Osseous lipoma: eleven new cases and review of the literature.

This study describes the clinical features, radiological appearance, and treatment of 11 new cases of osseous lipoma and reviews 301 other cases in the literature. Osseous lipomas are classified by the site of origin: either within bone (intraosseous lipoma) or on the surface of bone (juxtacortical). Intraosseous lipomas include intramedullary and intracortical lesions. Surface lipomas include subperiosteal and parosteal lesions. The authors added their cases to those found in the literature. Intramedullary osseous lipoma (n=262) : the most common presenting symptoms were pain and swelling (69%). The most frequent localisations were the calcaneus (24%) and the femur (22%). On plain radiographs, these lesions consisted of a well-circumscribed radiolucent area with central calcification and a sclerotic rim, occasionally with cortical expansion. Computed tomography (CT) and magnetic resonance imaging (MRI) showed that the lesions had attenuation values and a signal intensity identical to that of adipose tissue. In symptomatic lesions and in cases with impending fracture, operative treatment was indicated. Parosteal lipoma (n=47): the most common presenting symptoms were local swelling and pain (58%). This lesion was most frequent in the radius (31%) and in the femur (23%). The classic radiographic appearance of parosteal lipoma was that of an exostosis-like bony prominence capped with a radiolucent layer of fat. CT-scan and MRI showed similar features. Intracortical (n=2) and subperiosteal lipomas (n=11): only a few cases were found in the literature. Their localisation differs from that of the other osseous lipomas. The differential diagnosis of osseous lipoma in general is extensive and should include benign and malignant tumours. Combination of radiological and histological data is essential to determine whether an osseous lipoma is actually present.