Diagnosis and surgical treatment of non-lesional temporal lobe epilepsy with unilateral amygdala enlargement

Objective Exploring the role of amygdala enlargement (AE) in temporal lobe epilepsy (TLE) without ipsilateral mesial temporal sclerosis (MTS) using comprehensive presurgical workup tools including traditional tools, automatically volumetric analysis, high-density EEG (HD-EEG) source imaging (HD-ESI), and stereoelectroencephalography (SEEG). Methods Nine patients diagnosed with TLE-AE who underwent resective surgeries encompassing the amygdala were retrospectively studied. HD-ESI was obtained using 256-channel HD-EEG on the individualized head model. For automatic volumetric analysis, 48 matched controls were enrolled. Diagnosis and surgical strategies were based on a comprehensive workup following the anatomo-electro-clinical principle. Results At post-operative follow-up (average 30.9 months), eight patients had achieved Engel class I and one Engel class II recovery. HD-ESI yielded unifocal source estimates in anterior mesial temporal region in 85.7% of cases. Automatic volumetric analysis showed the AE sides were consistent with the values determined through other preoperative workup tools. Furthermore, the amygdala volume of the affected sides in AE was significantly greater than that of the larger sides in controls (p < 0.001). Meanwhile, the amygdala volume lateral index (LI) of AE was significantly higher than in controls (p < 0.001). SEEG analysis showed that ictal onsets arose from the enlarged amygdala (and hippocampus) in all cases. Conclusion In addition to traditional workup tools, automatic volumetric analysis, HD-ESI on individualized head model, and invasive SEEG can provide evidence of epileptogenicity in TLE-AE. Resective surgical strategies encompassing the amygdala result in better prognosis. In suspected TLE cases, more attention should be focused on detecting enlargement of amygdala which sometimes is "hidden" in "MR-negative" non-MTS cases.