Chiari II malformations is a structural defect at the base of the skull, where there is a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow.

Sometimes those with chiari are asymptomatic. Evanna's is not.

The classic symptoms in infants (and it varies by individual): may have difficulty swallowing, irritability when being fed, excessive drooling, a weak cry, gagging or vomiting, arm weakness, a stiff neck, breathing problems, developmental delays, and an inability to gain weight. (Clearly gaining weight is NOT an issue for Evanna!)