What is the characteristic histological finding of chronic radiation pneumonitis?

Ans. is 'a' i.e., Foam cells in vessel wall Radiation-Induced Lung Diseases Radiation pneumonitis is a well-known complication of therapeutic radiation of thoracic tumors (lung, esophageal, breast, mediastinal). It most often involves the lung within the radiation po and occurs in both acute and chronic forms. Acute radiation pneumonitis (lymphocytic alveolitis or hypersensitivity pneumonitis) occurs 1 to 6 months after irradiation in 3% to 44% of patients, depending on dose and age. It is manifest with fever, Dyspnea out of propoion to the volume of lung irradiated, pleural effusion, and infiltrates that usually correspond to an area of previous irradiation. With steroid therapy, these symptoms may resolve completely in some patients, while in others there is progression to chronic radiation pneumonitis (pulmonary fibrosis). Chronic radiation pneumonitis (pulmonary fibrosis) : The latter is a consequence of the repair of injured endothelial and epithelial cells. It may also occur without antecedent pulmonary symptoms. Morphologic changes are those of diffuse alveolar damage, including severe atypia of hyperplastic type II cells and fibroblasts. Epithelial cell atypia and foam cells within vessel walls are also characteristic of radiation damage.