Microcephaly with a Simplified Gyral Pattern (MSG) is a congenital disorder characterized by microcephaly and shallow (reduced number of) gyri.
Lissencephaly is similar to MSG however, in lissencephaly the cortex is thick showing an abnormal architecture, both features are usually absent in MSG
MSG may show corpus callosum hypogenesis or hypoplasia, hypomylination, or periventricular nodular heterotopia
Microcephaly is classified into:
- Primary: microcephaly with normal brain architecture. The cause is likely genetic. In some cases, this primary type may show a simplified gyral pattern without cortex thickening.
- Secondary: microcephaly secondary to cerebral cortical malformation (e.g. holoprosencephaly or lissencephaly). The cause is likely secondary to brain insult, such as hypoxic ischemic insult or infection or metabolic disorder