Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Simple Kidney Cysts ?
    ### Response:
    Simple kidney cysts are abnormal, fluid-filled sacs that form in the kidneys. Simple kidney cysts are different from the cysts that develop when a person has polycystic kidney disease (PKD), which is a genetic disorder. Simple kidney cysts do not enlarge the kidneys, replace their normal structure, or cause reduced kidney function like cysts do in people with PKD.
    