Figure 9a. Focal interstitial fibrosis in a 40-year-old woman. (a) Thin-section CT image at the level of the superior segmental bronchus shows a 25-mm well-defined nodular ground-glass opacity with no solid component in the lower lobe of the left lung. (b) Photomicrograph of a histologic specimen (original magnification, x40; hematoxylin-eosin stain) shows the lesion (arrow) with alveolar septal thickening and fibrosis and with intraalveolar infiltration by inflammatory cells. (c) High-power photomicrograph (original magnification, x200; hematoxylin-eosin stain) shows fibrosis of the alveolar wall, with intraalveolar lymphocytes and denuded pneumocytes (arrows).