lissencephaly

the diagnosis of lissencephaly may be inferred by a lack of gyri and sulci in the third trimester. the sylvian fissure is widened, and there is incomplete opercularization of the insula. these features are rarely diagnosed with confidence, even with high resolution ultrasound, so looking for associated abnormalities may assist in making the diagnosis of lissencephaly. principal among these are colpocephaly (hydrocephaly ex vacuo) and agenesis of the corpus callosum. less commonly, microcephaly, thalamic hypoplasia, midline calcification and cerebellar dysgenesis may be noted. systemic abnormalities which have been reported in association with lissencephaly include micromelia, talipes, polydactyly, syndactyly, micrognathia, duodenal atresia, omphalocele, congenital heart disease and renal anomalies. polyhydramnios and intrauterine growth restriction are common. there is a well documented association with monosomy of the distal part of the short arm of chromosome 17 (monosomy 17p13.3) which may represent a de novo terminal deletion, unbalanced translocation or inversion. lissencephaly has also been reported in association with trisomy 18. karyotyping is therefore recommended where there is a previous history or a clinical suspicion of lissencephaly. the spectrum of abnormality incorporating lissencephaly is seen in the miller-dieker, norman-roberts, walker-warburg, and neu-laxova syndromes. there is also an association with isotretinoin exposure. lissencephaly is invariably fatal in infancy or by early childhood.