Occasionally, a piece of tissue in a fetus develops into lung tissue that it is not connected to the pulmonary blood supply or to the bronchial airways – and this is called pulmonary sequestration. This tissue is described as a cyst or mass. It is sometimes mistakenly diagnosed as a lung infection, and often appears in patients with other congenital thoracic malformations. A prenatal ultrasound may reveal the condition prior to birth. Without treatment, pulmonary sequestration can result in a life-threatening hemorrhage, chronic infection such as tuberculosis or even lung cancer. Surgical removal of the tissue can occur after a baby is born and usually results in the child growing up with normal lung function.