8-Year-Old MN Labrador Mix

Signalment & History

  • This patient presents to your clinic for a mass over the left thorax.
  • On physical examination, his vitals are normal. Normal bronchovesicular sounds are ausculted in all lung fields. There is a large mass over his left side extending from his caudal ribs to his axilla and over the sternum.

Left lateral, cranial thorax Right lateral, caudal thorax Right lateral, cranial thorax VD thorax


There is lysis of the 6th rib at the level of the costochondral junction. There is a large, soft tissue opaque mass extending the length of the lateral thorax extending 16 cm laterally from the ribs and displacing the thoracic wall axially. There are multiple faint mineral opacities throughout this mass. On the VD view, there is soft tissue opacity superimposed over the left caudal lung fields causing displacement of the cardiac silhouette towards the right body wall. In the right lateral view, there is a soft tissue opaque nodule in the pulmonary parenchyma superimposed over the gastric fundus.


Large rib mass with extension into the thoracic cavity and pulmonary metastasis: primary differential diagnosis is osteosarcoma.



  • Bone tumors can involve the appendicular (long bone) or axial (flat bone) skeleton
  • These tumors are classified as primary or secondary
  • Four primary bone tumors include
    • Osteosarcoma
    • Chondrosarcoma
    • Fibrosarcoma
    • Hemangiosarcoma
  • Signalment
    • Frequently occurs in large breed dogs although small breed dogs can also be affected
    • Older dogs (common); can occur in young dogs
  • Most common bone tumor in the dog (95% of all bone tumors
  • Behaves aggressively – local invasiveness and distant metastases
  • Usually arise spontaneously from the appendicular skeleton
  • Dogs with rib osteosarcoma showed a higher metastatic rate than dogs with appendicular osteosarcoma


Kruse MA, Holmes ES, Balko JA, Fernandez S, Brown DC, Goldschmidt MH. Evaluation of clinical and histopathologic prognostic factors for survival in canine osteosarcoma of the extracranial flat and irregular bones. Vet Path 2013;50(4):704-708.

Dickerson ME, Page RL, LaDue TA, et al. Retrospective analysis of axial skeleton osteosarcoma in 22 large-breed dogs. J Vet Intern Med. 2001;15:120–124

Hammer AS, Weeren FR, Weisbrode SE, Padgett SL. Prognostic factors in dogs with osteosarcomas of the flat or irregular bones. J Am Anim Hosp Assoc 1995;31(4):321-326.

Prikey-Ehrhart N, Withrow SJ, Straw RC, Ehrhart EJ, Page RL, Hottinger HL, Hahn KA, Morrison WB, Albrecht ME, Hedlund CS, et al. Primary rib tumors in 54 dogs. J Am Anim Hosp Assoc 1995;31(1):65-69.