Histologic changes: Another feature of these lungs is the presence of light-brown, pigment-laden alveolar macrophages (A). These macrophages resemble those seen in cigarette smokers and in lungs of patients with desquamative interstitial pneumonia. Although the macrophages were most prevalent around the respiratory bronchioles in this case, they could also be found at the periphery of the acinus. They were often mixed with degenerating cells (right frame). Most did not stain for iron, but a few stained lightly, indicating a mixture of iron and other brown pigment. The latter probably represents lipoid products of cell digestion (lipochrome) in lysosomes.



B. Focal widening of alveolar walls by granulation tissue, and collections of interstitial, as well as alveolar, pigmented macrophages probably represent a later stage of the acute alveolar wall necrosis. Healing may result in resolution or scar.

Clinical summary Image 5

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