Bronchiectasis of the lung, gross specimen. Bronchiectasis is a disorder in which the bronchi and bronchioles, the airways of the lungs, are dilated and distorted. This damages the tissue, making it more prone to infection. Although in some cases the cause is unknown, the most common causes are tuberculosis and the abnormal mucus secretion associated with cystic fibrosis. Smoking and recurrent lung infections may also lead to scarring of the bronchi that results in bronchiectasis. Treatment is aimed at controlling infections.