Intraosseous "Lipoma" of the calcaneus developing in an intraosseous ganglion cyst

Intraosseous lipomas are rare primary bone tumors, most common to the calcaneus. There are several proposed theories of the natural etiology of intraosseous lipomas; however, all lack definitive support. In this report, an 18-year-old man presented with radiologic evidence of a simple bone cyst of the calcaneus. Over a 4-year period, the patient was followed with interval magnetic resonance imaging. The cyst demonstrated progressive development of peripheral intralesional fat with final magnetic resonance imaging features characteristic of an intraosseous lipoma. To our knowledge, this is the first longitudinal study that shows gradual peripheral fat deposition within an intraosseous ganglion cyst, illustrating a potential cause of intraosseous lipomas of the calcaneus.