Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Chiari Malformation ?
    ### Response:
    Chiari malformations (CMs) are structural defects in the cerebellum. The cerebellum is the part of the brain that controls balance. With CM, brain tissue extends into the spinal canal. It can happen when part of the skull is too small, which pushes the brain tissue down.
    