The term Chiari malformation describes a congenital structural abnormality of the base of the brain called the cerebellum.
A Chiari malformation is characterized by downward displacement of the inferior cerebellum into the upper cervical spinal canal, and may be associated with crowding and compression of nearby structures against the immobile skull base.
The Chiari malformation is sometimes diagnosed as an incidental finding when an imaging study is performed for an unrelated problem. Chiari malformations that are asymptomatic at the time of initial diagnosis may become symptomatic later.
The Chiari I malformation is usually an isolated abnormality, while the Chiari II malformation is almost always associated with a myelomeningocele (open spina bifida) at birth, hydrocephalus and other abnormalities of the nervous system. Both types of Chiari malformations may present with headache, progressive scoliosis (curvature of the spine), or a variety of other neurological problems.
The Chiari I malformation is occasionally associated with other neurosurgical conditions such as hydrocephalus and syringomyelia (excess cerebrospinal fluid in the brain and spinal cord, respectively).
The standard treatment of a symptomatic Chiari malformation involves surgery to make more room for the crowded cerebellum by removing surrounding bone and fibrous tissue. In carefully selected patients, the procedure is quite effective. Not everyone with a Chiari malformation on imaging studies requires surgery. Each child is evaluated individually to assess whether surgery is indicated.