Diencephalic-mesencephalic junction dysplasia: case report and literature review.

Diencephalic-mesencephalic junction (DMJ) dysplasia is a rare congenital brain malformation characterized by a poorly defined junction between the diencephalon and mesencephalon, often associated with a butterfly-like contour of the midbrain on magnetic resonance imaging (MR). We report the case of a newborn female diagnosed prenatally with DMJ dysplasia who presented with severe ventriculomegaly, hydrocephalus, and oligohydramnios. Prenatal MRI at 32 weeks revealed a thickened interthalamic adhesion, an elongated midbrain with ventral cleft, aqueductal stenosis, and corpus callosum dysgenesis. Postnatal MRI confirmed these findings, along with the characteristic "butterfly" midbrain morphology. Genetic analysis revealed a pathogenic 11.9 Mb terminal deletion in the 6q25.3q27 region, encompassing candidate neurodevelopmental genes, such as DLL1, and a 3.8 Mb partial duplication in 22q13.31q13.33, of unknown significance. Parental genetic testing revealed a maternal balanced reciprocal translocation between chromosomes 6 and 22 (asymptomatic carrier), which was inherited in an unbalanced form by the proband. A ventriculoperitoneal shunt was placed within the first 48 h of life to manage hydrocephalus, with subsequent adjustments and revisions as needed. This case highlights the importance of advanced prenatal imaging and genetic testing in the diagnosis of complex brain malformations as well as the need for multidisciplinary management of rare congenital anomalies. Further research is essential to elucidate the underlying genetic mechanisms and improve the outcomes in patients with DMJ dysplasia.