Presumed recurrent chondromyxoid fibroma of the proximal humerus.
The differential diagnosis is:
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Aneurysmal bone cyst (ABC): fluid/fluid level, periosteal reaction, no matrix mineralization. Chondromyxoid fibroma with secondary ABC is not uncommon.
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Fibrous dysplasia: central location, no internal septation or periosteal reaction. Ground glass attenuation is typical.
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Adamantinoma: older patient, vast majority in the upper tibia, cortical destruction with aggressive periosteal reaction.
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Fibrous cortical defect (FCD) and non-ossifying fibroma (NOF): Possible mild cortical expansion, no destruction or periosteal reaction, not painful.