Amygdala enlargement in mesial temporal lobe epilepsy: an alternative imaging presentation of limbic epilepsy

To assess imaging, clinical, and pathological features of mesial temporal lobe epilepsy (mTLE) patients with amygdala enlargement (AE) in comparison with those with mesial temporal sclerosis (MTS).

Clinical, imaging, and pathologic features were retrospectively reviewed in 40 mTLE patients with postoperative follow-up (10 with AE and 30 with MTS). The volumes and signal intensity of the amygdala and hippocampus were assessed in 10 AE, 10 age- and sex-matched MTS patients, and 12 controls (HC).

AE patients had a lower rate of concordant FDG PET (p < 0.05) and required more frequently intracerebral electrodes compared to MTS patients (p < 0.05). AE had larger ipsilateral amygdala (p < 0.0001) and hippocampus volumes (p < 0.0001) compared to MTS and to HC, with no significant differences for other brain structures. Normalized FLAIR signal was higher in the ipsilateral than contralateral amygdala in both AE and MTS (p < 0.001 and p < 0.05, respectively) and higher in the ipsilateral amygdala compared to HC (p < 0.05). In MTS, ADC in the ipsilateral amygdala (867 mm²/s) was higher compared to the contralateral one (804.8 × 10^-6 mm²/s, p < 0.01), compared to HC (773 × 10^-6 mm²/s, p < 0.01) and compared to the ipsilateral amygdala in AE (813.7 × 10^-6 mm²/s, p < 0.05). AE patients had dysplasia (50%) or astrocytic gliosis (50%) of the amygdala extending to the hippocampus and temporal isocortex, and only 2/10 cases had pathologic findings of MTS.

AE patients have distinct imaging and pathologic features compared to MTS, and require more extensive preoperative workup. Recognition of AE may improve preoperative assessment in TLE surgical candidates.