These images are from a patient with a "vanishingly" rare disease which affects children and young adults (age<40). Although almost any bone can be affected, the shoulder girdle, pelvis, and mandible are most common. The lesion is nonulcerative but locally aggressive. You take a biopsy which shows no malignant cells but intraosseous proliferation of hemangiomatous or lymphangiomatous tissue. Osteolysis is present. The disease is not hereditary. Some patients present with pain, swelling, or a pathologic fracture, while others are asymptomatic. There are no specific laboratory findings.
Challenge: Only 150 cases of this disease have been described; what is it?
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