Contra-lesional hippocampus in low grade glioma patients with no hippocampal infiltration - a study of structural remodelling

Background Low grade gliomas (LGG) are slowly growing tumours which induce neuroplasticity. It was previously shown that the invasion of hippocampus by LGG may induce enlargement of contra-lesional hippocampus, including its grey matter volume (GMV) and volumes of its subfields. Our goal was to assess if similar changes may occur also in patients with LGG which do not invade hippocampus. Objective To assess grey matter volume (GMV) and hippocampal subfields of the contra-lesional hippocampus in LGG patients with no hippocampal involvement. Methods This was a retrospective study of 3D T1 MRI scans of 30 LGG patients (17 left-, 13 right-sided) without hippocampal invasion and 26 healthy controls. GMV was analysed with voxel-based morphometry (VBM) and volume of hippocampal subfields with FreeSurfer 6.0. In analysis we focused on regions previously reported in the literature to be enlarged in LGG with hippocampal infiltration. Results Contra-lesional hippocampal GMV was significantly larger in left- (T = 7.78, p < 0.05) and right-sided LGG (T = 6.39, p < 0.05). A trend towards larger hippocampal-amygdala transitional area (HATA) was seen in both groups, reaching significance in right-sided LGG (Bonferroni corrected p  = 0.04). In right-sided LGGs, trends for enlargement were also observed in GC-ML-DG head (the granule cell molecular layer of the dentate gyrus head), CA1 head, and CA3 head. Conclusions The hippocampus contralateral to LGG may undergo structural remodelling even when the ipsilateral one is not affected by tumour infiltration.