Aneurysmal bone cyst

• benign bone lesion that arises from metaphysis and extends to growth plate.
• most common sites are femur and tibia.
• typically occurs before skeletal maturity.
• consists of a blood-filled space enclosed in a shell, ballooning up the overlying cortex.
• A gradually increasing swelling is the predominant presentation.

Radiologically, it is eccentric, extensively and asymmetrically expansile radiolucent metaphyseal lesion, that may show focal cortical destruction.

MRI shows fluid levels.