Imaging description

Intraosseous lipomas present as solitary lesions. Radiographic features often parallel the histologic stage of the lesion. Stage 1 and 2 typically reveal geographic, lytic lesions with well-defined sclerotic margin. The lesions vary in size from 1–9 cm. In stage 3 the radiographic features of the intraosseous lipoma are non-specific. In the calcaneus and the proximal femur the radiographic pattern can be characteristic. More than half the cases show a central calcification or ossification (Figures 75.1 and 75.2). On CT the lesion shows areas of low attenuation ranging between −40 and −60 Hounsfield units (Figure 75.3). The identification of fatty area on CT is diagnostic of intraosseous lipoma. Visualizing fat within these tumors is the primary role of MRI especially in lesions without significant amounts of involution. On MRI the fatty components of the lesion are iso-intense with subcutaneous fat on all sequences. Areas of dystrophic calcification and ossification show low signal intensity on all sequences. Cysts are common within intraosseous lipomas especially in the calcaneus and they show low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Figure 75.4). On bone scan an intraosseous lipoma may show mild increase in radionuclide uptake or it may be entirely negative.