Malformation producing a cranial defect at the occiput, with the brain exposed, often combined with a cervical rachischisis and retroflexion.
Source:
PAC, 2016, 88, 713. 'Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)' on page 769 (https://doi.org/10.1515/pac-2015-1202)