Abstracts

Rationale: Epilepsy arising from the insula is widely regarded as a challenging type of seizure, probably owing to the deep-seated location of the insula and the extensive connections it makes with adjacent structures. In recent years, we have rapidly gained insights into insular epilepsy-related obstacles. Here, we describe a detailed analysis of the electro-clinical manifestations of this type of epilepsy using intra-cerebral recordings performed with Stereo-electroencephalography (SEEG) and surgical outcome. Methods: We retrospectively analyzed 12 patients from the epilepsy monitoring unit in our institution who underwent insular exploration using SEEG between June 2013 and December 2018. Patient information reviewed included demographics, detailed clinical history, neurological examination, neuroimaging studies (Brain MRI and PET), Scalp video-EEG, intracranial recordings with SEEG, histopathological findings, and surgical outcomes. Results: 12 patients were found with seizures originating from either the insula alone (6 patients) or simultaneously originating from the insula and adjacent structures (6 patients). Two patients had a family history of epilepsy and another one had previous exposure to viral meningoencephalitis. Six patients had undergone prior surgery (three for epilepsy treatment, two for tumor resection and one for cavernous malformation resection). Five patients experienced seizures daily. The average of antiepileptic drugs trails was seven. The most common type of seizure observed was focal with impaired awareness, and this was observed in 10 patients (83%). The most common aura observed was somatosensory sensation, followed by cephalic sensation in 4 and 3 patients, respectively. 50% of the patients showed a tendency for secondary generalizations and 25% showed nocturnal predominance. Lesions were observed on brain MRI in five cases, three of them among peri insular group. Scalp EEG revealed different interictal discharge distributions: 6 patients showed ipsilateral regional frontotemporal spikes, 4 showed bilateral temporal spikes, and no spikes were detected in 2 patients. The location of ictal onset could be localized in only 58% of patients. The most common scalp EEG ictal pattern was rhythmic theta or delta activity (67%). Subsequent SEEG evaluation in seven patients found to have a combination of clinical and subclinical seizures. SEEG Clinical seizure onset from the insula alone was found in 50% of the patients: from the right insula in 3 patients, from the left insula in 2 patients, and from the bilateral insula in 1 patient. The other patients presented with simultaneous onset from the insula and adjacent structures: 4 from mesial temporal structures, 1 from the mesiotemporal and neocortical, and 1 from the frontal. The most common SEEG ictal pattern was low voltage fast activity in 67% of the patients. Surgical resections guided by SEEG findings were performed in 8 patients and led to excellent postoperative outcomes in most of the patients; five cases had Engle class 1 outcome at 6 - 24 months follow up and the remaining 3 patients have Engle class 2, 3, and 4. Conclusions: In this study, we observed that it is not uncommon for seizures to simultaneously originate from the insula and adjacent structures. However, noninvasive EEG monitoring tools are likely insufficient to detect such simultaneous seizures. For the given sample, SEEG proved beneficial in providing optimal surgical outcomes. The overall result of insular surgery is promising with significant improvement. Funding: No funding