FIG. 5.

Specimens collected from the mass where it abutted the pleura between the fourth and fifth ribs. A: Cystic spaces, some containing residual blood and separated by fibrous septa containing occasional osteoclast-like giant cells, are characteristic of an ABC. Basophilic reticulated chondroid-like foci, another common feature, appear in the center of the image. There is no atypia. B: In some areas, trabeculated osteoid and woven bone surrounded by activated osteoblasts predominate. Mitotic activity is minimal, and atypia is absent. Hematoxylin and eosin. Bar = 50 μm.