Diagnostic Imaging Features of Cranial Mediastinal Osteosarcoma in a Dog

Metastasis to the mediastinum from axial skeletal osteosarcoma (OSA) is rare in dogs, and extraskeletal osteosarcoma originating from the mediastinum is an extremely rare malignant tumor in the veterinary literature.A 12-year-old Maltese dog was presented with intrathoracic masses on thoracic radiographs.Computed tomography revealed two distinct osteoblastic cranial mediastinal masses and a bone lesion involving the second thoracic vertebra.A biopsy was performed on one of the mediastinal masses.A histopathological examination confirmed the presence of an osteoid matrix with atypical mesenchymal proliferation, consistent with OSA.Accordingly, two potential origins for the mediastinal OSA were considered: vertebral OSA with mediastinal metastasis or primary mediastinal extraskeletal OSA with vertebral metastasis.This case represents a rare occurrence of primary or metastatic OSA in an unusual anatomical location.Radiography and computed tomography examinations are useful for diagnosing tumors with mineralized opacities.