Candice Lange

Lissencephaly comprises a group of malformations caused by altered neuronal migration. It pathologically involves agyria (total loss of gyri) and pachygyria (fewer, broadened gyri).

Lissencephaly is radiologically classified into six grades, depending on the relative amounts of agyria and pachygyria, and the presence or absence of heterotopy [6].

The most frequently used and revised classification of lissencephaly includes classical lissencephaly formerly called type I and cobblestone lissencephaly formerly called type II [6, 7 and 8].

Classical lissencephaly is characterized by the presence of agyria and represents as Miller–Dieker and Norman–Roberts syndromes. Agyric regions of the cerebral cortex pathologically reveal a loosely organized four-layer cortex compared to normal six layers. It usually represents as absent or hypoplastic corpus callosum, decreased size of cerebellar hemispheres and specific craniofacial anomalies.

Cobblestone lissencephaly includes a group of syndromes, Fukuyama congenital muscular dystrophy, Walker Warburg syndrome and muscle-eye-brain disease. It is characterized by an almost complete absence of cortical layer formation and associated with hydrocephalus, brain stem and cerebellum hypoplasia, congenital eye malformations and muscular dystrophy.

The term of formerly classified type IV lissencephaly is revised (Corey was given grade 4) and divided into microlissencephaly and LCH [7, 8 and 9].

LCH involves a heterogeneous group of cortical malformations without severe congenital microcephaly (>−3 SD), but some overlap between these two groups is also expected [1]. The major cause of this heterogeneity is different gene mutations, which are responsible for gross brain malformation involving both cerebral and cerebellar cortices [8, 9 and 10]. LCH was classified into six subgroups due to phenotypic and genetic properties [1, 9 and 11]. Although existence of some distinctive phenotypic features of these subgroups, there is also some overlap between them.