Abstracts

Rationale: Hemispherotomy is a surgical disconnection of one cerebral hemisphere. This technic is widely used for the treatment of refractory epilepsy due to wide hemispheric cerebral malformations, ischemic lesions, and case affected by Rasmussen encephalitis or Sturge-Weber syndrome. Post-operative results are based on seizure freedom after hemispherotomy and on MR confirmation with the typical morphology of post-surgical scars. Diffusion tensor tractography is an extension of diffusion-based imaging, and can provide informations about white matter pathways. This technique is able to increase understanding of the effects of epilepsy on the structural organization of the brain, and can be used to optimize post-surgical evaluations in patients following hemispherotomy. Methods: After hemispherotomy patients underwent conventional magnetic resonance on a 1.5 T magnet (Achieva Nova Dual, PHILIPS).The standard protocol was followed by Diffusion Tensor Imaging sequences. Fiber tractography was used to obtain a visual hint on complete interruption of the interemispherical connections. Results: Four patients have been studied. Two male, mean age 6 years 2 months. All of them underwent hemispherotomy as treatment for refractory epilepsy. Etiology was hemimegalencephaly, Rasmussen encephalitis, hemispheric dysplasia and prenatal middle cerebral artery infarction hesitated in wide hemispheric ischemic lesion. All patients had focal seizures, one case with hemimegalencephaly had also epileptic spasms. Pre-surgical neurological examination showed hemiparesis in all cases which did not worsened in all cases but one who experienced a transient impairment after hemispherotomy. Soon after hemispherotomy all patients had seizures remission. In one case seizures reappeared after few months. Post-surgical MR with diffusion tensor imaging was performed. Fiber tractography showed a complete interruption of interemispheric connections in three out four cases studied, confirming clinical findings. Conclusions: Tractography is an extension of DTI, where by the directional information obtained in each voxel is used to generate virtual, three-dimensional white matter maps. Despite limitations tractography is the only technique available for tracing the white matter pathways in the living brain. Results of our study confirm that fiber tractography could be a valid method for post surgical assessment in patients with hemispherotomy together with EEGs and clinical follow-up.