Amygdalar volume asymmetry informs laterality in temporal lobe epilepsy: MRI-SEEG study
Subeikshanan Venkatesan1, Abbas Babajani-Feremi2, Kajal Patel3
1Department of Neurology, University of Florida, Gainesville FL, USA; Wilder Center for Epilepsy Research, University of Florida, Gainesville FL, USA.
Objective:
Amygdalar volumes are right-left asymmetric in normal humans. Asymmetric amygdalar hyperplasia is described in temporal lobe epilepsy (TLE), but has unclear lateralizing significance. In this study of TLE patients undergoing stereo-electroencephalography (SEEG) we examined the lateralizing value of amygdalar volume (AV) asymmetry, and its relationship to amygdalar involvement in seizures.
Methods:
Amygdalar volumes of 30 TLE patients without radiological hippocampal sclerosis undergoing SEEG were compared to those from a normative database. Devising a novel amygdalar (volume) asymmetry index (AAI), we correlated AAI to SEEG-ascertained TLE lateralization and amygdalar involvement in seizures.
Results:
At the group level, right AVs in right TLE (RTLE) and left AVs in left TLE (LTLE) were significantly higher than in controls (right difference: mean 226 mm3; left difference: mean 206 mm3). AAI was significantly higher than in RTLE and bitemporal epilepsy than in controls (16/17 patients; mean AAI difference 8.4 %) and significantly lower than in LTLE than in controls (8/9 patients; mean AAI difference -8.3 %). Amygdalar involvement in seizures correlated positively with absolute AAI (Spearman's ρ = 0.45, p < 0.05).
Conclusions:
Significant deviation from physiological right-left AV asymmetry is almost universal in TLE and has robust lateralizing value. Relatively positive AAI is associated with RTLE or bitemporal epilepsy; relatively negative AAI is associated with LTLE. Larger AAI deviations are associated with a higher proportion of seizures with amygdalar involvement, suggesting a causal influence of seizures on amygdalar expansion in TLE.
