Abstract
BackgroundMedial temporal lobe epilepsy (MTLE) is associated with limbic atrophy involving the hippocampus, peri-hippocampal and extra-temporal structures. While MTLE is related to static structural limbic compromise, it is unknown whether the limbic system undergoes dynamic regional perfusion network alterations during seizures. In this study, we aimed to investigate state specific (i.e. ictal versus interictal) perfusional limbic networks in patients with MTLE.MethodsWe studied clinical information and single photon emission computed tomography (SPECT) images obtained with intravenous infusion of the radioactive tracer Technetium- Tc 99 m Hexamethylpropyleneamine Oxime (Tc-99 m HMPAO) during ictal and interictal state confirmed by video-electroencephalography (VEEG) in 20 patients with unilateral MTLE (12 left and 8 right MTLE). Pair-wise voxel-based analyses were used to define global changes in tracer between states. Regional tracer uptake was calculated and state specific adjacency matrices were constructed based on regional correlation of uptake across subjects. Graph theoretical measures were applied to investigate global and regional state specific network reconfigurations.ResultsA significant increase in tracer uptake was observed during the ictal state in the medial temporal region, cerebellum, thalamus, insula and putamen. From network analyses, we observed a relative decreased correlation between the epileptogenic temporal region and remaining cortex during the interictal state, followed by a surge of cross-correlated perfusion in epileptogenic temporal-limbic structures during a seizure, corresponding to local network integration.ConclusionsThese results suggest that MTLE is associated with a state specific perfusion and possibly functional organization consisting of a surge of limbic cross-correlated tracer uptake during a seizure, with a relative disconnection of the epileptogenic temporal lobe in the interictal period. This pattern of state specific shift in metabolic networks in MTLE may improve the understanding of epileptogenesis and neuropsychological impairments associated with MTLE.
Highlights
For most patients with medial temporal lobe epilepsy (MTLE), the hippocampus is presumed to be the location of seizure onset [1]
We focused our analyses in the investigation of quantifiable measures of connectivity of the whole network and specific limbic regions of interest (ROIs)
Voxel-based comparison of tracer uptake We observed a significant increase in Tc-99 m HMPAO uptake within the medial temporal lobe ipsilateral to the side of seizure onset, based on the voxel-wise paired t-test
Summary
For most patients with medial temporal lobe epilepsy (MTLE), the hippocampus is presumed to be the location of seizure onset [1]. Structural imaging such as magnetic resonance imaging (MRI) can demonstrate abnormalities that are consistently associated with hippocampal sclerosis, such as hippocampal atrophy on T1 weighted images and increased hippocampal signal on T2 based sequences [4]. These abnormalities can be visually inspected on routine clinical scans, or quantified using post-processing techniques [5]. Medial temporal lobe epilepsy (MTLE) is associated with limbic atrophy involving the hippocampus, perihippocampal and extra-temporal structures. We aimed to investigate state specific (i.e. ictal versus interictal) perfusional limbic networks in patients with MTLE
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