Subcortical band heterotopia is a malformation of cortical development, where there is a band of cortical cells (grey matter) located between the lateral ventricular wall and the cortex. The overlying cortex has a largely normal appearance, but may have mildly shallow sulcation. It occurs due to failure of migration of a population of neuronal cells to their correct location in the cerebral cortex. Subcortical band heterotopia is typically bilateral, symmetric and anterior-predominant. Occasionally subcortical band heterotopia can be bifrontal only, or rarely biparieto-occipital. Subcortical band heterotopia usually occurs in isolation, without other associated structural brain abnormalities, though mild cerebellar hypoplasia can occur with DCX mutations.
The clinical presentation of subcortical band heterotopia is usually with developmental and cognitive impairments, with or without seizures. The severity of cognitive impairment and seizures correlates with the thickness of the subcortical band. Seizure onset can be at any age, and can be as late as the second or third decade of life. There is a strong female predominance.