 350 tomographic evaluations. Previous clinically diagnosed stroke, older age, and male sex were all significantly associated with the occurrence of tomographically verified infarcts (p less than 0.05). After controlling for stroke history and other important covariates, patients with tomographically verified infarcts had significantly shorter survival times than did patients without evidence of infarction on computed tomography (p = 0.035). Thus, cranial computed tomography findings appear to have important prognostic value for estimating survival following transient ischemic attack.

The Willis lecture: transient ischemic attacks, scientific method, and new realities

First described by Thomas Willis in 1679 and defined in the 1950s, transient ischemic attack is universally agreed to be an episode of focal neurologic deficit in a vascular distribution, sudden in onset and resolving without residual deficit in less than or equal to 24 hours. Transient ischemic attack is diagnosed by characteristic history and absence of residua on neurologic examination. After these criteria had been accepted, regional cerebral blood flow and computed cranial tomography in the 1970s, later positron emission tomography, and even more recently, magnetic resonance imaging reveal prolonged pathophysiologic and metabolic disturbances even in persons with all the definitional characteristics of transient ischemic attack. These persistent abnormalities necessitate reexamination of the validity of the concept of transient ischemic attack. Furthermore, our group suspects that transient ischemic attack is probably only a marker, and not itself the risk factor, for the cerebral infarction which frequently follows transient ischemic attack. Additionally, the surprising frequency with which cerebral infarction, unrecognized by patient or physician, is revealed using neuroimaging techniques has created a need to redefine the categories heretofore used for diagnosis and assessment of therapy and prognosis for transient ischemic attack and cerebral infarction.

Computed tomography in patients with transient ischaemic attacks: when is a transient ischaemic attack not a transient ischaemic attack but a stroke?

In a prospective community-based study, 184 patients with transient ischaemic attacks (TIAs) were identified from a study population of about 105,000 between 1981 and 1986. Computed tomography (CT) was attempted in all those with cerebral ischaemic attacks (n = 152, 83%); patients with amaurosis fugax only (n = 32, 27%) were not scanned routinely. Scans were obtained in 120 (79%) of those with cerebral attacks and 12 (38%) of those with amaurosis fugax. The scans were reported by a neuroradiologist who was blinded to the patients' clinical features. Of 120 (27%:95% confidence interval 19-35) scans in patients with cerebral attacks, 32 showed a focal area of hypodensity or cortical loss, but in only 14 (12%:95% confidence interval 6-18) was this in an area of the brain appropriate to the patients' symptoms. There were no significant differences in the clinical features, the duration of attacks or the prognosis (i.e., risk of death, stroke or myocardial infarction) of patients with and without ischaemic lesions on CT. It is concluded that patients with clinically definite TIAs who have a presumed ischaemic and appropriately sited lesion on CT should not be re-classified as having had a stroke.