Abstracts

We previously showed that hippocampal formation (HF) shape and position abnormalities occur in 49% of patients with malformations of cortical development (MCD), whereas they occur only in 10% of healthy subjects (Bernasconi, 2005). These abnormalities were neither lateralized to the side of the EEG focus nor to the side of the MCD. Here, our purpose was to evaluate shape and positioning of the HF in patients with various forms of epilepsy not related to MCD. We studied 96 age- and sex matched adult patients including 30 with temporal lobe epilepsy (TLE), 36 with non-lesional extra-temporal epilepsy (ETE) and 30 with idiopathic generalized epilepsy (IGE). Shape and positioning of the HF were evaluated using a set of eight predefined morphological characteristics on T1-weighted high-resolution MRI (Baulac, 1998; Bernasconi, 2005). We considered the HF shape and positioning as abnormal if at least 3 criteria were present in the same subject. Volumetric MRI of the hippocampus was performed in TLE patients. At least 3 criteria describing abnormal HF shape and positioning were found in 13/30 (43%) TLE, 12/36 (33%) ETE and 9/30 (30%) IGE. HF abnormalities were not related to the side of the EEG focus in both TLE and ETE, and were unrelated to side of hippocampal atrophy in TLE. HF shape and positioning abnormalities are found in similar proportions in patients with various forms of focal epilepsy and those with IGE. These proportions are similar to that found in MCD. Previous studies have suggested that a preexisting HF abnormality may contribute to the development of hippocampal sclerosis (Fernandez, 1997). Our results suggest that HF shape and positioning abnormalities are more likely to be a predisposing factor for epilepsy in general. (Supported by Canadian Institutes of Health Research (CIHR - grant #203707).)