Evaluation of cerebral white-matter micro-structural alterations in patients with medically refractory epilepsy using diffusion tensor tractography

Introduction: Diffusion tensor tractography (DTT) is a newer magnetic resonance imaging (MRI) technique that helps in evaluation of white matter. Presurgical planning with tractography may be valuable for evaluation of white matter tracts and their relationship with epileptogenic focus and for evaluation of cortical fibres around the epileptogenic zone.

Methods: This study was carried out on 33 patients diagnosed with medically refractory epilepsy (males, 27; females, 6) with a mean age of 31.93 (range: 19-50) years. Twenty age and sex matched controls were also included. DTT evaluation was done using a 3.0 TexlaMRI scanner. Single-shot spin-echo echo-planar imaging (with 32-different diffusion gradient directions) was acquired for reconstruction of the white matter tracts. Diffusion metrics within fibre bundles that were reconstructed by a continuous fibre-track algorithm were compared between groups.

Results: Patients had either partial seizures (21 patients; simple partial, complex partial or secondarily generalized seizure) or generalized seizures (12 patients; tonic clonic, tonic or myoclonic). Out of the 33 patients, 23 patients were classified into the lesional group and the rest into the non-lesional group. The lesions observed on conventional MRI included focal gliosis, hippocampal sclerosis, post-hypoxic encephalopathy, calcification and post-traumatic cavitation, in various parts of the brain. Significant differences were observed in terms of fractional anisotropy and mean diffusivity values amongst controls and patients, as well as on the lesional and non-lesional side of the brain; patients with a normal conventional imaging showed fractional anisotropy and mean diffusivity changes as well.

Conclusion: We conclude that widespread diffusion abnormalities occur in the white matter tracts on the side of lesion as well as distant from the epileptic focus.