Figure 3

Histologic progression of atypical adenomatous hyperplasia (AAH). (A) Low-grade AAH characterized by small atypical cells lining a delicate interstitium. (B) In this high-grade AAH the cells are more crowded, and there is increased thickening of the septal walls. (C) This lesion demonstrates morphologic transition between high-grade AAH and an early bronchioloalveolar carcinoma. It is characterized by further cellular crowding, increased cytologic atypia and more prominent fibrosis of the septal walls. (D) In contrast to AAH, this well-differentiated adenocarcinoma shows severe cytologic atypia and overt infiltration of the lung parenchyma.