 Primary bone tumors are conventionally classified by the World Health Organization as benign, intermediate (locally aggressive or rarely metastasizing), or malignant [1]. Benign tumors include a wide variety of developmental abnormalities and true neoplasms. Because most benign bone tumors are asymptomatic, the true incidence of these tumors is unknown, although they are not uncommon. Intermediate tumors include lesions such as giant cell tumor, osteoblastoma, and desmoplastic fibroma. Primary malignant bone tumors may also arise from malignant mesenchymal cells (sarcomas). Primary malignant bone tumors are quite rare, with an estimated incidence of 1 case per 100,000 persons per year [2]. Diagnosis of benign and malignant primary bone tumors relies on a coordinated evaluation of both clinical and radiologic information. Many primary bone tumors can be effectively stratified with respect to typical age of presentation as well as lesion size, location, and number. Classically, radiographs have played a substantial role in the characterization of primary bone tumors. An assortment of radiographic features, including tumor margin, periosteal reaction, and matrix mineralization, may be used to assess the biological activity of a bone lesion [3-6]. An asymptomatic nonaggressive-appearing lesion incidentally found on radiographs may, in many cases, require no further evaluation. In cases in which clinical or radiographic features are indeterminate or additional anatomic information is required, advanced imaging modalities, such as CT, MRI, or nuclear medicine, may provide a complementary role in the diagnosis and treatment stratification of primary bone tumors. Because primary bone sarcomas are rare, there is sparse level 1 evidence in the literature specifically addressing their imaging evaluation.
Primary Bone Tumors.  Primary bone tumors are conventionally classified by the World Health Organization as benign, intermediate (locally aggressive or rarely metastasizing), or malignant [1]. Benign tumors include a wide variety of developmental abnormalities and true neoplasms. Because most benign bone tumors are asymptomatic, the true incidence of these tumors is unknown, although they are not uncommon. Intermediate tumors include lesions such as giant cell tumor, osteoblastoma, and desmoplastic fibroma. Primary malignant bone tumors may also arise from malignant mesenchymal cells (sarcomas). Primary malignant bone tumors are quite rare, with an estimated incidence of 1 case per 100,000 persons per year [2]. Diagnosis of benign and malignant primary bone tumors relies on a coordinated evaluation of both clinical and radiologic information. Many primary bone tumors can be effectively stratified with respect to typical age of presentation as well as lesion size, location, and number. Classically, radiographs have played a substantial role in the characterization of primary bone tumors. An assortment of radiographic features, including tumor margin, periosteal reaction, and matrix mineralization, may be used to assess the biological activity of a bone lesion [3-6]. An asymptomatic nonaggressive-appearing lesion incidentally found on radiographs may, in many cases, require no further evaluation. In cases in which clinical or radiographic features are indeterminate or additional anatomic information is required, advanced imaging modalities, such as CT, MRI, or nuclear medicine, may provide a complementary role in the diagnosis and treatment stratification of primary bone tumors. Because primary bone sarcomas are rare, there is sparse level 1 evidence in the literature specifically addressing their imaging evaluation.