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Topographic distribution of seizure onset and hippocampal atrophy: relationship between MRI and depth EEG
D King1, R A Bronen, D D Spencer
1Department of Neurology, Yale University School of Medicine, New Haven, CT 06510, USA.
Abstract:
Medial temporal lobe epilepsy (MTLE) is associated with hippocampal cell loss and organization of the dentate gyrus. Some studies suggest a correlation between the topographic distribution of cell loss and site of epileptogenesis. We studied the relationship between the site of ictal onset with the presence of segmental atrophy in patients with non-lesional MTLE using magnetic resonance imaging (MRI) and depth EEG. Ictal recordings were obtained from 27 patients with longitudinal hippocampal depth electrodes and variable combinations of subdural strips sampling medial temporal structures. The location of the depth electrode contacts was correlated with anatomical landmarks. Seizures were analyzed for the distribution of onset along the long axis of the hippocampus. MRI analysis were performed to detect segmental atrophy. Outcome was assessed 1 year or more following anterior temporal lobectomy. Twenty-five patients had unilateral, and two had bilateral, hippocampal atrophy. One hundred and forty-seven seizures were reviewed: 21 showed focal onset and 126 showed regional onset. Ictal onset involved the amygdala and anterior half of the hippocampus in 80% of the seizures while only 40% of patients had atrophy of these segments. Most patients had excellent outcome. In patients with MTLE the primary area of epileptogenesis does not parallel the hippocampal segments with the greatest degree of volume loss.
Insights
In medial temporal lobe epilepsy (MTLE), the area where seizures begin doesn't always match the hippocampus sections with the most cell loss. This finding impacts understanding epilepsy progression and treatment.
Area of Science:
- Neuroscience
- Epileptology
- Medical Imaging
Background:
- Medial temporal lobe epilepsy (MTLE) is characterized by hippocampal cell loss and dentate gyrus disorganization.
- Previous research suggests a link between the location of cell loss and the origin of seizures (epileptogenesis).
Purpose of the Study:
- To investigate the relationship between the site of seizure onset and the presence of segmental atrophy in non-lesional MTLE.
- To compare the topographic distribution of ictal onset with MRI-detected hippocampal atrophy.
Main Methods:
- Utilized magnetic resonance imaging (MRI) and depth electroencephalography (EEG) in 27 patients with MTLE.
- Recorded ictal activity using hippocampal depth electrodes and subdural strips.
- Correlated electrode contact locations with anatomical landmarks and analyzed seizure onset distribution along the hippocampus.
Main Results:
- Twenty-five patients exhibited unilateral and two had bilateral hippocampal atrophy.
- Seizure onset frequently involved the amygdala and anterior hippocampus (80% of seizures).
- However, only 40% of patients showed atrophy in these specific hippocampal segments, indicating a mismatch.
Conclusions:
- In MTLE patients, the primary area of seizure generation (epileptogenesis) does not consistently align with the hippocampal segments exhibiting the most significant volume loss.
- This dissociation suggests complex mechanisms underlying MTLE pathology and epileptogenesis.