Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Hydranencephaly ?
    ### Response:
    Hydranencephaly is a rare condition in which the brain's cerebral hemispheres are absent and replaced by sacs filled with cerebrospinal fluid. An infant with hydranencephaly may appear normal at birth. The infant's head size and spontaneous reflexes such as sucking, swallowing, crying, and moving the arms and legs may all seem normal.
    