Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Chiari malformation type 1 ?
    ### Response:
    Chiari malformation type 1 is a structural abnormality of the cerebellum, the part of the brain that controls balance. It involves the extension of the lower part of the cerebellum into the foramen magnum (the large hole at the base of the skull which allows passage of the spinal cord), without involving the brainstem.
    