Abstracts

Rationale: Gray matter heterotopia are epileptogenic disorders of neuronal migration characterized by subcortical regions of misplaced neurons. Although the genetic and molecular bases of these conditions are increasingly understood, the relationship between the abnormal gray matter anatomy and functional outcomes, including cognitive ability, is still relatively unexplored. We performed a quantitative investigation of anatomical brain volumes in gray matter heterotopia to study the effect of migration failure on cognitive function. Methods: Fifteen adult epilepsy subjects with periventricular or subcortical forms of gray matter heterotopia were studied using high-resolution structural brain magnetic resonance imaging. Gray matter, white matter, and cerebrospinal fluid tissue compartments were segmented, followed by manual delineation of heterotopic and cortical gray matter subcompartments. Volumetric analysis was performed for each subject and correlations with full-scale intelligence quotient (FSIQ) and other cognitive measures were examined. Results: Total heterotopia volume varied widely, but on average occupied about 4% of total gray matter volume in these subjects. There was a significant negative correlation between total heterotopia volume and total cortical gray matter volume. There was also a significant negative correlation between the proportion of heterotopic gray matter and FSIQ, although this appeared to be driven by subjects with large subcortical bands. Conclusions: Neuronal migration disorders are characterized by regions of misplaced gray matter with quantifiable volume. Larger heterotopia volumes are associated with smaller cortical gray matter volumes, a finding consistent with the notion that heterotopia contain neurons that would normally have migrated to the cortex. A greater degree of migration failure may also be associated with more impaired cognition, but further study is required.