Abstracts

Rationale: Temporal lobe resection is an effective treatment for pharmacoresistant forms of temporal lobe epilepsy (TLE) with unilateral hippocampal sclerosis. Several studies reported changes in the white matter architecture following temporal lobe resections in patients with TLE at short intervals after surgery. To investigate how the Fractional Anisotropy, as a marker for the integrity and strength of white matter fiber tracts, develops after surgery, we included left-sided TLE patients before and at two different times after surgery (3-6 months and about 12 months) and investigated the diffusion weighted MR images applying Tract-based spatial statistics (TBSS). Methods: We investigated 20 patients with intractable left-sided TLE by applying TBSS on diffusion weighted MR images aquired before and after temporal lobe resection. The patients were scanned postoperative at an early (about 4 months, range 3-6 months; N13) and a late (about 12 months, range 10-23 months; N13) interval after surgery to investigate the postsurgical plasticity. Results: We observed an ongoing loss of fiber tract integrity mainly in the ipsilateral temporal fiber tracts: hippocampal part of the cingulum, stria terminalis of the fornix and in the late group also the uncinate fasciculus. In the late postoperative outcome group a significantly more widespread pattern of FA reduction in comparison to the preoperative data was observed than in the early postoperative scans. Conclusions: Our results suggests that the decline of white matter tracts directly associated to the resected epileptogenic focus is continuing over at least one year after surgery. Thus, our data shows that the remodeling of brain connectivity after surgical interventions continues and that structural alterations and modifications of the white matter architecture are progressive and long lasting. The remodelling seems to be essentially but not solely characterized by the loss of fiber tract integrity. Further longitudinal studies including larger sample sizes investigated over prolonged time periods after surgery are needed to identify the time course of white matter remodelling after TLE surgery in detail and its association to seizure and cognitive outcome.