Organizing pneumonia (OP) is a nonspecific term for proliferations of fibroblastic tissue within small airways, alveolar ducts, and alveolar spaces.
(36,37) Diffuse alveolar damage may contain organizing fibroblastic tissue within alveolar ducts in particular, but this is not the dominant finding, and OP lacks the hyaline membranes or acute DAD and does not show the prominent interstitial myxoid fibrosis or prominent type 2 pneumocyte hyperplasia of the organizing phase of DAD.
All four mouse labs observed that Ti[O.sub.2]-NB caused an inflammatory response at the terminal bronchiol ar region and the alveolar duct bifurcation region of the distal lung in mice 1 day after OPA delivery (Figure 2).
(A, D, G, J, B, E, H, K Bright-field light microscopy of representative sections of lung from control mice (A, D, G, J) and Ti[O.sub.2]-NB-exposed mice (B, E, H, K); sections from Ti[O.sub.2]-NB-exposed mice show inflammatory lesions primarily localized to alveolar duct bifurcations.
In paraseptal emphysema, almost the entire proximal part of the acinus is normal, whereas distal
alveolar ducts and sacs are abnormal (Figure 4).
Differentiated bronchiolar epithelium in
alveolar ducts of rats exposed to ozone for 20 months.
Organizing pneumonia: loose fibromyxoid plugs of granulation tissue with stellate myofibroblasts-filled
alveolar ducts and airspaces with mild alveolar septal mononuclear infiltrate (hematoxylin-eosin, original magnification X200).
Species with branching respiratory bronchioles between the terminal bronchiole and
alveolar ducts have more complex acini.
Axial dispersion in respiratory bronchioles and
alveolar ducts. J Appl Physiol 64(6): 2614-2621 (1988).
The changes involve terminal bronchioles, respiratory bronchioles, and
alveolar ducts. Predominantly respiratory bronchiole involvement is a distinctive feature of diffuse panbronchiolitis, as other forms of constrictive bronchiolitis predominantly affect membranous bronchioles.
Organizing fibroblastic tissue may be observed in air spaces, particularly the
alveolar ducts (
alveolar duct fibrosis), but this feature is typically not prominent and does not constitute the dominant finding as seen in cases of OP.
In the original article of Myers et al, (1) the major pathologic finding was the presence of RB: clusters of slightly golden colored alveolar macrophages ("smoker's macrophages") in the lumens of respiratory bronchioles,
alveolar ducts, and in the surrounding alveoli.
