What is arnold chiari malformation type one?

Mild malformation. AC type 1 involves low lying cerebellar tonsils. at the level of the foramen magnum. Usually asymptomatic and picked up as an incidental finding on work up for another condition.
Brain abnormality . This is an abnormality that is usually congenital. The back lowest compartment in the skull is slightly inadequate in size to contain the brain. The back bottom part of the cerebellum called the cerebellar tonsils protrude through the skull opening that the spinal cord passes through. This can cause pressure on the brainstem and spinal cord which can cause symptoms.