The acute/exudative phase is usually readily recognized by the presence of eosinophilic hyaline membranes
, along with intra-alveolar edema, capillary congestion, and interstitial widening (Figure 1).
The clinical course and the documented complications, some of them defining AIDS, would be sufficient to explain the poor outcome but the autopsy opened an unexpected underworld: Kaposi sarcoma was confirmed in the stomach and colon but also in the esophagus and mediastinal lymph nodes (Figure 1(b)); Candida species was found in the anal canal, colon (Figure 1(c)), and lung, where hyaline membranes
compatible with an acute respiratory distress syndrome were also seen (Figure 1(d)).
were present focally (Figure 4(g)).
Diffuse alveolar damage (DAD) is a pathology term that describes the presence of alveolar fibrin, hyaline membranes
and reactive epithelial cells within alveoli, with varied stages of inflammation.
RBCs and leukocyte infiltrates were seen in 13 and alveolar hyaline membranes
in 9 cases.
The presence of viral inclusions in the lungs with interstitial inflammation, hyaline membranes
, and giant cells is generally accepted as a diagnostic finding for CMV and MV pneumonia, respectively, despite the extent of virus-infected cells present.
The most common histopathologic finding was diffuse alveolar damage comprising intraalveolar edema, hyaline membranes
, fibrin, and hemorrhage.
Microscopic findings have included interstitial infiltrates of mononuclear cells in the alveolar septa, congestion, septal and alveolar edema with or without mononuclear cell exudate, focal hyaline membranes
, and occasional alveolar hemorrhage.
Radiologically, the early exudative phase shows bilateral and patchy ground-glass densities, corresponding to interstitial edema and hyaline membranes
. The geographic distribution of the patchy ground-glass densities, together with areas of lobular sparing and lower lobe consolidation, serve as radiologic hallmarks.
(3) Procoagulation is a critical factor in DAD, as evidenced by the presence of fibrin-rich hyaline membranes
, intra-alveolar fibrin, and in situ vascular thrombosis.
Pulmonary congestion with edema was note& but hyaline membranes
had not formed (Figure A).
The pathologic stages of ALI/ARDS or diffuse alveolar damage can be divided into 3 subsequent and somewhat overlapping phases: (1) exudative phase, characterized by neutrophilic infiltrate, hemorrhage, and the accumulation of a protein-rich pulmonary edema; (2) fibroproliferative phase, including chronic inflammation, early fibrosis, resorption of hyaline membranes
, and neovascularization; and (3) recovery phase, seen in surviving patients.