CT Features of an Extraskeletal Osteosarcoma Associated With a Retained Surgical Sponge in a Dog

An 8-year-old neutered female Labradoodle presented with acute restlessness and inability to stand. Point-of-care ultrasound revealed a large abdominal mass, prompting further imaging. Computed tomography (CT) demonstrated a mass with marked mineralization, a thick, enhancing rim, and signs of intra-abdominal dissemination. Surgical excision of the mass was performed, and histopathology confirmed extraskeletal osteosarcoma (ESOSA) secondary to a retained surgical sponge (gossypiboma). Four months post-surgery, the dog developed pulmonary metastases and was euthanized. This report is the first to describe CT findings of ESOSA secondary to a retained surgical sponge in a dog.