Refractory insular cortex epilepsy: clinical features, investigation and treatment

Drug resistant epilepsy of the insular lobe: A review and update article

Background:

Epilepsy is a chronic disease that affects millions of people around the world generating great expenses and psychosocial problems burdening the public health in different ways. A considerable number of patients are refractory to the drug treatment requiring a more detailed and specialized investigation to establish the most appropriate therapeutic option. Insular epilepsy is a rare form of focal epilepsy commonly drug resistant and has much of its investigation and treatment involved with the surgical management at some point. The insula or the insular lobe is a portion of the cerebral cortex located in the depth of the lateral sulcus of the brain; its triangular in shape and connects with the other adjacent lobes. The insular lobe is a very interesting and complex portion of the brain related with different functions. Insula in Latin means Island and was initially described in the 18^th century but its relation with epilepsy was first reported in the 1940–1950s. Insular lobe epilepsy is generally difficult to identify and confirm due to its depth and interconnections. Initial non-invasive studies generally demonstrate frustrating or incoherent information about the origin of the ictal event. Technological evolution made this pathology to be progressively better recognized and understood enabling professionals to perform the correct diagnosis and choose the ideal treatment for the affected population.

Methods:

A literature review was performed using MEDLINE/PubMed, Scopus, and Web of Science databases. The terms epilepsy/epileptic seizure of the insula and surgical treatment was used in various combinations. We included studies that were published in English, French, or Portuguese; performed in humans with insular epilepsy who underwent some surgical treatment (microsurgery, laser ablation, or radiofrequency thermocoagulation).

Results:

Initial search results in 1267 articles. After removing the duplicates 710 remaining articles were analyzed for titles and abstracts applying the inclusion and exclusion criteria. 70 studies met all inclusion criteria and were selected.

Conclusion:

At present, the main interests and efforts are in the attempt to achieve and standardize the adequate management of the patient with refractory epilepsy of the insular lobe and for that purpose several forms of investigation and treatment were developed. In this paper, we will discuss the characteristics and information regarding the pathology and gather data to identify and choose the best therapeutic option for each case.

[Clinical, structural and functional features of paroxismal syndrome in insular and temporal lobe tumors]

OBJECTIVE

To analyze the characteristics of paroxysmal syndrome in insular and temporal lobe tumors, to determine their relationship with the histological structure of tumor, to assess the effect of tumor growth nature on severity of disease.

MATERIAL AND METHODS

A retrospective analysis enrolled 80 patients aged 11 - 80 years with insular and temporal lobe tumors and symptomatic epilepsy. All patients underwent surgery at the Polenov National Research Neurosurgery Center in Almazov National Medical Research Center for the period from 2012 to 2018.

RESULTS

The main group consisted of 29 patients with tumors of temporal and insular lobes. Control group of 51 patients with temporal gliomas was formed for comparative analysis. It was found that involvement of insular lobe into paroxysmal syndrome is characterized by attacks with a motor component, somatosensory paroxysms, vegetative manifestations (respiratory attacks, salivation, nausea), speech disorders and taste hallucinations. Derealization, motor arrest and déjà vu/jamis vu paroxysms were more common in patients with temporal lobe lesion. Neoplastic lesion of the insular lobe shortens the period between manifestation of paroxysms and surgical treatment. Moreover, this type of disease is characterized by higher incidence of seizures compared to isolated temporal lobe tumors.

Magnetic resonance-guided laser interstitial thermal therapy for the treatment of non-lesional insular epilepsy in pediatric patients: thermal dynamic and volumetric factors influencing seizure outcomes

PURPOSE

To investigate the safety and efficacy of stereoelectroencephalography (sEEG) directed magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) in medically refractory insular epilepsy in pediatric patients, define the relationship between ablation volumes and seizure control, and analyze the relationship between thermal energy and ablation volumes.

METHODS

A single-institution, retrospective review of pediatric patients with insular epilepsy who underwent sEEG directed MRgLITT over a 10-month period was performed. Perioperative, imaging, and outcome data were analyzed. Seizure outcomes were determined based on Engel score (Engel I versus Engel II-IV). Insula and ablation volumes were measured, and the proportion of insula volume ablated was calculated. Thermal energy was calculated in joules.

RESULTS

Four patients underwent sEEG directed MRgLITT of insular epileptogenic foci. The ablation volume was higher in patients with Engel I outcome (3.93 cm³) compared to Engel II-IV outcome (1.02 cm³). The proportion of ablation to insula volume was lowest in patients with Engel II-IV outcome (25.09%). The mean energy requirement to create a unit volume of ablation in the insula is 1205.86 J. A linear trend was noted between thermal ablation energy and ablation volume (R² = 0.884). Over a mean follow-up period of 104 days, three patients were seizure-free (Engel I), and one patient saw significant improvement in seizure frequency (Engel III).

CONCLUSIONS

The proportion of insula ablated, as well as the volume of ablation, are related to seizure outcome with increasing ablation volumes corresponding to improved seizure control. Further analysis of insula laser ablation thermal dynamics and volumes is needed.

Cortical thickness analysis in operculo-insular epilepsy

Background

In temporal lobe epilepsy (TLE), advanced neuroimaging techniques reveal anomalies extending beyond the temporal lobe such as thinning of fronto-central cortices. Operculo-insular epilepsy (OIE) is an under-recognized and poorly characterized condition with the potential of mimicking TLE. In this work, we investigated insular and extra-insular cortical thickness (CT) changes in OIE.

Methods

All participants (14 patients with refractory OIE, 9 age- and sex-matched patients with refractory TLE and 26 healthy controls) underwent a T1-weighted acquisition on a 3 T MRI. Anatomical images were processed with Advanced Normalization Tools. Between-group analysis of CT was performed using a two-sided t-test (threshold of p < 0.05 after correction for multiple comparisons; cut-off threshold of 250 voxels) between (i) patients with OIE vs TLE, and (ii) patients with OIE vs healthy controls.

Results

Significant widespread thinning was observed in OIE patients as compared with healthy controls mainly in the ipsilateral insula, peri-rolandic region, orbito-frontal area, mesiotemporal structures and lateral temporal neocortex. Contralateral cortical shrinkage followed a similar albeit milder and less diffuse pattern.The CT of OIE patients was equal or reduced relative to the TLE group for every cortical region analyzed. Thinning was observed diffusely in OIE patients, predominantly inboth insulae and the ipsilateral occipito-temporal area.

Conclusion

Our results reveal structural anomalies extending beyond the operculo-insular area in OIE.

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.

Structural abnormalities in patients with insular/peri-insular epilepsy: spectrum, frequency, and pharmacoresistance

SUMMARY

Between 2002 and 2010, a total of 48 patients were seen at our epilepsy clinic with insular/peri-insular cortex epilepsy. Review of their MR imaging scans revealed a neoplastic lesion in 27% of patients, a malformation of cortical development in 21%, a vascular malformation in 19%, and atrophy/gliosis from an acquired insult in 17%. MR imaging results were normal in 4 patients. Other miscellaneous findings included a case of Rasmussen encephalitis, a nonspecific insular millimetric T2 signal abnormality, a neuroepithelial cyst, and hippocampal sclerosis without MR imaging evidence of dual insular pathologic features (despite depth electrode-proven insular seizures). Refractoriness to antiepileptic drug treatment was present in 56% of patients: 100% for patients with malformations of cortical development (1.0; 95% CI, 0.72-1.0), 50.0% (0.5; 95% CI, 0.21-0.78) in the presence of atrophy/gliosis from acquired insults, 39% (0.39; 95% CI, 0.14-0.68) for neoplastic lesions, and 22.2% (0.22; 95% CI, 0.06-0.55) for vascular malformations.

Temporal lobe epilepsy surgery failures: a review

Patients with temporal lobe epilepsy (TLE) are refractory to antiepileptic drugs in about 30% of cases. Surgical treatment has been shown to be beneficial for the selected patients but fails to provide a seizure-free outcome in 20–30% of TLE patients. Several reasons have been identified to explain these surgical failures. This paper will address the five most common causes of TLE surgery failure (a) insufficient resection of epileptogenic mesial temporal structures, (b) relapse on the contralateral mesial temporal lobe, (c) lateral temporal neocortical epilepsy, (d) coexistence of mesial temporal sclerosis and a neocortical lesion (dual pathology); and (e) extratemporal lobe epilepsy mimicking TLE or temporal plus epilepsy. Persistence of epileptogenic mesial structures in the posterior temporal region and failure to distinguish mesial and lateral temporal epilepsy are possible causes of seizure persistence after TLE surgery. In cases of dual pathology, failure to identify a subtle mesial temporal sclerosis or regions of cortical microdysgenesis is a likely explanation for some surgical failures. Extratemporal epilepsy syndromes masquerading as or coexistent with TLE result in incomplete resection of the epileptogenic zone and seizure relapse after surgery. In particular, the insula may be an important cause of surgical failure in patients with TLE.