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Serge Chassagnon, Lorella Minotti, Stéphane Kremer, Dominique Hoffmann and Philippe Kahane

Object

Surgery for frontal lobe drug-resistant epilepsies is often limited by the apparent widespread distribution of the epileptogenic zone. Recent advances in the parcellation of the medial premotor cortex give the opportunity to reconsider “seizures of the supplementary motor area” (SMA), and to assess the contribution of cingulate motor areas (CMAs), SMA proper (SMAp), and pre-SMA to the symptomatology of premotor seizures.

Methods

The authors reviewed the results of extraoperative electrical stimulation (ES) applied in 52 candidates for epilepsy surgery who underwent stereotactic intracerebral electroencephalographic recordings, focusing on ES of the different medial premotor fields; that is, the anterior and posterior CMA, the SMAp, and the pre-SMA. The ES sites were localized by superposition of the postoperative lateral skull x-ray and the preoperative sagittal MR imaging studies.

Results

Among 94 electrodes reaching the medial premotor wall, 57 responses were obtained from the anterior CMA (13 cases), the posterior CMA (11), the pre-SMA (18), and the SMAp (15). The ES of the pre-SMA and SMAp gave rise most often to a combination of motor (31 cases), speech-related (22), or somatosensory (3) elementary symptoms. The ES of the CMA yielded simple (17 of 24) more often than complex responses (7 of 24), among which sensory symptoms (7) were overrepresented. Irrepressible exploratory reaching/grasping movements were elicited at the vicinity of the cingulate sulcus, from the anterior CMA (3 cases) or the pre-SMA (1). Clinical responses to ES were not predictive of the postoperative neurological outcome.

Conclusions

These findings might be helpful in epilepsy surgery candidates, to better target investigation of the CMA, pre-SMA, and SMAp, and therefore to provide a better understanding of premotor seizures.

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Elie Lobel, Philippe Kahane, Ute Leonards, Marie-Hélène Grosbras, Stéphane Lehéricy, Denis Le Bihan and Alain Berthoz

Object. The goal of this study was to investigate the anatomical localization and functional role of human frontal eye fields (FEFs) by comparing findings from two independently conducted studies.

Methods. In the first study, 3-tesla functional magnetic resonance (fMR) imaging was performed in 14 healthy volunteers divided into two groups: the first group executed self-paced voluntary saccades in complete darkness and the second group repeated newly learned or familiar sequences of saccades. In the second study, intracerebral electrical stimulation (IES) was performed in 38 patients with epilepsy prior to surgery, and frontal regions where stimulation induced versive eye movements were identified. These studies showed that two distinct oculomotor areas (OMAs) could be individualized in the region classically corresponding to the FEFs. One OMA was consistently located at the intersection of the superior frontal sulcus with the fundus of the superior portion of the precentral sulcus, and was the OMA in which saccadic eye movements could be the most easily elicited by electrical stimulation. The second OMA was located more laterally, close to the surface of the precentral gyrus. The fMR imaging study and the IES study demonstrated anatomical and stereotactic agreement in the identification of these cortical areas.

Conclusions. These findings indicate that infracentimetric localization of cortical areas can be achieved by measuring the vascular signal with the aid of 3-tesla fMR imaging and that neuroimaging and electrophysiological recording can be used together to obtain a better understanding of the human cortical functional anatomy.

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Taylor J. Abel, René Varela Osorio, Ricardo Amorim-Leite, Francois Mathieu, Philippe Kahane, Lorella Minotti, Dominique Hoffmann and Stephan Chabardes

OBJECTIVE

Robot-assisted stereoelectroencephalography (SEEG) is gaining popularity as a technique for localization of the epileptogenic zone (EZ) in children with pharmacoresistant epilepsy. Here, the authors describe their frameless robot-assisted SEEG technique and report preliminary outcomes and relative complications in children as compared to results with the Talairach frame–based SEEG technique.

METHODS

The authors retrospectively analyzed the results of 19 robot-assisted SEEG electrode implantations in 17 consecutive children (age < 17 years) with pharmacoresistant epilepsy, and compared these results to 19 preceding SEEG electrode implantations in 18 children who underwent the traditional Talairach frame–based SEEG electrode implantation. The primary end points were seizure-freedom rates, operating time, and complication rates.

RESULTS

Seventeen children (age < 17 years) underwent a total of 19 robot-assisted SEEG electrode implantations. In total, 265 electrodes were implanted. Twelve children went on to have EZ resection: 4 demonstrated Engel class I outcomes, whereas 2 had Engel class II outcomes, and 6 had Engel class III–IV outcomes. Of the 5 patients who did not have resection, 2 underwent thermocoagulation. One child reported transient paresthesia associated with 2 small subdural hematomas, and 3 other children had minor asymptomatic intracranial hemorrhages. There were no differences in complication rates, rates of resective epilepsy surgery, or seizure freedom rates between this cohort and the preceding 18 children who underwent Talairach frame–based SEEG. The frameless robot-assisted technique was associated with shorter operating time (p < 0.05).

CONCLUSIONS

Frameless robot-assisted SEEG is a safe and effective means of identifying the EZ in children with pharmacoresistant partial epilepsy. Robot-assisted SEEG is faster than the Talairach frame–based method, and has equivalent safety and efficacy. The former, furthermore, facilitates more electrode trajectory possibilities, which may improve the localization of epileptic networks.

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Pauline Cuisenier, Bénédicte Testud, Lorella Minotti, Samuel El Bouzaïdi Tiali, Laurence Martineau, Anne-Sophie Job, Agnès Trébuchon, Pierre Deman, Manik Bhattacharjee, Dominique Hoffmann, Jean-Philippe Lachaux, Monica Baciu, Philippe Kahane and Marcela Perrone-Bertolotti

OBJECTIVE

The authors assessed the clinical relevance of preoperative task-induced high-frequency activity (HFA) for language mapping in patients with refractory epilepsy during stereoelectroencephalography recording. Although HFA evaluation was described as a putative biomarker of cognition, its clinical relevance for mapping language networks was assessed predominantly by studies using electrocorticography (ECOG).

METHODS

Forty-two patients with epilepsy who underwent intracranial electrode implantation during both task-induced HFA and direct cortical stimulation (DCS) language mapping were evaluated. The spatial and functional relevance of each method in terms of specificity and sensitivity were evaluated.

RESULTS

The results showed that the two methods were able to map classic language regions, and a large and bilateral language network was obtained with induced HFA. At a regional level, differences were observed between methods for parietal and temporal lobes: HFA recruited a larger number of cortical parietal sites, while DCS involved more cortical temporal sites. Importantly, the results showed that HFA predicts language interference induced by DCS with high specificity (92.4%; negative predictive value 95.9%) and very low sensitivity (8.9%; positive predictive value 4.8%).

CONCLUSIONS

DCS language mapping appears to be more appropriate for an extensive temporal mapping than induced HFA mapping. Furthermore, induced HFA should be used as a complement to DCS to preselect the number of stimulated sites during DCS, by omitting those reported as HFA−. This may be a considerable advantage because it allows a reduction in the duration of the stimulation procedure. Several parameters to be used for each method are discussed and the results are interpreted in relation to previous results reported in ECOG studies.