Histologic changes: Parenchyma surrounding nodules shows emphysema (pericicatricial emphysema) and mild interstitial inflammation (A). There is no type II cell hyperplasia. Bronchioles away from the nodules (left of photo) have increased black pigment, mild fibrosis, and chronic inflammation in their walls, which produce a constrictive bronchiolitis.


This section (B) shows the focal involvement of the pleura by the pigmented, cellular nodules. These lesions account for the irregularity of the pleural surface seen on CT.


Polarized light shows scattered, small, birefringent, needle-like and blocky crystals (arrows). What are these crystals? Answer

Clinical summary Image 4

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Answer: These birefringent particles are crystalline silica or silicates, or a combination. Specific identification of silica can be made by X-ray diffraction of an ashed specimen. Specific identification of silicates can be made by energy dispersive X-ray spectroscopy. These procedures are not needed for the routine histologic diagnosis of silicosis or silicatosis, but are sometimes used to confirm a diagnosis of acute silicoproteinosis when crystals are inapparent by light microscopy. Usually, the type of mineral is inferred on the basis of the histology--hyalinized nodules are caused by silica, mixed dust lesions are caused by a mixture of silica and silicates ± black dust, and silicatosis is caused by mainly silicates (see discussion).