| Once presumed to be primarily a unilateral temporal lobe condition, a growing body of neuropsychological, and both structural and functional neuroimaging, research suggests that brain abnormalities in TLE extend beyond the epileptogenic temporal lobe, into extratemporal regions in the hemisphere that is ipsilateral to the seizure focus and potentially the hemisphere that is contralateral to the seizure focus. In order to comprehensively evaluate the structural and functional integrity of the hemisphere contralateral to the seizure focus in unilateral TLE, 17 EEG-monitored, right TLE patients and 82 healthy controls underwent a MM brain scan and a comprehensive neuropsychological evaluation including 7 putative measures of left hemisphere function. Quantitative MRI volumetrics yielded volumes for the following bilateral regions of interest: total hemispheres (gray matter, white matter, and total), four lobes (gray matter, white matter, and total), and hippocampi. Clinical epilepsy variables (i.e., history of secondary generalized seizures, epilepsy duration, and age of onset) were identified through interview. Between-group comparisons supported the presence of contralateral brain abnormalities in TLE. Right TLE patients performed significantly worse than controls on 6 of 7 measures of left hemisphere function, four of which were significantly associated with left hemisphere white matter volume. The right TLE group also had significant bilateral brain volume reductions; white matter was particularly reduced and ipsilateral right volumes were generally more reduced than contralateral left volumes. Although the small right TLE sample size limited within-group analyses, exploratory analyses identified a significant correlation between ipsilateral right hippocampal volume and epilepsy duration. In conclusion, support was found for bilateral brain abnormalities in unilateral TLE, particularly with regard to white matter reductions. While ipsilateral hippocampal volume correlated with epilepsy duration, a causal relationship between seizure activity and hippocampal volume could not be established through the study's cross-sectional design, and the etiology of white matter reductions warrants further investigation. |
