Abstracts

The structural connections of an epileptic focus influence seizure spread and may underlie epileptogenic networks. Furthermore, the integrity of the connections of cortical areas subserving cognitive functions, such as language and memory are necessary for normal function. Identification of the major connections of these abnormally and normally functioning areas will be important in planning surgical resections to maximise the chance of seizure remission and to minimise the risks of cognitive impairment.
We have used the fast marching tractography (FMT) algorithm to visualise white matter tracts from data obtained using diffusion tensor imaging (DTI) with a fractional anisotropy threshold of 0.1. We selected a seed point in the anterior parahippocampal gyrus to plot a 3D connectivity map of this area in 10 healthy control subjects. We used a novel method of seed point selection, choosing 3 adjacent seed points in the x (left-right) axis and then generating a single connectivity map by selecting in any given voxel the maximum value from the 3 maps.
The resulting connectivity maps give an indication of the structural connectivity of the anterior medial temporal lobe with connections to orbitofrontal, prefrontal, posterior parietal and occipital areas. These medial temporal lobe connections have particular relevance in temporal lobe epilepsy, both in illustrating the clinical features of some seizures and in showing pathways that may be compromised by anterior temporal lobe resection.
The use of language and memory functional MRI as a means of selecting seed points for subsequent generation of connectivity maps for these regions is a promising tool for studying the structural basis of these functional networks in the human brain in vivo. It may come to be incorporated into the presurgical assessment of temporal lobe epilepsy patients and play an important role in the prediction of language and memory deficits seen following temporal lobe resection.
[Supported by: The Wellcome Trust.]