Sonography of fetal holoprosencephaly: a guide to recognize the lesser varieties

Background: Alobar holoprosencephaly (HPE) is easily detected during a first-trimester screening examination, conversely, recognizing the lesser varieties may be difficult even in the second trimester. Objectives: To describe the imaging findings of a cohort of fetuses with holoprosencephaly (HPE) and to elucidate the appearances of the different anatomical varieties. Materials and methods: We reviewed medical records and stored images of pregnant women referred to our clinic because of a diagnosis or the suspicion of various forms of HPE. We reported the imaging characteristics, the presence of other associated anomalies, magnetic resonance findings, karyotype and autoptic examinations when available. Results: Alobar forms show great distortion of normal brain anatomy, with a single ventricle detectable during the first trimester of pregnancy. Extracerebral, face and karyotype abnormalities are often associated. In semilobar and lobar forms the septum pellucidum is typically absent in axial planes, with fused frontal horns, while posterior fossa is often normal. At multiplanar neurosonogram, anomalies involving corpus callosum and cortex development can be detected. Face abnormalities are mild in lobar forms: receding forehead, various degrees of hypotelorism and the presence of a single central maxillary incisor are reported. Conclusions: The alobar forms are detectable since the first trimester, with a peculiar single ventricle and extremely frequent extracerebral and karyotype abnormalities. The semilobar and lobar forms are more challenging and the diagnosis is easily missed in a mid-trimester screening exam unless a careful evaluation of both cavum septi pellucidi and frontal horns as well is conducted.