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

Abstract

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.

Pilot Study of Voxel-Based Morphometric MRI Post-processing in Patients With Non-lesional Operculoinsular Epilepsy

“…This is a little lower than previous studies containing a mixed cohort of all types of seizures (18). The seizure-free rate (75%) of our cohort is higher than the previously reported insular epilepsy surgeries, which reported to be around 33.3-62.5% (6,43,44). These may due to the small sample size and the large resection range in the present study.…”

“…However, the results of MEG showed abnormalities in inferior frontal, temporal or central regions in all the patients. Alomar et al reported that in 39 patients without insular semiology, 15 patients had MEG abnormalities located in the insula, while only 8 patients showed MRI abnormalities of the insula (6).…”

“…Because of the above-mentioned reasons, stereo-EEG is often mandatory to determine the precise seizure onset zones of insular epilepsy, in particular when MRI proves to be negative (13,28,33). The frequently used techniques can be orthogonal, oblique, or a combination of both trajectories (6). Of course, the implantation of the intracranial electrodes can have some other benefits, such as spare part of the mesial temporal and decrease the risk of the post-operative memory alteration when the symptoms of temporal plus epilepsy was presented (37).…”

“…Although operculoinsular epilepsy is relatively rare, it accounts for a non-negligible proportion of drug-resistant epilepsy surgical candidates and sometimes it can be difficult to be recognized (4)(5)(6). Because of the complex physiology and the rich connections to surrounding and remote structures, the clinical manifestations of operculoinsular seizures can be diverse (7).…”

“…The apparent heterogeneous and sometimes non-specific clinical manifestations increase the difficulties of the diagnosis of operculoinsular seizures, especially in non-lesional patients. Lack of recognition of operculoinsular seizures may be responsible for some epilepsy surgery failures (6).…”