Longitudinal hippocampal and extra-hippocampal microstructural and macrostructural changes following temporal lobe...

Area of Science:

• Neuroimaging
• Epilepsy Research
• Brain Anatomy

Background:

• Temporal lobe epilepsy (TLE) surgery aims to reduce seizures but can impact brain structure and function.
• Understanding post-surgical changes in the hippocampus and connected brain regions is crucial for assessing outcomes.

Purpose of the Study:

• To investigate microstructural changes in the contralateral hippocampus using diffusion tensor imaging (DTI) after TLE surgery.
• To characterize volumetric changes in the fornix and mammillary bodies post-TLE surgery.
• To explore the relationship between these imaging changes and seizure control or cognitive function.

Main Methods:

• Longitudinal MRI scans (structural and DTI) were acquired from 25 TLE patients and 12 controls before and after surgery.
• Manual segmentation was used to define regions of interest in the hippocampus, fornix, and mammillary bodies.
• Diffusion parameters (FA, MD, AD, RD) and volumes were analyzed over time.

Main Results:

• The non-operated hippocampus showed decreased fractional anisotropy (FA) and increased mean diffusivity (MD) and radial diffusivity (RD) 1-3 years post-surgery.
• These diffusion changes occurred later than initial volume changes, suggesting ongoing microstructural alterations.
• Delayed volume loss was observed in the mammillary bodies (35%) and fornix (24%) following surgery.
• No significant correlation was found between DTI or volumetric changes and memory scores or seizure outcomes.

Conclusions:

• Post-surgical microstructural changes in the contralateral hippocampus and limbic circuits evolve over time, beyond the immediate postoperative period.
• These observed changes do not appear to be directly related to seizure control or cognitive performance in TLE patients.
• The findings suggest that TLE surgery can lead to delayed, progressive neurodegenerative changes in connected brain regions.