Ipsilateral and Contralateral MRI Volumetric Abnormalities in Chronic Unilateral Temporal Lobe Epilepsy and their Clinical Correlates

Abstract

Summary:Purpose: To assess the presence, extent, and clinical correlates of quantitative MR volumetric abnormalities in ipsilateral and contralateral hippocampus, and temporal and extratemporal lobe regions in unilateral temporal lobe epilepsy (TLE).Methods: In total, 34 subjects with unilateral left (n = 15) or right (n = 19) TLE were compared with 65 healthy controls. Regions of interest included the ipsilateral and contralateral hippocampus as well as temporal, frontal, parietal, and occipital lobe gray and white matter. Clinical markers of neurodevelopmental insult (initial precipitating insult, early age of recurrent seizures) and chronicity of epilepsy (epilepsy duration, estimated number of lifetime generalized seizures) were related to magnetic resonance (MR) volume abnormalities.Results: Quantitative MR abnormalities extend beyond the ipsilateral hippocampus and temporal lobe with extratemporal (frontal and parietal lobe) reductions in cerebral white matter, especially ipsilateral but also contralateral to the side of seizure onset. Volumetric abnormalities in ipsilateral hippocampus and bilateral cerebral white matter are associated with factors related to both the onset and the chronicity of the patients' epilepsy.Conclusions: These cross-sectional findings support the view that volumetric abnormalities in chronic TLE are associated with a combination of neurodevelopmental and progressive effects, characterized by a prominent disruption in ipsilateral hippocampus and neural connectivity (i.e., white matter volume loss) that extends beyond the temporal lobe, affecting both ipsilateral and contralateral hemispheres.

MRI volume loss of subcortical structures in unilateral temporal lobe epilepsy

“…This is consistent with the significant association observed between number of generalized seizures and corpus callosum volume abnormality. In addition, the large effect size for corpus callosum volume atrophy is consistent with recent findings of extensive bilateral whole brain white matter volume atrophy in unilateral TLE [7,34].…”

“…Ipsilateral hippocampal volume, but not contralateral hippocampal volume, was significantly correlated with both seizure onset-related factors and duration of epilepsy [7,15]. Ipsilateral hippocampal volume was significantly reduced compared to contralateral hippocampal volume only in a subgroup of patients with a positive history of a precipitating event.…”

“…The typical pattern is asymmetric hippocampal volume loss with greater abnormality in the ipsilateral hippocampus compared to the contralateral hippocampus. In addition, both disease course features (e.g., duration) and neurodevelopmental features (e.g., history of complex febrile seizures in childhood) have been implicated in hippocampal atrophy [4][5][6][7].…”

Thalamic atrophy and cognition in unilateral temporal lobe epilepsy

“…These findings are consistent with the hypothesis that different mechanisms contribute to the integrity of the hippocampus and thalamus in unilateral TLE. Hippocampal volume was influenced by both early neurodevelopmental features (e.g., an early neurologic insult) and course features such as duration (Bernasconi et al, 2005;Keller et al, 2002;Seidenberg et al, 2005;Theodore et al, 1999). In contrast, thalamic volume was affected only by course variables (e.g., duration of epilepsy).…”

“…Significant volume reduction in the ipsilateral hippocampus with a relatively intact contralateral hippocampal volume is the MRI signature of unilateral mesial temporal lobe epilepsy (Seidenberg et al, 2005;Van Paesschen et al, 1997). The ipsilateral hippocampus showed the largest volume reduction, but thalamic volume was also significantly reduced compared with controls and was evident on both the ipsilateral (9%) and contralateral side (6%).…”