A 16-year-old boy has knee pain and X-ray shows an eccentric lytic lesion in the distal femur metaphysis with a ground-glass matrix centrally, no periosteal reaction, and cortical expansion. MRI reveals fluid-fluid levels within the lesion. What is the most likely diagnosis?
- A Giant cell tumor of bone
- B Osteosarcoma
- C Chondrosarcoma
- D Aneurysmal bone cyst (ABC) ✓
Explanation
Aneurysmal bone cyst (ABC) classically shows fluid-fluid levels on MRI — the most characteristic finding — representing layering of blood products of different ages (hemosiderin-laden blood separating by density). ABCs are eccentric, expansile, lytic lesions in metaphyses of long bones; they show thin cortical shell with no periosteal reaction unless complicated. Ground-glass matrix centrally is less characteristic of ABC (more of fibrous dysplasia), but ABCs can have mixed attenuation. Giant cell tumor occurs at the epiphysis after physeal closure, is epiphyseal/subarticular in adults. Osteosarcoma shows aggressive periosteal reaction and matrix mineralization.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.