Prenatal Diagnosis of Chiari III Malformation by 2D and 3D Sonography: A Case Report and Synthesis of the Literature

Chiari III malformation is the most rare and severe form of the four types of Chiari malformations. It is characterized by a high cervical meningoencephalocele and caudal displacement of the cerebellum and brainstem. The encephalocele may contain cerebellum, brainstem, cerebrospinal fluid, and rarely the occipital lobe. This case describes a fetus with a large posterior occipitocervical encephalocele diagnosed by sonography at 21 weeks' gestation. We believe this is the first reported Chiari III malformation diagnosed prenatally by sonography alone, as well as the first to describe the diagnosis using 3D sonography.