Abstracts

Rationale: Recent evidence suggest that failure to recognize insular seizures may be responsible for part of epilepsy surgery failures. Confirmation of insular seizures requires an invasive study in absence of a clear epileptogenic lesion. The deep anatomical location of the insular cortex together with the dense sylvian vascularization explains why the insula is seldom sampled during invasive studies. We sought to investigate the feasibility, safety, and usefulness of two methods of sampling the insula. Methods: A retrospective analysis of all intracranial studies with insular sampling between 1996 and 2009 was performed. Results: Seventeen patients with suspected insular involvement during epileptic seizures had an intracranial study with insular coverage. Two types of implantation were used. The first type consisted in an unilateral craniotomy, insertion of insular electrodes by micro-dissection of the Sylvian fissure, orthogonal implantation of medial temporal structures with neuronavigation, extensive coverage of the three adjacent lobes with subdural electrodes. The second type consisted of MRI-stereotactic frame-guided depth electrode implantation into the insula and the hippocampus using sagittal axes, insertion of subdural electrodes through burr holes to cover the three adjacent lobes. The first type was used for 15 subjects (total: 25 insular electrodes; 51 insular contacts) and the second type was used in 2 subjects (total: 5 insular electrodes, 27 insular contacts). Insular spikes were found in 9 subjects and insular seizures in 6. Two reversible complications occurred with the first type of implantation: a foot drop due to migration of the electrode into the internal capsule and dysphasia due to temporal opercular retraction. Conclusions: The insula can be safely explored either by opened micro-dissection of the sylvian fissure or a combined Yale-Grenoble stereotactic implantation. The former, with less insular sampling, is better suited for unilateral insular and high spatial resolution investigation of adjacent lobes while the latter is indicated for unilateral or bilateral insular and adjacent lobes investigation.