Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) cerebral cavernous malformation ?
    ### Response:
    Cerebral cavernous malformations are collections of small blood vessels (capillaries) in the brain that are enlarged and irregular in structure. These capillaries have abnormally thin walls, and they lack other support tissues, such as elastic fibers, which normally make them stretchy.
    