Aspirated, crushed barium sulphate (black-appearing material) in an airway and adjacent lung parenchyma.
Barium sulphate is widely used for radiographic diagnosis of lesions in the GI tract. Small and, generally, non-birefringent crystals with smooth edges that are produced by a precipitation technique, are mainly used for studies of the colon. Crushing the naturally occurring compound produces large, birefringent, rhomboidal crystals which have rough edges. Crushed BaSO4 is used primarily for studies of the esophagus and stomach because the rough edges of the particles facilitate mucosal adherence. Small quantities of birefringent, crushed barium sulphate are sometimes added to precipitated commercial suspensions to enhance radiological contrast. This would explain why, in the experience of some, precipitated BaSO4 used for barium enemas exhibits birefringence while, in the experience of most, it does not.
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