Intramedullary sclerotic tumor and tumor-like bone lesions include, but are not limited to, bone islands (Fig. 10.1), bone infarction (Fig. 10.2), enchondroma, conventional osteosarcoma (Fig. 10.3), osteoblastic metastasis, mastocytosis (Fig. 10.4), and POEMS (polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes) syndrome (Fig. 10.5).

Bone islands appear as homogeneously sclerotic foci with spiculation. Bone infarction can be characterized with peripheral sclerosis. Enchondroma contains central chondroid matrix. Conventional osteosarcoma appears as aggressive lesion with amorphous osteoid matrix and soft tissue mass. Osteoblastic metastasis may be radiographically indistinguishable from bone islands, and may show enhancement on the postcontrast MR images. Mastocytosis may appear as multiple scattered sclerotic foci involving the axial skeleton and long bones, similar to metastatic disease, and clinical manifestation of skin rash, episodic vomiting, and diarrhea could be diagnostic hints. POEMS syndrome shows as homogeneously sclerotic lesion, and clinical clues are polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin changes.

Osteoid osteoma is most commonly localized within the cortex of the bone, and is surrounded by thick sclerotic reactive bone. Osteoblastoma is most commonly located within the cancellous bone and characteristically does not demonstrate extensive reactive bone formation. Occasionally, osteoid osteoma and osteoblastoma may occur on the surface of the bone. The two conditions may overlap and may be described as either osteoid osteoma or osteoblastoma.

Parosteal osteoma has been used to describe a benign compact bone-forming lesion arising from the periosteum, and appears as a well-circumscribed dense, rounded, or lobulated mass with no associated soft tissue masses on radiographs. Parosteal osteomas have intensely homogeneous sclerotic appearance.

In contrast, parosteal osteosarcoma (Fig. 10.6) may show a zone of decreased density at the periphery and usually appears less dense and homogeneous than parosteal osteoma. However, radiographically, parosteal osteoma and parosteal osteosarcoma may have indistinguishable features.

Periosteal osteosarcoma is fusiform and firmly attached to the surface of the bone without a cleavage line. Periosteal osteosarcoma may erode and permeate the outer cortex. The lesion is covered by periosteum and demonstrates spiculated perpendicular periosteal reaction.

High-grade surface osteosarcoma usually arises on the surface of the bone along the midshaft and usually does not invade the medullary cavity.

Lesions described as geographical show comparatively slow rates of growth and are typically less aggressive. These lesions may be subcategorized based on the radiographic appearance of their margins. Geographical osteolytic lesions with a sclerotic border show the slowest rate of growth and are generally considered benign. The slow rate of growth allows time for osteoblasts to form the reactive sclerotic rim that defines this category of lesions. Geographical osteolytic lesions with a sclerotic border and no intralesional matrix include subchondral cyst (Fig. 10.7), nonossifying fibroma, simple bone cyst (Fig. 10.8), Brodie abscess, intraosseous ganglion, intraosseous lipoma, and liposclerosing myxofibrous tumor (Fig. 10.9).

Trabeculae in normal unaffected bone may be seen extending to the edge of the lytic lesion, and the tumor cells rarely extend beyond this margin. Accordingly, these lesions are best detected in areas of cancellous bone because of the contrast provided by the adjacent trabeculae. If these lesions occur in the diaphysis, where the relative proportion of cancellous bone is lower, they may go undetected or show only endosteal scalloping. Examples of the geographical, osteolytic lesion with no sclerotic border and no intralesional matrix include benign lesion such as giant cell tumor (Fig. 10.10), Langerhans cell histiocytosis (Fig. 10.11), and fibrous dysplasia. However, the punched-out lesions of multiple myeloma (Fig. 10.12) and low-grade sarcoma may show similar appearance. Therefore, consideration of the patient’s age and clinical presentation can help guide the differential diagnosis.