Luc Valton

Microembolic Signals and Risk of Early Recurrence in Patients With Stroke or Transient Ischemic Attack

BACKGROUND AND PURPOSE Asymptomatic microembolic signals (MES) can be demonstrated in patients with cerebral ischemia using transcranial Doppler (TCD) ultrasonographic monitoring of the middle cerebral artery. However, the clinical relevance of MES remains uncertain. The purpose of this study was to estimate the independent contribution of microembolism to the risk of early ischemic recurrence (EIR) in patients with stroke or transient ischemic attack (TIA) of presumed arterial origin. METHODS We studied the incidence of EIR in 73 consecutive patients with carotid stroke or TIA in whom TCD scanning of the symptomatic middle cerebral artery was performed within 7 days from the onset of symptoms. Patients with a potential cardiac source of embolism were excluded from the study. RESULTS Eight patients had EIR during a mean+/-SD follow-up of 10+/-8 days. The incidence of EIR was 4.3 per 100 patient-days in patients with MES and only 0.5 per 100 patient-days in patients without MES. The presence of MES was a significant predictor of EIR after adjustment for the presence of carotid stenosis or aortic arch atheroma, antiplatelet therapy during follow-up, and other potential confounding variables (relative risk, 8.7; 95% confidence interval, 2 to 38.2; P=0.0015). CONCLUSIONS Microembolism is a significant independent predictor of EIR in patients with stroke or TIA of presumed arterial origin.

Impaired consciousness during temporal lobe seizures is related to increased long-distance cortical-subcortical synchronization.

Loss of consciousness (LOC) is a dramatic clinical manifestation of temporal lobe seizures. Its underlying mechanism could involve altered coordinated neuronal activity between the brain regions that support conscious information processing. The consciousness access hypothesis assumes the existence of a global workspace in which information becomes available via synchronized activity within neuronal modules, often widely distributed throughout the brain. Re-entry loops and, in particular, thalamo-cortical communication would be crucial to functionally bind different modules together. In the present investigation, we used intracranial recordings of cortical and subcortical structures in 12 patients, with intractable temporal lobe epilepsy (TLE), as part of their presurgical evaluation to investigate the relationship between states of consciousness and neuronal activity within the brain. The synchronization of electroencephalography signals between distant regions was estimated as a function of time by using non-linear regression analysis. We report that LOC occurring during temporal lobe seizures is characterized by increased long-distance synchronization between structures that are critical in processing awareness, including thalamus (Th) and parietal cortices. The degree of LOC was found to correlate with the amount of synchronization in thalamo-cortical systems. We suggest that excessive synchronization overloads the structures involved in consciousness processing, preventing them from treating incoming information, thus resulting in LOC.

Asymptomatic Cerebral Embolic Signals in Patients With Carotid Stenosis Correlation With Appearance of Plaque Ulceration on Angiography

BACKGROUND AND PURPOSE Asymptomatic cerebral emboli may be detected in patients with carotid stenosis by transcranial Doppler ultrasonography of the middle cerebral artery (MCA). The aim of this study was to determine the angiographic correlates of such embolic signals. METHODS Doppler signals from 48 MCAs in 26 patients with carotid stenosis that was either symptomatic (n = 20) or asymptomatic (n = 6) were recorded for 40 minutes. The grade of carotid stenosis and the ulcerated or nonulcerated appearance of the plaque were assessed using the criteria of the North American Symptomatic Carotid Endarterectomy Trial. RESULTS Embolic signals were detected in 8 MCAs from 7 patients; 4 (50%) of these MCAs were clinically symptomatic compared with 16 (40%) without embolic signal. Although there was a trend toward more severe stenosis in the cases with embolic signals, this was not significant (mean +/- SD, 67 +/- 29% versus 55 +/- 36%). In contrast, an image of ulceration was found on ipsilateral carotid angiography in 5 cases (63%) with embolic signals and in only 9 cases (23%) without embolic signals (odds ratio, 5.74; 95% confidence interval, 1.15 to 28.79, by multivariate regression analysis). CONCLUSIONS This study demonstrates that the occurrence of embolic signals in patients with carotid stenosis is associated with the appearance of plaque ulceration on angiography.

Functional interactions in brain networks underlying epileptic seizures in bilateral diffuse periventricular heterotopia

OBJECTIVE Our aim was to investigate relationships between heterotopic and remote cortical structures at seizure initiation, in a patient with bilateral periventricular nodular heterotopias (BPNH) explored by intracerebral electrodes. METHODS Stereoelectroencephalography (SEEG) was performed in a man with BPNH and refractory epilepsy to investigate the hypothesis of right temporal lobe epilepsy and the possible involvement of heterotopic structures during seizures. SEEG signals were analyzed with quantification of functional coupling between different brain structures during seizures, using nonlinear regression. We have used Z-score transformation of correlation values to reflect the change from the preictal period. Relationships between BPNH and cortical structures were investigated using analysis of stimulation-induced potentials. RESULTS Three spontaneous seizures were recorded and analyzed. Signal analysis of interdependencies in two seizures demonstrated a large initial network involving both heterotopia and cortical structures. Stimulations of heterotopia induced responses in remote cortical structures. CONCLUSIONS Distinct epileptogenic networks were identified, in which leader structures were either the heterotopic or the mesial temporal structures, with functional connections between heterotopic and cortical areas. SIGNIFICANCE These results confirm that a vast epileptogenic network, including heterotopic and cortical neurons, may be responsible for seizure generation in BPNH. This may explain certain surgical failures in this group.

Cerebral microembolism in patients with stroke or transient ischaemic attack as a risk factor for early recurrence

The incidence of early recurrence in 32 patients who had had a transient ischaemic attack or stroke in the anterior circulation was studied. Patients with a potential cardiac source of embolism were excluded from the study. All patients had transcranial Doppler (TCD) monitoring of the symptomatic middle cerebral artery for microembolic signal detection within seven days from the onset of symptoms. Four patients had early recurrence during a mean follow up of 15 (SD11) days. All early recurrences occurred in the same arterial territory as the initial ischaemic event. Three of the four patients with early recurrence had prior microembolic signals. The incidence of early recurrence was 50% (3/6) in patients with microembolic signals and 3.8% (1/26) in patients without microembolic signals (P=0.02). The findings suggest that TCD monitoring of patients with recent cerebral ischaemia of presumed arterial origin allows recognition of a subset of patients at high risk for early recurrence.

Risk factors of postictal generalized EEG suppression in generalized convulsive seizures

Objective: To identify the clinical determinants of occurrence of postictal generalized EEG suppression (PGES) after generalized convulsive seizures (GCS). Methods: We reviewed the video-EEG recordings of 417 patients included in the REPO2MSE study, a multicenter prospective cohort study of patients with drug-resistant focal epilepsy. According to ictal semiology, we classified GCS into 3 types: tonic-clonic GCS with bilateral and symmetric tonic arm extension (type 1), clonic GCS without tonic arm extension or flexion (type 2), and GCS with unilateral or asymmetric tonic arm extension or flexion (type 3). Association between PGES and person-specific or seizure-specific variables was analyzed after correction for individual effects and the varying number of seizures. Results: A total of 99 GCS in 69 patients were included. Occurrence of PGES was independently associated with GCS type (p < 0.001) and lack of early administration of oxygen (p < 0.001). Odds ratio (OR) for GCS type 1 in comparison with GCS type 2 was 66.0 (95% confidence interval [CI 5.4–801.6]). In GCS type 1, risk of PGES was significantly increased when the seizure occurred during sleep (OR 5.0, 95% CI 1.2–20.9) and when oxygen was not administered early (OR 13.4, 95% CI 3.2–55.9). Conclusion: The risk of PGES dramatically varied as a function of GCS semiologic characteristics. Whatever the type of GCS, occurrence of PGES was prevented by early administration of oxygen.

Asymptomatic cerebral embolic signals in patients with acute cerebral ischaemia and severe aortic arch atherosclerosis

Abstract Severe aortic arch atheroma (AAA) is a strong risk factor for ischaemic stroke, but it is unclear whether AAA is a source of cerebral emboli or simply a marker of cerebral atherosclerosis. The purpose of this study was to find out the prevalence of asymptomatic cerebral embolic signals (ES) in patients with acute cerebral ischaemia, AAA and no other potential source of cerebral embolism. Forty patients with anterior circulation ischaemic stroke or transient ischaemic attack (TIA) were prospectively studied using transesophageal echocardiography (TEE) and transcranial Doppler (TCD) scanning within seven days of symptom onset. Patients with a cardiac source of embolism or carotid stenosis > 50 % were excluded. ES were detected in 14.3 % (2/14) of patients with AAA ≥ 4 mm and in no patients with AAA < 4 mm or no AAA (p=0.14). The findings suggest that ES may be associated with severe AAA but their prevalence is low in this setting.

Can DTI fiber tracking of the optic radiations predict visual deficit after surgery

OBJECT Sparing optic radiations can be of paramount importance during epilepsy surgery of the temporal lobe. The anatomical heterogeneity of the Meyers loop of the optic radiations could be assessed by means of diffusion tensor tractography. We used temporal lobe surgery as a lesion model to validate this method. MATERIAL AND METHODS We analyzed the distance between the temporal pole (TP) and Meyers loop (ML) and the correlation between visual impairment and the percentage of virtual fibers injured. MRI studies were performed in 18 patients and 13 controls. Diffusion tensor imaging (DTI) with fiber tracking was performed using four different algorithms and various gradient directions (15 or 32) and fractional anisotropy (FA) thresholds (0.18, 0.20, and 0.22). To find the best DTI model, we tested each gradient direction and FA threshold on 16 operated patients by pre- and post-operative visual field testing that analyzed the percentage of virtual fibers damaged on 3-month-post-operative MRIs. RESULTS Marked individual differences were noted in the TP-ML distances (mean: 25.4mm; range 18.2-38.3mm; standard deviation: 4.7) but with no significant difference between patients and controls (p=0.9). The percentage of virtual fibers reconstructed by tracking and damaged by surgery was correlated with visual impairment. Significant differences appeared between algorithm types. The tensor-line algorithm with 15-direction resolution and an anisotropy threshold of 0.18 seemed to be the most relevant. A threshold of 5.5% of injured virtual fiber could predict a visual defect with a sensitivity of 71.4% and a specificity of 87.5%. CONCLUSION Optic radiation tractography by DTI could be a useful method to assess an individual patients risk of postoperative visual deficit.

Validity of Diagnosis Using the French Translation of the Semi‐Structured Interview for Seizure Classification

Summary: Purpose: The purpose of this study was to assess the acceptability and validity of the French cross‐cultural translation of a semistructured interview for seizure classification (SISC). We used the first revised version, the original of which was validated in 1990.

Memory scrutinized through electrical brain stimulation: A review of 80 years of experiential phenomena

HighlightsThe electrical parameters that reliably induce reminiscences remain to be specified.Memory networks can only be activated by some of their nodes: mostly temporal.The electrical parameters that reliably induce reminiscences remain to be specified. Abstract Electrical brain stimulations (EBS) sometimes induce reminiscences, but it is largely unknown what type of memories they can trigger. We reviewed 80 years of literature on reminiscences induced by EBS and added our own database. We classified them according to modern conceptions of memory. We observed a surprisingly large variety of reminiscences covering all aspects of declarative memory. However, most were poorly detailed and only a few were episodic. This result does not support theories of a highly stable and detailed memory, as initially postulated, and still widely believed as true by the general public. Moreover, memory networks could only be activated by some of their nodes: 94.1% of EBS were temporal, although the parietal and frontal lobes, also involved in memory networks, were stimulated. The qualitative nature of memories largely depended on the site of stimulation: EBS to rhinal cortex mostly induced personal semantic reminiscences, while only hippocampal EBS induced episodic memories. This result supports the view that EBS can activate memory in predictable ways in humans.