Magnetic Resonance Imaging Features of Intravascular Osteosarcoma Affecting the Ventral Internal Vertebral Venous Plexus Causing Cervical Myelopathy in a Dog.

A 10.5-year-old male castrated Standard Poodle was referred for the evaluation of chronic C6-T2 myelopathy. MRI revealed a severe asymmetric enlargement of the ventral internal vertebral venous plexus, intervertebral/vertebral veins, and possibly the C6 basivertebral vein, with secondary mild spinal cord compression. Intravascular neoplasm, particularly lymphoma, with probable concurrent thrombus formation, was prioritized. Due to the poor prognosis and subsequent development of severe anemia and melena, the patient was euthanized. Necropsy and histopathology diagnosed cervical intravascular osteosarcoma within the ventral internal vertebral venous plexus. This case represents the first description of magnetic resonance imaging features of intravascular osteosarcoma in a canine patient.