MRI of a 16-year-old male shows a lesion in the distal femoral metaphysis with low signal on T1, heterogeneous high signal on T2, and a well-defined dark 'blooming' on gradient-echo sequence. Fluid-fluid levels are present within the lesion. What is the most likely diagnosis?
- A Giant cell tumour
- B Aneurysmal bone cyst (ABC) ✓
- C Osteosarcoma (telangiectatic type)
- D Simple bone cyst
Explanation
Fluid-fluid levels on MRI are the hallmark of aneurysmal bone cyst (ABC), representing blood products of different ages layered within blood-filled locules. The dark blooming on gradient-echo (susceptibility-weighted) imaging reflects haemosiderin. ABC typically occurs in the metaphysis of long bones in adolescents. Telangiectatic osteosarcoma can rarely show fluid-fluid levels, but cortical destruction and soft-tissue mass would be more prominent. Simple bone cysts do not show fluid-fluid levels. Giant cell tumour extends to the epiphysis and lacks fluid-fluid levels as the dominant finding.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.