(i) To discover correlations between AE/AA and amygdalar epileptiform activity

(ii) To examine the predictive value of AE/AA vis-à-vis SEEG-identified TLE lateralization.

Amygdalar enlargement and/or asymmetry (AE/AA) in TLE is commonly reported as occurring ipsilaterally to the seizure focus. However, AE has also been described contralaterally to the seizure focus. Small SEEG case series report amygdalar epileptiform activity in all patients but have found no lateralization value. Significance of AE/AA in the pathogenesis of TLE and its clinical utility remain unclear.

We reviewed 20 pharmacoresistant TLE patients undergoing SEEG (12F) with one (14) or both (6) amygdalae sampled. We computed an amygdalar asymmetry index (AAI) from Freesurfer extracted segmentations of pre-operative structural MRIs, formulated as 200*(R_vol-L_vol)/(R_vol+L_vol). Normative amygdalar volumetric data were obtained from the ENIGMA consortium, representing lifespan data of 18000+ healthy controls.   

Both right and left amygdalar volumes of patients were significantly larger than controls (right mean difference (SE): 262 (302) (p< 0.001), left mean difference (SE): 114 (296) (p< 0.05)). AAI in patients (-19.5% to 31.4%; mean 12%, SD 11.1) was significantly different from controls (3.1-5.3%; mean 3.9%, SD 0.68) (p < 0.002). The overall accuracy of AAI in lateralizing TLE was 73%. Of 164 seizures captured, 78% involved the amygdala (at onset or later). Amygdalar involvement in seizure and AAI were significantly correlated (Spearman’s rho = 0.506, p = 0.023).  

TLE may have a nonspecific enlarging effect on amygdalae, an effect accentuated for the right amygdala. Left amygdalar enlargement is highly specific but not sensitive for left TLE and right amygdalar enlargement is highly sensitive but not specific for right TLE. High correlation between amygdalar involvement in seizures and AAI may indicate an active, two-way process between amygdalar hyperplasia and seizures involving the amygdala.