Representative photomicrograph of sheep lungs with adenomatosis. (A, B) Gross lesion showing voluminous, firm lungs with the presence of multifocal to coalescent grayish white, circumscribed nodules (arrowhead) of variable sizes embedded in the pulmonary tissue. (C-L) Microscopic lung sections stained with HandE (x200), (C) Neoplastic foci arising from the alveolar epithelium arranged in acinar pattern (arrowhead). (D) Tumor nodules composed of single to multiple layers of cuboidal to columnar neoplastic cells forming papillary projections (arrow), or cystic patterns (arrowhead). (E) Neoplastic alveoli (arrowhead) supported by fibrovascular stroma (asterisk) infiltrated with mononuclear inflammatory cells, especially lymphocytes and macrophages, surrounding the neoplastic lesions. (F) Interstitial fibrosis (asterisk) with leukocytes infiltration replacing large areas of pulmonary parenchyma. (G) Neoplastic alveoli lined with single to multiple layers of cuboidal to columnar neoplastic cells arranged in cords (arrowhead) within the alveolar spaces. (H) Neoplastic alveoli in different (cords or tubules or papillary) pattern with detached neoplastic mass (asterisk) within the alveolar spaces. (I) Tumor mass detached and completely occluded the lumen of alveoli (asterisk) along with adjacent pulmonary structure showing degenerative changes (arrow). (J) The tumor structures organized into alveoli-like formations, characterized by thin bands of stromal tissue lined by neoplastic cells (arrow) associated with presence of alveolar macrophages (arrowhead) within the adjacent alveoli. (K) Hyperplasia in the lining epithelium of the bronchiole (arrow) along with transformation of bronchial epithelium into papiliform growth almost completely filling the lumen (asterisk). (L) The bronchial epithelium shows hyperplasia (arrow) as well as prominent lymphoid nodules in the peribronchial area (asterisk).