Giant cell tumours (GCTs) of bone, also known as osteoclastomas, are relatively common bone tumours, usually benign which are arising from metaphysis and typically extending into the epiphysis of the long bones.
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GCTs are common, comprising 18-23% of benign bone neoplasms and 4-9.5% of all primary bone neoplasms 1. They almost invariably (97-99%) occur when the growth plate has closed and are therefore typically seen in early adulthood, with 80% of cases reported between the ages of 20 and 50, with a peak incidence between 20 and 30 1.
There is overall a mild female predilection, especially when located in the spine, however malignant transformation is far more common in men (M:F of ~3:1) 1.
Presentation is not specific, typically presents insidiously and relates to bone pain, soft tissue mass, compression of adjacent structures or acutely with a pathological fracture.
Giant cell tumours are believed to result from an over-expression in RANK/RANKL signalling pathway with resultant over-proliferation of osteoclasts 6.
These tumours contain numerous thin walled vascular channels predisposing to areas of haemorrhage and presumably related to the relatively frequent co-existence of aneurysmal bone cysts (ABC) found in 14% of cases 1-2,4.
Macroscopically, giant cell tumours are variable in appearance, depending on amount of haemorrhage, presence of co-existent ABC, and degree of fibrosis.
Microscopically they are characterised by prominent and diffuse osteoclastic giant cells and mononuclear cells ( round, oval, or polygonal and may resemble normal histiocytes). Frequent mitotic figures in the mononuclear cells may be seen, especially in pregnant women or those on the oral contraceptive pill (due to increased hormone levels) 1.
GCTs are low grade tumours even in radiologically aggressive appearing lesions. Approximately 5-10% of GCTs are malignant 1. Sarcomatous transformation is seen, especially in radiotherapy treated inoperable tumours. Although rare (~5%), lung metastases are possible, and have an excellent prognosis, hence, this entity has been called benign metastasising GCT 10,11.
It is important to realise that features may be difficult to interpret histologically with a relatively wide histological differential diagnosis (e.g. giant cell reparative granuloma, brown tumour, osteoblastoma, chondroblastoma, non-ossifying fibroma, and even osteosarcoma with abundant giant cells)1 thus making radiology indispensable to the interpretation of these lesions.
They typically occur as single lesions. Although any bone can be affected, the most common sites are 1-2:
- around the knee: distal femur and proximal tibia: 50-65%
- distal radius: 10-12%
- sacrum: 4-9%
- vertebral body
Multiple locations: ≈ 1% (multiple lesions usually occur in association with Paget disease)
There are four characteristic radiographic features when a GCT is located in a long bone:
- occurs only with a closed growth plate
- abuts articular surface: 84-99% come within 1 cm of the articular surface 1
- well defined with non-sclerotic margin (though < 5% may show some sclerosis 8)
- eccentric: if large this may be difficult to assess
Plain film and CT
General radiographic features include:
- narrow zone of transition: a broader zone of transition is seen in more aggressive GCTs
- no surrounding sclerosis: 80-85%
- overlying cortex is thinned, expanded or deficient
- periosteal reaction is only seen in 10-30% of cases
- soft tissue mass is not infrequent
- pathological fracture may be present
- no matrix calcification/mineralisation
Typical signal characteristics include:
- low to intermediate solid component
- low signal periphery
- solid components enhance, helping distinguish GCT with ABC from pure ABC 3-4
- some enhancement may also be seen in adjacent bone marrow
- heterogenous high signal with areas of low signal intensity (variable) due to haemosiderin or fibrosis 9
- if an ABC component present, then fluid-fluid levels can be seen
- high signal in adjacent bone marrow thought to represent inflammatory oedema 4
- T1 C+ (Gd): solid components will enhance, helping differentiate from ABCs 9
Scintigraphy: bone scan
Most GCT demonstrate increased uptake on delayed images, especially around the periphery, with a central photopenic region (doughnut sign). Increased blood pool activity is also seen, and can be seen in adjacent bones due to generalised regional hyperaemia (contiguous bone activity).
If performed, usually in the setting of pre-operative embolisation, angiography usually demonstrates a hypervascular tumour (2/3rd of cases) with the rest being hypo or avascular.
Treatment and prognosis
Classically, treatment is with curettage and packing with bone chips or polymethylmethacrylate (PMMA). Local recurrence is from the periphery of the lesion and has historically occurred in up to 40-60% of cases. Newer intraoperative adjuncts such as thermal or chemical treatment of the resection margins have lowered the recurrence rate to 2.5-10%1. Early work on monoclonal antibodies, as an adjuvent treatment, has been impressive in causing high rates of tumour necrosis.7 Wide local excision is associated with a lower recurrence rate, but has greater morbidity.
There is a relatively wide differential similar to that of a lytic bony lesion:
- chondroblastoma: epiphyseal, usually in skeletally immature patients
- chondromyxoid fibroma: metaphyseal, with a well defined sclerotic margin, multiloculated bubbly appearance 3
- aneurysmal bone cyst (ABC): younger age group, but may co-exist with GCT; fluid-fluid levels
- non-ossifying fibroma: usually younger age group 4
- brown tumour: in the setting of hyperparathyroidism
- enchondroma: only really a consideration in lesions of small bones of the hand and foot 3
- haemophilic pseudotumour
- chondrosarcoma: typically older age group
- metastases and multiple myeloma
- intraosseous ganglion cysts
- desmoplastic fibroma
The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.
- bone-forming tumours
- chondromyxoid fibroma
- fibrous bone lesions
- bone marrow tumours
- other bone tumours or tumour-like lesions
- aneurysmal bone cyst
- benign fibrous histiocytoma
- giant cell tumour of bone
- Gorham massive osteolysis
- haemophilic pseudotumour
- intradiploic epidermoid cyst
- intraosseous lipoma
- cockade sign
- musculoskeletal angiosarcoma
- musculoskeletal haemangiopericytoma
- primary intraosseous haemangioma
- simple bone cyst
- impending fracture risk
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