Prenatal diagnosis of microcephaly with simplified gyral pattern: series of eight cases

Microcephaly with simplified gyral pattern (MSG) is an intrinsic genetic central nervous system disorder, characterized by microcephaly (a reduction of brain volume) and a simplified gyral pattern (a 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 and define the prenatal imaging pattern, which should inform diagnosis and guide prenatal counseling in cases of fetal microcephaly. In this single-center retrospective study of fetuses with MSG, we assessed features on ultrasound and magnetic resonance imaging (MRI), as well as genetic and neuropathological/postnatal data. We included eight patients who had been referred following observation of microcephaly. Ultrasound examination confirmed microcephaly, with a mean growth delay in head circumference of 3.4 weeks, associated with both a lack of gyration and a lack of opercularization of the Sylvian fissure and without any extracephalic anomaly. Fetal brain MRI confirmed lack of gyration with normal cortical thickness and normal intensity of the white matter in all cases. These MRI features led to exclusion of migration/corticogenesis disorders (lissencephaly/polymicrogyria), instead suggesting MSG. The posterior fossa was normal in seven of the eight cases. The corpus callosum was thin in four cases, hypoplastic in two and dysgenetic in two. In four cases, the pregnancy was terminated. The diagnosis of MSG was confirmed from neuropathological and postnatal MRI data. MSG was associated with a genetic diagnosis of RTTN (n = 1) and ASPM (n = 2) biallelic variants in three of the six cases in which genetic work-up was performed. Mild or moderate intellectual deficit with speech delay was present in the three surviving children who were at least 5 years of age at their last examination, without seizures. In conclusion, in the presence of isolated fetal microcephaly with lack of gyration on ultrasound, fetal cerebral MRI is key to diagnosing MSG, which, in the majority of cases, affects the supratentorial space exclusively, and to ruling out other cortical malformations that show a similar sonographic pattern. In addition to imaging, genetic assessment may guide prenatal counseling, since the prenatal prognosis of MSG is different from that of both diffuse polymicrogyria and lissencephaly. © 2023 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.