• ABC
• osteoclastic giant cell rich tumour

Bone

Benign

M = F

Bone

• 1–6% of primary Bone tumours
• Peak incidence in 1st and 2nd decades (80% <20 years)
• Can be primary (de novo) or secondary (arising within another lesion)

• Pain and swelling at affected site
• Pathological fracture in 20% of cases
• Rapid growth may mimic malignancy
• Spinal lesions: neurological compromise

• Metaphysis of long bones (femur, tibia, humerus) most common
• Posterior elements of spine
• Flat bones (pelvis, ribs)
• Jaws (maxilla/mandible)

• Plain radiograph: Expansile eccentric lytic lesion with trabeculation, often metaphyseal
• MRI: fluid-fluid levels within multiloculated cysts is hallmark finding
• CT: Lytic lesion with cortical thinning but intact periosteal shell
• Bone scan: hot periphery (doughnut sign)

• Blood-filled cystic spaces separated by fibrous septa
• Septa contain osteoid, giant cells, and woven bone
• No endothelial lining to cystic spaces
• Solid variant ('solid ABC') may be confused with GCT or sarcoma

• USP6 gene rearrangement in 70% of primary ABCs
• Secondary ABCs lack USP6 rearrangement

• Curettage and bone grafting. Extended curettage with adjuvants reduces recurrence
• Percutaneous doxycycline sclerotherapy for selected cases
• Selective arterial embolisation - effective and may be used alone or as adjunct
• Denosumab - emerging role, especially in surgically difficult locations

• Recurrence rate 15–30% after simple curettage
• Lower recurrence with extended curettage (10%)
• No malignant transformation of primary ABC
• Secondary ABC prognosis determined by underlying lesion

• Fluid-fluid levels on MRI are characteristic but not pathognomonic
• USP6 FISH useful to confirm primary ABC vs secondary ABC
• Must exclude telangiectatic osteosarcoma - shares imaging features
• Sclerotherapy and embolisation effective alternatives to surgery

No blood tests required

• Plain radiograph
• CT
• MRI

Core biopsy if diagnosis uncertain

No staging required