Neuronal migration anomalies are abnormalities of the brain tissue that result from the blockage of the migration of adult neuronal cells from the embryonic germinal matrix to the surface of the brain during cortical development, including anencephaly-megalencephaly, gray matter heterotopia, cerebral fissure malformation, polymicrocephaly, hemimegalencephaly, and local cortical dysplasia. Each type has a specific etiology, pathological changes and imaging features. So, how should neuronal migration anomalies be examined? Anencephaly-megalimbic gyrus is a disorder that occurs early in the migration of primitive neurons. Anencephaly is the complete absence of gyrus, also known as “smooth brain”, often accompanied by giant gyrus; megalencephaly is the reduction, widening and shallowing of the gyrus. Both of them belong to the same type of neuronal migration lesion with different degrees, so some people call megalencephaly a special type of anencephaly. The anencephalic gyrus shows cortical thickening, white matter thinning, and vertical lateral fissures on cranial MRI, while the megalencephalic gyrus shows thick, sparse gyrus and shallow sulci on cranial MRI. Both have cortical thickening, white matter reduction and loss of gray-white matter junction.