Abstracts

Rationale: Corticoamygdalohippocampectomy (CAH) improves seizure control, quality of life, and decreases mortality for refractory mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). One third of patients continue having seizures, and it is pivotal to determine structural abnormalities that might influence post-operative outcome. Studies indicate that nonhippocampal regions may play a role in epileptogenic network in MTLE-HS and could generate seizures postoperatively. Our aim was to analyze areas of atrophy, not always detected on routine MRI, comparing patients who became seizure free (SF) with those not seizure free (NSF) after CAH, in an attempt to establish possible predictors of surgical outcome. Methods: One-hundred and five patients with refractory MTLE-HS submitted to CAH (59 left-MTLE; 46 males) and 47 controls were enrolled. Morphometric analyses using FreeSurfer was performed for cortical thickness and volumetric estimation comparing patients to controls and SF to NSF patients. The final sample after post processing procedures resulted in 99 patients. Results: Cortical thickness analyses showed reductions in left insula in patients compared to controls. Significant volume reductions in SF patients were present in bilateral thalami, hippocampi and pars opercularis, left parahippocampus and right temporal pole. In NSF patients reductions were present bilaterally in: thalami, hippocampi, entorhinal cortices, superior frontal and supramarginal gyri; on the left: superior and middle temporal gyri, temporal pole, parahippocampus, pars opercularis and middle frontal gyrus; and on the right: precentral, superior, middle and inferior temporal gyri. Comparison between SF and NSF patients showed ipsilateral GM reductions in right entorhinal cortex (p=0.003) and contralateral parahippocampal gyrus (p=0.05) in right MTLE-HS. Patients NSF had longer duration of epilepsy than SF (p=0.028). Conclusions: NSF patients exhibited more extensive areas of atrophy than SF. As entorhinal cortex and parahippocampal gyrus are reduced in NSF patients compared to those SF these structures might be implicated in the network responsible for the maintenance of postoperative seizures. Duration of epilepsy is a predictor of seizure outcome. MRI quantitative imaging may provide evidence suggesting that seizures are more likely to persist after surgery when preoperative abnormalities are observed in brain regions involved in the network of MTLE-HS, as well as in areas of the limbic system located outside the resected hippocampus. Funding: None