The diagnosis of<unk>  is usually made at birth or soon after by ultrasound, computed tomography (CT), or magnetic resonance imaging (MRI). However, these results should be interpreted cautiously since even experienced radiologists can misdiagnose polymicrogyria, a different developmental malformation of the brain, as<unk> . Before birth, complex ultrasounds performed routinely during pregnancy may indicate the presence of a cerebral abnormality, but this method of diagnosis should be complemented by other methods, such as genetic studies and NMR, and the examination is not recommended as part of routine ultrasound examinations, unless family medical history or other reasons for suspecting brain malformation are present. The earliest point during gestation when it is possible to observe abnormal development of the brain surface is approximately in week 20, although ultrasound examinations in week 25–30 are more common. Up to this time, the fetal brain normally has a smooth appearance. If<unk>  is suspected, chorionic villus sampling can test for some<unk>  variants, but only those with a known genetic mutation. Classification The spectrum of<unk>  is only now becoming more defined as neuroimaging and genetics have provided more insights into migration disorders. There are around 20 types of<unk>  that make up the spectrum. Other causes which have not yet been identified are likely as well. Different systems for classifying<unk>  exist. One major distinction is "classic" (type I) vs. "cobblestone" (type II), but some systems add additional forms that fit into neither of these categories. Some types of<unk>  are described below (OMIM numbers are included where available): Category Types Classic (or Type 1)<unk>  – * LIS1:<unk>  due to PAFAH1B1 gene mutation, which subdivides into: * type 1 isolated<unk>  () * Miller–Dieker syndrome () * LISX1:<unk>  due to doublecortin (DCX) gene mutation () *<unk> , type 1, isolated, without other known genetic defects * Cobblestone (or Type 2)<unk>  * Walker–Warburg syndrome (), also called HARD(E) syndrome * Fukuyama syndrome () * Muscle-eye-brain disease (MEB) () Other types * LIS2: Norman-Roberts syndrome (mutation of reelin gene, ) * LIS3: TUBA1A, * LISX2: ARX, * Microlissencephaly<unk>  and microcephaly)
Lissencephaly
Schizencephaly
Holoprosencephaly
Hemihydranencephaly
Microlissencephaly
Hydranencephaly
Microhydranencephaly
Megalencephaly