A benign neoplasm arising from glandular structures in epithelial tissue in the pulmonary parenchyma. Adenoma is derived from adeno, which means pertaining to a gland.’ It consists of distinct nodules that may compress the surrounding tissue or affect various organs. It is classified according to the cell lineage of origin. For instance, an adenoma that comes from the secretory epithelium of thyroid follicles is called thyroid adenoma.