Voxel-based morphometry reveals excess gray matter concentration in patients with focal cortical dysplasia

Many patients with focal cortical dysplasia (FCD) continue to have seizures after surgical treatment. The usual explanation for the poor surgical outcome is the presence of residual dysplastic tissue missed by the preoperative neuroimaging investigation and therefore not resected during surgery. We apply a voxel-based morphometry (VBM) analysis to the magnetic resonance imaging (MRI) scans from patients with epilepsy and visually detected FCD to investigate whether (a) VBM is able to detect gray-matter concentration (GMC) abnormalities in patients with FCD, and (b) whether the extent of GMC abnormalities in the brain of these patients differs from the regions observed by using visual inspection.

We studied 11 patients with visually detected FCD (eight of them with histologic confirmation of FCD). The GMC from each one of these patients was compared with the mean GMC from a control group of 96 normal healthy subjects by using an optimized VBM protocol.

Ten of 11 patients showed statistically significant GMC excess, and among patients with GMC excess, only one showed GMC excess that was not exactly correspondent to the visually detected FCD. Seven patients exhibited excess in GMC extending beyond the area of visually detected FCD.

This preliminary neuroimaging study suggests that (a) VBM can detect GMC excess in patients with FCD, and (b) GMC excess in these patients can extend to brain areas not visually defined as abnormal. Abnormal areas detected by VBM can possibly correspond to mild malformations of cortical development, supporting the notion that the surgical refractoriness observed in patients with FCD can be due to the incomplete resection of the dysplastic tissue.