Friday, July 1, 2011

Calcaneal Intraosseous Lipoma

Intraosseous or medullary lipomas are rare benign neoplasms of bone that are most commonly seen in the metaphyses of long bones (e.g., proximal femur and the fibula) and in the calcaneus. They are histologically characterized by mature lipocytes in a background of fibroblasts with occasional foci of fat necrosis.

As many as 2/3 of patients with intraosseous lipomas may be symptomatic, presenting with pain and/or soft tissue swelling. These lesions frequently involute spontaneously through infarction, calcification, and cyst and reactive bone formation.

Radiographs reveal a lucent lesion surrounded by a thin, well-defined sclerotic margin. Lobulations and thin septa may also be present. Intraosseous lipomas tend to be expansile when located in smaller bones such as the fibula. While an aggressive appearance is rarely encountered, these lesions are typically benign in appearance without cortical destruction or periosteal reaction.

While this radiographic appearance is usually nonspecific, intraosseous lipomas in the calcaneous have a characteristic appearance.

In the calcaneus, the lesion is almost invariably located in the tangle between major trabecular groups in the same location as simple cysts. A central calcified nidus is typically seen with intraosseous lipomas, but not in simple cysts. Lesions without central calcifications can be further evaluated with CT or MRI to demonstrate internal fat content.

CT can also reveal areas of higher attenuation corresponding to hemorrhage and cyst formation. MRI reveals areas of low T1 and high T2 signal intensity suggestive of necrosis and cyst formation. Areas of T1 hyperintensity and T2 hypointensity may also be seen, corresponding to foci of hemorrhage.

Case courtesy of Dr. Damon J. Spitz and New England Baptist Hospital.



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