Pathologically, cryptogenic organizing pneumonia was defined by the presence of granulation tissue in the bronchiolar lumen, alveolar duct
, and some alveoli, associated with a variable degree of interstitial and air space infiltration by mononuclear cells and foamy macrophages [1-3].
Organizing fibroblastic tissue within airspaces, particularly in alveolar ducts
fibrosis), may be seen in organizing DAD but does not constitute the dominant findings, as in cases of OP.
(28,29) Inflammation is followed by the formation of loose nonnecrotizing epitheliod cell granulomas in the bronchiolar wall and alveolar ducts
. (29) In chronic HP, peribronchiolar and alveolar fibrosis often occurs.
Abbreviations: a, alveolus; AD, alveolar ducts
; BV, blood vessel; TB, terminal bronchioles.
Thus, the acinus cannot be identified on a normal gross specimen but would require a 3-dimensional process to visualize the conelike arrangement of 3 generations of respiratory bronchioles with their branches of alveolar ducts
, alveolar saccules, and alveoli.
Additionally, there is evidence of bronchiolar metaplasia of the alveolar ducts
(Pinkerton et al.
Sometimes there is accompanying mild fibrosis of the walls of the respiratory bronchiole, more distal alveolar ducts
, or surrounding alveolar walls, although historically the question of how much fibrosis has been allowed in RB as opposed to RBILD is poorly defined and certainly confused (see below).
For each emission wavelength, we photographed five images from the proximal alveolar region, which are alveoli located near the first alveolar ducts
from the terminal bronchioles, the alveolar region most affected by particle deposition.
The last case of anti-KS disease demonstrated an OP pattern, with young granulation tissue plugs filling the lumens of small airways and tracking down alveolar ducts
to distal airspaces, resulting in cords of branching, arborizing granulation tissue at low magnification (Figures 3 and 4).
These mice progressively accumulated soot, primarily in alveolar macrophages, and septal fibrosis and bronchiolization of alveolar ducts
were observed in areas of soot accumulation.
Once initiated, the process, powered by the increasing disparity between the enlarging alveolar ducts
and the collapsing small alveoli that surround them, is more likely to continue.
The following histologic features were evaluated using a semiquantitative scale: macules, defined as collections of dust-laden macrophages in a size range of 0.1-0.6 mm within the walls of respiratory bronchioles and adjacent alveoli; nodules, defined as fibrotic lesions up to 1 cm in size with round, irregular, or serpiginous borders and containing dust-laden macrophages; and interstitial fibrosis, defined as diffuse or irregular fibrosis of alveolar septa and/or alveolar ducts
In Figure 1, A and B, normal lung parenchyma is shown for comparison, with its delicate, intact alveolar septa and open, aerated alveoli and alveolar ducts
. In contrast, lungs involved with diffuse alveolar damage exhibit widened alveolar septa, reduced numbers of aerated airspaces, and other histologic changes of injury, including the presence of hyaline membranes lying within airspaces, and type II pneumocyte hyperplasia (Figure 1, C through E).
In terms perhaps more useful for the pathologist on a daily basis, the term small airways includes membranous bronchioles, respiratory bronchioles, and alveolar ducts
(29,36) (Figures 1 and 2).
Hyaline membranes are composed of cellular and proteinaceous debris and appear as dense, glassy eosinophilic membranes lining the alveolar ducts
and alveolar spaces (Figure 1).