Intraoperative electrocorticography in children with medically intractable epilepsy

Intraoperative hippocampal electrocorticography frequently captures electrographic seizures and correlates with hippocampal pathology

OBJECTIVE

Relationship between electrographic seizures on hippocampal electrocorticography (IH-ECoG) and presence/type of hippocampal pathology remains unclear.

METHODS

IH-ECoG was recorded for 10-20 min from the ventricular surface of the hippocampus following removal of the temporal neocortex in 40 consecutive patients. Correlation between intraoperative hippocampal seizures and preoperative MRI, hippocampal histopathology, and EEG from invasive monitoring was determined.

RESULTS

IH-ECoG captured electrographic seizures in 15/40 patients (in 8/23 with abnormal hippocampal signal on MRI and 7/17 patients without MRI abnormality). Hippocampal neuronal loss was observed in 22/40 (Group 1), while 18/40 had no significant neuronal loss (Group 2). In Group 1, 4/22 had seizures on IH-ECoG, while 11/18 had electrographic seizures in Group 2. In 24/40 patients who underwent prolonged extraoperative intracranial EEG (IC-EEG) recording, hippocampal seizures were captured in 14. Of these, 7 also had seizures during IH-ECoG. In 10/24 IC-EEG patients without seizures, 3 had seizures on IH-ECoG.

CONCLUSIONS

IH-ECoG frequently captures spontaneous electrographic seizures. These are more likely to occur in patients with pathologic processes that do not disrupt/infiltrate hippocampus compared to patients with intractable epilepsy associated with disrupted hippocampal architecture.

SIGNIFICANCE

Intraoperative hippocampal seizures may result from deafferentation from the temporal neocortex and disinhibition of the perforant pathway.

Surgery for focal cortical dysplasia in children using intraoperative mapping

OBJECTIVE

Children with malformation of cortical development represent a significant proportion of pediatric epilepsy surgery candidates. Here, we describe a single-center experience with pediatric patients who underwent surgery for intractable epilepsy due to focal cortical dysplasia (FCD).

METHODS

Clinical data of 78 patients under 18 years of age with diagnosis of intractable epilepsy due to FCD who underwent surgery from January 1996 to January 2012 were reviewed comparing data of patients submitted to electrocorticography (ECoG) with those without ECoG.

RESULTS

Patients' mean age at surgery was 8.52 ± 4.99 years; mean age at epilepsy onset was 2.55 ± 3.01 years. Almost 80 % of the patients underwent ECoG register that was essential for delimitation of surgical resection in 66 out of 78 patients. ECoG was performed in all patients with extratemporal lesions, and the most common FCD found was type II. Seizure outcome was similar in groups with or without ECoG.

CONCLUSIONS

Tailored resection of FCD lesions for intractable epilepsy can be safely performed in children with a good seizure outcome and low complication rate. Epilepsy surgery should be considered for all patients with FCD and refractory epilepsy.

Intra-operative electrocorticography in lesional epilepsy

Intra-operative electrocorticography (ECoG) is useful in epilepsy surgery to delineate margins of epileptogenic zone, guide resection and evaluate completeness of resection in surgically remediable intractable epilepsies. The study evaluated 157 cases (2000-2008). The preoperative evaluation also included ictal SPECT (122) and PET in 32 cases. All were lesional cases, 51% (81) of patients had >1 seizure/day and another 1/3rd (51) had >1/week. Pre and post resection ECoG was performed in all cases. A total of 372 recordings were performed in 157 cases. Second post-operative recordings (42) and third post-operative recordings (16) were also performed. Site of recordings included lateral temporal (61), frontal (39), parietal (37), hippocampal (16) and occipital (4). 129/157 cases (82%) showing improvement on ECoG, 30/42 cases showed improvement in 2nd post resection, 8/16 showed improvement in the 3rd post-operative ECoG. 116/157 (73%) patients had good outcome (Engel I and II) at follow up (12-94 months, mean 18.2 months). Of these, 104 patients (80%) showed improvement on post-operative ECoG. 12 had good outcome despite no improvement on ECoG. The improvement in ECoG correlated significantly with clinical improvement [Sensitivity: 100% (95% CI; 96-100%); specificity: 68.3% (95% CI; 51.8-81.4%); positive predictive value: 89.9% (95% CI, 83.1-94.3%); negative predictive value: 100% (95% CI, 85-100%)]. The level of agreement was 91.72% (kappa: 0.76). Concluding, pre and post resection ECoG correlated with its grade of severity and clinical outcome.

Intraoperative electrocorticography and cortical stimulation in children

Intraoperative electrocorticography has been used in the surgical management of children with medically refractory epilepsy to localize anatomic areas of focal seizure onset, guide the extent, and completeness of resective epilepsy surgery, aid in functional mapping of cortical anatomy, and predict epilepsy surgical outcome. Evidence to support its utility for these purposes is somewhat controversial, particularly in children where the literature is substantially lacking. Usefulness is often dependent on the underlying pathology, and type of resective surgery. It seems to be valuable in the following circumstances: (1) tailoring the extent of hippocampal resection during temporal lobectomies, (2) guiding resection of cortical brain malformations, low-grade tumors, and other neocortical lesions, especially those involving eloquent cortex, and (3) monitoring for afterdischarges during functional cortical mapping. Most literature on this topic is not purely pediatric, and in most circumstances, is the result of combination of both children and adults cases. Cortical stimulation has been shown to be a useful, reliable and safe technique to assess motor, sensory, and speech function in children. As compared with adults, children manifest the following: (1) they need higher Amperage thresholds to elicit responses. In children younger than 10 years, cortical stimulation identifies language cortex at a lower rate than in children older than 10 years or in adults. (2) They have variability within the same individual in the stimulation threshold depending on the cortical site. This often results in the need to maximize stimulation of currents at each cortical site regardless of adjacent afterdischarge threshold. (3) They demonstrate more difficultly to evoke motor responses particularly with certain pathologies such as retrorolandic low-grade tumors. Often also the effective current intensity decreases after lesion removal. As a consequence of the above, the pulse width used for cortical stimulation in children often varies between 0.14 and 200 ms, the frequency ranges between 20 and 50 Hz, the current intensity between 0.5 and 20 mA, and the train between 3 and 25 seconds. Cortical stimulation can identify cortex with reorganized function secondary to congenital lesions and cerebral plasticity. These lesions include brain tumors, cortical dysplasia resulting in intractable epilepsy, and cavernous angioma causing epilepsy. When compared with other presurgical tests, cortical stimulation was shown to have results consistent with those of functional magnetic resonance imaging and Wada testing. It has the disadvantage of being invasive but the advantage of being highly accurate allowing for surgical tailored resections. Although the evidence for the utility of electrocorticography and cortical stimulation is exclusively level IV evidence, it is unlikely that randomized studies are going to be performed due to practical, ethical, and other reasons. The weight of the uncontrolled data at this stage is such that in children electrocorticography remains to be a useful test in some cases of cortical resection and that cortical stimulation is usually indicated when resection in or near eloquent cortex is needed.

Pre-surgical evaluation and surgical treatment in children with extratemporal epilepsy

INTRODUCTION

This review summarizes some patterns of pre-surgical evaluation and surgical treatment of extratemporal epilepsy in pediatric patients with medically refractory seizures, whose ictal behavior is variable. The most effective treatment for intractable partial epilepsy is a focal cortical resection with excision of the epileptogenic zone (the area of ictal onset and initial seizure propagation). This might be risky, though, in the case of a widespread lesion, sometimes encroaching one or more lobes, given the risk to the functional cerebral cortex. An anterior temporal lobectomy might prove more effective then in preventing seizures with fewer potential complications. If partial extratemporal epilepsy is associated with pharmaco-resistant seizures, the preoperative evaluation and operative strategy are determined according to the epileptogenic zone and to the relationship between a substrate-directed disorder and eloquent areas. The pediatric treatment of extratemporal epilepsy is aimed at controlling the seizures, avoiding morbidity, and improving the patient's quality of life through psychosocial integration. Since the immature brain is more plastic than when mature, the recovery of functions after surgery is greater in children than in adults.

RECOMMENDATION

Early surgery is recommended for children with intractable epilepsy, and is now accepted as an important therapeutic modality also for children with chronic epilepsy.

CONCLUSION

Technological advances in the last two decades, mainly in neuroimaging, have led many medical centers to consider surgical treatment of epilepsy, accuracy being granted by MRI-based neuronavigation systems-an interface between the lesion seen in the preoperative magnetic resonance imaging (MRI) and the operative field, often invisible to the surgeon.

The Effects of Sevoflurane and Hyperventilation on Electrocorticogram Spike Activity in Patients with Refractory Epilepsy

We investigated the effects of sevoflurane and hyperventilation on intraoperative electrocorticogram (ECoG) spike activity in 13 patients with intractable epilepsy. Grid electrodes were placed on the brain surface and ECoG was recorded under the following conditions: 1) 0.5 minimal alveolar anesthetic concentration (MAC) sevoflurane, 2) 1.5 MAC sevoflurane, and 3) 1.5 MAC sevoflurane with hyperventilation. The number of spikes per 5 min and the percentage of leads with spikes were assessed in each condition. In 4 patients with chronically implanted-subdural electrodes, the leads with seizure onset and with spikes during the interictal periods in the awake state were compared with those during sevoflurane anesthesia at 0.5 MAC and 1.5 MAC. The number of spikes and the percentage of leads with spikes were significantly more under 1.5 MAC sevoflurane anesthesia compared with those under 0.5 MAC sevoflurane (P < 0.05). The induction of hyperventilation significantly increased the number of spikes and percentage of leads with spikes (P < 0.05). With 0.5 MAC sevoflurane, the leads with spikes were similar to those at seizure onset in the awake state, whereas with 1.5 MAC sevoflurane, spikes were similar to those occurring during interictal periods in the awake state. These results indicate that sevoflurane and hyperventilation can affect the frequency and extent of ECoG spike activity in patients with intractable epilepsy. Careful attention should be paid to the concentration of sevoflurane used and ventilatory status when intraoperative EcoG is used to localize epileptic lesions.

IMPLICATIONS

Electrocorticogram can be used to define the location and extent of epileptic foci during epilepsy surgery. However, electrocorticogram can be affected by anesthetic technique. The present study found that sevoflurane concentration and hyperventilation affected the frequency and the extent of electrocorticogram spike activity in epileptic patients.

Surgical treatment of temporal lobe epilepsy. Personal experience

The authors present their results with epilepsy surgery of the temporal lobe performed during a 5 years period at the Hospital of the University of Jordan, in 12 patients. All patients underwent comprehensive presurgical evaluation, including neurological history, examination, video-Electroencefalogram, Electroencephalogram for intercritical and habitual seizures and optimum magnetic resonance. After appropriate selection, we performed epilepsy surgery in 12 patients (9 males and 3 females). The mean age at operation was 21.4 years (range 4-44 years). All patients were receiving high therapeutic doses of antiepileptic therapy. Abnormal findings in Magnetic Resonance were observed in all cases. Pre and post resection electrocorticogram were recorded and graded according to Jay Scale. Pathological findings showed, neoplasic lesion in 2 cases (16%); one ganglioglioma and a low grade astrocytoma) and 10 patients (84%) showed non-neoplasic lesions. Three patients (25%) had cortical dysplasia, another 3 (25%) had mesotemporal sclerosis, three more (25%) gliosis and one (8%) an arachnoid cyst. Post resection ECoG showed (84%) type A, (8%) type B, and (8%) type C. The present study has shown that intraoperative ECoG has an important role in the prediction of medically intractable epilepsy. Outcome of temporal lobe epilepsy surgery in our series was comparable to results reported by other authors despite of the absence of sophisticated functional tests.