Magnetic resonance imaging (MRI) has revolutionized  the diagnosis of many disorders. It gives detailed pictures of the brain, the spinal cord, and the surrounding tissues. The MRI of patients with the Chiari I Malformation will show crowding of the foramen magnum at the bottom of the skull.

Shown above are two MRI scans. The scan on the left is normal and shows spinal fluid below the Cerebellum. The MRI on the right is that of a patient with the Chiari I Malformation. The Tonsils hang down below the foramen magnum and crowd out the spinal fluid space.