An eccentric, lytic, subarticular lesion with a narrow non-sclerotic zone of transition in a skeletally mature patient — around the knee and distal radius — the report adds cortical breach, articular surface and pathological fracture.
Orient first
- Occurs after physeal closure, extends to the subchondral bone.
- Non-sclerotic margin, no matrix; can expand and breach the cortex.
- Secondary aneurysmal bone cyst change (fluid levels) is common; lung metastases occur rarely.
Acquire the study
- AP and lateral radiographs.
The manoeuvre
- Radiograph: eccentric epimetaphyseal lytic lesion extending to within ~1 cm of the articular surface.
- Margin: well-defined but non-sclerotic; no matrix.
- Cortical expansion or breach; pathological fracture.
What confirms it
- Typical imaging with histology.
What licenses you to exclude it
- Matrix mineralisation or a sclerotic margin argues against GCT.
The classic misread
- Calling it GCT in a skeletally immature patient — consider chondroblastoma or ABC.