Simple Partial Seizures with Hemisensory Phenomena and Dysgeusia: An Insular Pattern

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.

Insular seizures and epilepsies: Ictal semiology and minimal invasive surgery

PURPOSE OF REVIEW

The increased identification of seizures with insular ictal onset, promoted by the international development of stereo-electroencephalography (SEEG), has led to the recent description of larger cohorts of patients with insular or insulo-opercular epilepsies than those previously available. These new series have consolidated and extended our knowledge of the rich ictal semiology and diverse anatomo-clinical correlations that characterized insular seizures. In parallel, some experiences have been gained in the surgical treatment of insular epilepsies using minimal invasive procedures.

RECENT FINDINGS

The large majority of patients present with auras (mostly somatosensory and laryngeal) and motor signs (predominantly elementary and orofacial), an underlying focal cortical dysplasia, and an excellent postoperative seizure outcome. Many other subjective and objective ictal signs, known to occur in other forms of epilepsies, are also observed and clustered in five patterns, reflecting the functional anatomy of the insula and its overlying opercula, as well as preferential propagation pathways to frontal or temporal brain regions. A nocturnal predominance of seizure is frequently reported, whereas secondary generalization is infrequent. Some rare ictal signs are highly suggestive of an insular origin, including somatic pain, reflex seizures, choking spells, and vomiting. Minimal invasive surgical techniques have been applied to the treatment of insular epilepsies, including Magnetic Resonance Imaging-guided laser ablation (laser interstitial thermal therapy (LITT)), radiofrequency thermocoagulation (RFTC), gamma knife radiosurgery, and responsive neurostimulation. Rates of seizure freedom (about 50%) appear lower than that reported with open-surgery (about 80%) with yet a significant proportion of transient neurological deficit for LITT and RFTC.

SUMMARY

Significant progress has been made in the identification and surgical treatment of insular and insulo-opercular epilepsies, including more precise anatomo-clinical correlations to optimally plan SEEG investigations, and experience in using minimal invasive surgery to reduce peri-operative morbidity.

A study of perfusion changes with Insula Epilepsy using SPECT

PURPOSE

The non-invasive localisation of insular lobe epilepsy is a challenge. We aimed to determine if ictal SPECT is a reliable adjunctive test in insular cases and to explore its role in the tailoring of intracranial strategies.

METHOD

From a dataset of patients who underwent SEEG between December 2012 and December 2016, we collected patients with focal insular onset epilepsy. We examined semiology, EEG, PET and SPECT hyperperfusion pattern with SISCOM. We also reviewed relevant literature.

RESULTS

5 patients were identified, 4 females, from a dataset of 51 patients. Median age of seizure onset was 8 years old (8 months to 10 years). All patients had an ictal SPECT during pre-surgical work-up: median injection time was 7 s (3-17 sec) from clinical onset, and median seizure duration was 42 s (11-85 sec). Insula cortex showed focal hyperaemia in four patients, all bilateral, with the greatest hyperperfusion contralateral to the ictal onset in two cases, using SISCOM threshold at 1.5 standard deviation. Other sites with hyperaemia included basal ganglia and middle temporal gyrus. The SEEG confirmed insular onset seizures in all the cases. All patients had epilepsy surgery and were seizure free at 21 to 50 months follow up. The results from the literature review showed frequent hyperperfusion in structures outside insula and frequently over the contralateral hemisphere.

CONCLUSIONS

This study highlights the technical limitations of SPECT when attempting to assess seizures arising from the insula. Our findings and the literature show ictal SPECT can be localising but falsely lateralising in seizures arising from the insula.

Insular epilepsy surgery

Since it was originally described nearly 70 years ago, insular epilepsy has been increasingly recognized and may explain failures after apparently well-planned operations. We review the history of awareness of the phenomenon, techniques for its assessment, and its surgical management. Insular epilepsy can mimic features of frontal, parietal, or temporal seizures. It should be considered when a combination of somatosensory, visceral, and motor symptoms is observed early in a seizure. Extraoperative intracranial recordings are required to accurately diagnose insular seizures. Stereo-electroencephalography (EEG) or craniotomy with implantation of surface and depth electrodes have been used successfully to identify insular onset of seizures. Surgical resection of an insular focus may be performed with good success and acceptable risk.

Indications, technique, and safety profile of insular stereoelectroencephalography electrode implantation in medically intractable epilepsy

OBJECTIVE Insular epilepsy is relatively rare; however, exploring the insular cortex when preoperative workup raises the suspicion of insular epilepsy is of paramount importance for accurate localization of the epileptogenic zone and achievement of seizure freedom. The authors review their clinical experience with stereoelectroencephalography (SEEG) electrode implantation in patients with medically intractable epilepsy and suspected insular involvement. METHODS A total of 198 consecutive cases in which patients underwent SEEG implantation with a total of 1556 electrodes between June 2009 and April 2013 were reviewed. The authors identified patients with suspected insular involvement based on seizure semiology, scalp EEG data, and preoperative imaging (MRI, PET, and SPECT or magnetoencephalography [MEG]). Patients with at least 1 insular electrode based on the postoperative 3D reconstruction of CT fused with the preoperative MRI were included. RESULTS One hundred thirty-five patients with suspected insular epilepsy underwent insular implantation of a total of 303 electrodes (1-6 insular electrodes per patient) with a total of 562 contacts. Two hundred sixty-eight electrodes (88.5%) were implanted orthogonally through the frontoparietal or temporal operculum (420 contacts). Thirty-five electrodes (11.5%) were implanted by means of an oblique trajectory either through a frontal or a parietal entry point (142 contacts). Nineteen patients (14.07%) had insular electrodes placed bilaterally. Twenty-three patients (17.04% of the insular implantation group and 11.6% of the whole SEEG cohort) were confirmed by SEEG to have ictal onset zones in the insula. None of the patients experienced any intracerebral hemorrhage related to the insular electrodes. After insular resection, 5 patients (33.3%) had Engel Class I outcomes, 6 patients (40%) had Engel Class II, 3 patients (20%) had Engel Class III, and 1 patient (6.66%) had Engel Class IV. CONCLUSIONS Insula exploration with stereotactically placed depth electrodes is a safe technique. Orthogonal electrodes are implanted when the hypothesis suggests opercular involvement; however, oblique electrodes allow a higher insular sampling rate.

Surgery for Nontumoral Insular Epilepsy Explored by Stereoelectroencephalography

BACKGROUND

Hidden by the perisylvian operculi, insular cortex has long been underexplored in the context of epilepsy surgery. Recent studies advocated stereoelectroencephalography (SEEG) as a reliable tool to explore insular cortex and its involvement in intractable epilepsy and suggested that insular seizures could be an underestimated entity. However, the results of insular resection to treat pharmacoresistant epilepsy are rarely reported.

OBJECTIVE

We report 6 consecutive cases of right insular resection performed based on anatomoelectroclinical correlations provided by SEEG.

METHODS

Six right-handed patients (3 male, 3 female) with drug-resistant epilepsy underwent comprehensive presurgical evaluation. Based on video electroencephalographic recordings, they all underwent SEEG evaluation with bilateral (n = 4) or unilateral right (n = 2) insular depth electrode placement. All patients had both orthogonal and oblique (1 anterior, 1 posterior) insular electrodes (n = 4-6 electrodes). Preoperative magnetic resonance imaging findings were normal in 4 patients, 1 patient had right insular focal cortical dysplasia, and 1 patient had a right opercular postoperative scar (cavernous angioma). All patients underwent right partial insular corticectomy via the subpial transopercular approach.

RESULTS

Intracerebral recordings demonstrated an epileptogenic zone confined to the right insula in all patients. After selective insular resection, 5 of 6 patients were seizure free (Engel class I) with a mean follow-up of 36.2 months (range, 18-68 months). Histological findings revealed focal cortical dysplasia in 5 patients and a gliosis scar in 1 patient. All patients had minor transient neurological deficit (eg, facial paresis, dysarthria).

CONCLUSION

Insular resection based on SEEG findings can be performed safely with a significant chance of seizure freedom.

Somatosensory and pharyngolaryngeal auras in temporal lobe epilepsy surgeries

Purpose. Somatosensory (SSA) and pharyngolaryngeal auras (PLA) may suggest an extratemporal onset (e.g., insula, second somatosensory area). We sought to determine the prognostic significance of SSA and PLA in temporal lobe epilepsy (TLE) patients undergoing epilepsy surgery. Methods. Retrospective review of all patients operated for refractory TLE at our institution between January 1980 and July 2007 comparing outcome between patients with SSA/PLA to those without. Results. 158 patients underwent surgery for pharmacoresistant TLE in our institution. Eleven (7%) experienced SSA/PLA as part of their seizures. All but one had lesional (including hippocampal atrophy/sclerosis) TLE. Compared to patients without SSA or PLA, these patients were older (P = 0.049), had a higher prevalence of early ictal motor symptoms (P = 0.022) and prior CNS infection (P = 0.022), and were less likely to have a localizing SPECT study (P = 0.025). A favorable outcome was achieved in 81.8% of patients with SSA and/or PLA and 90.4% of those without SSA or PLA (P > 0.05). Conclusion. Most patients with pharmacoresistant lesional TLE appear to have a favorable outcome following temporal lobectomy, even in the presence of SSA and PLA.

Surgical techniques for investigating the role of the insula in epilepsy: a review

Intracranial electroencephalography monitoring of the insula is an important tool in the investigation of the insula in medically intractable epilepsy and has been shown to be safe and reliable. Several methods of placing electrodes for insular coverage have been reported and include open craniotomy as well as stereotactic orthogonal and stereotactic anterior and posterior oblique trajectories. The authors review each of these techniques with respect to current concepts in insular epilepsy.

A gut feeling about insular seizures

A 43-year-old man presented to the Prince of Wales Hospital, Sydney, New South Wales, Australia, after experiencing his first tonic-clonic seizure. For the previous 2 years he had undergone gastroenterological investigation of episodes of gagging associated with hypersalivation and lachrymation, occurring three or four times per week. EEG showed epileptiform discharges in the right anterior temporal region; brain MRI revealed a lesion in the right insular cortex. Video-EEG telemetry demonstrated that the episodes of gagging were focal seizures. Antiepileptic drug therapy resulted in no further episodes occurring over the next 10 months.

Stereotactic depth electrode investigation of the insula in the evaluation of medically intractable epilepsy

Object

The authors describe their experience with stereotactic implantation of insular depth electrodes in patients with medically intractable epilepsy.

Methods

Between 2001 and 2009, 20 patients with epilepsy and suspected insular involvement during seizures underwent intracranial electrode array implantation at the authors' institution. All patients had either 1 or 2 insular depth electrodes placed as part of an intracranial array.

Results

A total of 29 insular depth electrodes were placed using a frontal oblique trajectory. Eleven patients had a single insular electrode placed and 8 patients had 2 insular electrodes placed unilaterally. One patient had bilateral insular electrodes implanted. Postoperative imaging demonstrated satisfactory placement in all but 1 instance, and there was no associated morbidity or mortality. Fourteen patients underwent a subsequent resection, involving the frontal lobe (9 patients), temporal lobe (4), or frontotemporal lobes (1), and of these, 11 currently have Engel Class I outcome. Two patients (10%) had seizures originating within the insula and another 5 patients (25%) demonstrated early specific insular involvement. Neither patient with an insular seizure focus went on to resection. All 5 of the patients with early specific insular involvement underwent an insula-sparing resective procedure with Engel Class I outcome in all cases.

Conclusions

Stereotactic placement of insular electrodes via a frontal oblique approach is a safe and efficient technique for investigating insular involvement in medically intractable epilepsy. The information obtained from insular recording can be valuable for appreciating the degree of insular contribution to seizures, allowing localization to the insula or clearer implication of other sites.

Insular epilepsy masquerading as multifocal cortical epilepsy as proven by depth electrode

The insular cortex is an uncommon epileptogenic location from which complex partial seizures may arise. Seizure activity in insular epilepsy may mimic temporal, parietal, or other cortical areas. Semiology, electroencephalography, and even surface electrocorticography recordings may falsely localize other cortical foci, leading to inaccurate diagnosis and treatment. The use of insular depth electrodes allows more precise localization of seizure foci. The authors describe the case of a young girl with seizures falsely localized to the cortex, with foci arising from the insula, as proven by depth electrode recordings. Resection of the insula yielded seizure control.

Morphological characteristics of brain tumors causing seizures

OBJECTIVE

To quantify size and localization differences between tumors presenting with seizures vs nonseizure neurological symptoms.

DESIGN

Retrospective imaging survey. We performed magnetic resonance imaging-based morphometric analysis and nonparametric mapping in patients with brain tumors.

SETTING

University-affiliated teaching hospital.

PATIENTS OR OTHER PARTICIPANTS

One hundred twenty-four patients with newly diagnosed supratentorial glial tumors.

MAIN OUTCOME MEASURES

Volumetric and mapping methods were used to evaluate differences in size and location of the tumors in patients who presented with seizures as compared with patients who presented with other symptoms.

RESULTS

In high-grade gliomas, tumors presenting with seizures were smaller than tumors presenting with other neurological symptoms, whereas in low-grade gliomas, tumors presenting with seizures were larger. Tumor location maps revealed that in high-grade gliomas, deep-seated tumors in the pericallosal regions were more likely to present with nonseizure neurological symptoms. In low-grade gliomas, tumors of the temporal lobe as well as the insular region were more likely to present with seizures.

CONCLUSIONS

The influence of size and location of the tumors on their propensity to cause seizures varies with the grade of the tumor. In high-grade gliomas, rapidly growing tumors, particularly those situated in deeper structures, present with non-seizure-related symptoms. In low-grade gliomas, lesions in the temporal lobe or the insula grow large without other symptoms and eventually cause seizures. Quantitative image analysis allows for the mapping of regions in each group that are more or less susceptible to seizures.

Microsurgery of epileptic foci in the insular region

OBJECT

The insular region has long been neglected in the investigation and treatment of refractory epilepsy. Surgery in the insular region is rarely performed because of the risk of injury to the opercula, the arteries transiting on the surface of the insula, and the deep structures such as the basal ganglia and the internal capsule. This study was undertaken to report the results of insular surgery using modern microsurgical techniques in patients with epilepsy.

METHODS

The authors performed a retrospective study of cases involving patients who underwent surgery for insular lesions associated with epilepsy over the last 10 years. In the majority of patients, intracranial electrodes were implanted with neuronavigation guidance to confirm the localization of the epileptic foci.

RESULTS

Nine patients underwent insular surgery: 7 for refractory epilepsy with no tumor and 2 for tumors associated with seizures. Four of the resections were performed in the left hemisphere. After an average follow-up of 54 months (range 14-122 months), Engel Class IA outcome had been achieved in 6 of 7 cases in the Epilepsy Surgery Group. The remaining patient had an Engel Class III outcome after partial insular resection but later became seizurefree (Engel Class IA) following insular Gamma Knife surgery. Postoperatively, the majority of patients suffered from minor reversible hemipareses that disappeared completely within a few months. There was no surgical mortality.

CONCLUSIONS

Insular surgery is both safe and beneficial when it is well planned and performed with modern microsurgical techniques and good anatomical knowledge. Insulectomy is associated with little permanent morbidity and a high rate of seizure control. To the authors' knowledge, this is the first series of insulectomies predominantly performed for refractory epilepsy since those performed by Penfield.

Safety and usefulness of insular depth electrodes implanted via an oblique approach in patients with epilepsy

OBJECTIVE

This study investigates the feasibility, safety, and usefulness of depth electrodes stereotactically implanted within the insular cortex.

METHODS

Thirty patients with suspected insular involvement during epileptic seizure underwent presurgical stereotactic electroencephalographic recordings using 10 to 16 depth electrodes per patient. Among these, one or two electrodes were implanted via an oblique approach to widely sample the insular cortex.

RESULTS

Thirty-five insular electrodes were implanted in the 30 patients without morbidity. A total of 226 recording contacts (mean, 7.5 contacts/patient) explored the insular cortex. Stereotactic electroencephalographic recordings of seizures allowed the differentiation into groups: Group 1, 10 patients with no insular involvement; Group 2, 15 patients with secondary insular involvement; and Group 3, five patients with an initial insular involvement. In temporal epilepsy (n = 17), the insula was never involved at the seizure onset but was frequently involved during the seizures (11 out of 17). In frontotemporal or frontal epilepsy, the insula was involved at the onset of seizure in five out of 13 patients. All patients in Groups 1 and 2 underwent surgery, with a seizure-free outcome in 76.2% of patients. In Group 3, only two of the five patients underwent surgery, with a poor outcome. In temporal lobe epilepsy, surgical outcome tended to be better in Group 1 compared with Group 2 in this small series: results were good in 83.3% (Engel I) versus 72.7%.

CONCLUSION

Insula can be safely explored with oblique electrodes. In temporal lobe epilepsy, insular involvement does not significantly modify the short-term postoperative outcome. Future larger studies are necessary to clarify the long-term prognostic value of insular spread.

Seizure freedom after functional hemispherectomy and a possible role for the insular cortex: the Dutch experience

OBJECT

The authors undertook this study to identify predictors of persistent postoperative seizures in their group of 28 Dutch pediatric and adolescent patients with medically intractable epilepsy who underwent functional hemispherectomy.

METHODS

The records of 28 pediatric and adolescent patients who underwent a functional hemispherectomy in the University Medical Center Utrecht were retrospectively analyzed. The authors performed a Cox regression analysis, using the first postoperative seizure as the event. Pathology, age at surgery, age at seizure onset, duration of epilepsy, type of surgery, surgeon, possible incomplete disconnection on MR images, and presence of residual insular cortex were analyzed as potential associated variables during the follow-up period.

RESULTS

The patients' mean age at surgery was 69.9 months (range 3.0-294.2 months) and mean duration of follow-up was 39.0 months (range 6.0-132.0 months). Six patients had postoperative seizures (21%). One patient had persistent bilateral status epilepticus and died 4 months after surgery. The Cox regression analysis showed presence of insular cortex to be the only variable statistically associated with postoperative seizures (p = 0.021) in this group of 28 patients.

CONCLUSIONS

In this group of Dutch pediatric and adolescent patients, residual insular cortex was positively correlated with persistent postoperative seizures. Given the small sample size in this study, however, caution should be used in drawing conclusions about the role of the insular cortex.

Diagnostik sylvischer und perisylvischer Epilepsien

The insula is a hidden part in the cerebral cortex about which relatively little neurological research has been done. The present manuscript describes architectural and evolutionary aspects of the insula reilii as well as its function, towards a better understanding of seizure semiology. As the literature of such casuistry is poor, some own cases are presented. Seizure semiology, imaging, magnetoencephalographic reports, resective epilepsy surgery, radiosurgical treatments, and thermolesions are described. Magnetic source imaging as noninvasive treatment can deliver important information for the involvement of sylvian and perisylvian regions in focal pharmacoresistant epilepsies.

Sudden unexpected death in epilepsy: from mechanisms to prevention

PURPOSE OF REVIEW

To discuss the pathophysiology and potential prevention of sudden unexpected death in epilepsy.

RECENT FINDINGS

Long-term electrocardiogram monitoring over several months has detected ictal asystole in three out of 20 (15%) patients with refractory epilepsy, suggesting that high-risk ictal arrhythmias occur in a greater proportion of patients with refractory epilepsy than previously thought. In case-control studies, sudden unexpected death in epilepsy was found to be associated with frequent generalized tonic-clonic seizures and greater ictal maximal heart rate, especially during nocturnal attacks. Conversely, supervision at night was associated with a lower risk of occurrence. The impact of epilepsy surgery on the risk of death and sudden unexpected death in epilepsy remains unclear, with comparable long-term survival in an epilepsy surgery cohort compared with a matched population of patients with refractory epilepsy who did not undergo surgery. Previous results may have been partly confounded by the association observed between preoperative decreased heart rate variability and poor postoperative seizure outcome.

SUMMARY

Ictal arrhythmias may represent a more prevalent cause of sudden unexpected death in epilepsy than previously thought. No clear recommendations have emerged from the literature regarding the most appropriate therapeutic strategies to prevent the event, apart from the supervision at night of patients with refractory epilepsy.