Certain histologic features support the diagnosis of organizing pneumonia.
Sampling:
(1) while the diagnosis can be made on a transbronchial biopsy, a wedge biopsy is more reliable
(2) diagnostic foci may migrate in time and space, with a tendency to change involvement as the disease evolves
The key histologic feature is the Masson body, which is a polypoid proliferation of fibroblasts and myofibroblasts within the lumen of alveoli and within bronchiole walls.
Additional histologic features:
(1) injury to and necrosis of the Type 1 pneumocytes lining the alveoli
(2) variable accumulation of fibrin and proteins within the lumen of alveoli
(3) relative preservation of the alveolar architecture
(4) mixed inflammation with lymphocytes, plasma cells and macrophages
(5) absence of giant cells and granulomas
In cryptogenic organizing pneumonia no cause is identified. Organizing pneumonia secondary to viral or bacterial infection may show organisms.
