Cranial and vertebral osteosarcoma commonly has T2 signal heterogeneity, contrast enhancement, and osteolysis on MRI: A case series of 35 dogs.

Magnetic resonance imaging (MRI) is commonly used to evaluate the central nervous system (CNS) in dogs; however, published studies describing the MRI appearance of cranial and vertebral osteosarcoma are scarce. In this multicenter, retrospective, case series study, MRI studies of 35 dogs with cranial or vertebral osteosarcoma were prospectively scored by consensus of two veterinary radiologists. Recorded characteristics were location, signal intensity (compared to gray matter), homogeneity, contrast enhancement, margin delineation, local invasion, osteolysis, osteosclerosis, zone of transition, periosteal proliferation, pathological fracture, meningeal/CNS involvement, and presence of metastatic disease. Locations included the parietal bone (n = 1), occipital bone (n = 2), or cervical (n = 5), thoracic (n = 17), lumbar (n = 7), or sacral vertebrae (n = 3). Common features included signal heterogeneity in T2-weighted (T2W) images (n = 35), contrast enhancement (in all 34 dogs with postcontrast MRI), osteolysis (n = 34), compression of the CNS or cauda equina (n = 33), an associated soft tissue mass (n = 33), a long zone of transition (n = 30), osteosclerosis (n = 28), signal isointensity to normal-appearing gray matter in T1-weighted images (T1W, n = 26), and T2W hyperintensity of adjacent brain or spinal cord (n = 23). Other findings included periosteal proliferation (n = 18), meningeal contrast enhancement (n = 17), T1W and T2W hypointense foci in the soft tissue mass (n = 14), invasion into adjacent bones (n = 10), pathological vertebral fractures (n = 7), regional lymphadenopathy (n = 6), skip metastases (n = 2), lung nodule (n = 1), diaphragmatic nodule (n = 1), and brain invasion (n = 1). Contrast enhancement was typically strong and heterogeneous. Magnetic resonance imaging features of cranial and vertebral osteosarcoma were analogous to those previously reported for other imaging modalities. Osteosarcoma should be a differential diagnosis for compressive, contrast-enhancing, osteolytic lesions of the cranium or vertebrae.