If your doctor tells you that you have cystic lung disease, it means you have one of a group of conditions that cause lung cysts -- sacs of tissue filled with air or fluid. Treatments can help, but your options depend on which type you have. The symptoms are similar, so your doctor may suggest you get an imaging test called high-definition computed tomography (CT) to figure out which cystic lung disease you have. If that doesn't work, you may need to get a lung biopsy.