Paper II
Question
A 45-year-old male presents with a swelling over the right knee joint of three months duration. X-Ray reveals an expansile lytic lesion, predominantly in the epiphyseal region of right lower femur without any cortical breach. What is the likely diagnosis and why Describe the radiological, gross and microscopic findings in this condition. (3+5)
Answer
Likely diagnosis and why
- Giant Cell Tumour of Bone (Osteoclastoma)
- Justification: The classic epidemiology (young to middle-aged adult, typically 20-45 years) and location (epiphyseal, extending to the subchondral bone, at the knee — the single most common site) strongly support this diagnosis; the radiological appearance of an eccentric, expansile, purely lytic lesion without a sclerotic rim (and typically without cortical breach until advanced stages) is highly characteristic of giant cell tumour, which is classically epiphyseal-based, in contrast to most other primary bone tumours which favour the metaphysis
Radiological findings
- Eccentric, expansile, lytic lesion located in the epiphysis, extending to the subchondral bone plate
- Well-defined but non-sclerotic margins (“geographic” pattern of bone destruction)
- Classic “soap bubble” appearance due to trabeculated, multilocular internal architecture
- Cortical thinning, though typically without cortical breach in earlier/uncomplicated lesions (as in this case); more aggressive/recurrent lesions may show cortical destruction and soft tissue extension
- No significant periosteal reaction (a helpful distinguishing feature from more aggressive malignant lesions)
Gross findings
- Soft, red-brown, haemorrhagic tissue, often with cystic degeneration and areas of necrosis
- Thinned, eggshell-like overlying cortex
Microscopic findings
- Numerous osteoclast-like multinucleated giant cells (containing many nuclei) uniformly scattered throughout the tumour
- A background of mononuclear, oval to spindle-shaped stromal cells — these are the actual neoplastic cell population, while the giant cells are considered reactive (recruited)
- The nuclei of the mononuclear stromal cells closely resemble those of the giant cells (an important diagnostic feature)
- Areas of haemorrhage, haemosiderin deposition, and occasional reactive new bone formation
- Mitotic activity may be present in the stromal cells but is not itself indicative of malignancy in this tumour