MR Imaging of Primary Bone Tumors and Tumor-like Conditions in Children
Section snippets
Malignant tumors
About 6% of all childhood malignancies are malignant bone tumors, most commonly osteosarcoma and Ewing sarcoma.7
Unicameral or simple bone cyst
Most simple bone cysts (Fig. 7) occur in the long tubular bones, especially the proximal humerus, proximal femur, and proximal tibia, and are seen in children between 9 and 15 years of age.27 Patients usually present with pain caused by pathologic fracture. The lesion arises centrally in the metaphysis, but may extend into the diaphysis, and is a well-defined lytic expansile lesion that may show internal trabeculation, especially after prior fracture. A fallen fragment may be seen in the
Giant cell tumor
GCT are very rare in children under 15 years of age,9, 32 and are seen more commonly in girls. Radiographically, these tumors are solitary, well-defined, eccentric lytic lesions usually located about the knee. They lack matrix calcification and have a nonsclerotic margin. Cortical thinning is common, but periosteal reaction is unusual. GCT are located in the metaphysis and do not cross the open physis,32 but may extend to the subchondral bone if the physis is closed. At MR imaging, GCT
Osteochondroma
Solitary osteochondroma (Fig. 10) is the most common benign tumor of bone in children,33 and occurs more commonly in boys. Some question if this lesion is a tumor, or a developmental abnormality of physeal growth. Multiple hereditary exostoses (diaphyseal aclasis) is an autosomal-dominant disease characterized by multiple osteochondromas. Osteochondromas may also be found in the radiation field of children who have undergone radiation therapy.9 Osteochondromas may grow during childhood, but
Osteoid Osteoma
Osteoid osteoma (Fig. 13) is a benign tumor most common in the second decade of life, and more common in boys. This hypervascular tumor composed of primitive woven bone and osteoid is painful, with the pain typically described as worse at night and relieved by aspirin.9, 36 It is found most commonly in the shafts of tubular bones, with the femur and tibia being most common. It may also be seen in the posterior elements of the vertebra.
Radiographically, this tumor is characterized by intense
Nonossifying Fibroma and Fibrous Cortical Defect
Nonossifying fibromas (Fig. 15) and fibrous cortical defects are common in children and adolescents, and are usually a painless, incidental finding. They regress over time, and are not seen after 25 years of age.29 There is an association between multiple nonossifying fibromas and neurofibromatosis. Nonossifying fibromas and fibrous cortical defects are eccentric, well-defined, and cortically based lesions with marginal sclerosis.36 Fibrous cortical defects measure less than 2 cm in size,
Vascular lesions
Most vascular lesions rarely present as primary bone tumors in the pediatric population.9
Histiocytosis
Langerhans cell histiocytosis results from an abnormal proliferation of antigen- presenting histiocytes, or Langerhans cells.40, 41 The etiology is unknown. Patients may be asymptomatic, or may develop bone pain.9 Early in the course of the disease, there is an inflammatory infiltrate within the lesion, followed by a granulomatous phase, and lastly a fibrous phase.40 Solitary bony lesions occur more commonly than multifocal disease.9 The lesions may arise in any bone, but the skull (Fig. 18),
Summary
This article has reviewed the MR imaging features of both benign and malignant tumors and tumor-like conditions of the pediatric skeleton with focus on their MR imaging features. Although the plain radiographic features remain the primary tool for the initial analysis of a pediatric bony neoplasm, MR imaging plays an important role. MR imaging offers superior assessment of the extent of bony, intramedullary, joint, and soft tissue involvement by the tumor. Certain anatomic MR imaging features,
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