This is a pathologically proven case of Langerhans cell histiocytosis.
This bizarre appearance is not typical of most entertainable pathologies, but other differentials could include: PVNS, low grade lytic mets, desmoplastic fibroma, intraosseous amyloidosis, cystic angiomatosis, angiomatosis (hemangiomatosis and/or lymphangiomatosis) and Gorham's disease.