Cyst in a lung. Coloured X-ray of the chest of a seven year old child showing a large hydatid cyst (round, centre right) in a lung. Hydatid cysts are caused by the larvae of the tapeworm Echinococcus granulosus. The larvae settle in the lungs, liver or brain, and cause slow-growing cysts. In the lung, the cyst may cause inflammation, chest pain, coughing up of blood and wheezing. The tapeworms usually live out their life cycle in dogs and sheep, but humans can become infected if they accidentally swallow eggs in dog faeces. The cyst can be removed surgically, or sterilised and drained.