Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Brain Aneurysm ?
    ### Response:
    A brain aneurysm is an abnormal bulge or "ballooning" in the wall of an artery in the brain. They are sometimes called berry aneurysms because they are often the size of a small berry. Most brain aneurysms produce no symptoms until they become large, begin to leak blood, or burst.
    