Case Report: Osteosarcoma following traumatic injury in a juvenile Argentine black and white tegu (Salvator merianae).

Osteosarcoma (OSA) is a malignant neoplasm of mesenchymal origin characterized by osteoid or immature bone production and is rarely reported in reptiles. A 3-month-old Argentine black and white tegu presented with a subcutaneous mass on the left flank, approximately 2 months after a dog bite. Physical and radiographic examination revealed no initial internal abnormalities, but follow-up examination revealed a rapidly enlarging soft tissue mass. Ultrasonography confirmed a well-encapsulated mass, while contrast-enhanced computed tomography demonstrated mineralization, rib osteolysis, and multiple bilateral nodules, indicating a malignant process. Histopathological examination of the excised mass demonstrated features consistent with giant cell-rich osteosarcoma, including irregular bony trabeculae, numerous multinucleated giant cells, and peripheral osteoid matrix. This case highlights the diagnostic challenges of OSA in reptiles, the value of integrating diagnostic imaging and histopathology, and the need for species-specific imaging protocols in ectothermic species, thereby expanding the literature on reptilian neoplasia.