Morphometrics of the preserved post-surgical hemisphere in paediatric drug-resistant epilepsy

Characterization of the postoperative structural integrity of cortex in adults who have undergone cortical resection surgery for the management of epilepsy has yielded mixed findings. In some cases, patients show persistent or accelerated cortical atrophy, while in others, atrophy decelerates or even reverses. Whether this variability applies as well to a paediatric population, for whom postoperative plasticity may be greater, remains to be determined. In this case-control study, high resolution structural T1 MRI data were acquired from 32 patients with childhood epilepsy surgery and 51 non-neurological matched controls. Using enhanced automated segmentation capabilities of FreeSurfer Software Suite, we quantified morphometrics of the preserved hemisphere at the level of gross anatomy (lateral ventricle size, volume of grey matter and white matter). Additionally, cortical thickness, volume, and surface area were measured for 34 cortical regions segmented based on the Desikan-Killiany atlas, and, last, volumes of nine subcortical regions were also measured. Morphometry comparisons were made between patients’ preserved hemisphere be it left (LH) or right (RH) against the corresponding hemisphere of age-matched, typically developing controls; and then the two patients groups (LH versus RH) were compared. Patient groups had larger ventricles and reduced total white matter volume relative to controls, and only patients with a preserved RH, but not patients with a preserved LH, had reduced total grey matter volume relative to controls. Furthermore, patients with a preserved RH had lower cortical thickness and cortical volume and significantly greater cortical surface area of several cortical regions, relative to controls. Patients with a preserved LH had largely no differences in thickness, volume, or area, of any of the 34 cortical regions, relative to controls. Moreover, both LH and RH patients showed reduced volumes in select subcortical structures, relative to controls. That left-sided, but not right-sided, resection is associated with more pronounced reduction in cortical thickness and volume and increased cortical surface area relative to typically developing, age-matched controls suggests that the preserved RH undergoes plastic processes to an extent not observed in cases of right-sided paediatric resection. Given the importance of understanding outcomes following surgery to the LH versus RH, the post-operative characterisation of morphometrics noted here provides a foundation for future work to understand differences in plasticity as a function of the side preserved post-resection. Future work probing the association of the current findings with neuropsychological outcomes will be necessary to understand the implications of these structural findings for clinical practice.