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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. [ABSTRACT FROM AUTHOR]

DATA AVAILABILITY STATEMENT Data available on request from the authors GRAPH: Videoclip S1 Transabdominal sagittal grayscale sonography of the thorax, showing a large cyst and a significantly enlarged and hyperechoic right lung, most likely due to compression of the right main bronchus. The right lung () is hyperintense compared with the left one, most likely due to compression of the right main bronchus. gl Although IFDC is a well-known type of mediastinal cyst, an IFDC of this size is rare5. Intrathoracic foregut duplication cysts (IFDC), associated with incomplete recanalization or abnormal budding of the primitive foregut, represent approximately 10% of all mediastinal lesions1,2. [Extracted from the article]

Objectives: To describe clinical and molecular findings in a French multicenter cohort of fetuses with prenatal diagnosis of congenital abnormality and suspicion of a localized overgrowth disorder (LOD) suggestive of genetic variants in the PI3K‐AKT‐mTOR signaling pathway. Methods: We analyzed retrospectively data obtained between 1 January 2013 and 1 May 2020 from fetuses with brain and/or limb overgrowth referred for molecular diagnosis of PI3K‐AKT‐mTOR pathway genes by next‐generation sequencing (NGS) using pathological tissue obtained by fetal autopsy. We also assessed the diagnostic yield of amniotic fluid. Results: During the study period, 21 subjects with LOD suspected of being secondary to a genetic variant of the PI3K‐AKT‐mTOR pathway were referred for analysis. Of these, 17 fetuses had brain overgrowth, including six with isolated megalencephaly (MEG) and 11 with hemimegalencephaly (HMEG). Of the six with MEG, germline variants were identified in four cases, in either PIK3R2, AKT3 or MTOR, and a postzygotic PIK3R2 variant was found in the other two cases. Of the 11 with HMEG, a postzygotic PIK3CA variant was found in three fetuses with extracerebral features of PIK3CA‐related overgrowth spectrum, and in seven fetuses with isolated HMEG. No pathogenic variant was identified in the 11th case with HMEG. Four fetuses with limb overgrowth also had one or more lymphatic malformations (LM) and harbored a postzygotic PIK3CA variant. NGS on cultured amniocytes performed in 10 cases, of which nine had been found positive on analysis of pathological fetal tissue, showed variants in four, in either PIK3CA, PIK3R2 or AKT3. Conclusions: Isolated MEG or HMEG may lead to identification of genetic variants in the PI3K‐AKT‐mTOR signaling pathway. Cases of limb overgrowth and LM or isolated HMEG are likely associated with PIK3CA variants. © 2021 International Society of Ultrasound in Obstetrics and Gynecology. [ABSTRACT FROM AUTHOR]