Figure 11b. Atypical adenomatous hyperplasia in a 44-year-old man. (a) Transaxial thin-section (1-mm collimation) CT scan (lung window) shows an 8-mm focal nodular area of ground-glass attenuation in the right upper lobe (arrow). The nodule did not change in size over a follow-up period of 12 months. (b) High-power photomicrograph (original magnification, x100; H-E stain) shows atypical epithelial cell proliferation along thickened alveolar septa (arrows), findings that indicate atypical adenomatous hyperplasia.