Amygdala subnuclear volumes in temporal lobe epilepsy with hippocampal sclerosis and in non-lesional patients

Abstract

Together with hippocampus, the amygdala is important in the epileptogenic network of patients with temporal lobe epilepsy. Recently, an increase in amygdala volumes (i.e., amygdala enlargement) has been proposed as morphological biomarker of a subtype of temporal lobe epilepsy patients without MRI abnormalities, although other data suggest that this finding might be unspecific and not exclusive to temporal lobe epilepsy. In these studies, the amygdala is treated as a single entity, while instead it is composed of different nuclei, each with peculiar function and connection. By adopting a recently developed methodology of amygdala’s subnuclei parcellation based of high-resolution T1-weighted image, this study aims to map specific amygdalar subnuclei participation in temporal lobe epilepsy due to hippocampal sclerosis (n = 24) and non-lesional temporal lobe epilepsy (n = 24) with respect to patients with focal extra temporal lobe epilepsies (n = 20) and healthy controls (n = 30). The volumes of amygdala subnuclei were compared between groups adopting multivariate analyses of covariance and correlated with clinical variables. Additionally, a logistic regression analysis on the nuclei resulting statistically different across groups was performed. Compared to other populations, temporal lobe epilepsy with hippocampal sclerosis showed a significant atrophy of the whole amygdala (pBonferroni = .040), particularly the basolateral complex (pBonferroni = .033), while the non-lesional temporal lobe epilepsy group demonstrated an isolated hypertrophy of the medial nucleus (pBonferroni = .012). In both scenarios, the involved amygdala was ipsilateral to the epileptic focus. The medial nucleus demonstrated a volume increase even in extra temporal lobe epilepsies although contralateral to the seizure onset hemisphere (pBonferroni = .037). Non-lesional patients with psychiatric comorbidities showed a larger ipsilateral lateral nucleus compared to those without psychiatric disorders. This exploratory study corroborates the involvement of the amygdala in temporal lobe epilepsy, particularly in mesial temporal lobe epilepsy and suggests a different amygdala subnuclei engagement depending on the etiology and lateralization of epilepsy. Furthermore, the logistic regression analysis indicated that the basolateral complex and the medial nucleus of amygdala can be helpful to differentiate temporal lobe epilepsy with hippocampal sclerosis and with MRI negative, respectively, versus controls with a consequent potential clinical yield. Finally, the present results contribute to the literature about the amygdala enlargement in temporal lobe epilepsy, suggesting that the increased volume of amygdala can be regarded as epilepsy-related structural changes common across different syndromes whose meaning should be clarified.

The role of the amygdala in ictal central apnea: insights from brain MRI morphometry

“…Of note, considering the presence of hippocampal sclerosis, only one ICA‐TLE patient presented with this radiological finding, while this was evident in five noICA‐TLE patients. As already reported in the literature, it was demonstrated that HS was significantly associated with volumetric reduction of the ipsilateral amygdala and, in particular, of the BLA 27 . It could be argued that amygdalar atrophy could partially explain the volumetric differences between these two groups.…”

Amygdala dismantled: the role of amygdala subregions in epilepsy

“…Recently in Brain Communications , Ballerini et al . 2 add further evidence to the above by ‘dismantling’ the amygdala. Previous studies 3 , 4 already demonstrated trophic changes of the amygdala as a whole, in patients with temporal lobe epilepsy (TLE).…”

“…The current study by Ballerini and colleagues 2 has limitations. While the subregional amygdala segmentation is clearly an advance, its validity in people with epilepsy still needs to be established.…”

“…The amygdala has initially received some attention in the field of psychiatry, where amygdala volume enlargement was identified in people with psychosis. Ballerini and colleagues 2 also found the association of amygdala hypertrophy affecting the ipsilateral lateral nucleus with psychiatric comorbidities. Although the exact mechanisms underlying these changes are not understood, they highlight the importance of the amygdala as an affective processing hub.…”

“…The work of Ballerini et al . 2 adds important building stones to modern epilepsy neuroimaging research on top of its established foundations. Dismantling the amygdala into its subregions, allowed for the recognition of focal changes that are hidden for visual analysis.…”