Operculo-Insular Epilepsy: Scalp and Intracranial Electroencephalographic Findings

[Insular lobe epilepsy. Part 2: presurgical evaluation & surgical interventions with stereo-electroencephalography]

Identification of insular lobe epilepsy (ILE) presents a major clinical challenge in the diagnosis and treatment of drug-resistant focal epilepsies. ILE has diverse clinical presentations due to the multifaceted functions of the insula. Surface EEG findings do not provide straightforward information to predict this deeply-situated origin of seizures; they are even misleading, masquerading as those of other focal epilepsies, such as temporal and frontal ones. Non-invasive imagings may disclose insular abnormalities, but extra-insular abnormalities can coexist or even stand out. Careful reading and a second-look guided by other clinical information are crucial in order not to miss subtle insulo-opercular abnormalities. Furthermore, a possible insular origin of seizures should be considered in MRI-negative frontal/temporal/parietal epilepsies. Therefore, exploration/exclusion of insular-origin seizures is necessary for a great majority of surgical candidates. As for the stereo-electroencephalography, considered as the gold standard method for intra-cranial EEG investigations with suspicion of ILE, planning of electrode positions/trajectories require sufficient knowledge of the functional localization and anatomo-functional connectivity of the insula. Dense sampling within the insula is required in patients with probable ILE, because the seizure-onset zone can be restricted to a single insular gyrus or even a part of it. It is also crucial to explore extra-insular regions on the basis of non-invasive investigation results while considering their anatomo-functional relationships with the insula. From a surgical perspective, differentiating seizures strictly confined to the insula from those extending to the opercula is of particular importance. Pure insular seizures can be treated with less invasive measures, such as radiofrequency thermocoagulation. To conclude, close attention must be paid to the possibility of ILE throughout the diagnostic workup. The precise identification/exclusion of ILE is a prerequisite to provide appropriate and effective surgical treatment in pharmaco-resistant focal epilepsies.

Resting-State Functional Connectivity Profile of Insular Subregions

The insula is often considered the fifth lobe of the brain and is increasingly recognized as one of the most connected regions in the brain, with widespread connections to cortical and subcortical structures. As a follow-up to our previous tractography work, we investigated the resting-state functional connectivity (rsFC) profiles of insular subregions and assessed their concordance with structural connectivity. We used the CONN toolbox to analyze the rsFC of the same 19 insular regions of interest (ROIs) we used in our prior tractography work and regrouped them into six subregions based on their connectivity pattern similarity. Our analysis of 50 healthy participants confirms the known broad connectivity of the insula and shows novel and specific whole-brain and intra-connectivity patterns of insular subregions. By examining such subregions, our findings provide a more detailed pattern of connectivity than prior studies that may prove useful for comparison between patients.

Pearls & Oy-sters: Severe Case of Ictal Asystole in Temporal Lobe Epilepsy

Ictal asystole is a rare condition associated primarily with temporal lobe epilepsy that can cause syncope, falls, and head trauma. It is also associated with increased rates of sudden unexplained death in epilepsy. We present a case of a 33-year-old woman with a history of childhood epilepsy who presented with 3 years of recurrent syncope. Video-EEG revealed temporal lobe seizures with ictal asystole. EKG showed stepwise progression of bradycardia, asystole, and tachycardia. MRI showed focal cortical thickening at the right insular cortex with blurring of the gray-white matter interface, consistent with insular focal cortical dysplasia. The patient was transitioned from lacosamide to clobazam because of concern for PR interval prolongation and was referred to cardiology for pacemaker placement. Ictal asystole should be considered as a rare but serious cause of unexplained recurrent syncope, particularly in patients with a history of seizures. Management includes antiepileptic drug regimen optimization, consideration of epilepsy surgery, and referral for cardiac pacing when asystole lasts longer than 6 seconds.

Localizing and lateralizing value of auditory phenomena in seizures

BACKGROUND

Auditory seizures (AS) are a rare type of focal seizures. AS are classically thought to involve a seizure onset zone (SOZ) in the temporal lobe, but there remain uncertainties about their localizing and lateralizing value. We conducted a narrative literature review with the aim of providing an up-to-date description of the lateralizing and localizing value of AS.

METHODS

The databases PubMed, Scopus, and Google Scholar were searched for literature on AS in December 2022. All cortical stimulation studies, case reports, and case series were analyzed to assess for auditory phenomena that were suggestive of AS and to evaluate if the lateralization and/or localization of the SOZ could be determined. We classified AS according to their semiology (e.g., simple hallucination versus complex hallucination) and the level of evidence with which the SOZ could be predicted.

RESULTS

A total of 174 cases comprising 200 AS were analyzed from 70 articles. Across all studies, the SOZ of AS were more often in the left (62%) than in the right (38%) hemisphere. AS heard bilaterally followed this trend. Unilaterally heard AS were more often due to a SOZ in the contralateral hemisphere (74%), although they could also be ipsilateral (26%). The SOZ for AS was not limited to the auditory cortex, nor to the temporal lobe. The areas more frequently involved in the temporal lobe were the superior temporal gyrus (STG) and mesiotemporal structures. Extratemporal locations included parietal, frontal, insular, and rarely occipital structures.

CONCLUSION

Our review highlighted the complexity of AS and their importance in the identification of the SOZ. Due to the limited data and heterogeneous presentation of AS in the literature, the patterns associated with different AS semiologies warrant further research.

Insula in epilepsy - "untying the gordian knot": A systematic review

PURPOSE

Despite significant advances in epileptology, there are still many uncertainties about the role of the insula in epilepsy. Until recently, most insular onset seizures were wrongly attributed to the temporal lobe. Further, there are no standardised approaches to the diagnosis and treatment of insular onset seizures. This systematic review gathers the available information about insular epilepsy and synthesizes current knowledge as a basis for future research.

METHOD

Adhering to the PRISMA guidelines, studies were meticulously extracted from the PubMed database. The empirical data pertaining to the semiology of insular seizures, insular networks in epilepsy, techniques of mapping the insula, and the surgical intricacies of non-lesional insular epilepsy were reviewed from published studies. The corpus of information available was then subjected to a process of concise summarization and astute synthesis.

RESULTS

Out of 235 studies identified for full-text review, 86 studies were included in the systematic review. The insula emerges as a brain region with a number of functional subdivisions. The semiology of insular seizures is diverse and depends on the involvement of particular subdivisions. The semiological heterogeneity of insular seizures is explained by the extensive connectivity of the insula and its subdivisions with all four lobes of the brain, deep grey matter structures, and remote brainstem areas. The mainstay of the diagnosis of seizure onset in the insula is stereoelectroencephalography (SEEG). The surgical resection of the insular epileptogenic zone (when possible) is the most effective treatment. Open surgery on the insula is challenging but magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) also holds promise.

CONCLUSION

The physiological and functional roles of the insula in epilepsy have remained obfuscated. The dearth of precisely defined diagnostic and therapeutic protocols acts as an impediment to scientific advancement. This review could potentially facilitate forthcoming research endeavours by establishing a foundational framework for uniform data collection protocols, thereby enhancing the feasibility of comparing findings across future studies and promoting progress in this domain.

Optimized SEEG-guided three-dimensional radiofrequency thermocoagulation for insular epilepsy

PURPOSE

The high risk of resection surgery for drug-resistant insular epilepsy has driven interest in new treatment techniques. Stereo-electroencephalography-guided three-dimensional radiofrequency thermocoagulation (SEEG-3D RFTC) offers an alternative option. Herein, we present the detailed protocol and investigation of the efficacy and safety of a preliminary observational study.

METHODS

From February 2017 to April 2021, ten patients diagnosed with insular epilepsy were enrolled in the study. They underwent implantation of a combination of SEEG electrodes to form a high-density focal stereo-array in insula, including oblique electrodes through the long axis of insula and orthogonal electrodes to widely cover the medial and lateral insula. SEEG-3D RFTC was performed between two contiguous contacts of the same electrode, or between two adjacent contacts of different electrodes.

RESULTS

Surgical procedures were well tolerated, with no related long-term complications. Seizure-free outcome was achieved in seven patients (70%), including ILAE I in four and ILAE II in three. Two other (20%) patients had rare seizures (ILAE III). One (10%) patient experienced an ILAE IV outcome (follow-up = 12--63 months). The responder rate (including ILAE I-IV) was 100%.

CONCLUSION

The optimized SEEG-3D RFTC is an effective and safe option for the treatment of drug-resistant insular epilepsy.

Outcome following surgery for insulo-opercular epilepsies

OBJECTIVE

The purpose of this study was to evaluate the clinical outcome in patients with medically refractory epilepsy who had undergone resective or ablative surgery for suspected insulo-opercular epileptogenic foci.

METHODS

The prospectively maintained database of patients undergoing epilepsy surgery was reviewed, and all patients who underwent insulo-opercular surgery for medically refractory epilepsy with a minimum of 12 months of postoperative follow-up were identified, excluding those who had insulo-opercular resection in combination with temporal lobectomy. The presurgical electroclinicoradiological data, stereo-EEG (SEEG) findings, resection/ablation patterns, surgical pathology, postoperative seizure outcome, and neurological complications were analyzed.

RESULTS

Of 407 patients undergoing epilepsy surgery in a 5-year period at the Amrita Advanced Centre for Epilepsy, 24 patients (5.9%) who underwent exclusive insulo-opercular interventions were included in the study. Eleven (46%) underwent surgery on the right side, 12 (50%) on the left side, and the operation was bilateral in 1 (4%). The mean age at surgery was 24.5 ± 12.75 years. Onset of seizures occurred on average at 10.6 ± 9.7 years of life. Characteristic auras were identified in 66% and predominant seizure type was hypermotor (15.4%), automotor (15.4%), hypomotor (11.5%), or a mixed pattern. Seventy-five percent of the seizures recorded on scalp video-EEG occurred during sleep. The 3T MRI results were normal in 12 patients (50%). Direct single-stage surgery was undertaken in 5 patients, and SEEG followed by intervention in 19. Eighteen patients (75%) underwent exclusive resective surgery, 4 (16.7%) underwent exclusive volumetric radiofrequency ablation, and 2 (8.3%) underwent staged radiofrequency ablation and resective surgery. Immediate postoperative neurological deficits occurred in 10/24 (42%), which persisted beyond 12 postoperative months in 3 (12.5%). With a mean follow-up of 25.9 ± 14.6 months, 18 patients (75%) had Engel class I outcome, 3 (12.5%) had Engel class II, and 3 (12.5%) had Engel class III or IV. There was no statistically significant difference in outcomes between MRI-positive versus MRI-negative cases.

CONCLUSIONS

Surgery for medically refractory epilepsy in insulo-opercular foci is less common and remains a challenge to epilepsy surgery centers. Localization is aided significantly by a careful study of auras and semiology followed by EEG and imaging. The requirement for SEEG is generally high. Satisfactory rates of seizure freedom were achievable independent of the MRI lesional/nonlesional status. Morbidity is higher for insulo-opercular epilepsy surgery compared to other focal epilepsies; hence, the practice and development of minimally invasive strategies for this subgroup of patients undergoing epilepsy surgery is perhaps most important.

Insulo-opercular stereoelectroencephalography exploration in children and young adults: Indications, techniques, and safety

OBJECTIVE

Sampling the insulo-opercular region with invasive recordings is crucial given the importance of this region in epileptic networks and a variety of electroclinical presentations. However, implantation of the insulo-opercular region via stereoelectroencephalography (sEEG) is considered technically challenging given complex vascular and gray matter relationships in this region. We investigated the safety of insulo-opercular sEEG exploration in children and young adults using standard sEEG approaches: (1) orthogonal insulo-opercular (including the pseudo-orthogonal insulo-opercular approach) and (2) medial-lateral insular oblique approach.

METHODS

We performed a retrospective cohort study of 30 consecutive patients who underwent 33 sEEG implantations. All patients had drug-resistant focal epilepsy, were between the ages of 4 and 21, and were operated at one institution between January 2019 and March 2021. Medical records and neuroimaging were reviewed. Hemorrhage, infection, and other complications were considered as outcome variables.

RESULTS

A total of 519 electrodes were placed. Eighty-one were placed orthogonally into the temporal operculum, 53 orthogonally into the frontal operculum, and 19 obliquely into the insula. sEEG electrodes localized seizure onset to the insulo-opercular region in eight patients, leading to a resection three times, an ablation four times, and one peri-insular hemispherectomy. Of the 519 electrodes placed, none of them exhibited hemorrhage or serious complications. Of the 153 electrodes placed into the insula, none had any permanent deficits or complications and one had minor bleeding due to the electrode breaking.

SIGNIFICANCE

These results demonstrate that the orthogonal (including pseudo-orthogonal) and medial approaches to sampling the insula are safe.

Insular Involvement in Cases of Epilepsy Surgery Failure

Background: Epilepsy surgery failure is not uncommon, with several explanations having been proposed. In this series, we detail cases of epilepsy surgery failure subsequently attributed to insular involvement. Methods: We retrospectively identified patients investigated at the epilepsy monitoring units of two Canadian tertiary care centers (2004–2020). Included patients were adults who had undergone epilepsy surgeries with recurrence of seizures post-operatively and who were subsequently determined to have an insular epileptogenic focus. Clinical, electrophysiological, neuroimaging, and surgical data were synthesized. Results: We present 14 patients who demonstrated insular epileptic activity post-surgery-failure as detected by intracranial EEG, MEG, or seizure improvement after insular resection. Seven patients had manifestations evoking possible insular involvement prior to their first surgery. Most patients (8/14) had initial surgeries targeting the temporal lobe. Seizure recurrence ranged from the immediate post-operative period to one year. The main modality used to determine insular involvement was MEG (8/14). Nine patients underwent re-operations that included insular resection; seven achieved a favorable post-operative outcome (Engel I or II). Conclusions: Our series suggests that lowering the threshold for suspecting insular epilepsy may be necessary to improve epilepsy surgery outcomes. Detecting insular epilepsy post-surgery-failure may allow for re-operations which may lead to good outcomes.

Automated electrical source imaging with scalp EEG to define the insular irritative zone: Comparison with simultaneous intracranial EEG

OBJECTIVE

To evaluate the accuracy of automatedinterictallow-density electrical source imaging (LD-ESI) to define the insular irritative zone (IZ) by comparing the simultaneous interictal ESI localization with the SEEG interictal activity.

METHODS

Long-term simultaneous scalp electroencephalography (EEG) and stereo-EEG (SEEG) with at least one depth electrode exploring the operculo-insular region(s) were analyzed. Automated interictal ESI was performed on the scalp EEG using standardized low-resolution brain electromagnetic tomography (sLORETA) and individual head models. A two-step analysis was performed: i) sublobar concordance betweencluster-based ESI localization and SEEG-based IZ; ii) time-locked ESI-/SEEG analysis. Diagnostic accuracy values were calculated using SEEG as reference standard. Subgroup analysis wascarried out, based onthe involvement of insular contacts in the seizure onset and patterns of insular interictal activity.

RESULTS

Thirty patients were included in the study. ESI showed an overall accuracy of 53% (C.I. 29-76%). Sensitivity and specificity were calculated as 53% (C.I. 29-76%), 55% (C.I. 23-83%) respectively. Higher accuracy was found in patients with frequent and dominant interictal insular spikes.

CONCLUSIONS

LD-ESI defines with good accuracy the insular implication in the IZ, which is not possible with classical interictalscalpEEG interpretation.

SIGNIFICANCE

Automated LD-ESI may be a valuable additional tool to characterize the epileptogenic zone in epilepsies with suspected insular involvement.

Structural Connectivity Alterations in Operculo-Insular Epilepsy

Operculo-insular epilepsy (OIE) is an under-recognized condition that can mimic temporal and extratemporal epilepsies. Previous studies have revealed structural connectivity changes in the epileptic network of focal epilepsy. However, most reports use the debated streamline-count to quantify ‘connectivity strength’ and rely on standard tracking algorithms. We propose a sophisticated cutting-edge method that is robust to crossing fibers, optimizes cortical coverage, and assigns an accurate microstructure-reflecting quantitative conectivity marker, namely the COMMIT (Convex Optimization Modeling for Microstructure Informed Tractography)-weight. Using our pipeline, we report the connectivity alterations in OIE. COMMIT-weighted matrices were created in all participants (nine patients with OIE, eight patients with temporal lobe epilepsy (TLE), and 22 healthy controls (HC)). In the OIE group, widespread increases in ‘connectivity strength’ were observed bilaterally. In OIE patients, ‘hyperconnections’ were observed between the insula and the pregenual cingulate gyrus (OIE group vs. HC group) and between insular subregions (OIE vs. TLE). Graph theoretic analyses revealed higher connectivity within insular subregions of OIE patients (OIE vs. TLE). We reveal, for the first time, the structural connectivity distribution in OIE. The observed pattern of connectivity in OIE likely reflects a diffuse epileptic network incorporating insular-connected regions and may represent a structural signature and diagnostic biomarker.

The electroclinical features and surgical outcomes of inferior perisylvian epilepsy

OBJECTIVE

To summarize the clinical and electrophysiological observations of epilepsy originating from the inferior perisylvian cortex, and analyze the potential epileptic networks underlying the semiological manifestations.

METHODS

We retrospectively analyzed patients with refractory inferior perisylvian epilepsy (IPE) who had undergone resective surgery, and then reviewed the demographic, clinical, neuroelectrophysiological, neuroimaging, surgical, histopathological, and follow-up data of the patients from the respective medical records. The selected patients were then categorized in accordance with the results of semiological analysis. Quantitative ¹⁸F-fluorodeoxyglucose-positron emission tomography (FDG-PET) analysis was performed to investigate the underlying neural network.

RESULTS

Of the 18 IPE patients assessed in this study, ipsilateral frontotemporal epileptic discharges or its onsets were the dominant interictal or ictal scalp EEG observations. In addition, oroalimentary or manual automatism was the most frequently documented manifestation, followed by facial tonic or clonic movements. Moreover, the semiological analysis identified and classified the patients into 2 patterns, and the PET statistical analyses conducted on these 2 groups revealed differences in the neural network between them.

CONCLUSION

Inferior perisylvian epilepsy possesses semiological manifestations similar to those of mesial temporal lobe epilepsy or rolandic opercular epilepsy, hence these conditions should be carefully differentiated. Performing lesionectomy or cortectomy, sparing the mesial temporal structures, was found to be an effective and safe treatment modality for IPE.

The Rolandic operculum generates different semiologies in insulo-opercular and temporal lobe epilepsies

PURPOSE

The role of the Rolandic operculum in in mesial temporal lobe epilepsy (MTLE) is to produce oroalimentary automatisms (OAAs). In insulo-opercular epilepsy (IOE), the Rolandic operculum may produce perioral muscle clonic or tonic movements or contractions. This paper aims to confirm the symptomatogenic zone of facial symptoms in IOE and to explain this phenomenon.

METHODS

A total of 45 IOE patients and 15 MTLE patients were analyzed. The patients with IOE were divided into facial (+) and (-) groups according to the facial symptoms. The interictal positron emission tomography (PET) data were compared among groups. Furthermore, electroclinical correlation, functional connectivity and energy ratio (ER) were analyzed with stereo-electroencephalography (SEEG).

RESULTS

Intergroup PET differences were observed mainly in the Rolandic operculum. Electroclinical correlation showed that the Rolandic operculum was the only brain area showing any correlations. Compared with the facial (-) group, the facial (+) group showed stronger functional connectivity and a higher ER in the alpha 1, alpha 2 and beta sub-bands. In the Rolandic operculum, compared with those of the MTLE group, the h² and ER of the facial (+) group were higher in the high frequency sub-bands. Intergroup comparison of the ER in the seizure onset zones (SOZ) showed no significant difference.

SIGNIFICANCE

The symptomatogenic zone of facial symptoms in IOE is the Rolandic operculum. Seizure propagation to the Rolandic operculum generates different semiologies because of the different synchronization frequencies and energies of the sub-bands depending on the site of seizure origin. This may be due to the complex spreading pathway from the SOZ to the symptomatogenic zone.

Insular epilepsy, an under-recognized seizure semiology. A review for general neurologist

Understanding seizure semiology is one of the most important and crucial steps in diagnosing a seizure disorder. Insular epilepsy may mimic other focal seizure semiologies, leading to misdiagnosis and failed epilepsy surgery. Insular seizures may begin as brief ictal symptoms, such as laryngeal discomfort and unpleasant throat sensations, and spread rapidly to the temporal or frontal regions, causing prominent ictal symptoms different to the initial insular ictal manifestation. Moreover, insular seizures are associated with complex epileptogenic networks and multiple connections. For this reason, accurate seizure semiology helps to lateralize and localize the seizure onset. The insular cortex is deep, and thus scalp electroencephalography is not always beneficial as the epileptic discharges will not be easily recorded, or they will be seen over other cortical regions like the temporal or frontal areas. Insular surgical resection is generally safe, but it requires extensive presurgical workup and surgical precautions in order to minimize mortality.

Operculoinsular cortectomy for refractory epilepsy. Part 1: Is it effective?

OBJECTIVE

Patients with refractory epilepsy of operculoinsular origin are often denied potentially effective surgical treatment with operculoinsular cortectomy (also termed operculoinsulectomy) because of feared complications and the paucity of surgical series with a significant number of cases documenting seizure control outcome. The goal of this study was to document seizure control outcome after operculoinsular cortectomy in a group of patients investigated and treated by an epilepsy team with 20 years of experience with this specific technique.

METHODS

Clinical, imaging, surgical, and seizure control outcome data of all patients who underwent surgery for refractory epilepsy requiring an operculoinsular cortectomy were retrospectively reviewed. Tumors and progressive encephalitis cases were excluded. Descriptive and uni- and multivariate analyses were done to determine seizure control outcome and predictors.

RESULTS

Forty-three patients with 44 operculoinsular cortectomies were studied. Kaplan-Meier estimates of complete seizure freedom (first seizure recurrence excluding auras) for years 0.5, 1, 2, and 5 were 70.2%, 70.2%, 65.0%, and 65.0%, respectively. With patients with more than 1 year of follow-up, seizure control outcome Engel class I was achieved in 76.9% (mean follow-up duration 5.8 years; range 1.25-20 years). With multivariate analysis, unfavorable seizure outcome predictors were frontal lobe-like seizure semiology, shorter duration of epilepsy, and the use of intracranial electrodes for invasive monitoring. Suspected causes of recurrent seizures were sparing of the language cortex part of the focus, subtotal resection of cortical dysplasia/polymicrogyria, bilateral epilepsy, and residual epileptic cortex with normal preoperative MRI studies (insula, frontal lobe, posterior parieto-temporal, orbitofrontal).

CONCLUSIONS

The surgical treatment of operculoinsular refractory epilepsy is as effective as epilepsy surgeries in other brain areas. These patients should be referred to centers with appropriate experience. A frontal lobe-like seizure semiology should command more sampling with invasive monitoring. Recordings with intracranial electrodes are not always required if the noninvasive investigation is conclusive. The complete resection of the epileptic zone is crucial to achieve good seizure control outcome.

Operculoinsular cortectomy for refractory epilepsy. Part 2: Is it safe?

OBJECTIVE

Operculoinsular cortectomy (also termed operculoinsulectomy) is increasingly recognized as a therapeutic option for perisylvian refractory epilepsy. However, most neurosurgeons are reluctant to perform the technique because of previously experienced or feared neurological complications. The goal of this study was to quantify the incidence of basic neurological complications (loss of primary nonneuropsychological functions) associated with operculoinsular cortectomies for refractory epilepsy, and to identify factors predicting these complications.

METHODS

Clinical, imaging, and surgical data of all patients investigated and surgically treated by our team for refractory epilepsy requiring an operculoinsular cortectomy were retrospectively reviewed. Patients with tumors and encephalitis were excluded. Logistic regression analysis was used for uni- and multivariate statistical analyses.

RESULTS

Forty-four operculoinsular cortectomies were performed in 43 patients. Although postoperative neurological deficits were frequent (54.5% of procedures), only 3 procedures were associated with a permanent significant neurological deficit. Out of the 3 permanent deficits, only 1 (2.3%; a sensorimotor hemisyndrome) was related to the technique of operculoinsular cortectomy (injury to a middle cerebral artery branch), while the other 2 (arm hypoesthesia and hemianopia) were attributed to cortical resection beyond the operculoinsular area. With multivariate analysis, a postoperative neurological deficit was associated with preoperative insular hypometabolism on PET scan. Postoperative motor deficit (29.6% of procedures) was correlated with fewer years of neurosurgical experience and frontal operculectomies, but not with corona radiata ischemic lesions. Ischemic lesions in the posterior two-thirds of the corona radiata (40.9% of procedures) were associated with parietal operculectomies, but not with posterior insulectomies.

CONCLUSIONS

Operculoinsular cortectomy for refractory epilepsy is a relatively safe therapeutic option but temporary neurological deficits after surgery are frequent. This study highlights the role of frontal/parietal opercula resections in postoperative complications. Corona radiata ischemic lesions are not clearly related to motor deficits. There were no obvious permanent neurological consequences of losing a part of an epileptic insula, including on the dominant side for language. A low complication rate can be achieved if the following conditions are met: 1) microsurgical technique is applied to spare cortical branches of the middle cerebral artery; 2) the resection of an opercula is done only if the opercula is part of the epileptic focus; and 3) the neurosurgeon involved has proper training and experience.

Multimodal noninvasive evaluation in MRI-negative operculoinsular epilepsy

OBJECTIVE

Presurgical evaluation of patients with operculoinsular epilepsy and negative MRI presents major challenges. Here the authors examined the yield of noninvasive modalities such as voxel-based morphometric MRI postprocessing, FDG-PET, subtraction ictal SPECT coregistered to MRI (SISCOM), and magnetoencephalography (MEG) in a cohort of patients with operculoinsular epilepsy and negative MRI.

METHODS

Twenty-two MRI-negative patients were included who had focal ictal onset from the operculoinsular cortex on intracranial EEG, and underwent focal resection limited to the operculoinsular cortex. MRI postprocessing was applied to presurgical T1-weighted volumetric MRI using a morphometric analysis program (MAP). Individual and combined localization yields of MAP, FDG-PET, MEG, and SISCOM were compared with the ictal onset location on intracranial EEG. Seizure outcomes were reported at 1 year and 2 years (when available) using the Engel classification.

RESULTS

Ten patients (45.5%, 10/22) had operculoinsular abnormalities on MAP; 5 (23.8%, 5/21) had operculoinsular hypometabolism on FDG-PET; 4 (26.7%, 4/15) had operculoinsular hyperperfusion on SISCOM; and 6 (30.0%, 6/20) had an MEG cluster (3 tight, 3 loose) within the operculoinsular cortex. The highest yield of a 2-test combination was 59.1%, seen with MAP and SISCOM, followed by 54.5% with MAP and FDG-PET, and also 54.5% with MAP and MEG. The highest yield of a 3-test combination was 68.2%, seen with MAP, MEG, and SISCOM. The yield of the 4-test combination remained at 68.2%. When all other tests were negative or nonlocalizing, unique information was provided by MAP in 5, MEG in 1, SISCOM in 2, and FDG-PET in none of the patients. One-year follow-up was available in all patients, and showed 11 Engel class IA, 4 class IB, 4 class II, and 3 class III/IV. Two-year follow-up was available in 19 patients, and showed 9 class IA, 3 class IB, 1 class ID, 3 class II, and 3 class III/IV.

CONCLUSIONS

This study highlights the individual and combined values of multiple noninvasive modalities for the evaluation of nonlesional operculoinsular epilepsy. The 3-test combination of MAP, MEG, and SISCOM represented structural, interictal, and ictal localization information, and constituted the highest yield. MAP showed the highest yield of unique information when other tests were negative or nonlocalizing.

Anatomoelectroclinical features of SEEG-confirmed pure insular-onset epilepsy

PURPOSE

In this study, we aimed to improve our knowledge of insular epilepsy by studying anatomoelectroclinical correlations in pure insular-onset epilepsy and characterizing differences between anterior and posterior insular-onset seizures.

METHODS

Patients in whom seizure-onset zone was confined to the insula and peri-insular sulcus were selected from 301 consecutive presurgical stereo-electroencephalography (EEG) recordings performed between years 2010 and 2017 in two epilepsy centers. Ictal-onset zone in stereo-EEG was delineated visually and quantitatively using epileptogenic index method. Seizure characteristics were reanalyzed, and anatomoelectroclinical correlations were assessed. Characteristics of posterior and anterior insular-onset seizures were compared.

RESULTS

Eleven insular cases were identified, five of them with an anterior insular seizure onset and six with a posterior one. Nonpainful somatosensory symptoms and autonomic symptoms were the most common symptoms (73% of patients) followed by speech-related symptoms (55%) and ipsilateral eye blinking (45%). Six patients had seizures restricted to somatosensory or viscerosensory symptoms. In all patients, seizures progressed to motor symptoms. Somatosensory symptoms did not differentiate anterior from posterior insular seizures. However, hyperkinetic signs, speech modifications, and viscerosensory symptoms were related to an anterior insular seizure-onset zone. Pain, asymmetric tonic, focal clonic, and tonic symptoms were more frequent in patients with a posterior insular seizure onset.

CONCLUSIONS

Seizure semiology is heterogeneous in pure insular-onset epilepsy. Differences between the anterior and posterior insular seizures reflect the functional organization of the insula. Particularly, the different types of motor symptoms may help to distinguish anterior from posterior insular seizure onset.

Stereo-EEG exploration in the insula/operculum in paediatric patients with refractory epilepsy

PURPOSE

Failure to recognise involvement of the insula / opercula (I/O) region is associated with poor outcome in epilepsy surgery. Recognition is challenging due to high connectivity with adjacent structures resulting in variable and misleading semiology, often subjective and therefore likely to be underreported by children. In this study we explored prevalence and characteristics of I/O involvement in paediatric patients undergoing sEEG exploration.

METHOD

We retrospectively included all consecutive patients undergoing sEEG at our centre between 11/2014 and 01/2018 with at least three contacts within I/O and excluded those with undetermined seizure onset zone (SOZ) by sEEG. We divided patients into three groups: 1) SOZ in I/O, 2) spread to I/O and 3) no I/O involvement. We compared pre-invasive characteristics, sEEG results, surgery and outcome for each group.

RESULTS

29 of all 53 consecutive patients had an identified SOZ by sEEG and at least three contacts within the I/O and were included. 41% had I/O SOZ, 38% had I/O spread and 21% had no I/O involvement. Insula associated symptoms described in adult literature were not statistically different between the three groups. Complications due to sEEG were low (2 of 53 patients). Following I/O surgery, 63% were seizure free while an additional 26% of patients achieved seizure reduction. Postoperative deficits were seen in 75% of the patients but completely resolved in all but one patient.

CONCLUSIONS

Our data suggest an important role of the I/O region with frequent onset or propagation to the I/O region (at least 64% of all 53 sEEG cases). Semiology appears less specific than in adults. Insula depth electrode insertion is safe with subsequent good surgical outcomes albeit common transient deficits.

Altered effective connectivity network in patients with insular epilepsy: A high-frequency oscillations magnetoencephalography study

OBJECTIVE

The project aimed to determine the alterations in the effective connectivity (EC) neural network in patients with insular epilepsy based on interictal high-frequency oscillations (HFOs) from magnetoencephalography (MEG) data.

METHODS

We studied MEG data from 22 insular epilepsy patients and 20 normal subjects. Alterations in spatial pattern and connection properties of the patients with insular epilepsy were investigated in the entire brain network and insula-based network.

RESULTS

Analyses of the parameters of graph theory revealed the over-connectivity and small-world configuration of the global connectivity patterns observed in the patients. In the insula-based network, the insular cortex ipsilateral to the seizure onset displayed increased efferent and afferentEC. Left insular epilepsy featured strong connectivity with the bilateral hemispheres, whereas right insular epilepsy featured increased connectivity with only the ipsilateral hemisphere.

CONCLUSIONS

Patients with insular epilepsy display alterations in the EC network in terms of both whole-brain connectivity and the insula-based network during interictal HFOs.

SIGNIFICANCE

Alterations of interictal HFO-based networks provide evidence that epilepsy networks, instead of epileptic foci, play a key role in the complex pathophysiological mechanisms of insular epilepsy. The dysfunction of HFO networks may prove to be a novel promising biomarker and the cause of interictal brain dysfunctions in insular epilepsy.

Drug-responsive versus drug-refractory mesial temporal lobe epilepsy: a single-center prospective outcome study

Objectives: To evaluate clinical, electrophysiological, and neuroradiological factors which correlate with the prognosis in patients with mesial temporal lobe epilepsy (MTLE). Methods: This was a single-center prospective outcome study in patients with MTLE. The patients' family history, clinical characteristics, neurophysiological data (electroencephalography - EEG), neuroimaging, antiepileptic therapy, and outcome were collected and analyzed. The population was divided into four groups depending on the frequency of the seizures when they attended their last follow up. All variables and outcome measures were compared between the four groups. Results: In total 83 consecutive patients were included within the four groups. Group 1 (seizure-free) consisted of 7 patients, (9%), Group 2 (rare seizures) consisted of 15 patients (18%), Group 3 (often seizures) consisted of 30 patients (36%), and Group 4 (very often seizures) consisted of 31 patients (37%). The groups did not differ significantly in demographic characteristics. There was a strong positive correlation between resistance to therapy and sleep activation on EEG (p = 0.005), occurrence of focal to bilateral seizures (p = 0.007), automatisms (p = 0.004), and the number of previously used antiepileptic drugs (AEDs) (p = 0.002). There was no association between febrile convulsions (FC), hippocampal sclerosis (HS), and the outcome that was found. Conclusion: MTLE is a heterogeneous syndrome. Establishing the factors responsible for, and associated with, drug resistance is important for optimal management and treatment, as early identification of drug resistance should then ensure a timely referral for surgical treatment is made. This prospective study shows that sleep activation on EEG, ictal automatisms, occurrence of focal to bilateral tonic-clonic seizures, and increased number of tried AEDs are negative prognostic factors.

Electroclinical features of insulo-opercular epilepsy: an SEEG and PET study

Objective

To report clinical experience with presurgical evaluation in patients with insulo‐opercular epilepsy. Quantitative analysis on PET imaging and stereoelectroencephalography (SEEG) signals was used to summarize their electroclinical features.

Methods

Twenty‐two patients with focal epilepsy arising from the insular and/or opercular cortex according to SEEG were retrospectively analyzed. Presurgical noninvasive data were analyzed in detail. Interictal PET data of patients were then statistically compared with those of healthy controls to identify the interictal hypometabolic network. The epileptogenicity index (EI) of ictal SEEG signal was computed to identify areas of spread at the beginning of seizure onset.

Results

Focal tonic seizures of the face and/or neck (16/22, 73%) were the most prevalent early objective signs. Epileptic discharges in the interictal and ictal scalp‐EEG mostly showed an ipsilateral perisylvian distribution. Statistical analysis of interictal PET showed significant hypometabolism in the insular lobe, central operculum, supplementary motor area, middle cingulate cortex, bilateral caudate nuclei, and putamen. According to the EI analysis, insulo‐opercular epilepsy could be classified as insulo‐opercular epilepsy (50%), opercular epilepsy (41%), and insular cortex epilepsy (9%).

Significance

Clinical diagnosis of insulo‐opercular epilepsy is challenging because of its complex seizure semiology and nonlocalizing discharges on scalp‐EEG. A common hypometabolic network involving the insulo‐opercular cortex, mesial frontal cortex and subcortical nuclei may be involved in the organization of the insulo‐opercular epilepsy network. Furthermore, quantified SEEG analysis suggested that pure insular epilepsy is rare, and the close connection between insular and opercular cortex necessitates SEEG implantation to define the epileptogenic zone.

Symptomatogenic zone and network of oroalimentary automatisms in mesial temporal lobe epilepsy

OBJECTIVE

Oroalimentary automatisms (OAAs) are common clinical manifestations of medial temporal lobe epilepsy. Nevertheless, the location of the symptomatogenic zone of OAAs remains unclear. The generation mechanism of OAAs also has not been clarified. We attempt to explain these problems by analyzing interictal [¹⁸ F]-fluorodeoxyglucose positron emission tomography (¹⁸ FDG-PET) imaging and ictal stereo-electroencephalography (SEEG) recordings in patients with medial temporal lobe epilepsy.

METHODS

Fifty-seven patients with mesial temporal lobe epilepsy were analyzed retrospectively. All underwent anterior temporal lobectomy (ATL) and were seizure-free. The patients were divided into OAA (+) and OAA (-) groups according to the occurrence of consistent stereotyped OAAs. The interictal PET data were compared with those of 18 healthy controls and were then compared between groups using statistical parametric mapping (SPM). Functional connectivity using linear regression analysis was performed between the target brain regions. To clarify the network of OAAs, ictal epileptogenicity index (EI) values, and the nonlinear correlation method h² were performed with SEEG on patients.

RESULTS

Compared to OAAs (-), the rolandic operculum was the only area with significant differences. Hippocampus and rolandic operculum showed significant correlations in the OAA (+) group (y = 0.758x+0.470, R²  = 0.456, P = 0.000). No correlation was found in the OAA (-) group (P = 0.486). The EI values of the OAA (+) group (median 0.20) were significantly higher (P < 0.0001) than those of the OAA (-) group (median 0). The h² in the OAA (+) group (h²  = 0.23 ± 0.13) showed stronger functional connectivity (t = 6.166, P < 0.0001) than that of the OAA (-) group (h²  = 0.08 ± 0.05).

SIGNIFICANCE

The rolandic operculum is most likely to be the symptomatogenic zone of OAAs. In medial temporal lobe epilepsy, unilateral functional connection from the hippocampus to the rolandic operculum during seizure onset is the basis for the generation of OAAs.

The Insula and Its Epilepsies

Insular seizures are great mimickers of seizures originating elsewhere in the brain. The insula is a highly connected brain structure. Seizures may only become clinically evident after ictal activity propagates out of the insula with semiology that reflects the propagation pattern. Insular seizures with perisylvian spread, for example, manifest first as throat constriction, followed next by perioral and hemisensory symptoms, and then by unilateral motor symptoms. On the other hand, insular seizures may spread instead to the temporal and frontal lobes and present like seizures originating from these regions. Due to the location of the insula deep in the brain, interictal and ictal scalp electroencephalogram (EEG) changes can be variable and misleading. Magnetic resonance imaging, magnetic resonance spectroscopy, magnetoencephalography, positron emission tomography, and single-photon computed tomography imaging may assist in establishing a diagnosis of insular epilepsy. Intracranial EEG recordings from within the insula, using stereo-EEG or depth electrode techniques, can prove insular seizure origin. Seizure onset, most commonly seen as low-voltage, fast gamma activity, however, can be highly localized and easily missed if the insula is only sparsely sampled. Moreover, seizure spread to the contralateral insula and other brain regions may occur rapidly. Extensive sampling of the insula with multiple electrode trajectories is necessary to avoid these pitfalls. Understanding the functional organization of the insula is helpful when interpreting the semiology produced by insular seizures. Electrical stimulation mapping around the central sulcus of the insula results in paresthesias, while stimulation of the posterior insula typically produces painful sensations. Visceral sensations are the next most common result of insular stimulation. Treatment of insular epilepsy is evolving, but poses challenges. Surgical resections of the insula are effective but risk significant morbidity if not carefully planned. Neurostimulation is an emerging option for treatment, especially for seizures with onset in the posterior insula. The close association of the insula with marked autonomic changes has led to interest in the role of the insula in sudden unexpected death in epilepsy and warrants additional study with larger patient cohorts.

Focal epilepsies and focal disorders

Electroencephalographic (EEG) investigations are crucial in the diagnosis and management of patients with focal epilepsies. EEG may reveal different interictal epileptiform discharges (IEDs: abnormal spikes, sharp waves). The EEG visibility of a spike depends on the surface area of cortex involved (>10cm²) and the brain localization of cortical generators. Regions generating IEDs (defining the "irritative zone") are not necessarily equivalent to the seizure onset zone. Focal seizures are dynamic processes originating from one or several brain regions (that generate fast oscillations and are called the epileptogenic zone) before spreading to other structures (that generate lower frequency oscillations and are called the propagation zone). Several factors limit the expression of seizures on scalp EEG, such as the area involved, degree of synchronization, and depth of the cortical generators. Different scalp EEG seizure onset patterns may be observed: fast discharge, background flattening, rhythmic spikes, sinusoidal discharge, or sharp activity. However, to a large extent EEG changes are linked to seizure propagation. Finally, in the context of presurgical evaluation, the combination of interictal and ictal EEG features is crucial to provide an optimal hypothesis concerning the epileptogenic zone.