Bilateral intracranial electrodes for lateralizing intractable epilepsy: efficacy, risk, and outcome

Non-lesional mesial temporal lobe epilepsy requires bilateral invasive evaluation

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Bilateral ictal onsets may lead to surgery failure in mesial temporal lobe epilepsy.

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Bitemporal SEEG seizures were recorded despite of unilateral non-invasive tests.

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Patients with non-lesional MTLE need bitemporal invasive evaluation before resection.

Purpose

Mesial temporal lobe epilepsy (MTLE) usually responds well to surgical treatment, although in non-lesional cases up to 50% of patients experience seizure relapse. The possibility of bilateral independent seizure onset should be considered as a reason for epilepsy surgery failure.

Methods

In a cohort of 177 patients who underwent invasive presurgical evaluation with stereo-tactically placed electrodes in two level four epilepsy centers, 29 had non-lesional MTLE. Invasive evaluation results are described.

Results

Among 29 patients with non-lesional MRI and mesial temporal lobe seizure onset recorded during stereo-EEG (SEEG) evaluation, four patients with unilateral preimplantation hypothesis had independent bilateral mesial temporal seizures on SEEG despite of unilateral non-invasive evaluation data. Three of these patients were treated with bitemporal responsive neurostimulator system (RNS). Independent bilateral mesial temporal seizures have been confirmed on RNS ECoG (electrocorticography). The fourth patient underwent right anterior temporal lobectomy.

Conclusion

We propose that patients with non-lesional mesial temporal lobe epilepsy would benefit from bilateral invasive evaluation of mesial temporal structures to predict those patients who would be at most risk for surgical failure. Neurostimulaiton could be an initial treatment option for patients with independent bitemporal seizure onset.

Method of invasive monitoring in epilepsy surgery and seizure freedom and morbidity: A systematic review

OBJECTIVE

Invasive monitoring is sometimes necessary to guide resective surgery in epilepsy patients, but the ideal method is unknown. In this systematic review, we assess the association of postresection seizure freedom and adverse events in stereoelectroencephalography (SEEG) and subdural electrodes (SDE).

METHODS

We searched three electronic databases (MEDLINE, Embase, and CENTRAL [Cochrane Central Register of Controlled Trials]) from their inception to January 2018 with the keywords "electroencephalography," "intracranial grid," and "epilepsy." Studies that presented primary quantitative patient data for postresection seizure freedom with at least 1 year of follow-up or complication rates of SEEG- or SDE-monitored patients were included. Two trained investigators independently collected data from eligible studies. Weighted mean differences (WMDs) with 95% confidence interval (CIs) were used as a measure of the association of SEEG or SDE with seizure freedom and with adverse event outcomes.

RESULTS

Of 11 462 screened records, 48 studies met inclusion criteria. These studies reported on 1973 SEEG patients and 2036 SDE patients. Our systematic review revealed SEEG was associated with 61.0% and SDE was associated with 56.4% seizure freedom after resection (WMD = +5.8%, 95% CI = 4.7-6.9%, P = .001). Furthermore, SEEG was associated with 4.8% and SDE was associated with 15.5% morbidity (WMD = -10.6%, 95% CI = -11.6 to -9.6%, P = .001). SEEG was associated with 0.2% mortality and SDE was associated with 0.4% mortality (WMD = -0.2%, 95% CI = -0.3 to -0.1%, P = .001).

SIGNIFICANCE

In this systematic review of SEEG and SDE invasive monitoring techniques, SEEG was associated with fewer surgical resections yet better seizure freedom outcomes in those undergoing resections. SEEG was also associated with lower mortality and morbidity than SDE. Clinical studies directly comparing these modalities are necessary to understand the relative rates of seizure freedom, morbidity, and mortality associated with these techniques.

Surgery for epilepsy

BACKGROUND

This is an updated version of the original Cochrane review, published in 2015.Focal epilepsies are caused by a malfunction of nerve cells localised in one part of one cerebral hemisphere. In studies, estimates of the number of individuals with focal epilepsy who do not become seizure-free despite optimal drug therapy vary between at least 20% and up to 70%. If the epileptogenic zone can be located, surgical resection offers the chance of a cure with a corresponding increase in quality of life.

OBJECTIVES

The primary objective is to assess the overall outcome of epilepsy surgery according to evidence from randomised controlled trials.Secondary objectives are to assess the overall outcome of epilepsy surgery according to non-randomised evidence, and to identify the factors that correlate with remission of seizures postoperatively.

SEARCH METHODS

For the latest update, we searched the following databases on 11 March 2019: Cochrane Register of Studies (CRS Web), which includes the Cochrane Epilepsy Group Specialized Register and the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid, 1946 to March 08, 2019), ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP).

SELECTION CRITERIA

Eligible studies were randomised controlled trials (RCTs) that included at least 30 participants in a well-defined population (age, sex, seizure type/frequency, duration of epilepsy, aetiology, magnetic resonance imaging (MRI) diagnosis, surgical findings), with an MRI performed in at least 90% of cases and an expected duration of follow-up of at least one year, and reporting an outcome related to postoperative seizure control. Cohort studies or case series were included in the previous version of this review.

DATA COLLECTION AND ANALYSIS

Three groups of two review authors independently screened all references for eligibility, assessed study quality and risk of bias, and extracted data. Outcomes were proportions of participants achieving a good outcome according to the presence or absence of each prognostic factor of interest. We intended to combine data with risk ratios (RRs) and 95% confidence intervals (95% CIs).

MAIN RESULTS

We identified 182 studies with a total of 16,855 included participants investigating outcomes of surgery for epilepsy. Nine studies were RCTs (including two that randomised participants to surgery or medical treatment (99 participants included in the two trials received medical treatment)). Risk of bias in these RCTs was unclear or high. Most of the remaining 173 non-randomised studies followed a retrospective design. We assessed study quality using the Effective Public Health Practice Project (EPHPP) tool and determined that most studies provided moderate or weak evidence. For 29 studies reporting multivariate analyses, we used the Quality in Prognostic Studies (QUIPS) tool and determined that very few studies were at low risk of bias across domains.In terms of freedom from seizures, two RCTs found surgery (n = 97) to be superior to medical treatment (n = 99); four found no statistically significant differences between anterior temporal lobectomy (ATL) with or without corpus callosotomy (n = 60), between subtemporal or transsylvian approach to selective amygdalohippocampectomy (SAH) (n = 47); between ATL, SAH and parahippocampectomy (n = 43) or between 2.5 cm and 3.5 cm ATL resection (n = 207). One RCT found total hippocampectomy to be superior to partial hippocampectomy (n = 70) and one found ATL to be superior to stereotactic radiosurgery (n = 58); and another provided data to show that for Lennox-Gastaut syndrome, no significant differences in seizure outcomes were evident between those treated with resection of the epileptogenic zone and those treated with resection of the epileptogenic zone plus corpus callosotomy (n = 43). We judged evidence from the nine RCTs to be of moderate to very low quality due to lack of information reported about the randomised trial design and the restricted study populations.Of the 16,756 participants included in this review who underwent a surgical procedure, 10,696 (64%) achieved a good outcome from surgery; this ranged across studies from 13.5% to 92.5%. Overall, we found the quality of data in relation to recording of adverse events to be very poor.In total, 120 studies examined between one and eight prognostic factors in univariate analysis. We found the following prognostic factors to be associated with a better post-surgical seizure outcome: abnormal pre-operative MRI, no use of intracranial monitoring, complete surgical resection, presence of mesial temporal sclerosis, concordance of pre-operative MRI and electroencephalography, history of febrile seizures, absence of focal cortical dysplasia/malformation of cortical development, presence of tumour, right-sided resection, and presence of unilateral interictal spikes. We found no evidence that history of head injury, presence of encephalomalacia, presence of vascular malformation, and presence of postoperative discharges were prognostic factors of outcome.Twenty-nine studies reported multi-variable models of prognostic factors, and showed that the direction of association of factors with outcomes was generally the same as that found in univariate analyses.We observed variability in many of our analyses, likely due to small study sizes with unbalanced group sizes and variation in the definition of seizure outcome, the definition of prognostic factors, and the influence of the site of surgery AUTHORS' CONCLUSIONS: Study design issues and limited information presented in the included studies mean that our results provide limited evidence to aid patient selection for surgery and prediction of likely surgical outcomes. Future research should be of high quality, follow a prospective design, be appropriately powered, and focus on specific issues related to diagnostic tools, the site-specific surgical approach, and other issues such as extent of resection. Researchers should investigate prognostic factors related to the outcome of surgery via multi-variable statistical regression modelling, where variables are selected for modelling according to clinical relevance, and all numerical results of the prognostic models are fully reported. Journal editors should not accept papers for which study authors did not record adverse events from a medical intervention. Researchers have achieved improvements in cancer care over the past three to four decades by answering well-defined questions through the conduct of focused RCTs in a step-wise fashion. The same approach to surgery for epilepsy is required.

Localization yield and seizure outcome in patients undergoing bilateral SEEG exploration

OBJECTIVE

We aimed to determine the rates and predictors of resection and seizure freedom after bilateral stereo-electroencephalography (SEEG) implantation.

METHODS

We reviewed 184 patients who underwent bilateral SEEG implantation (2009-2015). Noninvasive and invasive evaluation findings were collected. Outcomes of interest included subsequent resection and seizure freedom. Statistical analyses employed multivariable logistic regression and proportional hazard modeling. Preoperative and postoperative seizure frequency, severity, and quality of life scales were also compared.

RESULTS

Following bilateral SEEG implantation, 106 of 184 patients (58%) underwent resection. Single seizure type (P = 0.007), a family history of epilepsy (P = 0.003), 10 or more seizures per month (P = 0.004), lower number of electrodes (P = 0.02), or sentinel electrode placement (P = 0.04) was predictive of undergoing a resection, as were lack of nonlocalized (P < 0.0001) or bilateral (P < 0.0001) ictal-onset zones on SEEG. Twenty-six of 81 patients (32% with follow-up greater than 1 year) remained seizure-free. Predictors of seizure freedom were single seizure type (P = 0.01), short epilepsy duration (P = 0.008), use of 2 or fewer antiepileptic drugs (AEDs) at the time of surgery (P = 0.0006), primary localization hypothesis involving the frontal lobe (P = 0.002), sentinel electrode placement only (P = 0.02), and lack of overlap between ictal-onset zone and eloquent cortex (P = 0.04), along with epilepsy substrate histopathology (P = 0.007). Complete resection of a suspected focal cortical dysplasia showed a trend to increased likelihood of seizure freedom (P = 0.09). The 44 of 55 patients (80%) who underwent resection and experienced seizure recurrence had >50% seizure reduction, as opposed to 26 of 45 patients (58%) who continued medical therapy alone (P = 0.003). Seventy-two percent of patients had a clinically meaningful quality of life improvement (>10% decrease in the Quality of Life in Epilepsy [QOLIE-10] score) at 1 year.

SIGNIFICANCE

A strong preimplantation hypothesis of a suspected unifocal epilepsy increases the odds of resection and seizure freedom. We discuss a tailored approach, taking into account localization hypothesis and suspected epilepsy etiology in guiding implantation and subsequent surgical strategy.

Safety and Utility of Hybrid Depth Electrodes for Seizure Localization and Single-Unit Neuronal Recording

BACKGROUND

Invasive electrode monitoring provides more precise localization of epileptogenic foci in patients with medically refractory epilepsy. The use of hybrid depth electrodes that include microwires for simultaneous single-neuron monitoring is becoming more widespread.

OBJECTIVE

To determine the safety and utility of hybrid depth electrodes for intracranial monitoring of medically refractory epilepsy.

METHODS

We reviewed the medical charts of 53 cases of medically refractory epilepsy operated on from 2006 to 2017, where both non-hybrid and hybrid microwire depth electrodes were used for intracranial monitoring. We assessed the localization accuracy and complications that arose to assess the relative safety and utility of hybrid depth electrodes compared with standard electrodes.

RESULTS

A total of 555 electrodes were implanted in 52 patients. The overall per-electrode complication rate was 2.3%, with a per-case complication rate of 20.8%. There were no infections or deaths. Serious or hemorrhagic complications occurred in 2 patients (0.4% per-electrode risk). Complications did not correlate with the use of any particular electrode type, and hybrids were equally as reliable as standard electrodes in localizing seizure onset zones.

CONCLUSIONS

Hybrid depth electrodes appear to be as safe and effective as standard depth electrodes for intracranial monitoring and provide unique opportunities to study the human brain at single-neuron resolution.

Safety and efficacy of stereoelectroencephalography in pediatric focal epilepsy: a single-center experience

OBJECTIVE

Patients with medically refractory localization-related epilepsy (LRE) may be candidates for surgical intervention if the seizure onset zone (SOZ) can be well localized. Stereoelectroencephalography (SEEG) offers an attractive alternative to subdural grid and strip electrode implantation for seizure lateralization and localization; yet there are few series reporting the safety and efficacy of SEEG in pediatric patients.

METHODS

The authors review their initial 3-year consecutive experience with SEEG in pediatric patients with LRE. SEEG coverage, SOZ localization, complications, and preliminary seizure outcomes following subsequent surgical treatments are assessed.

RESULTS

Twenty-five pediatric patients underwent 30 SEEG implantations, with a total of 342 electrodes placed. Ten had prior resections or ablations. Seven had no MRI abnormalities, and 8 had multiple lesions on MRI. Based on preimplantation hypotheses, 7 investigations were extratemporal (ET), 1 was only temporal-limbic (TL), and 22 were combined ET/TL investigations. Fourteen patients underwent bilateral investigations. On average, patients were monitored for 8 days postimplant (range 3-19 days). Nearly all patients were discharged home on the day following electrode explantation. There were no major complications. Minor complications included 1 electrode deflection into the subdural space, resulting in a minor asymptomatic extraaxial hemorrhage; and 1 in-house and 1 delayed electrode superficial scalp infection, both treated with local wound care and oral antibiotics. SEEG localized the hypothetical SOZ in 23 of 25 patients (92%). To date, 18 patients have undergone definitive surgical intervention. In 2 patients, SEEG localized the SOZ near eloquent cortex and subdural grids were used to further delineate the seizure focus relative to mapped motor function just prior to resection. At last follow-up (average 21 months), 8 of 15 patients with at least 6 months of follow-up (53%) were Engel class I, and an additional 6 patients (40%) were Engel class II or III. Only 1 patient was Engel class IV.

CONCLUSIONS

SEEG is a safe and effective technique for invasive SOZ localization in medically refractory LRE in the pediatric population. SEEG permits bilateral and multilobar investigations while avoiding large craniotomies. It is conducive to deep, 3D, and perilesional investigations, particularly in cases of prior resections. Patients who are not found to have focally localizable seizures are spared craniotomies.

New Techniques and Progress in Epilepsy Surgery

While open surgical resection for medically refractory epilepsy remains the gold standard in current neurosurgical practice, modern techniques have targeted areas for improvement over open surgical resection. This review focuses on how a variety of these new techniques are attempting to address these various limitations. Stereotactic electroencephalography offers the possibility of localizing deep epileptic foci, improving upon subdural grid placement which limits localization to neocortical regions. Laser interstitial thermal therapy (LITT) and stereotactic radiosurgery can minimally or non-invasively ablate specific regions of interest, with near real-time feedback for laser interstitial thermal therapy. Finally, neurostimulation offers the possibility of seizure reduction without needing to ablate or resect any tissue. However, because these techniques are still being evaluated in current practice, there are no evidence-based guidelines for their use, and more research is required to fully evaluate their proper role in the current management of medically refractory epilepsy.

Trans-falcine and contralateral sub-frontal electrode placement in pediatric epilepsy surgery: technical note

INTRODUCTION

Phase II monitoring with intracranial electroencephalography (ICEEG) occasionally requires bilateral placement of subdural (SD) strips, grids, and/or depth electrodes. While phase I monitoring often demonstrates a preponderance of unilateral findings, individual studies (video EEG, single photon emission computed tomography [SPECT], and positron emission tomography [PET]) can suggest or fail to exclude a contralateral epileptogenic onset zone. This study describes previously unreported techniques of trans-falcine and sub-frontal insertion of contralateral SD grids and depth electrodes for phase II monitoring in pediatric epilepsy surgery patients when concern about bilateral abnormalities has been elicited during phase I monitoring.

METHODS

Pediatric patients with medically refractory epilepsy undergoing stage I surgery for phase II monitoring involving sub-frontal and/or trans-falcine insertion of SD grids and/or depth electrodes at the senior author's institution were retrospectively reviewed. Intra-operative technical details of sub-frontal and trans-falcine approaches were studied, while intra-operative complications or events were noted. Operative techniques included gentle subfrontal retraction and elevation of the olfactory tracts (while preserving the relationship between the olfactory bulb and cribriform plate) to insert SD grids across the midline for coverage of the contralateral orbito-frontal regions. Trans-falcine approaches involved accessing the inter-hemispheric space, bipolar cauterization of the anterior falx cerebri below the superior sagittal sinus, and sharp dissection using a blunt elevator and small blade scalpel. The falcine window allowed contralateral SD strip, grid, and depth electrodes to be inserted for coverage of the contralateral frontal regions.

RESULTS

The study cohort included seven patients undergoing sub-frontal and/or trans-falcine insertion of contralateral SD strip, grid, and/or depth electrodes from February 2012 through June 2015. Five patients (71%) experienced no intra-operative events related to contralateral ICEEG electrode insertion. Intra-operative events of frontal territory venous engorgement (1/7, 14%) due to sacrifice of anterior bridging veins draining into the SSS and avulsion of a contralateral bridging vein (1/7, 14%), probably due to prior anterior corpus callosotomy, each occurred in one patient. There were no intra-operative or peri-operative complications in any of the patients studied. Two patients required additional surgery for supplemental SD strip and/or depth electrodes via burr hole craniectomy to enhance phase II monitoring. All patients proceeded to stage II surgery for resection of ipsilateral epileptogenic onset zones without adverse events.

CONCLUSIONS

Trans-falcine and sub-frontal insertion of contralateral SD strip, grid, and depth electrodes are previously unreported techniques for achieving bilateral frontal coverage in phase II monitoring in pediatric epilepsy surgery. This technique obviates the need for contralateral craniotomy and parenchymal exposure with limited, remediable risks. Larger case series using the method described herein are now necessary.

The Value of Diagnostic Bilateral Intracranial Electroencephalography in Treatment-Resistant Focal Epilepsy

OBJECTIVES

We assessed the efficacy and risks of diagnostic bilateral intracranial electroencephalography (bICEEG) in patients with treatment-resistant epilepsy (TRE) with poorly lateralized epileptogenic zone on noninvasive studies as reflected by progress to resection, Engel outcome, and complication rate.

METHODS

This is a retrospective chart review of 199 patients with TRE who had diagnostic bICEEG at New York University Medical Center between 1994 and 2013. Study end points were progress to resection, surgical outcome, and perioperative complications. Univariate analysis was performed with analysis of variance, t test, or Fisher exact test; multivariable analysis was performed using discriminant function analysis.

RESULTS

bICEEG lateralized the epileptogenic zone and the patient had resection in 60.3% of cases. The number of depth electrodes used was positively correlated with resection, and surgical complications during bICEEG negatively correlated. Vagal nerve stimulators were implanted in 58.2% of patients who did not undergo resection and 20.7% of those who did. Among the 87 patients who progressed to resection and had more than 1-year follow-up, 47.1% were seizure free compared with 12.7% of the 55 who did not. Male sex correlated with good postoperative seizure control. The most common complication was infection requiring debridement, occurring in 3.1% of admissions (9 of 290).

CONCLUSIONS

At our center, 60% of patients undergoing bICEEG progress to resection and 57% of these had more than 90% reduction in seizures. We conclude that bICEEG allows the benefits of epilepsy surgery to be extended to patients with poorly lateralized and localized TRE.

Diagnostic utility of invasive EEG for epilepsy surgery: Indications, modalities, and techniques

Many patients with medically refractory epilepsy now undergo successful surgery based on noninvasive diagnostic information, but intracranial electroencephalography (IEEG) continues to be used as increasingly complex cases are considered surgical candidates. The indications for IEEG and the modalities employed vary across epilepsy surgical centers; each modality has its advantages and limitations. IEEG can be performed in the same intraoperative setting, that is, intraoperative electrocorticography, or through an independent implantation procedure with chronic extraoperative recordings; the latter are not only resource intensive but also carry risk. A lack of understanding of IEEG limitations predisposes to data misinterpretation that can lead to denying surgery when indicated or, worse yet, incorrect resection with adverse outcomes. Given the lack of class 1 or 2 evidence on IEEG, a consensus-based expert recommendation on the diagnostic utility of IEEG is presented, with emphasis on the application of various modalities in specific substrates or locations, taking into account their relative efficacy, safety, ease, and incremental cost-benefit. These recommendations aim to curtail outlying indications that risk the over- or underutilization of IEEG, while retaining substantial flexibility in keeping with most standard practices at epilepsy centers and addressing some of the needs of resource-poor regions around the world.

Spontaneous ripples in the hippocampus correlate with epileptogenicity and not memory function in patients with refractory epilepsy

INTRODUCTION

High-frequency oscillations (HFOs, 80-500Hz) are newly-described EEG markers of epileptogenicity. The proportion of physiological and pathological HFOs is unclear, as frequency analysis is insufficient for separating the two types of events. For instance, ripples (80-250Hz) also occur physiologically during memory consolidation processes in medial temporal lobe structures. We investigated the correlation between HFO rates and memory performance.

METHODS

Patients investigated with bilateral medial temporal electrodes and an intellectual capacity allowing for memory testing were included. High-frequency oscillations were visually marked, and rates of HFOs were calculated for each channel during slow-wave sleep. Patients underwent three verbal and three nonverbal memory tests. They were grouped into severe impairment, some impairment, mostly intact, or intact for verbal and nonverbal memory. We calculated a Pearson correlation between HFO rates in the hippocampi and the memory category and compared HFO rates in each hippocampus with the corresponding (verbal - left, nonverbal - right) memory result using Wilcoxon rank-sum test.

RESULTS

Twenty patients were included; ten had bilateral, five had unilateral, and five had no memory impairment. Unilateral memory impairment was verbal in one patient and nonverbal in four. There was no correlation between HFO rates and memory performance in seizure onset areas. There was, however, a significant negative correlation between the overall memory performance and ripple rates (r=-0.50, p=0.03) outside the seizure onset zone.

CONCLUSION

Our results suggest that the majority of spontaneous hippocampal ripples, as defined in the present study, may reflect pathological activity, taking into account the association with memory impairment. The absence of negative correlation between memory performance and HFO rates in seizure onset areas could be explained by HFO rates in the SOZ being generally so high that differences between areas with remaining and impaired memory function cannot be seen.

Statistical modeling of ICEEG features that determine resection planning

OBJECT

The interpretation of intracranial EEG (ICEEG) recordings is a complex balance of the significance of specific rhythms and their relative timing to seizure onset. Ictal and interictal findings are evaluated in light of findings from cortical stimulation of eloquent cortex to determine the area of resection.

PATIENTS AND METHODS

Patients with ICEEG electrodes and subsequent surgical resection were retrospectively identified. Only the first 15s of ictal activity, which was divided into five 3-s epochs, was considered. Every electrode in each patient was considered a separate observation in a logistic regression model to predict whether the cortex under a given electrode was included in the planned resection.

RESULTS

19 included patients had a total of 37 unique seizures. Recordings from a total of 1306 electrodes were analyzed. The strongest predictors of resection of cortex underlying a given electrode was the presence of low-voltage fast activity in Epoch 1, rhythmic spikes in Epoch 1, interictal paroxysmal fast activity, and low-voltage fast activity in Epoch 2. High-amplitude beta spikes and rhythmic slow waves were also significant predictors in Epoch 1. Interictal spikes had a higher odds ratio of affecting the planned resection if described as "continuous" or "very frequent". The presence of motor or language cortex were the strongest negative predictors of resecting underlying cortex.

CONCLUSIONS

Here we describe a novel model of ictal and interictal patterns significantly associated with the inclusion of cortex underlying a given ICEEG electrode in the surgical resection plan.

Subdural electrodes in focal epilepsy surgery at a typical academic epilepsy center

PURPOSE

To assess the use of subdural intracranial EEG (iEEG) on postoperative outcomes at an epilepsy center.

METHODS

Ninety-one epilepsy patients underwent iEEG. Array design was compared with noninvasive EEG with over 1 year of outcome. Patient demographics, implanted brain sites, electrodes, contacts/site, and surgical location were correlated with outcome. Fisher exact test and logistics regression were used to evaluate significance (P ≤ 0.05).

RESULTS

Of ninety-one women, 55 (mean age, 32.3 years; range, 11-60) underwent tailored iEEG. Seventy of ninety-one (76.9%) resections (70% temporal) yielded 24/91 (26.4%) seizure free (SF). Strips (57.1%), grids (5.5%), or both (37.4%) for iEEG use was commonly bilateral (58.2%; 65.3% bitemporal) but did not predict outcome (P = NS). A lesion (28/91) did predict a SF outcome (42.9%). The iEEG localized 45.7% of seizures beyond scalp EEG and changed the localization or lateralization in 75.7% of resected patients. Electrode design, localization, lateralization, and site of resection did not correlate with outcome (P = NS). Overall, iEEG use portended a non-SF outcome (P ≤ 0.0001).

CONCLUSIONS

The use of iEEG selected 46% additional patients for surgery, yet only 26% became SF. A magnetic resonance imaging lesion predicted a SF or seizure-improved outcome. Although iEEG changed the localization and lateralization of scalp ictal EEG in three quarters of patients, its use was a negative predictor for a favorable outcome. Preoperative counseling should emphasize expectations for seizure reduction in patients requiring iEEG.

Major and minor complications in extraoperative electrocorticography: A review of a national database

The risk profile of extraoperative electrocorticography (ECoG) is documented almost exclusively by case series from a limited number of academic medical centers. These studies tend to underreport minor complications, like urinary tract infections (UTIs) and deep venous thromboses (DVTs), that nevertheless affect hospital cost, length of stay, and the patient's quality of life. Herein, we used data from the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) to estimate the rate of adverse events in extraoperative ECoG surgeries. NSQIP is a validated dataset containing nearly 3 million procedures from over 600 North American hospitals, and uses strict criteria for the documentation of complications. Major complications occurred in 3.4% of 177 extraoperative ECoG cases, while minor complications occurred in 9.6%. The most common minor complication was bleeding requiring a transfusion in 3.4% of cases, followed by sepsis, DVT, and UTI each in 2.3% of cases. No mortality was reported. Overall, in a national database containing a heterogeneous population of hospitals, major complications of extraoperative ECoG were rare (3.4%). Complications such as UTI and DVT tend to be underreported in retrospective case series, yet make up a majority of minor complications for ECoG patients in this dataset.

The Usefulness of Intraoperative Cerebral C-Arm CT Angiogram for Implantation of Intracranial Depth Electrodes in Stereotactic Electroencephalography Procedure

BACKGROUND

Stereotactic electroencephalography (SEEG) is an invasive diagnostic tool for localizing the epileptic zone in patients with medically refractory focal epilepsy. Despite technical and imaging advances in guiding the electrode placement, vascular injury is still one of its most serious complications.

OBJECT

To investigate the usefulness of intraoperative cerebral C-arm CT angiogram (CCTA) in avoiding intracranial hemorrhagic complications during SEEG electrode implantation.

METHODS

Trajectory data from 12 patients who underwent SEEG electrode implantation were studied in detail. This included an analysis of the implantation of 146 SEEG electrodes, which were guided by intraoperative CCTA, as well as the standard planning based on preoperative contrast-enhanced MRI. In addition, a prospective analysis of SEEG hemorrhagic complications using the studied methodology was performed in a total of 87 patients receiving 1,310 electrodes.

RESULTS

There was no complication related to the CCTA itself. Intraoperative CCTA entailed modification of the original trajectory based on the preoperative MRI in 27 of 146 electrode implantations (18.5%). In 10 of them, a severe vascular complication was adverted by intraoperative CCTA. The safety of this new approach was also confirmed by the analysis of postinterventional CT, which revealed a symptomatic hematoma caused by 1 single electrode out of the 1,310 implanted.

CONCLUSIONS

This study showed that intraoperative CCTA in addition to preoperative MRI is useful in guiding a safer SEEG electrode implantation. The combination of both imaging modalities essentially minimizes the risk of serious hemorrhagic complications.

Reduced complications from intracranial grid insertion by using a small grid size and a precise protocol during monitoring

BACKGROUND

A study of the risk factors associated with complications during intracranial EEG monitoring led to a change in protocol for monitoring and implantation at our centres. We conducted a study to identify any reduction in complications following the changed protocols involving the use of smaller subdural electrode arrays, continuous ICP monitoring, use of a central line, and intake of prophylactic antibiotics and dexamethasone.

METHODS

We prospectively collected data on patient outcomes between 2005 and 2012 (group B) compared with patients between 1988 and 2004 (group A) before the protocol changes.

RESULTS

Seventy-one patients in group A and 58 patients in group B underwent intracranial electrode implantation. Complications directly related to grids occurred in 25 % of group A vs. 8.6 % in group B (p < 0.05) and those indirectly related to grids were 11.2 % in group A vs. none in group B. The rate of transient complications requiring no treatment was 12.5 % in group A versus 1.7 % in group B. The rate of transient complications requiring treatment was 10 % in group A and 6.9 % in group B. There were two deaths in group A. The infection rate was higher in group B than group A (5.2 % vs. 2.8 %; p = 0.90). Since 2008 there have been no infective complications. Complications directly related to intracranial EEG monitoring were significantly reduced using the revised protocol (p < 0.05). Regression analysis identifying only the size of the grids (≤4 × 8 grid arrays) implanted was an independent predictor of more complications in group A (P < 0.05).

CONCLUSIONS

Complication rates following intracranial implantation decreased following the use of a small grid size and adherence to a stringent protocol.

Effect of invasive EEG monitoring on cognitive outcome after left temporal lobe epilepsy surgery

OBJECTIVES

The objective of this cohort study was to compare neuropsychological outcomes following left temporal lobe resection (TLR) in patients with epilepsy who had or had not undergone prior invasive monitoring.

METHODS

Data were obtained from an institutional review board-approved, neuropsychology registry for patients who underwent epilepsy surgery at Cleveland Clinic between 1997 and 2013. A total of 176 patients (45 with and 131 without invasive EEG) met inclusion criteria. Primary outcome measures were verbal memory and language scores. Other cognitive outcomes were also examined. Outcomes were assessed using difference in scores from before to after surgery and by presence/absence of clinically meaningful decline using reliable change indices (RCIs). Effect of invasive EEG on cognitive outcomes was estimated using weighting and propensity score adjustment to account for differences in baseline characteristics. Linear and logistic regression models compared surgical groups on all cognitive outcomes.

RESULTS

Patients with invasive monitoring showed greater declines in confrontation naming; however, when RCIs were used to assess clinically meaningful change, there was no significant treatment effect on naming performance. No difference in verbal memory was observed, regardless of how the outcome was measured. In secondary outcomes, patients with invasive monitoring showed greater declines in working memory, which were no longer apparent using RCIs to define change. There were no outcome differences on other cognitive measures.

CONCLUSIONS

Results suggest that invasive EEG monitoring conducted prior to left TLR is not associated with greater cognitive morbidity than left TLR alone. This information is important when counseling patients regarding cognitive risks associated with this elective surgery.

Surgery for epilepsy

BACKGROUND

Focal epilepsies are caused by a malfunction of nerve cells localised in one part of one cerebral hemisphere. In studies, estimates of the number of individuals with focal epilepsy who do not become seizure-free despite optimal drug therapy vary according to the age of the participants and which focal epilepsies are included, but have been reported as at least 20% and in some studies up to 70%. If the epileptogenic zone can be located surgical resection offers the chance of a cure with a corresponding increase in quality of life.

OBJECTIVES

The primary objective is to assess the overall outcome of epilepsy surgery according to evidence from randomised controlled trials.The secondary objectives are to assess the overall outcome of epilepsy surgery according to non-randomised evidence and to identify the factors that correlate to remission of seizures postoperatively.

SEARCH METHODS

We searched the Cochrane Epilepsy Group Specialised Register (June 2013), the Cochrane Central Register of Controlled Trials (CENTRAL 2013, Issue 6), MEDLINE (Ovid) (2001 to 4 July 2013), ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) for relevant trials up to 4 July 2013.

SELECTION CRITERIA

Eligible studies were randomised controlled trials (RCTs), cohort studies or case series, with either a prospective and/or retrospective design, including at least 30 participants, a well-defined population (age, sex, seizure type/frequency, duration of epilepsy, aetiology, magnetic resonance imaging (MRI) diagnosis, surgical findings), an MRI performed in at least 90% of cases and an expected duration of follow-up of at least one year, and reporting an outcome relating to postoperative seizure control.

DATA COLLECTION AND ANALYSIS

Three groups of two review authors independently screened all references for eligibility, assessed study quality and risk of bias, and extracted data. Outcomes were proportion of participants achieving a good outcome according to the presence or absence of each prognostic factor of interest. We intended to combine data with risk ratios (RR) and 95% confidence intervals.

MAIN RESULTS

We identified 177 studies (16,253 participants) investigating the outcome of surgery for epilepsy. Four studies were RCTs (including one that randomised participants to surgery or medical treatment). The risk of bias in the RCTs was unclear or high, limiting our confidence in the evidence that addressed the primary review objective. Most of the remaining 173 non-randomised studies had a retrospective design; they were of variable size, were conducted in a range of countries, recruited a wide demographic range of participants, used a wide range of surgical techniques and used different scales used to measure outcomes. We performed quality assessment using the Effective Public Health Practice Project (EPHPP) tool and determined that most studies provided moderate or weak evidence. For 29 studies reporting multivariate analyses we used the Quality in Prognostic Studies (QUIPS) tool and determined that very few studies were at low risk of bias across the domains.In terms of freedom from seizures, one RCT found surgery to be superior to medical treatment, two RCTs found no statistically significant difference between anterior temporal lobectomy (ATL) with or without corpus callosotomy or between 2.5 cm or 3.5 cm ATL resection, and one RCT found total hippocampectomy to be superior to partial hippocampectomy. We judged the evidence from the four RCTs to be of moderate to very low quality due to the lack of information reported about the randomised trial design and the restricted study populations.Of the 16,253 participants included in this review, 10,518 (65%) achieved a good outcome from surgery; this ranged across studies from 13.5% to 92.5%. Overall, we found the quality of data in relation to the recording of adverse events to be very poor.In total, 118 studies examined between one and eight prognostic factors in univariate analysis. We found the following prognostic factors to be associated with a better post-surgical seizure outcome: an abnormal pre-operative MRI, no use of intracranial monitoring, complete surgical resection, presence of mesial temporal sclerosis, concordance of pre-operative MRI and electroencephalography (EEG), history of febrile seizures, absence of focal cortical dysplasia/malformation of cortical development, presence of tumour, right-sided resection and presence of unilateral interictal spikes. We found no evidence that history of head injury, presence of encephalomalacia, presence of vascular malformation or presence of postoperative discharges were prognostic factors of outcome. We observed variability between studies for many of our analyses, likely due to the small study sizes with unbalanced group sizes, variation in the definition of seizure outcome, definition of the prognostic factor and the influence of the site of surgery, all of which we observed to be related to postoperative seizure outcome. Twenty-nine studies reported multivariable models of prognostic factors and the direction of association of factors with outcome was generally the same as found in the univariate analyses. However, due to the different multivariable analysis approaches and selective reporting of results, meaningful comparison of multivariate analysis with univariate meta-analysis is difficult.

AUTHORS' CONCLUSIONS

The study design issues and limited information presented in the included studies mean that our results provide limited evidence to aid patient selection for surgery and prediction of likely surgical outcome. Future research should be of high quality, have a prospective design, be appropriately powered and focus on specific issues related to diagnostic tools, the site-specific surgical approach and other issues such as the extent of resection. Prognostic factors related to the outcome of surgery should be investigated via multivariable statistical regression modelling, where variables are selected for modelling according to clinical relevance and all numerical results of the prognostic models are fully reported. Protocols should include pre- and postoperative measures of speech and language function, cognition and social functioning along with a mental state assessment. Journal editors should not accept papers where adverse events from a medical intervention are not recorded. Improvements in the development of cancer care over the past three to four decades have been achieved by answering well-defined questions through the conduct of focused RCTs in a step-wise fashion. The same approach to surgery for epilepsy is required.

National trends and complication rates for invasive extraoperative electrocorticography in the USA

Invasive electrocorticography (ECoG) is used in patients when it is difficult to localize epileptogenic foci for potential surgical resection. As MR neuroimaging has improved over the past decade, we hypothesized the utilization of ECoG diminishing over time. Using the USA Nationwide Inpatient Sample, we collected demographic and complication data on patients receiving ECoG over the years 1988-2008 and compared this to patients with medically refractory epilepsy during the same time period. A total of 695 cases using extraoperative ECoG were identified, corresponding to 3528 cases nationwide and accounting for 1.1% of patients with refractory epilepsy from 1988-2008. African Americans were less likely to receive ECoG than whites, as were patients with government insurance in comparison to those with private insurance. Large, urban, and academic hospitals were significantly more likely to perform ECoG than smaller, rural, and private practice institutions. The most frequent complication was cerebrospinal fluid leak (11.7%) and only one death was reported from the entire cohort, corresponding to an estimated six patients nationally. Invasive ECoG is a relatively safe procedure offered to a growing number of patients with refractory epilepsy each year. However, these data suggest the presence of demographic disparities in those patients receiving ECoG, possibly reflecting barriers due to race and socioeconomic status. Among patients with nonlocalized seizures, ECoG often represents their only hope for surgical treatment. We therefore must further examine the indications and efficacy of ECoG, and more work must be done to understand if and why ECoG is preferentially performed in select socioeconomic groups.

Invasive EEG in refractory epilepsy: insertion of subdural grids through linear craniectomy reduces complications and remains effective

OBJECTIVE

To evaluate our technique of implanting subdural grids by linear craniectomy under computer-assisted navigation for invasive electroencephalography in medically refractory epilepsy.

MATERIAL AND METHOD

We report results from our first 38 consecutive patients with medically refractory epilepsy who underwent subdural grids implantation by linear craniectomy. For each case, a preoperative MRI was performed for navigation followed by a postoperative MRI for localization control of the intracranial electrode contacts. A linear skin incision, adapted to the depth and type of subdural electrode (strip or grid) and compatible with possible subsequent therapeutic surgery, was carried out. One or two linear craniectomies (maximal length 6cm, width 1cm) were then drilled with a bevel. The dura mater was incised under microscopic guidance to avoid opening the arachnoid. The required subdural electrodes were then slipped subdurally through each linear craniectomy (letter-box technique).

RESULTS

Forty-one invasive electroencephalographies were performed with 28 (68%) bilateral. For all invasive electroencephalographies, at least one subdural grid was implanted. Sixty-one subdural grids were implanted in total, 52 with 20 contacts and nine with 32 contacts. No cerebrospinal fluid leakage, no infection, no neurological deficit and no permanent complications were observed. Three subdural grids (5%) were not positioned exactly as planned but this had no consequence for the invasive electroencephalography analysis.

CONCLUSION

The implantation of 61 consecutive subdural grids for invasive electroencephalography through linear craniectomies was associated with no transient or permanent complications in this population. This letter-box technique appears to be practical and safe without limiting explorative efficacy.

Brain-Machine Interfaces for Motor Control: A Guide for Neuroscience Clinicians

With the growing interdependence between medicine and technology, the prospect of connecting machines to the human brain is rapidly being realized. The field of neuroprosthetics is transitioning from the proof of concept stage to the development of advanced clinical treatments. In one area of brain-machine interfaces (BMIs) related to the motor system, also termed ‘motor neuroprosthetics’, research successes with implanted microelectrodes in animals have demonstrated immense potential for restoring motor deficits. Early human trials have also begun, with some success but also highlighting several technical challenges. Here we review the concepts and anatomy underlying motor BMI designs, review their early use in clinical applications, and offer a framework to evaluate these technologies in order to predict their eventual clinical utility. Ultimately, we hope to help neuroscience clinicians understand and participate in this burgeoning field.

Evolution of cranial epilepsy surgery complication rates: a 32-year systematic review and meta-analysis

Object

Surgical interventions for medically refractory epilepsy are effective in selected patients, but they are underutilized. There remains a lack of pooled data on complication rates and their changes over a period of multiple decades. The authors performed a systematic review and meta-analysis of reported complications from intracranial epilepsy surgery from 1980 to 2012.

Methods

A literature search was performed to find articles published between 1980 and 2012 that contained at least 2 patients. Patients were divided into 3 groups depending on the procedure they underwent: A) temporal lobectomy with or without amygdalohippocampectomy, B) extratemporal lobar or multilobar resections, or C) invasive electrode placement. Articles were divided into 2 time periods, 1980–1995 and 1996–2012.

Results

Sixty-one articles with a total of 5623 patients met the study's eligibility criteria. Based on the 2 time periods, neurological deficits decreased dramatically from 41.8% to 5.2% in Group A and from 30.2% to 19.5% in Group B. Persistent neurological deficits in these 2 groups decreased from 9.7% to 0.8% and from 9.0% to 3.2%, respectively. Wound infections/meningitis decreased from 2.5% to 1.1% in Group A and from 5.3% to 1.9% in Group B. Persistent neurological deficits were uncommon in Group C, although wound infections/meningitis and hemorrhage/hematoma increased over time from 2.3% to 4.3% and from 1.9% to 4.2%, respectively. These complication rates are additive in patients undergoing implantation followed by resection.

Conclusions

Complication rates have decreased dramatically over the last 30 years, particularly for temporal lobectomy, but they remain an unavoidable consequence of epilepsy surgery. Permanent neurological deficits are rare following epilepsy surgery compared with the long-term risks of intractable epilepsy.

Clinical effects of surgical and Gamma Knife treatments on hippocampal sclerosis-induced intractable epilepsy of children below age 10 years

OBJECTIVE

To discuss the treatment effects and costs of surgery and Gamma Knife on hippocampal sclerosis (HS)-induced intractable epilepsy of children below age 10 years.

METHODS

The children below age 10 years who suffered from HS-induced intractable epilepsy from June 2010 to June 2012 were subjected to surgical and Gamma Knife treatments respectively according to their preference.

RESULTS

The short-term curative rates of the surgical group and the Gamma Knife group were 93.51% and 54.87%, respectively. The average expenses of the two groups were 10,000 CNY (Chinese Yuan) and 22,000 CNY, respectively.

CONCLUSION

The two groups were treated safely and effectively, but the surgical treatment led to better results at a reduced cost.

Safety of Staged Epilepsy Surgery in Children

BACKGROUND:

Surgical resection of epileptic foci relies on accurate localization of the epileptogenic zone, often achieved by subdural and depth electrodes. Our epilepsy center has treated selected children with poorly localized medically refractory epilepsy with a staged surgical protocol, with at least 1 phase of invasive monitoring for localization and resection of epileptic foci.

OBJECTIVE:

To evaluate the safety of staged surgical treatments for refractory epilepsy among children.

METHODS:

Data were retrospectively collected, including surgical details and complications of all patients who underwent invasive monitoring.

RESULTS:

A total of 161 children underwent 200 admissions including staged procedures (&gt;1 surgery during 1 hospital admission), and 496 total surgeries. Average age at surgery was 7 years (range, 8 months to 16.5 years). A total of 250 surgeries included resections (and invasive monitoring), and 189 involved electrode placement only. The cumulative total number of surgeries per patient ranged from 2 to 10 (average, 3). The average duration of monitoring was 10 days (range, 1–30). There were no deaths. Follow-up ranged from 1 month to 10 years. Major complications included unexpected new permanent mild neurological deficits (2%/admission), central nervous system or bone flap infections (1.5%/admission), intracranial hemorrhage, cerebrospinal fluid leak, and a retained strip (each 0.5%/admission). Minor complications included bone absorption (5%/admission), positive surveillance sub-/epidural cultures in asymptomatic patients (5.5%/admission), noninfectious fever (5%/admission), and wound complications (3%/admission). Thirty complications necessitated additional surgical treatment.

CONCLUSION:

Staged epilepsy surgery with invasive electrode monitoring is safe in children with poorly localized medically refractory epilepsy. The rate of major complications is low and appears comparable to that associated with other elective neurosurgical procedures.

Minimum norm estimates in MEG can delineate the onset of interictal epileptic discharges: A comparison with ECoG findings

The analysis of epileptic discharges in magnetoencephalography with minimum norm estimates (MNE) is expected to provide more precise localization of epileptic discharges compared with electroencephalographic estimations. However, the clinical feasibility of MNE remains unclear. In this study, we aimed to elucidate the onset and propagation patterns of interictal spikes using MNE. Seven patients with intractable epilepsy whose epileptogenicity was assumed to exist in the convexity of the cerebral cortex were studied. For MNE and electrocorticography (ECoG), we characterized the propagation patterns of interictal epileptic discharges according to the area in which they originated and where they extended; we then examined whether the propagation patterns observed in MNE were identified by ECoG. We also examined the relationship between the positions of spikes estimated by the equivalent current dipole (ECD) method and MNE. Among the seven patients, nine propagation patterns of epileptic discharges were observed by MNE, all of which were also identified by ECoG. In seven patterns, the epileptic activity propagated around the initial portion. However, in two patterns, the center of activities moved according to propagation with maintained activity of the initial portion. The locations of spikes identified by the ECD method were within the areas estimated by MNE when the epileptic activity propagated. However, the ECD method failed to detect onset activities identified by MNE in three of nine patterns. Thus, MNE is more useful as a means of presurgical evaluation for epilepsy than the ECD method because it can delineate the onset of epileptic activities as shown in ECoG.

Depth electrodes in pediatric epilepsy surgery

BACKGROUND

The surgical removal of the epileptogenic zone in medically intractable seizures depends on accurate localization to minimize the neurological sequelae and prevent future seizures. To date, few studies have demonstrated the use of depth electrodes in a pediatric epilepsy population. Here, we report our study of pediatric epilepsy patients at our epilepsy center who were successfully operated for medically intractable seizures following the use of intracranial depth electrodes. In addition, we detail three individuals with distinct clinical scenarios in which depth electrodes were helpful and describe our technical approach to implantation and surgery.

METHODS

We retrospectively reviewed 18 pediatric epilepsy patients requiring depth electrode studies who presented at the University of Alberta Comprehensive Epilepsy Program between 1999 and 2010 with medically intractable epilepsy. Patients underwent cortical resection following depth electrode placement according to the Comprehensive Epilepsy Program surgical protocols after failure of surface electroencephalogram and magnetic resonance imaging to localize ictal onset zone.

RESULT

The ictal onset zone was successfully identified in all 18 patients. Treatment of all surgical patients resulted in successful seizure freedom (Engel class I) without neurological complications.

CONCLUSION

Intracranial depth electrode use is safe and able to provide sufficient information for the identification of the epileptogenic zone in pediatric epilepsy patients previously not considered for epilepsy surgery.

A primer on brain-machine interfaces, concepts, and technology: a key element in the future of functional neurorestoration

Conventionally, the practice of neurosurgery has been characterized by the removal of pathology, congenital or acquired. The emerging complement to the removal of pathology is surgery for the specific purpose of restoration of function. Advents in neuroscience, technology, and the understanding of neural circuitry are creating opportunities to intervene in disease processes in a reparative manner, thereby advancing toward the long-sought-after concept of neurorestoration. Approaching the issue of neurorestoration from a biomedical engineering perspective is the rapidly growing arena of implantable devices. Implantable devices are becoming more common in medicine and are making significant advancements to improve a patient's functional outcome. Devices such as deep brain stimulators, vagus nerve stimulators, and spinal cord stimulators are now becoming more commonplace in neurosurgery as we utilize our understanding of the nervous system to interpret neural activity and restore function. One of the most exciting prospects in neurosurgery is the technologically driven field of brain-machine interface, also known as brain-computer interface, or neuroprosthetics. The successful development of this technology will have far-reaching implications for patients suffering from a great number of diseases, including but not limited to spinal cord injury, paralysis, stroke, or loss of limb. This article provides an overview of the issues related to neurorestoration using implantable devices with a specific focus on brain-machine interface technology.

[Resection of frontal lobe epileptogenic foci identified after corpus callosotomy: long term results]

OBJECTIVES

To analyse the results of resective surgery in patients in whom it was possible to identify a frontal epileptogenic focus through corpus callosotomy.

MATERIAL AND METHODS

Data from patients suffering drug-resistant epilepsy showing persistence of disabling seizures after undergoing corpus callosotomy and subsequent treatment with frontal lobe resective surgery were prospectively reviewed. Classifications according to Engel's scale before and after each intervention were evaluated, as were the percentages of seizure reduction. Additionally, the satisfaction of family members with surgical outcomes was also assessed.

RESULTS

Eleven patients were identified. After a median follow-up period of 7 years (IQR: 3-8 years), 63.6% of patients showed improvement of seizures according to Engel's scale, 27.2% remained unchanged and one worsened. One patient was categorised as class i, 8 as class ii, one as class iii and one as class iv. The percentage reduction in the number of seizures was over 90% in 54.5% of patients, between 50% and 90% in 36.4% and less than 50% in 9.1%. Family satisfaction was reported as good or excellent in 90.9% of cases.

CONCLUSIONS

In addition to providing better seizure control, corpus callosotomy also appears to be a diagnostic tool allowing the identification of potential targets for resective surgery. Therefore, it should be considered upon suspicion of a frontal epileptogenic focus which could be surgically treated.

Role of electroencephalography in presurgical evaluation of temporal lobe epilepsy

Surgery remains a therapeutic option for patients with medically refractory epilepsy. Comprehensive presurgical evaluation includes electroencephalography (EEG) and video EEG in identifying patients who are likely to benefit from surgery. Here, we discuss in detail the utility of EEG in presurgical evaluation of patients with temporal lobe epilepsy along with illustrative cases.

Anchoring depth electrodes for bedside removal: a "break-away" suturing technique for intracranial monitoring

BACKGROUND

Intracranial depth electrodes for epilepsy are easily dislodged during long-term monitoring unless adequately anchored, but a technique is not available that is both secure and allows easy explantation without reopening the incision.

OBJECTIVE

To describe a convenient and inexpensive method for anchoring depth electrodes that prevents migration and incidental pullout while allowing electrode removal at the bedside.

METHODS

An easily breakable suture (eg, MONOCRYL) is tied around both the depth electrode and a heavy nylon suture and anchored to a hole at the edge of the burr hole; the tails of both are tunneled together percutaneously. The "break-away" MONOCRYL suture effectively anchors the electrode for as long as needed. At the completion of the intracranial electroencephalography session, the 2 tails of the nylon suture are pulled to break their encompassing MONOCRYL anchor suture, thus freeing the depth electrode for easy removal.

RESULTS

The break-away depth electrode anchoring technique was used for 438 electrodes in 68 patients, followed by explantation of these and associated strip electrodes without reopening the incision. Only 1 electrode (0.2%) migrated spontaneously, and 3 depth electrodes (0.7%) fractured in 2 patients (2.9%) on explantation, necessitating open surgery to remove them in 1 of the patients (1.5%).

CONCLUSION

An easy and inexpensive anchoring configuration for depth electrodes is described that provides an effective and safe means of securing the electrodes while allowing easy explantation at the bedside.

Surgical treatment for refractory epilepsy: review of patient evaluation and surgical options

Treatment of epilepsy often imposes an exposure to various antiepileptic drugs and requires long-term commitment and compliance from the patient. Although many new medications are now available for the treatment of epilepsy, approximately 30% of epilepsy patients still experience recurrent seizures and many experience undesirable side effects. Treatment of epilepsy requires a multidisciplinary approach. For those patients with medically refractory seizures, surgical treatment has increased in prevalence as techniques and devices improve. With increased utilization, proper patient selection has become crucial in evaluating appropriateness of surgical intervention. Epilepsy syndromes in which surgery has shown to be effective include mesial temporal sclerosis, cortical dysplasia, many pediatric epilepsy syndromes, and vascular malformations. Monitoring in an epilepsy monitoring unit with continuous scalp or intracranial EEG is an important step in localization of seizure focus. MRI is the standard imaging technique for evaluation of anatomy. However, other imaging studies including SPECT and PET have become more widespread, often offering increased diagnostic value in select situations. In addition, as an alternative or adjunct to surgical resection, implantable devices such as vagus nerve stimulators, deep brain stimulators, and direct brain stimulators could be useful in seizure treatment.

Bilateral invasive electroencephalography in patients with tuberous sclerosis complex: a path to surgery?

OBJECT

Many children with epilepsy and tuberous sclerosis complex (TSC) have multiple tubers on MR imaging and poorly localized/lateralized video electroencephalography (EEG) findings. Given the long-term risks associated with frequent seizures and multiple antiepileptic drugs, along with improved success in identifying focal epileptogenic zones in patients with multifocal lesions, the authors used bilateral intracranial EEG to lateralize the epileptogenic zone in patients with nonlateralizable noninvasive preoperative evaluations.

METHODS

A retrospective analysis from January 1, 1998, to June 30, 2008, identified 62 children with TSC who were presented at a surgical conference. Of the 52 patients undergoing diagnostic or therapeutic procedures during the study period, 20 underwent bilateral intracranial EEG. The presurgical testing results, intracranial EEG findings, surgical interventions, and outcomes were reviewed.

RESULTS

Fourteen of 20 patients had intracranial EEG findings consistent with a resectable epileptogenic zone. One patient is awaiting further resection. Five patients had findings consistent with a nonresectable epileptogenic zone, and 1 of these patients underwent a callosotomy. Seven patients had Engel Class I outcomes, 1 was Class II, 3 were Class III, and 3 were Class IV (mean follow-up 25 months).

CONCLUSIONS

Bilateral intracranial EEG can identify potential resectable seizure foci in nonlateralizable epilepsy in TSC. Although 6 of 20 patients did not undergo resection (1 patient is pending future resection), significant improvements in seizures (Engel Class I or II) were noted in 8 patients. In the authors' experience, this invasive monitoring provided a safe method for identifying the ictal onset zone.

Comparison between Initial and Recent Surgical Outcome of 15-Year Series of Surgically Remediable Epilepsy

OBJECTIVE

The aim of this study is to compare the surgical outcome of the initial and recent surgical cases, during our 15-years experience, in terms of the surgical strategies and the prognostic factors for surgically remediable epilepsy.

METHODS

We retrospectively reviewed and compared the surgical outcomes between the initial 256 (Group I) and recent 139 (Group II) patients according to the time period of operation for a total of 518 consecutive epilepsy surgeries at our institution since 1992. The patients of the middle intermediate period, which were subjected to changed surgical strategies, were excluded.

RESULTS

The surgical outcome data from the initial and recent groups showed a much improved outcome for patients who underwent temporal lobe epilepsy (TLE) surgery over time. The number of patients with a good outcome (Engel class I-II) was much increased from 87.7% (178 TLE cases of Group I) to 94.8% (79 TLE cases of Group II) and this was statistically significant (p = 0.0324) on univariate analysis. Other remarkable changes were the decreased performance of intracranial invasive studies from 43.5% in Group I to 30.9% in Group II due to the advanced neuroimaging tools. The strip/grid ratio was reduced from 131/32 in Group I to 17/25 in Group II, because of a markedly reduced mesial TLE surgery and an increased extratemporal epilepsy surgery.

CONCLUSION

Our results show that surgical outcome of epilepsy surgery has improved over time and it has shown to be efficient to control medically intractable epilepsy. Appropriate patient selection, comprehensive preoperative assessments and more extensive resection are associated with good postoperative outcomes.