- May be seen radiographically
- Must be distinguished from neoplasia
- Expansile lytic masses
- Do not appear aggressive
- Subchondral cysts
- Common in horses and pigs
- Usually manifestations of osteochondrosis and DJD
- Simple cysts
- May contain clear colourless fluid, or serosanguinous
- Wall of dense fibrous tissue, woven or lamellar bone
- Aneurysmal bone cysts
- Expansie lesions
- Arise from disturbance of vascular tissue of bone marrow
- Grossly:
- Appear as blood filled sponge
- Spaces separated by fibrous trabeculae
- Histologically:
- Proliferation of undifferentiated mesenchymal cell with multinucleated osteoclast-like cells
- Haemorrhage and haemosiderosis
- Radiography is essential to help differentiate with cavity of a neoplasm