Diffusion and volumetry abnormalities in subcortical nuclei of patients with absence seizures

The thalamus and basal ganglia play an important role in the propagation and modulation of generalized spike and slow-wave discharges (SWDs) in absence epilepsy. Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) technique sensitive to microstructural abnormalities of cerebral tissue by quantification of diffusion parameter. The purpose of this study is to investigate the diffusion and volume changes in the basal ganglia and thalamus of patients with absence seizures.

In 11 patients with absence seizures and 11 controls, the thalamus, caudate nucleus, putamen, and pallidum were segmented using an automated atlas-based method on the DTI and three-dimensional (3D) anatomic T₁ -weighted images. Then the fractional anisotropy (FA), mean diffusivity (MD), and volume were extracted and quantified.

Compared with controls, patients reveal increased MD values bilaterally in thalamus, putamen, and left caudate nucleus; increased FA value in bilateral caudate nuclei; and loss of volume in bilateral thalamus, putamen, and pallidum. Significant correlations were observed between age of onset and diffusion parameter alterations in caudate nucleus or putamen.

These findings provide preliminary evidence demonstrating that microstructural changes of subcortical structures are related to the chronic abnormal epileptic activity, and add further evidence for the involvement of thalamus and basal ganglia in propagation and modulation of SWDs in absence epilepsy. These results also indicate that DTI is more sensitive for detection of abnormal structure than the conventional MRI, and it may be adopted as a noninvasive means to understand the pathophysiologic evolution of absence seizures.