Amygdalar volume asymmetry informs laterality in temporal lobe epilepsy: MRI-SEEG study

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.