Intraosseous lipoma. A clinicopathologic study of nine cases.

Intraosseous lipoma is one of the rarest benign primary tumors of the bone. The clinicopathologic features of nine cases of intraosseous lipoma, including one with multiple lesions of the lumbar spinous processes, were studied and analyzed. They represented 2.5% of all primary bone tumors seen in our institutions. They were subdivided into three groups according to their histologic appearances: Group 1, tumors consisting predominantly of viable fat cells; Group 2, tumors showing, in addition, areas of fat necrosis and calcification; and Group 3, lesions with extensive reactive ischemic bone formation and calcification, viable lipocytes and fat necrosis may or may not be visible. Since the tumor is located within the rigid confines of the bony trabeculae, the internal pressure created as it enlarges is believed to be most significant in the morphogenesis of the tumor. The recognition of this spectrum of morphologic features is important, since the secondary changes may predominate and overshadow the original lipomatous component, leading to the possibility of confusing it with other benign bone tumors, cysts, and bone infarction. A combined clinical, radiologic, and pathologic approach should be adopted in the diagnosis of this tumor.