INTERSTITIAL pneumonia may appear in different morphological forms and may be caused by various agents. Besides the interstitial pneumonia found in various known viral, rickettsial, fungal, and protozoal diseases,1 and besides the syphilitic pneumonia alba, there are certain forms of unknown origin which may be differentiated on morphological or clinical grounds. This group includes the following conditions:
The condition described by Hamman and Rich2 as acute diffuse interstitial fibrosis, characterized clinically by acute symptoms and histologically by fibroblastic invasion of the alveolar walls.
The disease entity called eosinophilic pneumonia (Loeffler), characterized by focal infiltrations of the interstitial tissue with eosinophilic cells.
The so-called acute interstitial pneumonitis or atypical pneumonia, which occurs mainly in adults.3
A group of diseases, including the so-called plasma cell pneumonia, the virus pneumonia of infants, and the interstitielle Pneumonie der Frühgeburten, which are possibly identical and which occur mainly in infants.4