Interstitial lung disease. Coloured 3D computed tomography (CT) scan of a right inferior view of the lungs of a patient with interstitial lung disease (ILD). ILD is a group of lung diseases that affect the tissue in the alveoli (air sacs) of the lungs. Most of these diseases later develop fibrosis (the formation of thickened scar tissue) in the lungs. ILD results in loss of lung volume, impairing gaseous exchange and causing shortness of breath. Impaired areas are purple, co-existing emphysema is red, and relatively unaffected lung areas are shown in yellow.