Hippocampal cell density and subcortical metabolism in temporal lobe epilepsy

Purpose: Correlations between hippocampal cell density and subcortical meta bolism in patients with temporal lobe epilepsy (TLE) were studied to explor e possible Links between subcortical function and the regulation of hippoca mpal excitability. Methods: Resected hippocampal cell densities were correlated with cortical and subcortical regional cerebral metabolic rate fur glucose (CMRglu), as m easured by [F-18]-fluorodeoxyglucose positron emission tomography (18-FDG-P ET), in 39 patients with intractable TLE who underwent anterior temporal lo bectomy (ATL). CMRglu was measured ipsilateral and contralateral to the res ected temporal lobe. Linear regression techniques were used for statistical analysis. Results: Hilar cell densities correlated positively and significantly with CMRglu in the bilateral thalamus, putamen and globus pallidus, and the ipsi lateral caudate. Dentate granule cell densities correlated positively and s ignificantly with CMRglu in the bilateral thalamus and putamen. There was n o significant correlation between cell densities and CMRglu in any cortical region, including the hippocampus. Conclusions: We postulate that hippocampal cell loss results in decreased e fferent synaptic activity to the thalamus and basal ganglia, causing decrea sed neuronal activity in these structures with consequent hypometabolism. T his synaptic activity has a significant bilateral component. Subcortical hy pometabolism in patients with TLE may reinforce the epileptogenic potential of mesial temporal lobe discharges.