Arnold Chiari is defined as:
Chiari malformation (also called Arnold-Chiari malformation) is a rare congenital anomaly in
which two parts of the brain, the brainstem and the cerebellum, are longer than normal
and protrude down into the spinal canal. Chiari malformation may be
associated with many other anomalies including myelomeningocele,
syringomyelia, and spina bifida. Hydrocephalus (increased intracranial
pressure) may also occur. In most cases, symptoms begin during infancy,
however onset of symptoms may be delayed until adolescence or adulthood.
Symptoms usually include vomiting, muscle weakness in the head and face,
difficulty swallowing, and varying degrees of mental impairment. Paralysis
of the arms and legs may also occur.
Adults and adolescents with Chiari malformation who previously were
asymptomatic may show signs of progressive brain impairment as they grow
older, such as involuntary, rapid, downward eye movements. Other symptoms
include dizziness, headache, double vision, deafness, an impaired ability to coordinate movement, and episodes of acute pain in and around the eyes. (thanks WACMA for the definition)
My Non clinical definition-I have a brain that is sagging lower than usual, constricting the cerebral spinal fluid. This sometimes can cause symptoms,
some not. The symptoms can vary from individual to individual as well.
To be accurately diagnosed, you need to get an MRI of the brain.
Full spine MRI is also suggested.