Middle interhemispheric variant of holoprosencephaly in a 21-week fetus: a case report

Abstract

Highlights: Middle interhemispheric variant (MIH) is a rare subtype of holoprosencephaly (HPE). The differential diagnosis between variants of HPE may be difficult. Prenatal MRI has a fundamental role in the diagnosis. Careful attention to specific neurosonographic features can help in early diagnosis. Holoprosencephaly (HPE) is the most common malformation of the forebrain in humans. It is a structural anomaly of the brain resulting from failed or incomplete forebrain division in the fourth week of gestation. According to De Myer’s classification, three types of HPE, of increasing severity, are described: lobar, semilobar and alobar. Milder subtypes of HPE include the middle interhemispheric (MIH) variant, also known as “synthelencephaly”, which is characterized by a midline connection of the two hemispheres in posterior frontal and parietal regions with separation of the anterior frontal and occipital lobes. Most severe HPE cases are diagnosed by ultrasound examination (US) and magnetic resonance imaging (MRI) during pregnancy. We present a case of MIH variant, diagnosed in a 21-week fetus by US and confirmed by MRI.