Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most common focal epilepsy and is mainly caused by hippocampal sclerosis (HS). Because the hippocampal formation is an essential part of the Papez circuit, a specific neural circuit which plays an important role for memory function, we investigated alterations of the Papez circuit network associated with HS. Diffusion-weighted MRI is a very promising tool for monitoring microstructural changes. The aim of this “proof of concept” study was to determine whether the Papez circuit can be consistently characterized by applying a new DTI method called “Global Tracking”.Methods: Whole brain “Global Tracking” based on high-angular diffusion weighted imaging in 61 directions was performed in 15 TLE-patients with unilateral (n=13) and bilateral (n=2) hippocampal sclerosis. The fiber tracts of interest, i.e. the fornix, mammillothalamic tract, and the hippocampal part of the cingulum were selected on color coded DTI images superimposed on a T1w 3D sequence.Results: Using “Global Tracking” we were able to differentiate altered subregions of the Papez circuit consistently in all hippocampal sclerosis patients including very small structures as the mamillo-thalamic tract (see image 1).Conclusions: The ability to delineate the substructures of the Papez circuit offers the basis for monitoring structural white matter changes in the latter in patients with HS. Therefore we will use the results of this study to analyze the fiber tracts of the Papez circuit by evaluating individual fiber characteristics as the streamline counts, the fiber length as well as the tract-specific diffusivity parameters. Our results support that in terms of understanding intracerebral connectivity, we have to consider focal lesions like HS in the ZNS in the context of alterations in the intracerebral network.