Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Pineal cyst ?
    ### Response:
    Pineal cysts are cysts of the pineal gland which is a small organ in the brain that produces melatonin (a sleep-regulating hormone). Pineal cysts are relatively common and may be found by chance in up to 10% of people undergoing CT or MRI brain imaging. The exact cause of pineal cysts is unknown.
    