Assessment of severe damage to the brain by multiregional measurements of cerebral blood flow

Regional cerebral blood flow (rCBF) was measured with a 32-detector device in patients with severe injury to the central nervous system. Most suffered head injiries in traffic accidents. Many patients were severely demented. Several were comatose or in a so-called persistent vegetative state. Flow was measured at rest and during various forms of stimulation. The resting values were on the whole markedly reduced. The flow patterns often showed distinct correlations with the original brain injury. In the best preserved patients, mental activation caused increases in flow with a normal or near-normal distribution. Cutaneous electric stimulation gave rise to increases in cortical flow even in highly reduced patients with severe brain damage. Patients with total or less than total loss of telencephalic structures with retained brainstem reflexes and respiration ('apallic' patients) did not show any changes in flow on sensory stimulation. We conclude that the technique for measuring rCBF enables us to assess severe damage to the central nervous system quantitatively and also to estimate whether higher functions are retained in severely reduced patients in coma, stupor and apallic state--patients who more or less completely lack behavioural responses.

November 1996--premature baby with lethargy and coma

A premature male baby (28 weeks gestational age) was delivered by Cesarean section and required ventilation for respiratory distress syndrome during the first postnatal week. Four weeks postnatally, he had an episode of transient renal failure followed by lethargy leading to coma. Ultrasound changes were interpreted as intraventricular hemorrhage, grade 2. The baby died 31 days after birth. Autopsy showed bilateral thrombosis of the deep cerebral veins.

Primary systemic amyloidosis with ischemic stroke as a presenting complication

BACKGROUND

Amyloidosis is an uncommon disorder that ultimately leads to fatal multiorgan failure. Ischemic strokes have been sporadically described but are not well characterized. The purpose of this study was to review the pathophysiologic relationship between primary systemic amyloidosis and ischemic stroke, and to determine how often stroke is the first defining manifestation.

METHODS

Retrospective study of 49 patients with confirmed primary amyloidosis and ischemic stroke. All included patients had biopsy proven amyloidosis.

RESULTS

Forty patients were included in the study. Ischemic strokes occurred in 13 patients (32.5%) as the initial presentation of amyloidosis. Patients with initial stroke presentation had the worst outcome, with average survival of 6.9 months after established diagnosis with amyloidosis; strokes developed 9.6 months before diagnosis with primary amyloidosis. Thirty-seven percent experienced recurrent ischemic stroke. The majority (70%) of patients had cardioembolic infarctions.

CONCLUSIONS

Ischemic stroke is an underappreciated complication of primary amyloidosis. In the absence of obvious clinical and cardiogenic manifestations, primary amyloidosis should be considered when echocardiography demonstrates thickening of the valves, restrictive pattern, and increased echogenicity. Ischemic strokes as an initial presentation of primary amyloidosis carries a worse prognosis.

Frequent Atrial Premature Beats Predict Paroxysmal Atrial Fibrillation in Stroke Patients

Background and Purpose— For patients having suffered ischemic stroke, the current diagnostic strategies often fail to detect atrial fibrillation as a potential cause of embolic events. The aim of the study was to identify paroxysmal atrial fibrillation in stroke patients. We hypothesized that patients with frequent atrial premature beats (APBs) recorded in 24-hour ECG will show more often atrial fibrillation when followed by repeated long-term ECG recordings than patients without or infrequent APBs.

Methods— 127 patients with acute ischemic stroke and without known AF were enrolled in a prospective study to detect paroxysmal AF. Patients were stratified according to the number of APBs recorded in a 24-hour ECG (≥70 APBs versus <70 APBs). Subsequently, they all underwent serial 7-day event-recorder monitoring at 0, 3, and 6 months.

Results— Serial extended ECG monitoring identified AF in 26% of patients with frequent APBs but only in 6.5% when APBs were infrequent ( P =0.0021). A multivariate analysis showed that the presence of frequent APBs in the initial 24-hour ECG was the only independent predictor of paroxysmal AF during follow-up (odds ratio 6.6, 95% confidence intervals 1.6 to 28.2, P =0.01).

Conclusions— In patients with acute ischemic stroke, frequent APBs (≥70/24 hours) are a marker for individuals who are at greater risk to develop or have paroxysmal AF. For such patients, we propose a diagnostic workup with repeated prolonged ECG monitoring to diagnose paroxysmal AF.

Plaque rupture in the carotid artery is localized at the high shear stress region: a case report

BACKGROUND AND PURPOSE

Cerebrovascular events are related to atherosclerotic disease in the carotid arteries and are frequently caused by rupture of a vulnerable plaque. These ruptures are often observed at the upstream region of the plaque, where the wall shear stress (WSS) is considered to be highest. High WSS is known for its influence on many processes affecting tissue regression. Until now, there have been no serial studies showing the relationship between plaque rupture and WSS. Summary of Case- We investigated a serial MRI data set of a 67-year-old woman with a plaque in the carotid artery at baseline and an ulcer at 10-month follow up. The lumen, plaque components (lipid/necrotic core, intraplaque hemorrhage), and ulcer were segmented and the lumen contours at baseline were used for WSS calculation. Correlation of the change in plaque composition with the WSS at baseline showed that the ulcer was generated exclusively at the high WSS location.

CONCLUSIONS

In this serial MRI study, we found plaque ulceration at the high WSS location of a protruding plaque in the carotid artery. Our data suggest that high WSS influences plaque vulnerability and therefore may become a potential parameter for predicting future events.

Correlation between carotid intraplaque hemorrhage and clinical symptoms: systematic review of observational studies

BACKGROUND AND PURPOSE

We sought to investigate the association between carotid intraplaque hemorrhage (IPH) and ipsilateral symptoms of cerebral ischemia.

METHODS

A search was performed for clinical observational studies comparing the incidence of IPH between symptomatic and asymptomatic patients. Odds ratios (ORs) for IPH as a factor in the pathogenesis of neurologic events were calculated and combined by a meta-analysis. Interstudy heterogeneity, estimated effects, and methodologic quality of the studies were assessed.

RESULTS

Thirty-one studies were included for analysis. The reported ORs varied widely. Overall, the incidence of IPH in the symptomatic groups was significantly higher than in the asymptomatic group. However, there was an apparent trend for heterogeneity (P<0.00001) between studies. The random-effects summary estimator of ORs was 2.25 (95% CI, 1.57 to 3.22; P<0.00001). To identify potential sources of heterogeneity, subgroup analyses were performed. The pooled ORs varied greatly by stratification. Major heterogeneity was found among studies with low quality, microscopic methods of examination, significant effects, small sizes, early publication, and unequal severity of carotid stenosis in both groups. Large, recent, macroscopic, or high-quality studies, as well as studies with equal degrees of stenosis, tended to yield insignificant associations. The methods in defining and evaluating hemorrhage were very heterogeneous. Characterizations of the age, size, number, and location of hemorrhages were poorly reported and highly variable. In addition, a lack of control of confounders and selection bias were frequently identified among studies.

CONCLUSIONS

Statistical inferences have suggested a plausible role in the production of cerebral ischemia; however, reliable interpretation was strongly undermined by poor methodologic quality, substantial heterogeneity, and suspicious publication bias. To preciously estimate the underlying correlation, a well-designed study with uniformity in definition and evaluation for IPH might be warranted.

Cerebral Protection During Retrograde Carotid Artery Stenting for Proximal Carotid Artery Stenosis-Technical Note-

Carotid artery stenting for carotid bifurcation stenosis usually uses the transfemoral approach. However, in patients with proximal common carotid artery (CCA) stenosis, the guiding catheter is difficult to introduce into the narrow origin of the CCA without risking cerebral embolization before activation of the protection device. A technique of cerebral protection by internal carotid artery (ICA) clamping with or without simultaneous external carotid artery (ECA) clamping was used to treat patients with proximal CCA stenosis by the retrograde direct carotid approach. The carotid bifurcation was surgically exposed and retrograde catheterization was performed to approach the stenosis. The ICA was clamped during angioplasty and stenting to avoid cerebral embolization. The ECA was clamped simultaneously if any extracranial-intracranial anastomosis was present. None of five patients treated with this technique experienced ischemic complications attributable to this technique.

Angiogenesis and improved cerebral blood flow in the ischemic boundary area detected by MRI after administration of sildenafil to rats with embolic stroke

To dynamically investigate the long-term response of an ischemic lesion in rat brain to the administration of sildenafil, male Wistar rats subjected to embolic stroke were treated with sildenafil (n=11) or saline (n=10) at a dose of 10 mg/kg administered subcutaneously 24-h after stroke and daily for an additional 6 days. Magnetic resonance images were acquired and functional performance was measured in all animals at 1 day, 2 days and weekly for 6 weeks post-stroke. All rats were sacrificed 6 weeks after stroke and endothelial barrier antigen immunostaining was employed for morphological analysis and quantification of cerebral vessels. Map-ISODATA was computed from T(1), T(2) and T(1sat) maps. ISODATA derived tissue signatures characterize the degree of ischemic injury. Based on the map-ISODATA calculated at 6 weeks, the ischemic lesion for each animal was divided into two specific regions, the ischemic boundary and ischemic core. The temporal profiles of cerebral blood flow (CBF) and tissue signature were retrospectively tracked in these two regions and were compared with histological evaluation and functional outcome. After 1 week of sildenafil treatment, the ischemic lesion exhibited two significantly different regions, with higher CBF level and correspondingly, lower tissue signature value in the boundary region than in the core region. Sildenafil treatment did not significantly reduce the lesion size, but did enhance angiogenesis. Functional performance was significantly increased after sildenafil treatment compared with the control group. Administration of sildenafil to rats with embolic stroke enhances angiogenesis and selectively increases the CBF level in the ischemic boundary, and improves neurological functional recovery compared to saline-treated rats.

Brain injury from cardiac bypass procedures

Patients who undergo coronary artery bypass grafting (CABG) are at increased risk for brain injury. Surgical techniques have advanced so that the risk of neurological sequelae is decreased, but there remains significant morbidity and mortality related to the postoperative period as well as to the surgery itself. In addition, patients who undergo CABG have comorbidities or demographic factors that may increase their likelihood of developing neurological complications. Pathophysiological mechanisms of cerebral injury after CABG range from hemodynamic compromise to embolization, either intraoperatively or postoperatively. Biochemical markers such as S100 and neuron-specific enolase may play a role in the prediction of outcome after CABG, and because of this may help elucidate other potential risk factors. Specific neurological sequelae are discussed, such as stroke, with summaries of the apparent risk factors, as well as encephalopathy, seizure, and both short- and long-term cognitive deficits. Changes in surgical technique have led to some improvements, but there is no definitive information yet as to the role of some of these, such as the use of off-pump CABG. Other techniques such as the use of an arterial filter are discussed, as are their potential benefits in the prevention of neurological complications.

Acute stroke: therapeutic transcranial color duplex sonography

The enhancement of thrombolysis by ultrasound energy (sonothrombolysis) is an emerging field of interest in the treatment of acute ischemic stroke. Recent in vitro and clinical studies have investigated the effects of using transcranially applied 'diagnostic' ultrasound for this purpose. Using transcranial color duplex sonography (TCDS) allows an examiner to identify the site of occlusion and focus the ultrasound beam on it. Clinical studies using TCDS to enhance thrombolysis in acute middle cerebral artery occlusions have revealed an accelerating effect on recanalization, as well as a tendency for a better outcome. Data from small sample studies suggest that this effect on recanalization is present not only in combination with recombinant tissue plasminogen activator (rt-PA), but also with any thrombolytic drug. However, when TCDS was used in combination with rt-PA, an increase in the rate of asymptomatic and symptomatic intracerebral hemorrhages tended to occur compared to patients treated with thrombolysis alone. Larger sample-sized clinical studies should be conducted in the future to evaluate the safety and efficacy of using TCDS for sonothrombolysis. This method should also be further developed to determine its effect when used in combination with other types of ultrasound and thrombolytic drugs.

Acute stroke: therapeutic transcranial Doppler sonography

Ultrasound (US) has emerged as a new tool to treat ischemic stroke. The potential advantage of US is decreased risk of systemic bleeding complications due to its site-specific effect. Moreover, external application is noninvasive and is readily available. Experimental studies showed that low intensity (<or=2W/cm2) US safely enhanced thrombolytic drug activity within a wide range of frequencies (0.04-3.4 MHz). In humans, transcranial sonothrombolysis with mid-kHz frequencies showed an unacceptably high rate of intracranial bleeding, while the use of 2MHz yielded promising results in The Combined Lysis of Thrombus in Brain Ischemia Using Transcranial Ultrasound and Systemic TPA (CLOTBUST) study. This study was a phase II randomized clinical trial that included patients with middle cerebral artery (MCA) occlusion within 3 h of stroke onset, who were treated with standard dose of tissue plasminogen activator (t-PA). Residual flow in MCA was monitored with 2MHz US in one group, and the rate of complete recanalization and dramatic clinical recovery significantly increased as compared to t-PA alone. This chapter further discusses diagnosis of an acute occlusion and recanalization using the thrombolysis in brain ischemia (TIBI) waveform flow grading scale, application of fast track insonation protocol, and administration of US. Also, the potential enhancement of sonothrombolysis with microbubbles is discussed.

Detection of microembolic signals with transcranial Doppler ultrasound

Detection of microembolic signals (MES) with transcranial Doppler was introduced in the late 1980s; several animal and in vitro models reported a high sensitivity and specificity with this technique. Monitoring for MES in various patient groups has provided valuable insights on stroke pathophysiology, although its clinical value remains a matter of debate. Diagnosis of imminent occlusion of the internal carotid artery following carotid endarterectomy, selection of high-risk patients with asymptomatic carotid disease, and evaluation of drug efficacy constitute potential applications of this technique.

Sonothrombolysis: experimental evidence

Reopening of the occluded artery is the primary therapeutic goal in hyperacute ischemic stroke. Systemic treatment with tissue recombinant plasminogen activator (tPA) has been shown to be beneficial at least in a 3-hour door to needle window. Intra-arterial thrombolysis is favorable and opens the window of treatment up to at least 6 h but consequences invasive intra-arterial angiography in a high number of patients, of whom a significant number do not finally receive thrombolysis. The combination of ultrasound with thrombolytic agents may enhance the potential benefit by means of enzyme-mediated thrombolysis. When ultrasound is applied externally through skin or chest, attenuation will be very low. Attenuation, however, is significantly higher if penetration through the skull is required. Attenuation is frequency dependent, with ultrasound intensity being <10% of the output intensity for diagnostic frequencies (>1 MHz). This ratio nearly reverses in the kiloHertz range (>500 kHz). Ultrasound insonation is efficient for accelerating enzymatic thrombolysis within a wide range of intensities, from 0.5W/cm2 (MI approximately 0.3) to several watts per square centimeter, particularly in the nonfocused ultrasound field. Insonation with ultrasound increased tPA-mediated thrombolysis up to 20% in a static model, while it enhanced the recanalization rate from 30 to 90% in a flow model. Results from embolic rat models suggest that low-frequency ultrasound with 0.6W/cm2 significantly reduces infarct volume compared to pure tPA treatment. Safety of ultrasound exposure of the brain for therapeutic purposes has to address hemorrhage, heating, and direct tissue damage. Since animal studies suggested no increase of bleeding rate or harm to the blood-brain barrier, a clinical phase II study applying low-frequency ultrasound at approximately 300 kHz found a high number of secondary hemorrhages. Heating depends critically on the characteristics of the ultrasound. The most significant heating of the brain tissue itself is >1 degrees C per hour using a 2W/cm2 probe; however, no significant heating could be found when using an emission protocol pulsing the ultrasound. The current experimental data helps to identify the optimal ultrasound characteristics for sonothrombolysis and supports the hypothesis combined treatment being a perspective in optimizing thrombolytic therapy in acute stroke.

Contrast-enhanced transcranial Doppler ultrasound for diagnosis of patent foramen ovale

The suspected cause of clinical manifestations of patent foramen ovale (PFO) is a transient or a permanent right-to-left shunt (RLS). Contrast-enhanced transcranial Doppler ultrasound (c-TCD) is a reliable alternative to transesophageal echocardiography (TEE) for diagnosis of PFO, and enables also the detection of extracardiac RLS. The air-containing echo contrast agents are injected intravenously and do not pass the pulmonary circulation. In the presence of RLS, the contrast agents bypass the pulmonary circulation and cause microembolic signals (MES) in the basal cerebral arteries, which are detected by TCD. The two main echo contrast agents in use are agitated saline and D-galactose microparticle solutions. At least one middle cerebral artery (MCA) is insonated, and the ultrasound probe is fixed with a headframe. The monitored Doppler spectra are stored for offline analysis (e.g., videotape) of the time of occurrence and number of MES, which are used to assess the size and functional relevance of the RLS. The examination is more sensitive, if both MCAs are investigated. In the case of negative testing, the examination is repeated using the Valsalva maneuver. Compared to TEE, c-TCD is more comfortable for the patient, enables an easier assessment of the size and functional relevance of the RLS, and allows also the detection of extracardiac RLS. However, c-TCD cannot localize the site of the RLS. Therefore, TEE and TCD are complementary methods and should be applied jointly in order to increase the diagnostic accuracy for detecting PFO and other types of RLS.

Ischemic stroke in young HIV-positive patients in Kwazulu-Natal, South Africa

Cerebrovascular disease occurs in HIV-positive individuals, but no relationship between the two has been established. The authors reviewed a cohort of patients aged 15 to 44 years to evaluate stroke in HIV-positive and negative subjects. Patients who were HIV-positive with no other identifiable etiology were compared to age- and race-matched HIV-negative patients. HIV-positive and HIV-negative groups did not differ in angiographic, cardiac, or serologic tests. A positive HIV test does not provide causal information or diagnosis.

Céphalées au cours des thromboses veineuses cérébrales

Headache is the most frequent symptom of cerebral venous thrombosis. They do not have particular characteristics and can mimic other numerous varieties of headache. Frequently associated with other neurological symptoms, such as intracranial hypertension, seizures, focal deficits or disorders of consciousness, they are sometimes isolated, which stresses the need for investigations in all recent and unusual headache.

Comparison of transesophageal echocardiographic identification of embolic risk markers in patients with lone versus non-lone atrial fibrillation

Although transesophageal echocardiographically derived parameters, notably spontaneous echocardiographic contrast (SEC) in the left atrium or left atrial appendage (LAA), are known predictors of embolism in atrial fibrillation, their value is less well known in patients who have lone atrial fibrillation (LAF). This study describes transesophageal echocardiographic findings and identifies clinical predictors of SEC in the left atrium or LAA in a cohort of patients who had LAF. Eighty-two patients who had LAF and 289 patients who had non-LAF and underwent transesophageal echocardiography were enrolled from July 1998 to March 2002. LAA abnormality was defined as the presence of an LAA area >5 cm(2), emptying or filling LAA velocities <25 cm/s, or the presence of SEC or thrombus in the left atrium or LAA; LAA abnormalities were significantly less frequent in patients who had LAF than in those who had non-LAF. SEC in the left atrium or LAA was significantly less frequent in patients who had LAF than in those who had non-LAF (29.3% vs 49.8%, respectively, p <0.001). In patients who had LAF, SEC in the left atrium or LAA was significantly (p <0.05) less frequent in patients who were </=60 years old (17.9%) than in patients who were >60 years old (39.5%) and in patients who had paroxysmal LAF (5.9%) than in those who had persistent LAF (45.8%). On multivariate analysis, age and persistent LAF were the only clinical variables independently associated with SEC. Thus, transesophageal echocardiography detects thromboembolism risk markers in patients who have LAF. These abnormalities are less frequent in patients who have LAF than in those who are at low risk and have non-LAF; however, in patients who have LAF, older age and persistent atrial fibrillation are associated with these risk markers.

Quantitative EEG Monitoring During Cerebral Air Embolism and Hyperbaric Oxygen Treatment in a Pig Model

The purpose of this study was to evaluate the contribution of quantitative EEG (qEEG) to an animal model of cerebral air embolism (CAE). In 12 anesthetized pigs, air was injected into the internal carotid artery, and hyperbaric oxygen (HBO) treatment was started either after 3 minutes or after 60 minutes (United States Navy Treatment Table 6). Off-line spectral analysis was used to determine the frequency content of the EEG signal, and factor analysis was performed to determine the frequency ranges that optimally showed the changes in the power spectrum. Factor analysis revealed two factors that represented different and independent spectral changes during embolization: 0.5 to 7.3 Hz (band 1) and 26.4 to 30.3 Hz (band 2). Shortly after embolization, the power in both bands decreased to a minimum, representing an isoelectric EEG in 11 out of the 12 animals. EEG differences between animals were considerable, despite standardized doses of injected air, and qEEG can objectively assess and quantify these differences in immediate impact of air embolism on brain function. Also, qEEG enabled monitoring of the recovery from the initial embolic event and of the response on treatment. The initial recovery was much more protracted in band 2 than in band 1, but even after completing HBO treatment, qEEG values did not return to baseline values in all animals. In addition, two animals did not survive until the end of the HBO treatment, and qEEG proved to be superior to the other measured hemodynamic variables to detect and ensure a deterioration of brain function. This study showed that qEEG monitoring has significant additional value to monitoring HBO treatment.

Differential alterations of the inactivation properties of high voltage activated calcium currents in area CA1 and CA3 of the rat following photothrombotic lesion

There are many indications that focal brain ischemia may alter the properties of remote brain tissue. We investigated whether changes of neuronal properties can be observed in the unlesioned ipsilateral hippocampus following cortical photothrombosis in the somatosensory cortex of rats. The whole-cell patch-clamp technique was used to investigate calcium current properties of hippocampal neurons (CA1 and CA3) 7 days after infarct induction. A significant alteration in the half-maximal potential of inactivation (V(h,i)) could be demonstrated, when comparing lesioned with sham operated animals, while other current parameters remained unchanged. The alterations of the V(h,i) in the CA1 and CA3 regions were of opposite directions: V(h,i) in CA1 neurons was shifted negatively by 5.6 mV, and positively by 5.0 mV in neurons from the CA3 region. It has been speculated that these differential alterations may be due to different subunit compositions of calcium channels in these two brain areas. The data indicate that small cortical lesions can lead to widespread alterations of the neuronal network's excitability in the hippocampal formation.

Protocol of a thromboembolic stroke model in the rat: review of the experimental procedure and comparison of models

RATIONALE AND OBJECTIVE

Different models to study the pathophysiology of cerebral ischemia and to evaluate therapeutic strategies exist. Described is the detailed procedure of a thromboembolic stroke model in the rat most closely resembling human embolic stroke and compare the model to other equivalent rodent models.

MATERIALS AND METHODS

An evaluation of a new thromboembolic stroke model was performed on 35 male Wistar rats. After preparation of the carotid artery, a catheter was introduced into the external carotid artery. During injection of autologous, fibrin-rich emboli into the internal carotid artery the common carotid artery was temporarily occluded. Regional cerebral blood flow (rCBF) and lesion size were determined.

RESULTS

Twelve fibrin-rich blood clots of 1.5 mm in length were necessary in order reliably to occlude the origin of the middle cerebral artery. A stable decrease of rCBF and lesion size was confirmed by autoradiography, diffusion, and perfusion MRI, TTC-staining, biochemical imaging, and histology.

CONCLUSION

In this animal model, the situation of human cerebral ischemia is simulated closely. The model is suitable for investigations of the pathophysiology of stroke and facilitates studies on the effects of thrombolytic therapy.

Time courses of progress to the chronic stage of middle cerebral artery occlusion models in rats

Several kinds of middle cerebral artery occlusion model in rats have been developed. Variable ischemic inductions are attributed to the different contributing factors in ischemic damage formation. In the present study, we examined the differences in ischemic induction attributed to chronic stage. Male Sprague-Dawley rats were subjected to two kinds of middle cerebral artery occlusion model, a thermocoagulation and a photothrombosis model. We compared the changes in body weight, neurological outcome, size of ischemic damage, brain edema and atrophy formation, and histological data for 84 days between a thermocoagulation and a photothrombosis model in rats. Although the time courses of infarction formation were no different, there were differences in the time courses of brain edema, atrophy formation, and neuronal deficits between the models. Microinfarction formation was observed as a characteristic of the photothrombosis model. The present study demonstrated that differences in ischemic induction did not affect maturation of infarct size, brain atrophy, or neuronal deficits 84 days after ischemia. However, the progress of maturation was different between the models. The possibility that reperfusion contributed to the time course of brain edema and atrophy was considered, and it was suggested that brain edema formation influenced neurological outcome.

Dynamics and embolic activity of symptomatic intra-cranial cerebral artery stenoses

OBJECTIVE

To investigate the occurrence of microembolic signals (MES) and hemodynamic features in patients with acute symptomatic intracranial cerebral artery stenoses by transcranial Doppler (TCD).

MATERIAL AND METHODS

Twelve patients with acute hemispheric ischemic events and corresponding intracranial cerebral artery stenoses as identified by TCD, and exclusion of extracranial or cardiac emboli sources were repeatedly studied by TCD monitoring of the affected and the contralateral vessel. The occurrence of MES and MES clusters (> or =3 MES per second) and of flow velocity changes was examined.

RESULTS

Nine patients presented with MES in the affected artery during the first measurement. In seven patients sudden flow velocity changes could be detected in the affected vessel. In five patients these changes were accompanied by MES clusters. MES and velocity changes disappeared in all patients during follow-up, and the degree of stenosis decreased in nine patients.

CONCLUSIONS

The high prevalence of MES and sudden velocity changes in acute intracranial cerebral artery stenoses indicates that acute intracranial stenoses may be formed at least in part by mobile thrombotic material.

Impairment of adenylyl cyclase and of spatial memory function after microsphere embolism in rats

The purpose of the present study was to characterize alterations in the adenylyl cyclase (AC), cyclic adenosine 3',5'-monophosphate (cAMP), and spatial memory function after sustained cerebral ischemia. Sustained cerebral ischemia was induced by injection of 900 microspheres (48 microm in diameter) into the right (ipsilateral) hemisphere of rats. Alterations in the AC and cAMP in the cerebral cortex and hippocampus were examined up to 7 days after the embolism. A decrease in the cAMP content was seen in the ipsilateral hemisphere throughout the experiment. Microsphere embolism (ME) decreased the activity of Ca(2+)/calmodulin (CaM)-sensitive AC in the ipsilateral hemisphere throughout the experiment, whereas the basal and 5'-guanylyl imidodiphosphate (Gpp(NH)p)-sensitive AC activities were not altered. Immunoblotting analysis of AC subtypes with specific antibodies showed a decrease in the immunoreactivity of AC-I in the ipsilateral hemisphere during these periods. No significant differences in the immunoreactivity of AC-V/VI and AC-VIII were observed after ME. The levels of GTP-binding proteins Galpha(s), Galpha(i), and Gbetawere unchanged. Furthermore, microsphere-embolized rats showed prolongation of the escape latency in the water maze task determined on the seventh to ninth day after the operation. These results suggest that sustained cerebral ischemia may induce the impairment of the AC, particularly a selective reduction in the AC-I level and activity, coupled with the decrease in cAMP content. This reduction may play an appreciable role in the disturbance in cAMP-mediated signal transduction system, possibly leading to learning and memory dysfunction.

Massive haemorrhagic transformation in cardioembolic stroke: the role of arterial wall trauma and dissection

The pathogenesis of massive haemorrhagic transformation is not well established. Fatal haemorrhagic transformation associated with in situ dissection after acute middle cerebral artery (MCA) occlusion in a patient with atrial fibrillation is reported. An 80 year old woman with atrial fibrillation developed mild hemiparesis and aphasia. Brain CT and MRI at 4 and 5 hours, respectively, of symptom onset showed proximal MCA trunk occlusion with developing striatocapsular infarct and hypoperfusion in the superficial MCA territory. A few hours later, she developed massive bleeding into the ischaemic area and died. Pathological examination showed MCA trunk dissection, surrounded by a subarachnoid clot which communicated with the cerebral haematoma. It is suggested that direct arterial wall trauma as a result of cardioembolic MCA occlusion caused bleeding into the infarct. Secondary in situ dissection may be an overlooked mechanism of haemorrhagic transformation.

Serial changes in cerebral blood flow and flow-metabolism uncoupling in primates with acute thromboembolic stroke

The authors recently developed a primate thromboembolic stroke model. To characterize the primate model, the authors determined serial changes in cerebral blood flow (CBF) and the relation between CBF and cerebral metabolic rate of glucose (CMRglc) using high-resolution positron emission tomography. Thromboembolic stroke was produced in male cynomolgus monkeys (n = 4). Acute obstruction of the left middle cerebral artery was achieved by injecting an autologous blood clot into the left internal carotid artery. Cerebral blood flow was measured with [15O]H2O before and 1, 2, 4, 6, and 24 hours after embolization. CMRglc was measured with 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) 24 hours after embolization. Lesion size and location 24 hours after embolization was determined by the 2,3,5-triphenyltetrazolium chloride (TTC) staining method. The results are summarized as follows: (1) 1 hour after embolization, CBF in the temporal cortex and the basal ganglia decreased to < 40% of the contralateral values. In these regions, regarded as an ischemic core, CBF decreased further with time and CMRglc at 24 hours also decreased. Infarcted lesions as indicated by being unstained with TTC were consistently observed in these regions. (2) In the parietal cortex and several regions surrounding the ischemic core, CBF was > 40% of the contralateral values 1 hour after embolization and recovered gradually with time (ischemic penumbra). In these regions, CMRglc at 24 hours increased compared with that in the contralateral regions, indicating an uncoupling of CBF and CMRglc. No obvious TTC-unstained lesions were detected in these regions. The authors demonstrated a gradual recovery of reduced CBF, an elevated CMRglc and a CBF-CMRglc uncoupling in the penumbra regions of the primate model. Positron emission tomography investigations using this model will provide better understanding of the pathophysiology of thromboembolic stroke in humans.

High speed diffusion magnetic resonance imaging of ischemia and spontaneous periinfarct spreading depression after thromboembolic stroke in the rat

Spontaneous episodes of transient cell membrane depolarization (spreading depression [SD]) occur in the surroundings of experimental stroke lesions and are believed to contribute to infarct growth. Diffusion-weighted imaging (DWI) is capable of detecting the water shifts from extracellular to intracellular space associated with SD waves and ischemia, and can make in vivo measurements of these two features on a pixel-by-pixel basis with good temporal resolution. Using continuous high speed DWI with a temporal resolution of 12 seconds over a period of 3 hours, the in vivo contribution of spontaneous SDs to the development of ischemic tissue injury was examined in 8 rats using a thromboembolic stroke model. During the observation period, the initial lesion volume increased in 4 animals, remained unchanged in 1 animal, and decreased in 3 animals (most likely because of spontaneous clot lysis). Irrespective of the lesion evolution patterns, animals demonstrated 6.5 +/- 2.1 spontaneous SDs outside of the ischemic core. A time-to-peak analysis of apparent diffusion coefficient (ADC) changes for each SD wave demonstrated multidirectional propagation patterns from variable initiation sites. Maps of the time constants of ADC recovery, reflecting the local energy supply and cerebral blood flow, revealed prolonged recovery times in areas close to the ischemic core. However, repetitive SD episodes in the periinfarct tissue did not eventually lead to permanent ADC reductions. These results suggest that spontaneous SD waves do not necessarily contribute to the expansion of the ischemic lesion volume in this model.

Transcranial Doppler evaluation of blood flow velocity changes in basal cerebral arteries in cerebral AVMs following embolisation and surgery

Blood flow velocities in the basal cerebral arteries were evaluated in 41 patients with supratentorial arteriovenous malformation (AVM), using a transcranial doppler 64-B instrument. The AVM was surgically excised in 20 patients and embolised in 21 patients. Blood flow velocities in feeding basal cerebral arteries were found markedly decreased in both the groups, at 24 hours after intervention. On follow up study at 3 months, blood flow velocity in feeding cerebral artery was found to be increased in 47 percent of patients who were embolised, but remained normal in all the patients who underwent surgery.

Pathophysiologic correlates of thromboembolism in nonvalvular atrial fibrillation: II. Dense spontaneous echocardiographic contrast (The Stroke Prevention in Atrial Fibrillation [SPAF-III] study)

We analyzed transesophageal echocardiograms from 772 participants in the Stroke Prevention in Atrial Fibrillation (SPAF-III) study, characterizing spontaneous echocardiographic contrast (SEC) in the left atrium or appendage as faint or dense. The association of dense SEC with stroke risk factors and anatomic, hemodynamic, and hemostatic parameters related to specific thromboembolic mechanisms was evaluated by multivariate analysis. Spontaneous echocardiographic contrast was present in 55% of patients and was dense in 13%. Age (odds ratio [OR] 2.4/decade, P <.001), constant atrial fibrillation (OR 6.9, P <.001), history of hypertension (OR 3. 2, P <.001), and current tobacco smoking (OR 2.6, P =.04) were independent clinical predictors of dense SEC. Multivariate analysis of clinical, echocardiographic, and hemostatic parameters yielded age as the sole independent clinical predictor of dense SEC (OR 2. 4/decade, P <.001). Other independent predictors were measures of left atrial/appendage flow dynamics, left atrial size (OR 2.4/cm diameter, M-mode, P <.001), atherosclerotic aortic plaque (OR 2.8, P =.002), and plasma fibrinogen >350 mg/dL (P <.001). Results were similar when SEC of any density was analyzed. In conclusion, SEC occurred in more than half of these patients with prospectively defined nonvalvular atrial fibrillation but was usually faint. Dense SEC was strongly associated with previously reported clinical predictors of stroke, linking them to thromboembolism through atrial stasis. Diverse pathophysiologic factors including atrial stasis, fibrinogen level, and aortic plaque influence SEC.

Pathophysiologic correlates of thromboembolism in nonvalvular atrial fibrillation: I. Reduced flow velocity in the left atrial appendage (The Stroke Prevention in Atrial Fibrillation [SPAF-III] study)

Stroke associated with atrial fibrillation (AF) is mainly due to embolism of thrombus formed during stasis of blood in the left atrial appendage (LAA). Pathophysiologic correlates of appendage flow velocity as assessed by transesophageal echocardiography (TEE) in patients with AF have not been defined. To evaluate the hypothesis that reduced velocity is associated with spontaneous echocardiographic contrast and thrombus in the LAA and with clinical embolic events, we measured LAA flow velocity by TEE in 721 patients with nonvalvular AF entering the Stroke Prevention in Atrial Fibrillation (SPAF-III) study. Patient features, TEE findings, and subsequent cardioembolic events were correlated with velocity by multivariate analysis. Patients in AF during TEE displayed lower peak antegrade (emptying) flow velocity (Anu(p)) than those with intermittent AF in sinus rhythm during TEE (33 cm/s vs 61 cm/s, respectively, P <.0001). Anu(p) < 20 cm/s was associated with dense spontaneous echocardiographic contrast (P <.001), appendage thrombus (P <.01), and subsequent cardioembolic events (P <.01). Independent predictors of Anu(p) < 20 cm/s included age (P =.009), systolic blood pressure (P <.001), sustained AF (P =.01), ischemic heart disease (P =.01), and left atrial area (P =.04). Multivariate analysis found both Anu(p) <20 cm/s (relative risk 2.6, P =.02) and clinical risk factors (relative risk 3.3, P =.002) independently associated with LAA thrombus. LAA Anu(p) is reduced in AF and associated with spontaneous echocardiographic contrast, appendage thrombus, and cardioembolic stroke. Systolic hypertension and aortic atherosclerosis, independent clinical predictors of stroke in patients with AF, also correlated with LAA Anu(p). Our results support the role of reduced LAA Anu(p) in the generation of stasis, thrombus formation, and embolism in patients with AF, although other mechanisms also contribute to stroke.

Changes in the constant potential in brain structures in rats during focal ischemia and systemic hypoxia

The functional consequences of spreading depression (SD) during the evolution of ischemic damage was studied in two models: focal cortical ischemia induced by photothrombosis of the middle cerebral artery (MCA) and systemic hypoxia induced by 0.8% carbon monoxide (CO). These studies showed that cortical waves of SD, arising spontaneously during MCA thrombosis and after arterial occlusion delayed thrombus formation and promoted the establishment of a collateral blood supply in the perifocal zone of ischemic lesions. The underlying mechanism consisted of episodes of intense vasodilation at the decay phase of every wave of SD. Respiration of 0.8% CO increased the blood carboxyhemoglobin level to 50-60%. In lightly anesthetized rats (pentobarbital 20 mg/kg), cortical and subcortical spontaneous waves of SD were transformed into stable hypoxic depolarization, leading to death of 60% of the animals or severe lesions of the central nervous system, in 20% of animals. Increases in the level of anesthesia (50 mg/kg anesthetic) prevented the spontaneous appearance of SD during long-lasting exposure to CO. In these conditions, experimentally induced waves of SD demonstrated that the hippocampus has a high sensitivity to moderate levels of hypoxia. The duration of hypoxic depolarization of the hippocampus, provoking a single SD wave, reached 30-60 min. Selective neuron damage in field CA1 was seen 30 days after hypoxia. Additionally, the left hippocampus of rats frequently showed profound morphological lesions in the form of "granules." Cerebrolysine (2.5 ml/kg daily for 10 days) completely prevented the formation of these lesions.

Improved automated detection of embolic signals using a novel frequency filtering approach

BACKGROUND AND PURPOSE

Asymptomatic embolic signal detection with the use of Doppler ultrasound has a number of potential clinical applications. However, its more widespread clinical use is severely limited by the lack of a reliable automated detection system. Design of such a system depends on accurate characterization of the unique features of embolic signals, which allow their differentiation from artifact and background Doppler speckle. We used a processing system with high temporal resolution to describe these features. We then used this information to design a new automated detection system.

METHODS

We used a signal processing approach based on multiple overlapping band-pass filters to characterize 100 consecutive embolic signals from patients with carotid artery disease as well as both episodes of artifact resulting from probe tapping and facial movement and episodes of Doppler speckle. We then designed an automated detection system based both on these embolic signal characteristics and on the fact that embolic signals have maximum intensity over a narrow frequency range. This system was tested in real time on stored 5-second segments of data.

RESULTS

The value of peak velocity at maximal intensity discriminated best between embolic signals and artifact and allowed differentiation with 100% sensitivity and specificity. Relative intensity increase, intensity volume, area under volume, average rise rate, and average fall rate appeared to discriminate best between embolic signals and Doppler speckle. For the majority of embolic signals, the intensity increase was spread over a narrow frequency or velocity range. The automated system we developed detected 296 of 325 carotid stenosis embolic signals from a new data set (sensitivity, 91.1%). All 200 episodes of artifact from a new data set were differentiated from embolic signals. Only 2 of 100 episodes of speckle were misidentified as embolic signals.

CONCLUSIONS

Using a novel system for automated detection, which utilizes the fact that embolic signals have maximum intensity over a narrow frequency range, we have achieved detection with a high sensitivity and high specificity. These results are considerably better than those previously reported. We tested this initial system on short 5-second segments of data played in real time. This approach now needs to be developed for use in a true online system to determine whether it has sufficient sensitivity and specificity for clinical use.

Acute deterioration from thrombosis and rerupture of a giant intracranial aneurysm

The authors describe a patient with an unusual clinicopathologic picture of giant aneurysmal hemorrhage followed by sudden deterioration due to acute intra-aneurysmal thrombosis and fatal rebleeding. This patient underscores the poor natural history associated with this devastating disease and serves to highlight the dangers inherent in the delayed treatment of these life-threatening lesions.

[Recanalization of cerebral cortical venous thrombosis: a case report]

Several clinical cases of sinus thrombosis have been reported, but localized cerebral cortical venous thrombosis is a fairly rare clinical entity. We report a case of a 51-year-old woman who presented with right hemiparesis on admission. CT scan revealed subcortical hemorrhage with perifocal edema in the left front-parietal lobe. A T2W image revealed a large area of hyperintensity indicating edema, and coronal Gd enhanced T1 weighted image showed a reverse-triangle-shaped enhanced lesion. Left carotid angiogram showed cerebral cortical venous thrombosis in the left frontal lobe, but the superior sagittal sinus was not occluded. A month after admission, right hemiparesis had suddenly improved and the patient could walk without any support. Left carotid angiogram showed recanalization of thrombosed cortical veins and CT scan showed disappearance of any low density lesion indicative of edema. It is an important fact that neurological deficit improved quickly a month after onset, and it was suspected that, even without resorting to fibrinolytic therapy, recanalization of thrombosed cerebral veins would still eventually occur. We found the reverse-triangle-shaped enhanced lesion on MRI and we suspected that it was typical finding for cerebral cortical venous thrombosis.

[The significance of duplex ultrasonography examination in the acute cardioembolic stroke patients--with special attention to evaluation of internal carotid arteries]

The aim of this study is to clarify whether it is possible to diagnose occlusions of internal carotid arteries in the acute cardioembolic stroke patients by observing internal carotid arteries with duplex ultrasonography. Twenty-two consecutive patients underwent both duplex ultrasonography examination and cerebral angiography within 24 hours from the onset. Two cases who had no flow velocity and 8 cases who had systolic flow velocity but no anterograde diastolic flow velocity were all diagnosed as having internal carotid occlusions by cerebral angiography. Eleven of 22 cases who had anterograde diastolic flow velocity were diagnosed as having occlusions at distal side of M 1 portion or no occluded lesions. Besides, among 11 cases who were diagnosed as having occlusions of internal carotid arteries by cerebral angiography, five had end diastolic ratios (ED ratio) of common carotid arteries that were less than 4.0s. It is useful to evaluate the existence of anterograde diastolic flow velocity by duplex ultrasonography for the diagnosis of internal carotid occlusions in the acute cardioembolic stroke patients.

The simple indicator for revascularization of acute middle cerebral artery occlusion using angiogram and ultra-early embolectomy

BACKGROUND

The purpose of the study was: (1) to find a clinical indicator for revascularization of acute middle cerebral artery (MCA) occlusion using angiograms of 100 patients examined immediately after onset and treated medically and (2) to investigate 10 ultra-early MCA embolectomies.

METHODS

Quantity of collateral circulation, based on time required for conduction of contrast media to the insular portion of the MCA from the anterior cerebral artery, MCA conduction time (MCT) was graded as: Grade 1: In the arterial phase, there was conduction not only to the insular portion of the MCA but also to proximal M2; Grade 2: Conduction to the insular portion was present in late arterial phase; Grade 3: Conduction was present in capillary phase; Grade 4: Conduction was present in venous phase; Grade 5: No conduction was seen. The results of embolectomy are discussed.

RESULTS

MCT can predict the extent of resultant low-density area on computed tomographic scan. For Grades 3, 4, or 5, embolectomy could be considered superior to medical treatment, if the low-density area was localized in the basal ganglia or centrum semiovale after surgery. Consequently, embolectomy was effective in four cases recanalized within 6 hours of onset. Except for one Grade 5 case, the remaining nine cases showed neither lethal hemorrhagic infarction nor brain edema. Overall outcome was significantly better than cases treated medically (p < 0.05), but some cases did not recover from hemiparesis due to infarcts in the area of the lenticulostriate arteries.

CONCLUSIONS

MCT helps to predict the applicability of revascularization of acute MCA occlusion. Efficacy of embolectomy depends on revascularization within 6 hours of onset. Even after complete MCA flow restoration, infarcts in the area of the lenticulostriate arteries cannot always be prevented.

Monitoring of venous hemodynamics in patients with cerebral venous thrombosis by transcranial Doppler ultrasound

OBJECTIVES

To test the assumption that transcranial Doppler ultrasound (TCD) is able to detect and to monitor intracranial venous blood flow velocities in patients with confirmed cerebral venous thrombosis (CVT).

DESIGN

Prospective case study in 18 patients.

SETTING

Inpatient neurologic service in a university hospital.

SUBJECTS AND METHODS

Serial TCD examinations were performed in 18 consecutive patients with CVT (14 females, 4 males) aged 16 to 64 years (mean+/-SD, 36.8+/-13.1 years) during a mean follow-up ranging from 34 to 783 days (mean+/-SD, 201+/-185 days) between 1993 and 1997. Venous TCD was performed with a 2-MHz range-gated transducer.

RESULTS

Venous blood flow velocities were successfully measured in all patients. The highest measured velocities in the monitored intracranial venous vessels ranged from 20 to 150 cm/s (mean+/-SD, 58.9+/-38.8 cm/s), and the lowest were from 9 to 84 cm/s (mean+/-SD, 27.9+/-17.0 cm/s). Fifteen patients (83%) showed a decrease of velocities-2 of them after a transient increase during cessation of heparin therapy. The percentage of velocity decrease ranged from 34% to 73% (mean+/-SD, 56.4%+/-10.9%). A plateau phase, defined as no further decrease in velocities, was reached in these patients within 4 to 314 days (mean+/-SD, 59.9+/-73.7 days). Three patients (17%) showed no changes in velocities as defined by a limit of velocity variation of 30% during the course of CVT. High venous velocities were significantly associated with altered consciousness (P = .001). A nonsignificant relationship was observed with affliction of the superior sagittal sinus. No correlations were noted for onset of disease, initial motor deficits, and presence of bleeding. No predictive value was gained from analyzing the outcome in relation to absolute velocities or their decrease.

CONCLUSIONS

Serial TCD studies allow monitoring of venous hemodynamics and collateral pathways in patients with CVT. Normal venous velocities in serial measurements, however, do not exclude a diagnosis of CVT.

Functional correlates with left-right asymmetry of visual evoked potentials in stroke patients: modeling and experimental results

OBJECTIVE

To determine the correlation between a clinical measure of function in patients after first stroke and left-right scalp amplitude of visual evoked potentials using a theoretical model of the head.

DESIGN

A random sample of first-stroke patients underwent routine function measurement and investigation of left-right scalp potential asymmetry. Results of the encephalographic tests were compared with those of a healthy subject. To examine the effect of the conductivity in the damaged area on the potential asymmetry, numerical calculations were performed on a model, with four concentric circular compartments representing the brain, cerebrospinal fluid layer, skull, and scalp. The damaged region was modeled as a circular section.

SETTING

Neurologic rehabilitation ward of a major rehabilitation hospital and university-affiliated biomedical engineering laboratory.

PATIENTS

Four men aged 58 to 71 years, 3 with brain thrombosis and 1 with hemorrhagic stroke. The patients were admitted for rehabilitation an average of 3 weeks after the stroke and stayed for an average of 137 days. Damage was confined to the right brain in all cases; three of the patients had neglect syndrome and/or sensory disturbances. A healthy subject without stroke was also examined.

MEASURES

Function was measured with the Functional Independence Measure (FIM) at 48 to 72 hours from admission and during the last week before discharge. Functional gain was calculated by subtracting the FIM admission score from the discharge score. Left-right scalp visual evoked potential amplitude was studied with flash stimuli according to the 10-20 international system and a theoretical model of the head based on two-dimensional computed tomography images; the volume conductor equation was solved numerically using the finite volume method. Left-right potential asymmetry and the damaged-region-to-brain-area ratio were calculated and correlated with the FIM values by linear regression analysis. Negative asymmetry indicates that the activity in the right damaged hemisphere is lower than in the undamaged one.

RESULTS

A negative correlation was noted between the FIM score on admission and the left-right scalp potential amplitude asymmetry, and between the FIM gain and the damaged-region-to-brain-area ratio obtained from the computed tomography image. Asymmetry was negative in the thrombotic patients and positive in the hemorrhagic one. The healthy subject showed nonsignificant asymmetry.

CONCLUSION

A relationship might exist between the left-right asymmetry of the scalp visual evoked potential and both the damaged-region-to-brain-area ratio and the functional outcome of rehabilitation in poststroke patients. The modeling study shows that the left-right asymmetry is most likely the result of changes in the conductivity at the damaged area, which, in turn, are probably associated with patient functional status and evolution. Further validation in larger groups of patients and normal subjects is needed before these parameters can serve as useful indices for clinical purposes.

Assessment of intracranial venous hemodynamics in normal individuals and patients with cerebral venous thrombosis

BACKGROUND AND PURPOSE

Despite ongoing improvements in noninvasive imaging techniques, transcranial color-coded duplex sonography (TCCS) has so far been used only on a limited basis in patients with cerebral venous thrombosis. We evaluated the diagnostic value of both noncontrast and contrast-enhanced TCCS by comparing normal volunteers and patients with acute cerebral venous thrombosis.

METHODS

In 75 healthy volunteers (aged 45.8+/-17.4 years), normal values for the deep cerebral veins (DCVs) and the posterior fossa sinuses were established by transtemporal insonation. Eight patients with cerebral venous thrombosis were assessed by TCCS, through which the hemodynamics of the DCVs were measured, and the patients were followed-up over a period of between 33 and 387 days after examination. MR angiography served as the "gold standard" technique for confirming the venous status in all 8 patients.

RESULTS

No side differences in flow velocities were detected in the paired venous structures in normal volunteers. As indirect signs of (and diagnostic criteria for) cerebral venous thrombosis, pathologically increased flow velocities or significant side differences in the DCVs were registered in 5 of the 8 patients; the other patients showed nonsignificant increases in flow velocity which decreased over time. During follow-up, the status of the posterior fossa sinuses could be diagnosed correctly in seven patients after contrast enhancement when these results were compared with those of venous MR angiography. In 1 patient, a partial recanalization was mistakenly diagnosed as an occlusion.

CONCLUSIONS

TCCS allows a reliable evaluation of the major DCVs and posterior fossa sinuses. The anterior and mid portions of the superior sagittal sinus and cortical veins cannot be assessed. Increased venous blood flow velocity can be used as an indirect criterion for indicating a cerebral venous thrombosis. Clinical recovery coincided with decreases in blood flow velocity in the series of patients investigated in this study.

Perception of first- and second-order motion: separable neurological mechanisms?

An unresolved issue in visual motion perception is how distinct are the processes underlying "first-order" and "second-order" motion. The former is defined by spatiotemporal variations of luminance and the latter by spatiotemporal variations in other image attributes, such as contrast or depth. Here we describe two neurological patients with focal unilateral lesions whose contrasting perceptual deficits on psychophysical tasks of "first-order" and "second-order" motion are related to the maps of the human brain established by functional neuroimaging and gross anatomical features. We used a relatively fine-grained neocortical parcellation method applied to high-resolution MRI scans of the patients' brains to illustrate a subtle, yet highly specific dissociation in the visual motion system in humans. Our results suggest that the two motion systems are mediated by regionally separate mechanisms from an early stage of cortical processing.

Bihemispheric reduction of GABAA receptor binding following focal cortical photothrombotic lesions in the rat brain

Focal brain lesions may lead to neuronal dysfunctions in remote (exofocal) brain regions. In the present study, focal lesions were induced in the hindlimb representation area of the parietal cerebral cortex in rats using the technique of photothrombosis. Photothrombosis occurs after illumination of the brain through the intact skull following intravenous injection of the photosensitive dye Rose Bengal. This resulted in cortical lesions with a diameter of about 2 mm. Quantitative receptor autoradiography was used to study alterations in the density of [3H]muscimol binding sites to GABAA receptors seven days after lesion induction. A reduced GABAA receptor binding (-13 to -27% of the control value) was found in layers II and III of remote exofocal regions in the ipsi- and contralateral cortex. The reduction was consistently more intense in the ipsilateral cortical areas than in those of the contralateral hemisphere. Using extracellular recordings, significant correlations between GABAA receptor binding and paired pulse inhibition could be demonstrated. The present investigation demonstrates that focal brain lesions cause a widespread, functionally effective down-regulation of GABAA receptors. These postlesional changes may result from lesion-induced alterations in cortical connectivity.

Prothrombotic disorders in infants and children with cerebral thromboembolism

BACKGROUND

To our knowledge, the contribution of prothrombotic conditions to cerebral thromboembolism has never been prospectively studied in a large series of pediatric patients.

METHODS

The Hospital for Sick Children, Toronto, Ontario, established a program in January 1992 to diagnose and treat children (term newborn to 18 years old) with arterial ischemic stroke or sinovenous thrombosis. The routine evaluation for prothrombotic conditions included plasminogen, antithrombin, protein C, free protein S, activated protein C resistance, IgG and IgM anticardiolipin antibody, and lupus anticoagulant. We analyzed samples taken within 2 years of the event. We report results on patients seen from January 1, 1992, to January 1, 1997.

RESULTS

Ninety-two patients (47 males and 45 females) entered the program during the study interval. Patients ranged from newborn to 18 years in age. Arterial ischemic stroke occurred in 78% of patients while sinovenous thrombosis occurred in 22%. All were tested for prothrombotic disorders. One or more abnormal results were present in 35 (38%) of the 92 patients. The majority (21/35) had multiple abnormal test results. The abnormal test results were anticardiolipin antibody (33%), plasminogen (9.5%), activated protein C resistance (9%), protein C (7%), antithrombin (12.5%), lupus anticoagulant (8%), and free protein S (11.5%). Male sex predicted the presence of prothrombotic abnormalities (relative risk, 1.7; 95% confidence interval, 1.2-2.5), but stroke type (relative risk, 0.8; 95% confidence interval, 0.7-1.1), age group, and presence of other risk factors did not predict abnormal testing.

CONCLUSIONS

A significant proportion (38%) of children with cerebral thromboembolism had evidence of prothrombotic conditions. In particular, there was a predominance of children with anticardiolipin antibody (33%). These data support a recommendation that children with cerebral thromboembolism be evaluated for prothrombotic disorders.