Chiari type III and IV malformations are generally fatal. Chiari malformations refer to a group of congenital abnormalities of the brain that affect the structural relationships between the cerebellum, brainstem, the upper cervical cord (craniocervical junction), and the bony cranial base. There are four main types of Chiari malformations:

https://www.emedicinehealth.com/is_having_a_chiari_malformation_life_threatening/article_em.htm