Prenatal US and MR imaging findings of lissencephaly: review of fetal cerebral sulcal development.

The cerebral cortex develops in three overlapping stages: cell proliferation, neuronal migration, and cortical organization. Abnormal neuronal migration may result in lissencephaly, which is characterized by either the absence (agyria) or the paucity (pachygyria) of cerebral convolutions. The two main clinicopathologic types of lissencephaly may be differentiated according to their prenatal imaging features. Other cranial and extracranial abnormalities also may occur in association with lissencephaly. The prognosis is often poor, but prenatal diagnosis allows appropriate counseling and optimization of obstetric management. Familiarity with the normal ultrasonographic (US) and magnetic resonance (MR) imaging appearances of the fetal cerebral cortex at various stages of gestation is essential for the early detection of abnormal sulcal development. The primary fissures and sulci that can be examined with prenatal US and MR imaging include the parieto-occipital fissure, calcarine fissure, cingulate sulcus, convexity sulci, and sylvian fissure and insula.