Computed Tomographic Findings of Primary Hepatic Extraskeletal Osteosarcoma With Peritoneal Metastasis via Periportal Space in a Dog

A 15-year-old castrated male Shih Tzu presented with anorexia and lethargy. Computed tomography (CT) revealed a hepatic mass with extensive central mineralization and an ill-defined hypoattenuating peripheral zone. The periportal halo sign extending to the lesser omentum was compatible with neoplastic infiltration of the periportal space, suggesting a potential metastatic pathway via this anatomical route. Whole-body CT excluded primary skeletal involvement, and histopathology confirmed extraskeletal osteosarcoma of hepatic origin. This case illustrates the value of CT in characterizing mineralized hepatic neoplasia and identifying potential routes of intra-abdominal dissemination.