Significance of crystalline inclusions in lung granulomas

We describe six examples of nonnecrotizing lung granulomatosis in which there were numerous polarizable crystalline inclusions. The crystals were easily visible in routine H&E-stained slides and were so prominent that the question of a pneumoconiosis or other exogenous source was raised. There was no clinical history to suggest an inhalational source, however, and no patient used intravenous drugs. In one case, an atypical mycobacterial infection was proven to be etiologic, while sarcoidosis was documented in three. A review of 63 additional consecutive lung biopsies and 24 extrapulmonary biopsies showing nonnecrotizing granulomatous inflammation demonstrated crystals in almost two-thirds of cases. X-ray spectroscopy and histochemistry demonstrated that the crystals contained mainly calcium oxalate and calcium carbonate and thus represented products of cellular metabolism. These findings emphasize that crystalline inclusions are common in lung granulomas of varying etiology. They may be numerous, and their presence does not necessarily indicate a pneumoconiosis or other exogenous source.