Prenatal diagnosis of microcephaly with simplified gyral pattern: series of 8 cases.

Microcephaly with simplified gyral pattern (MSG) is an intrinsic genetic CNS disorder characterized by microcephaly and reduced number of gyri and shallow sulci associated with normal cortical thickness and neuroanatomical architecture related to a reduced number of neuronal progenitors in the germinal matrix. We report the first prenatal series of MSG to define the prenatal imaging pattern which should suggest the diagnosis and guide prenatal counselling when facing fetal microcephaly. We launched a monocentric retrospective study including sonographic and MR features as well as genetic and neuropathologic/postnatal data in fetuses with MSG. Eight patients were included, all referred for microcephaly at a mean age of 28 WG (range [23-31.5]) with a suspected diagnosis of polymicrogyria in one case, including two cases with history of microcephaly in siblings. Sonographic exam confirmed microcephaly with a mean head circumference growth delay of 3.4 weeks (between 0 and -4 SD) associated with both lack of gyration and operculation of the Sylvian fissure without any extra-encephalic anomaly. Fetal brain MR confirmed lack of gyration with normal cortical thickness and normal intensity of the white matter. Posterior fossa was normal in all cases, except one. Corpus callosum was thin in all cases, short in four cases. These MR features led to exclude migration/corticogenesis disorders (lissencephaly/polymicrogyria) and to suggest MSG. Pregnancy was terminated in four cases (between 25 and 33 WG). Diagnosis was confirmed on neuropathologic and postnatal MR data in four cases respectively, associated with a genetic diagnosis of RTTN (n=1)/ASPM (n=2) biallelic variants in the six cases in which genetic work-up was performed. Mild/moderate intellectual deficit with speech delay was present in the three living children up to 5-year-old (age range [0.25-7] at last examination) without seizure. Finally, when facing isolated fetal microcephaly with lack of gyration, fetal cerebral MR is the key exam to diagnose MSG, involving in the majority of cases exclusively the supratentorial space, and to rule out other cortical malformations demonstrating a similar sonographic pattern. In addition to imaging, genetics guide prenatal counselling since prenatal prognosis of MSG is quite different than the one of both diffuse polymicrogyria and lissencephay. This article is protected by copyright. All rights reserved.