Ferruginous bodies in BAL (Bronchoalveolar Lavage).
Dumbbell-shaped, golden yellow to black with Pap stain (bottom left), blue with Perls stain (bottom right) and golden yellow with H&E (top).
Ferruginous bodies usually form around asbestos fibers but a variety of other fibers may incite the formation of similar structures. Ferruginous bodies, when seen in the lungs, are almost always indicative of asbestos exposure.
Asbestos fibers that reach the air spaces of the lungs become coated with iron, usually in a beaded fashion, forming typical ferruginous bodies that stain blue with Perls stain.
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Images contributed by Dr. Tamara Zudaire - @LangerPath