Chiari Malformation

Chiari malformation is a relatively common occurrence. It is not necessarily a disease, nor is it truly a malformation. It perhaps should be considered, in the adult form (Chiari I malformation), to be a variant of normal. Its diagnosis is established by observing the cerebellar tonsils to be below the foramen magnum on MRI studies. Depending on the examiner's definition of the Chiari I malformation (as assessed by the amount of descent below the foramen magnum in mm), the incidence of the diagnosis may vary considerably. The extent of descent of cerebellar tonsils, however, does not necessarily correlate with symptoms, physical findings, or neurological findings. The co-existence of a Chiari I malformation with syringomyelia indicates that the Chiari I malformation has physiological significance. However, this does not necessarily imply that surgery is indicated.