Bilateral Structural Network Abnormalities in Epilepsy Associated With Bottom-of-Sulcus Dysplasia.

Objective: To identify white matter fibre tracts that exhibit structural abnormality in patients with bottom-of-sulcus dysplasia (BOSD), and investigate their association with seizure activity. Methods: Whole-brain fixel-based analysis of diffusion MRI data was performed to identify white matter fibre tracts with significant reductions in fibre density and cross-section in BOSD patients (n = 20) when compared to healthy control participants (n = 40). Results from whole-brain analysis were used as priors to investigate the association of fibre tract abnormality with seizure frequency and epilepsy duration. Results: Despite the focal nature of the dysplasia, BOSD patients showed widespread abnormality in white matter fibre tracts, including the bilateral corticospinal, corticothalamic, and cerebellothalamic tracts, superior longitudinal fasciculi, corpus callosum (body) and the forceps major. This pattern of bilateral connectivity reduction was not related to the laterality of the lesion. Exploratory post-hoc analyses showed that high seizure frequency was associated with greater reduction in fibre density at the forceps major, bilateral corticospinal and cerebellothalamic tracts. Conclusions: We demonstrate evidence of a bilaterally-distributed, specific white matter network that is vulnerable to disruption in BOSD. The degree of tract abnormality is partly related to seizure activity, but additional contributors such as the genetic background and effects of treatment or environment have not been excluded.