Figure 9d. Fibrous dysplasia of bone in a 28-year-old man. (a) Axial nonenhanced CT scan at the level of the pulmonary artery (P) shows an expansile mass (M) with areas of ground-glass attenuation in a left rib that indicate mineralization. (b) Axial T2-weighted (5,000/120) MR image shows heterogeneous signal intensity in the tumor (arrow). (c) Photograph of the cut surface of a resected rib specimen reveals a dense fibrous lesion (L) that has not invaded the surrounding structures. (d) High-power photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows immature osteoblasts and osteoid formation (arrowheads).