Fig 1a: Dorsomedial view of the mass at first clinical inspection. Fig 1b: Dorsopalmar radiograph of the third metacarpal bone. There is excessive bone production with trabeculae and bone lysis centered on the proximomedial aspect of the left third metacarpal bone. Fig 1c: Dorsomedial - palmarolateral oblique radiograph showing periostal reaction at the diaphyseal aspect of the second and third metacarpal bone. Centrally there is a radiolucent zone (lysis) at the palmaromedial edge of the third metacarpal bone and at the dorsal edge of the second metacarpal bone.
Fig 2: Histological slides with hematoxylin (A) and eosin (B) staining of the mass. Multiple partially mineralized bone trabeculae (black arrow) are present. In between the trabeculae, there is a dense proliferation of fibroblasts forming bundles and vortices. The fibroblasts have an oval nucleus with fine-grained chromatin and an indistinctly delineated, fibrous eosinophilic cytoplasm. Occasionally, there are osteoclasts (asterisk) and some large dilated veins. Morphologically the mass is diagnosed as a peripheral fibroblastic osteosarcoma .