Fluid-fluid level containing bone lesions

Fluid-fluid level containing bone lesions are best seen on MRI, although with narrow window width they can also be appreciated on CT.

Epidemiology

Their prevalence is estimated at ~3% of bone and soft tissue tumors ¹.

Differential diagnosis

Their presence is non-specific, as they are seen in both benign and malignant lesions:

• aneurysmal bone cyst (ABC)
  • primary
  • secondary to other underlying lesions such as
    • giant cell tumors (GCT)
    • fibroxanthoma
    • chondroblastoma
    • osteoblastoma
• simple bone cyst: especially after fracture
• telangiectatic osteosarcoma
• uncommon causes
  • metastasis: especially from renal cell carcinoma (RCC)  and lung cancer ³
  • synovial sarcoma
  • synovial hemangioma
  • myositis ossificans
  • adamantinoma ²
  • neurogenic tumors ³

There is a mnemonic for fluid-fluid levels on MRI.