Medial temporal lobe epilepsy without hippocampal atrophy

The incidence and structural basis of nonlesional medial temporal lobe epilepsy (MTLE) without hippocampal atrophy (HA) is not known. Reports suggest that 5-15% of patients with hippocampal sclerosis (HS) do not have HA. We reviewed 57 patients with MTLE who underwent magnetic resonance imaging (MRI) volumetric studies, anteromedial temporal lobectomy (TL), and quantitative cell counts of the resected hippocampus and who had at least 1 year of surgical follow-up. We compared demographic, pathologic, and outcome data among patients with and without HA. Ten of the 57 patients did not have HA. Nine of the 10 patients had depth EEG for localization of seizure onset because of discordance or insufficient localization. Five patients had pathologic evidence of HS. Longer duration of epilepsy correlated inversely with the presence of HA. Outcome was not significantly different between patients with and without HA. We conclude that the incidence of MTLE and HS without HA. is 9%. Except for duration of epilepsy, there were no differences in the clinical syndrome or surgical outcome of patients with and without HA.