Reactive changes include atypia and mitoses in reactive seromucinous bronchial glands that may suggest malignancy; goblet cell metaplasia and squamous metaplasia of bronchial and bronchiolar epithelium (see Chapter 14); collections of macrophages containing smoker’s pigment as a result of smoking and around areas of fibrosis or mass lesions; type 2 pneumocyte hyperplasia; and mesothelial cell hyperplasia.

Nonspecific findings include peribronchial anchoring fibers and nonspecific focal peribronchial scars that may suggest interstitial fibrosis; large, dark, multilobed megakaryocytes within alveolar capillaries that may resemble viral inclusions or malignant cells; intra-alveolar fibrin that may mimic fungal hyphae; Gomori methenamine-silver (GMS) staining of mucin (which may suggest fungus when round foci of apical mucin in goblet cells or seromucinous glands are stained); collagen is often birefringent under polarized light and should not be confused with foreign material.

In exfoliative cytology specimens, Creola bodies may be present, especially in asthma but also in other reactive or inflammatory conditions involving the bronchial mucosa; Creola bodies consist of highly cellular, tightly packed papillary fragments of bronchial epithelium that may mimic adenocarcinoma; on closer inspection the absence of cytologic dysplasia of carcinoma and the presence of cilia visible along the borders indicate the benign reactive nature of the papillary fragments.