Abstracts

Rationale: Despite surgery being highly effective in temporal lobe epilepsy (TLE), the proportion with long term seizure freedom following surgery is suboptimal. Persistent seizures after surgery suggest that hippocampal or extrahippocampal epileptogenic tissue remains in situ. Temporal plus epilepsy is a proposed explanation, describing a complicated epileptogenic network involving the temporal lobe and neighbouring structures such as the insula (1). The prospective identification of patients with temporal plus epilepsy is crucial as this cohort have worse postoperative seizure outcomes compared to purely temporal lobe epilepsy (2). We sought to explore whether insular volume was related to TLE, febrile seizures, secondary generalised tonic clonic seizures (SGTCS), and postoperative seizure outcomes. Methods: We studied 77 patients (left TLE n=50, right TLE n=27) with well-characterised refractory unilateral TLE who had undergone amygdalohippocampectomy and 36 healthy controls. All patients had ipsilateral hippocampal sclerosis, no other potentially epileptogenic lesion, and were followed up at a mean time of two years after surgery. All patients (prior to surgery) and controls had 3D T1-weighted MRI performed. Left and right insular volumes were acquired using methodology based on the Cavalieri method of design-based stereology and point counting (3). A multivariate analysis controlling for sex and age was carried out using SPSS with post hoc Bonferroni correction. Results: There was a significant difference in both left (F=20.27, p<0.001) and right (F=19.16, p<0.001) insular volumes between patients with TLE and controls. Insular volumes were reduced bilaterally in both left TLE (left insula p<0.0001, right insula p<0.0001) and right TLE patients (left insula p=0.0003, right insula p=0.006) compared to controls. Patient sub-group analysis revealed no statistically significant difference in insular volumes between patients with and without a history of febrile seizures and in those with and without SGTCS. Further analysis found no statistically significant relationship between insular volumes and postoperative seizure outcomes. Conclusions: Volume atrophy of the right and left insula is present regardless of TLE laterality. We were unable to identify relationships between gross insular morphology and clinical features of TLE. In future we will investigate the relationship between postoperative outcome and regionally-specifically insular morphological changes.References:1. Barba C et al. Brain. 2007 Jul;130(Pt 7):1957-672. Barba C et al. Brain. 2016 Feb;139(Pt 2):444-513. Keller SS et al. J Cogn Neurosci. 2011 Aug;23(8):2013-29 Funding: No funding