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Abstract
Seizure freedom is not achieved in a third of patietns who undergo temporal lobectomy for temporal lobe epilepsy (TLE). The cause of such surgical failures is unclear. Assoicated pathologies, such as Focal Cortical Dysplasia (FCD) IIIA, are described in the International League Against Epilepsy (ILAE) classification, but pre-operative electroclinical correlates, neuroimaging findings, and post-operative seizure outcomes have not been established for these entities. Furthermore, pathological gliosis is a common accompaniment of hippocampal sclerosis (HS). Few studies have correlated teh degree of gliosis with post-operative outcome.
This was a retrospective study examining a cohort of children and adults (n=73) who had undergone TLE surgery. Pre-operative features of patients' epilepsy, EEG, neuroimaging and post-operative outcome were compared to the underlying pathoogy (FCD IIIA and other pathologies). Pathological diagnosis was reviewed according to the ILAE classification. The degree of gliosis was ascertained in a subgroup (n=43) with HS. Surgical specimens of hippocampus and neocortex were examined by immunohistochemistry for Glial Fibrillary Acidic Protein (GFAP) to detect astrocytes, and for Cluster of Differentiation epitope (CD68) to detect microglia, using quantitation of cell coutns and density of immunoreactivity.
The results demonstrated FCD IIIA was a common pathology in this cohort. FCD IIIA had neuroimaging features distinguishing it from other pathologies. The pre-operative electroclinical features were similar to isolated HS, but significantly different from other pathologies. Surgical outcome was poorest in FCD IIIA in this cohort.
Acute seizure burden at operation was correlated with reactive astrogliosis. Microglial activation was correlated with the presence of pre-operative bilateral convulsive seizures. Epilepsy chronicity was positively correlated with fibrillary gliosis in the hippocampus/neocortex. Pre-operative atrophy on MRI was correlated with the extent of neocortical gliosis. The degree of astrogliosis in CA3 was significantly correlated with post-operative seizure outcome.
In conclusion, this study provides comprehensive data on the electroclinical presentation, neuroimaging features and post-operative outcome for TLE patients with associated and acquired pathologies. This knowledge will enable clinicians to refine pre-operative counselling and post-operative management of epilepsy surgery patients.