Spectrum of cortical malformations on fetal MRI: A pictorial essay

The aim of this article was to illustrate the major stages in cerebral cortical development, review the spectrum of cortical malformations based on the affected developmental stage, describe the characteristics of the major cortical malformations that may be diagnosed prenatally on fetal magnetic resonance imaging (MRI), and to understand the limitations of fetal MRI. Fetal MRI may show large dysmorphic cortex in hemimegalencephaly, cortical tubers, and subependymal nodules in tuberous sclerosis, smooth featureless cortex in classic lissencephaly, bumpy cortex in cobblestone lissencephaly, ectopic gray matter in heterotopia, excessive microgyri in polymicrogyria, and transmantle cerebral clefts in schizencephaly. We conclude that fetal MRI is of major value in diagnosing many of the cortical malformations including those suspected on prenatal ultrasound. However, fetal MRI is of limited sensitivity in detecting few cortical abnormalities like microdysgenesis especially in the second trimester, as gyration continues to evolve during late pregnancy and even after birth.