Pushing the Limits of Prenatal Ultrasound: A Case of Dorsal Dermal Sinus Associated with an Overt Arnold–Chiari Malformation and a 3q Duplication

We present a case of a fetus with cranial abnormalities typical of open spina bifida but with an intact spine shown on both ultrasound and fetal MRI. Expert ultrasound examination revealed a very small tract between the spine and the skin, and a postmortem examination confirmed the diagnosis of a dorsal dermal sinus. Genetic analysis found a mosaic 3q23q27 duplication in the form of a marker chromosome. This case emphasizes that meticulous prenatal ultrasound examination has the potential to diagnose even closed subtypes of neural tube defects. Furthermore, with cerebral anomalies suggesting a spina bifida, other imaging techniques together with genetic tests and measurement of alpha-fetoprotein in the amniotic fluid should be performed.