Osteoid osteoma—osteoblastoma

In view of the clinical and pathological similarities, osteoid osteoma and osteoblastoma can be considered variants of one benign osteoblastic process. We suggest classifying these lesions according to their location in the bone, for that location determines the nature of reaction evoked. For lesions arising within compacta, we suggest the name cortical osteoblastoma (synonymous with osteoid osteoma). For lesions arising in the spongiosa, we propose the term spongious osteoblastoma (synonymous with benign osteoblastoma). A series of 24 cases is reviewed. Eleven were of die cortical type, characterized by a striking perifocal bone reaction with nidus size averaging 1.3 cm. Thirteen were classified as a spongious osteoblastoma, with slight or no perifocal bony reaction. Frequently the nidus showed calcification and a thin ring of sclerotic-appearing trabeculae. The nidus size averaged 2.5 cm. The cortical type was more frequent in the diaphysis of long bones while the spongious type was more common in the spine, metaphyses, and short bones.