Bilateral intracranial electroencephalographic monitoring immediately following corpus callosotomy

Although many patients with medically refractory focal epilepsy are candidates for resective surgery, patients with multifocal epilepsy and symptomatic generalized epilepsy remain difficult to treat medically and surgically. Corpus callosotomy has been utilized since 1940 for the treatment of seizures, with reports of efficacy in multiple seizure types. Previous studies have demonstrated subsequent lateralization of bilateral/bisynchronous epileptiform activity following callosotomy. To investigate the efficacy of bilateral intracranial electroencephalographic studies immediately following corpus callosotomy, we retrospectively identified 26 patients who underwent corpus callosotomy at our center, 18 of whom had intracranial monitoring following corpus callosotomy. Five of the 18 had focal resections following intracranial electroencephalography (EEG). No patients were seizure free following callosotomy or resection. No differences in postoperative outcomes were seen between patients with intracranial EEG versus those without.     

Lateralization of interictal spikes after corpus callosotomy

Objective

Corpus callosotomy may limit secondary bilateral synchrony into the primary epileptogenic hemisphere. This study investigated whether pre-operative EEG can predict post-operative spike lateralization.

Methods

The subjects included 14 patients with medically intractable drop attacks who underwent total corpus callosotomy. Pre-operative patterns of inter-hemispheric propagation were quantified by peak-latency analysis with the template-based spike averaging technique.

Results

Postoperative lateralization of interictal spikes was observed in 5 of the 14 patients. Inter-hemispheric latency was significantly longer in these 5 patients (mean 14.0 ms, range from 0 to 78 ms, versus mean 5.2 ms, range from 0 to 29 ms, p < 0.01). The lateralization occurred in association with the presence of structural lesions (p < 0.05). The post-operative spikes were lateralized to the lesion side in 3 of 4 patients with unilateral epileptogenic lesion. Three patients presented one-way inter-hemispheric propagation pattern pre-operatively. The post-operative spikes were lateralized to the hemisphere of the leading spikes in two.

Conclusions

Interictal spikes are lateralized to the epileptogenic hemisphere in some patients after callosotomy. Lateralization can be expected in the presence of structural lesions and/or longer inter-hemispheric latency.

Significance

Analysis of pre-operative EEG spikes may predict the primary epileptogenic hemisphere before corpus callosotomy.     

Effectiveness of total corpus callosotomy for diffuse bilateral polymicrogyria: Report of three pediatric cases

Purpose

Polymicrogyria, a malformation of the cerebral cortex, frequently causes epilepsy. Diffuse bilateral polymicrogyria (DBP) is related to poor epilepsy prognosis, but most patients with DBP are not good candidates for resective epilepsy surgery and effectiveness of corpus callosotomy (CC), a palliative surgery, for patients without resective epileptogenic cortices, has not been established in DBP. Because CC might be effective against DBP-related epilepsy, we conducted total CC in three pediatric DBP cases.

Is a Cortical Spike Discharge “Transferred” to the Contralateral Cortex via the Corpus Callosum?: An Intraoperative Observation of Electrocorticogram and Callosal Compound Action Potentials

PURPOSE: By means of the intraoperative electrophysiologic observation, we reevaluated the "transfer" theory that a transcallosal volley invoked by a cortical spike discharge in one hemisphere directly causes its contralateral counterpart via the corpus callosum (CC). METHODS: Twenty-six patients who underwent corpus callosotomy were the subjects of this study. Intraoperatively, electrocorticograms from both hemispheres were simultaneously monitored with callosal compound action potentials (CCAPs) from the CC. Analysis was conducted on (a) the interhemispheric delay of bilaterally synchronous spike-and-wave discharges (BSSWs), and (b) the chronological relation between BSSWs and CCAPs. RESULTS: The side of prior spike discharges was never fixed but was occasionally reversed. Interhemispheric delays between the BSSWs were not constant, regardless of direction, and fluctuated in all patients. Most of the interhemispheric delays were distributed within 20 ms with a mode of 0 ms. The waveform of the CCAP was characterized by slow-rising negative potential change that attained its peak after a cortical spike discharge. These findings were identical in all the patients regardless of whether the BSSWs were changed or unchanged after callosotomy. CONCLUSIONS: If the "transfer" role of the CC is true, interhemispheric delays between BSSWs must be longer than interhemispheric axonal conduction time (about 20 ms), and a preceding cortical spike discharge must produce a CCAP and then a contralateral one in order of time. However, this hypothesis was not confirmed in the present study. We propose the interhemispheric recruitment of the epileptogenic state as a different role of the CC on epileptogenesis.     

Outcome and long term follow-up after corpus callosotomy in childhood onset intractable epilepsy

Introduction Epilepsy surgery is a standard of care in the treatment of medically intractable epilepsy. Twenty five percent of patients with intractable epilepsy in childhood can be candidates for epilepsy surgery. Corpus callosotomy is a surgical treatment option for patients with potentially injurious drop attacks and disabling generalized seizures. Postoperative improvement of cognition and speech are important gains after epilepsy surgery particularly during childhood. The aim of this study is to evaluate the outcome of corpus callosotomy for the treatment of childhood onset medically intractable epilepsy in a developing pediatric epilepsy surgery center.Method We report 16 patients who underwent two thirds anterior corpus callosotomy for treatment of refractory seizures in childhood.Results All patients had drop attacks or multiple types of seizures, yet some showed focal onset with secondary generalization on electroencephalogram (EEG). One patient was seizure free (class 1 outcome), five had class 2A outcome, five had class 2B outcome, and five had class 3 outcome. Overall 11/16 (69%) of our patients improved significantly after anterior callosotomy.Conclusion Corpus callosotomy remains to be a fairly good choice of surgical treatment for childhood onset medically intractable epilepsy in selected patients.     

Refractory generalized seizures: response to corpus callosotomy and vagal nerve stimulation

PURPOSE: The vagal nerve stimulator (VNS) and corpus callosotomy can reduce seizure frequency when seizures are refractory to medications. However, the efficacy and safety of these two procedures have not been compared. This study evaluates the two procedures for generalized seizures. METHODS: All patients with refractory generalized seizures (generalized tonic-clonic, tonic, or atonic) who underwent a corpus callosotomy (anterior or complete) (n = 53) without other forms of epilepsy surgery and those who underwent VNS placement (n = 25) were evaluated for this study. Seizure response and procedure complications were evaluated. RESULTS: For those with a corpus callosotomy and generalized tonic-clonic seizures (n = 50), 79.5% had >or=50% decrease in the frequency of generalized tonic-clonic seizures, and 60% had >or=80% seizure reduction. For those with a VNS and generalized tonic-clonic seizures (n = 21), 50% had >or=50% seizure reduction, and 33% had >or=80% seizure reduction. Tonic and atonic seizures decreased after either VNS or a corpus callosotomy. The complication rate for corpus callosotomy was higher (21% all complications, 3.8% permanent) than that for VNS (8%; none permanent), but complications for both corpus callosotomy and VNS were rarely permanent. CONCLUSIONS: Both corpus callosotomy and VNS are effective in reducing generalized seizures. Corpus callosotomy is associated with greater efficacy but higher risk for complications, although these were generally transient.     

Eyebrow incision with supraorbital trephination for endoscopic corpus callosotomy: a feasibility study

Objective We describe a novel technique for the partial bisection of the corpus callosum in order to increase the minimally invasiveness of this procedure.Methods Brow incisions with midline trephinations were performed in six adult cadavers. An endoscope was next introduced and used to transect approximately the anterior two-thirds of the corpus callosum.Results No complications such as injury to the superior sagittal sinus or anterior cerebral artery were encountered in any of our cadaveric specimens. The corpus callosum was easily transected in each specimen.Conclusion As a feasibility study, we believe this technique could provide a less invasive mechanism for patients who require corpus callosotomy and will minimize much of the morbidity associated with the traditional methods of sectioning the corpus callosum.     

Acute effect of callosotomy on cortical temporal coupling in humans: Intraoperative electrocorticographic recording

Objective

To investigate the acute role of the corpus callosum in inter- and intrahemispheric temporal coupling.

Methods

Intraoperative electrocorticography (ECoG) makes it possible to investigate the acute role of the corpus callosum in cortical temporal coupling, or synchrony, without additional surgical intervention, thus avoiding the confounding effects of scalp recordings and the long-term reorganization of functional connectivity. ECoGs were recorded in three patients during callosotomies. Bilateral electrode grids were placed over the frontal cortex. ECoGs were recorded immediately before and after performing the anterior two-thirds callosal transection, were digitalized at a sampling rate of 512 Hz, inspected for artifacts, and later analyzed offline. Cross-correlation between inter- and intrahemispheric electrode pairs were obtained for 1 Hz bins and special broad bands obtained by principal component analysis for each patient pre- and post-callosotomy.

Results

A statistically significant change was observed in intrahemispheric temporal coupling between electrode pairs that exceeded the confidence limit of correlation.

Conclusions

Present results show that interrupting the influence of the corpus callosum has an acute effect on intrahemispheric activity by decreasing temporal coupling between cortical areas.

Significance

Intrahemispheric temporal coupling does not depend exclusively on ipsilateral cortico-cortical pathways or on subcortical influences, but also on callosal pathways.     

Source activity in the human secondary somatosensory cortex depends on the size of corpus callosum

If corpus callosum (CC) mediates the activation of the secondary somatosensory area (SII) ipsilateral to the side of stimulation, then the peak latencies of the contra- and ipsilateral SII activity as well as the amplitude of the ipsilateral SII activity should correlate with the size of CC. Innocuous electrical stimuli of five different intensities were applied to the ventral surface of the right index finger in 15 right-handed men. EEG was recorded using 82 closely spaced electrodes. The size of CC and of seven callosal regions was measured from the mid-sagittal slice of a high-resolution anatomical MRI. The activation in the contralateral and ipsilateral SII was evaluated using spatio-temporal source analysis. At the strongest stimulus intensity, the size of the intermediate part of the callosal truncus correlated negatively with the interpeak latency of the sources in ipsi- and contralateral SII (r = -0.83, P < 0.01). Stepwise regression analysis showed that the large size of the intermediate truncus of CC was paralleled by a latency reduction of peak activity of the ipsilateral SII, whereas both contra- and ipsilateral peak latencies were positively correlated. The peak amplitude of the ipsilateral SII source correlated positively with the size of the intermediate truncus of CC, and with the peak amplitudes of sources in the primary somatosensory cortex (SI) and in the mesial frontal cortex. The results suggest that in right-handed neurologically normal men, the size of the intermediate callosal truncus contributes to the timing and amplitude of ipsilateral SII source activity.     

Recovering EEG brain signals: artifact suppression with wavelet enhanced independent component analysis

Independent component analysis (ICA) has been proven useful for suppression of artifacts in EEG recordings. It involves separation of measured signals into statistically independent components or sources, followed by rejection of those deemed artificial. We show that a "leak" of cerebral activity of interest into components marked as artificial means that one is going to lost that activity. To overcome this problem we propose a novel wavelet enhanced ICA method (wICA) that applies a wavelet thresholding not to the observed raw EEG but to the demixed independent components as an intermediate step. It allows recovering the neural activity present in "artificial" components. Employing semi-simulated and real EEG recordings we quantify the distortions of the cerebral part of EEGs introduced by the ICA and wICA artifact suppressions in the time and frequency domains. In the context of studying cortical circuitry we also evaluate spectral and partial spectral coherences over ICA/wICA-corrected EEGs. Our results suggest that ICA may lead to an underestimation of the neural power spectrum and to an overestimation of the coherence between different cortical sites. wICA artifact suppression preserves both spectral (amplitude) and coherence (phase) characteristics of the underlying neural activity.     

The integrity of corpus callosum and cluster B personality disorders: A quantitative MRI study in juvenile myoclonic epilepsy

Evidence suggests increased prevalence of cluster B personality disorders (PD) among patients with juvenile myoclonic epilepsy (JME), which has been associated with worse seizure control and more psychosocial dysfunctions. A preliminary voxel-based morphometry study demonstrated corpus callosum (CC) volume reduction in patients with JME and cluster B PD, particularly in the posterior midbody and isthmus. In this study we aimed to follow up these results with region of interest analysis. Sixteen JME patients with cluster B PD, 38 JME patients without any psychiatric disorder, and 30 demographically matched healthy controls submitted to a psychiatric evaluation and a magnetic resonance imaging scan. The total and regional callosal areas were obtained from the midsagittal slice using a semi-automated program. Psychiatric evaluation was performed through SCID-I and -II. Significant reductions in the posterior region of the CC were observed in the JME with PD group relative to the other groups. These data support previous findings of callosal reductions in cluster B PD, as well as a possible involvement of CC in patients with JME and such personality characteristics.     

Functional and effective brain connectivity for discrimination between Alzheimer’s patients and healthy individuals: A study on resting state EEG rhythms

Objective

This exploratory study provided a proof of concept of a new procedure using multivariate electroencephalographic (EEG) topographic markers of cortical connectivity to discriminate normal elderly (Nold) and Alzheimer’s disease (AD) individuals.