• Children
• Proximal humerus & Femur
• Fallen fragment
Lytic
Well demarcated
Central
Metaphyseal
occ extends to epiphysis then with healing and limb growth extends into diaphysis
Apparent septae probably represents endosteal ridges
may fracture, and any loose fragments sink to bottom of cyst confirming the fluid nature
may heal following fracture
• Markedly expansile
• Fluid levels
• Unfused skeleton
Around 2% of primary bone tumours
Usually less than 20 years old
Metaphyseal
Unfused growth plates usually, Helps differentiate from GCT
Central, eccentric & Subperiosteal described
sharp but non sclerotic margin
Septations
Periosteal reaction: lamillated or solid
Finger in balloon appearance on x ray due to mature periosteal reaction
Fluid levels characteristic on MRI
If more than 80% then lesion is ABC
Ddx telangiectatic osteosarcoma
Can be primary or secondary (30%)
Some crossover with giant cell reparative granuloma
Aneurysmal bone cyst
Chondroid lesion
Giant cell tumour
Nonossifying fibroma
Angiomatous lesiong (eg, hemangioma; lymphangioma)
Brown tumor of hyperparathyroidism
Chondromyxoid fibroma
Cortical/periosteal desmoid
Desmoplastic fibroma