[Radiation pneumonitis. Morphology and pathogenesis].

Radiation-induced pulmonary damage is an inflammatory process which progresses in stages. The quantity rather than quality of pulmonary reactions depends on the given radiation dose. Damage to endothelial cells of capillaries and of respiratory epithelium is the initial event in the development of radiation pneumonitis. Release or activation of cytogenic and serum-derived mediators, increased permeability of the capillary wall, and damage to pneumocytes II are the most important factors in pathogenesis. There is no morphological latent stage. The latency between exposure to irradiation and manifestation of clinical symptoms of pneumonitis may be explained by the morphologic findings. Several non-radiation-induced lung diseases are predisposing factors. There is a tendency to bacterial, viral or mycological superinfections in patients with radiation pneumonitis. Radiotherapy leaves behind a latent pulmonary lesion with continuously changing reactions to most various irritations.