Chapter 25 Benign Bone Tumors and Nonneoplastic Conditions Simulating Bone Tumors
Bone-Forming Tumors
Bone Island
Bone islands usually can be diagnosed by plain radiographs. They typically are small, round or oval areas of homogeneous increased density within the cancellous bone (Fig. 25-3A). Radiating spicules on the periphery of the bone islands merge with the native bone creating a brushlike border. No bony destruction or periosteal reaction is noted. They may show mildly increased uptake on bone scans; however, markedly positive scans should raise suspicion of more aggressive lesions. CT scans show thickened trabeculae that merge with the surrounding bone. MRI usually shows well-defined lesions that are isointense to cortical bone and thus dark on T1- and T2-weighted images (Fig. 25-3B and C) with no surrounding edema. There are no aggressive imaging features.
Cartilage Lesions
Chondroma
Radiographically, enchondromas are benign-appearing tumors with intralesional calcification (Fig. 25-4A and B). The calcification is irregular and has been described as “stippled,” “punctate,” or “popcorn.” In the small bones of the hands and feet there may be considerable erosion and expansion of the overlying cortex. In more proximal locations (e.g., the pelvis, proximal humerus, or proximal femur), deep endosteal erosion (two thirds of the thickness of the cortex) frequently indicates a chondrosarcoma. An associated soft tissue mass is never present with an enchondroma and always indicates a chondrosarcoma. Juxtacortical chondromas usually are small (<3 cm), well-defined lesions that frequently appear to fit in a saucer-shaped defect on the surface of the bone (Fig. 25-5). The underlying cortex appears sclerotic, and the edges of the lesion appear to be buttressed by a thick rind of cortical bone. Plain radiographs usually are sufficient to diagnose a chondroma. If the diagnosis is in question, CT is best to evaluate endosteal erosion that could indicate a chondrosarcoma (see Fig. 25-4C).

FIGURE 25-5 Anteroposterior radiograph of left proximal humerus of 18-year-old man with a juxtacortical chondroma.
Fibrous Lesions
Fibrous Dysplasia
The radiographic appearance is characteristic, with the lucent area having a granular, ground-glass appearance with a well-defined sclerotic rim (Fig. 25-13). Occasionally, biopsy is necessary to establish the diagnosis. The histopathological appearance is that of irregular woven bone spicules with a fibrous stroma. Small areas of cartilaginous metaplasia and cystic changes may be present (Fig. 25-14). Surgical treatment is indicated when significant deformity or pathological fracture occurs or when significant pain exists. Actual and impending pathological fractures are best treated with intramedullary fixation when possible. Deformities are corrected by osteotomy with internal fixation. Because recurrence rates are high after curettage and bone grafting, cortical bone grafts are preferred over cancellous grafts (or bone graft substitutes) because of their slower resorption. Studies suggest that treatment with bisphosphonates probably is beneficial for patients with extensive disease.