Abstracts

In a previous study we demonstrated bilateral symmetrical abnormal diffusion of water molecules in the major pathways of the limbic system (i.e. fornix and cingulum) in a group of eight patients with temporal lobe epilepsy (TLE) and unilateral mesial temporal sclerosis (MTS) using diffusion tensor magnetic resonance imaging (DTI) [Concha et al. 2005, Ann. Neurol;57:188-196]. While the pattern of diffusion change suggested diffuse axonal damage within the limbic system, fluid shifts (which can occur due to ongoing seizures) can result in similar findings. The purpose of the present study was to determine whether limbic DTI abnormalities are still observed in patients with TLE and MTS who are seizure free following surgery. Three patients (who were included in our previous study) were scanned at one year following surgery using the same CSF-suppressed DT-MRI protocol. All three patients had pathological confirmation of MTS and were seizure free at one year follow-up. Virtual dissection (tractography) of the crus of the fornix (contralateral to the resection) and the cingulum (bilateral) was performed and fractional anisotropy (FA) measurements were obtained from the resulting structures. The ipsilateral fornix was not analyzed due to variability in the extent of surgical resection. The diffusion anisotropy estimates were compared to their pre-operative values. None of the patients had an increase in the post-operative FA value of the contralateral fornix. All patients demonstrated a further reduction in FA of the ipsilateral cingulum while FA of the contralateral cingulum demonstrated mixed findings. Seizure freedom did not translate into increased diffusion anisotropy relative to pre-operative scans. This implies that our previous findings were not due to a reversible cause (i.e. fluid shift) and would be most consistent with structural axonal abnormalities. Whether these findings in the fornix and cingulum are a cause or consequence of MTS and TLE remains to be elucidated. Of interest, further reduction of FA in the ipsilateral cingulum suggests axonal degeneration downstream of the resection.[table1] (Supported by Savoy Foundation, Alberta Heritage Foundation for Medical Research, Canadian Institutes of Health Research and Promep.)