The smooth pebbled appearance of the cerebral cortex with a thickened cortex and reduced and abnormal white matter, which results from migration of heterotopic neurons beyond the marginal zone into the leptomeninges through gaps in the external basement membrane. There is also enlarged ventricles, underdeveloped BRAINSTEM and cerebellum, and absence of the corpus callosum. These abnormalities occur as a syndrome without other birth defects (cobblestone complex) or in other syndromes associated with congenital MUSCULAR DYSTROPHY, often involving the eye, such as the walker-warburg syndrome, Fukuyama congenital muscular dystrophy, and muscle-eye-brain disease.