Lissencephaly is a malformation of the brain in which the brain surface is smooth rather than convoluted. The name comes from the Greek words ‘lissos’ which means smooth and ‘enkephalos’ which means brain.

The surface of the brain is formed by a complex series of ridges and valleys. The ridges are called gyri or convolutions, and the valleys are called sulci. In children with lissencephaly, the normal convolutions are absent or only partly formed, so the surface is smooth as shown in at right. Lissencephaly is usually diagnosed based on interpretation of either CT or MRI scan of the brain. It can be suspected based on ultrasound in newborn children. Several other brain abnormalities occur secondary to the lissencephaly.