Serge Vulliemoz

Reaching beyond the midline: why are human brains cross wired?

The crossing of nerve tracts from one hemisphere in the brain to the contralateral sense organ or limb is a common pattern throughout the CNS, which occurs at specialised bridging points called decussations or commissures. Evolutionary and teleological arguments suggest that midline crossing emerged in response to distinct physiological and anatomical constraints. Several genetic and developmental disorders involve crossing defects or mirror movements, including Kallmanns and Klippel-Feil syndrome, and further defects can also result from injury. Crossed pathways are also involved in recovery after CNS lesions and may allow for compensation for damaged areas. The development of decussation is under the control of a host of signalling molecules. Growing understanding of the molecular processes underlying the formation of these structures offers hope for new diagnostic and therapeutic interventions.

Yield of MRI, high-density electric source imaging (HD-ESI), SPECT and PET in epilepsy surgery candidates.

OBJECTIVE Preoperative workup aims at localizing the epileptogenic focus to achieve postoperative seizure-freedom. We studied the predictive value of non-invasive techniques, i.e. structural magnetic resonance imaging [MRI], high-density electric source imaging [HD-ESI] and metabolic imaging (positron emission tomography [PET]; single-photon emission computed tomography [SPECT]), in surgically treated patients. METHODS A prospective study of 190 epileptic operated patients, with >12 months follow-up and analyzed with state-of-the-art algorithms. 58 patients underwent all techniques. We computed sensitivity, specificity, predictive value and diagnostic odds ratio (OR) in relation to postoperative outcome. RESULTS Of 190 patients, 148 (77.9%) were seizure-free at follow-up. Resection of the epileptogenic focus was associated with favorable postsurgical outcome (p<0.05). Among 58 patients who underwent all tests, only MRI and HD-ESI were favorable outcome predictors (MRI: OR 10.9, p=0.004; HD-ESI: OR 13.1, p=0.004). Patients with concordant structural MRI and HD-ESI results had 92.3% (24/26) probability of favorable outcome. When both results were negative, probability was 0% (0/5); and when they disagreed, it was 63.0% (17/27). CONCLUSIONS Combination of MRI and HD-ESI offered the highest predictive value for postoperative seizure-freedom. SIGNIFICANCE This finding highlights the added value of HD-ESI in the presurgical workup, in particular in combination with an informative MRI.

Comparison of high gamma electrocorticography and fMRI with electrocortical stimulation for localization of somatosensory and language cortex

OBJECTIVE We investigated the contribution of electrocortical stimulation (ECS), induced high gamma electrocorticography (hgECoG) and functional magnetic resonance imaging (fMRI) for the localization of somatosensory and language cortex. METHODS 23 Epileptic patients with subdural electrodes underwent a protocol of somatosensory stimulation and/or an auditory semantic decision task. 14 Patients did the same protocol with fMRI prior to implantation. RESULTS ECS resulted in the identification of thumb somatosensory cortex in 12/16 patients. Taking ECS as a gold standard, hgECoG and fMRI identified 53.6/33% of true positive and 4/12% of false positive contacts, respectively. The hgECoG false positive sites were all found in the hand area of the post-central gyrus. ECS localized language-related sites in 7/12 patients with hgECoG and fMRI showing 50/64% of true positive and 8/23% of false positive contacts, respectively. All but one of the hgECoG/fMRI false positive contacts were located in plausible language areas. Four patients showed post-surgical impairments: the resection included the sites positively indicated by ECS, hgECoG and fMRI in 3 patients and a positive hgECoG site in one patient. CONCLUSIONS HgECoG and fMRI provide additional localization information in patients who cannot sufficiently collaborate during ECS. SIGNIFICANCE HgECoG and fMRI make the cortical mapping procedure more flexible not only by identifying priority cortical sites for ECS or when ECS is not feasible, but also when ECS does not provide any result.

Noninvasive language mapping in patients with epilepsy or brain tumors

BACKGROUND Functional magnetic resonance imaging (fMRI) has become part of routine brain mapping in patients with epilepsy or tumor undergoing resective surgery. However, robust localization of crucial functional areas is required. OBJECTIVE To establish a simple, short fMRI task that reliably localizes crucial language areas in individual patients who undergo respective surgery. METHODS fMRI was measured during an 8-minute auditory semantic decision task in 28 healthy controls and 35 consecutive patients who had focal epilepsy or a brain tumor. Nineteen underwent resective surgery. Group and individual analyses were performed. Results in patients were compared with postsurgical language outcome and electrocortical stimulation when available. RESULTS fMRI activations concordant with the anterior and posterior language areas were found in 96% and 89% of the controls, respectively. The anterior and posterior language areas were both activated in 93% of the patients. These results were concordant with electrocortical stimulation results in 5 patients. Transient postsurgical language deficits were found in 2 patients in whom surgery was performed in the vicinity of the fMRI activations or who had postsurgical complications implicating areas of fMRI activations. CONCLUSION The proposed fast fMRI language protocol reliably localized the most relevant language areas in individual subjects. It appears to be a valuable complementary tool for surgical planning of epileptogenic foci and of brain tumors.

Recurrent secondary generalization in frontal lobe epilepsy: Predictors and a potential link to surgical outcome?

Frontal lobe epilepsy (FLE) frequently leads to secondary generalized tonic–clonic seizures (SGTCS). However, little is known about the clinical, electrophysiologic, and radiologic correlates of SGTCS and whether these could influence diagnosis and treatment.

MP2RAGE and Susceptibility-Weighted Imaging in Lesional Epilepsy at 7T.

Surgery is the first choice therapeutic approach in case of drug‐resistant epilepsy. Unfortunately, up to 43% of patients referred for presurgical assessment do not have a lesion detectable by routine 3T magnetic resonance imaging (MRI) (MRI‐negative), although most of them likely have an underlying epileptogenic lesion. Thus, new MRI modalities with increased sensibility for epileptogenic lesions are required. This paper describes the magnetization‐prepared two rapid acquisition gradient echoes (MP2RAGE) and susceptibility‐weighted imaging (SWI) findings at 7T in a series of patients with drug‐resistant epilepsy of different etiologies.

P01. Transient spike-related connectivity changes in temporal lobe epilepsy: A high density EEG study

Purpose We aimed to analyze the dynamic behavior of epileptic networks through the study of the effective connectivity at a whole-brain scale during interictal spikes in temporal lobe epilepsy patients (TLE) using high-resolution EEG signals. We aimed to understand the connectivity pattern differences in right versus left TLE (RTLE vs LTLE). Method Sixteen patients, 8 with RTLE and 8 with LTLE, were selected for the study. We assessed the connectivity changes of cortical networks during interictal spikes compared to baseline periods at high-temporal resolution, using high-density EEG recordings. The source activity was obtained for 82 regions of interest using an individual head model and a distributed linear inverse solution. A multivariate, time-varying and frequency-resolved Granger causality analysis was applied to the source signal of all ROIs. A non-parametric statistical test was carried out to assess the difference in outflow between interictal spikes vs baseline in each ROI. Results In both groups, the key driving structures were located in the anterior temporal pole, and their driving towards other regions was higher at the time of the spike. In LTLE the keys drivers were only ipsilateral while in RTLE the key drivers were both ipsilateral and contralateral. Moreover, in RTLE we observed a driving pattern from the ipsilateral to the contralateral regions that was not seen in LTLE. Both groups showed driving from the anterior temporal structures to the frontal lobe. In the RTLE and LTLE groups, the pattern of connectivity changes was concordant with the cognitive impairment. Conclusion The used approach was able to identify the major contributors to interictal epileptic activity in both RTLE and LTLE, concordant with invasive electro-clinical findings. Furthermore, a different connectivity pattern was observed in RTLE and LTLE, suggesting that they are not simply symmetrical entities. This enhanced characterization of the epileptic networks increases our understanding of these conditions and could have clinical implications for epilepsy surgery.