Introduction: clinical presentation and general diagnostic approach
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Does the lesion have features suggestive of an aggressive nature (Table 2)?
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Is further imaging necessary and which technique is best adapted to the residual questions?
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Is a biopsy of the lesion required?
Nonossifying fibroma/cortical defect/cortical desmoid |
Fibrous dysplasia |
Exostosis |
Solitary bone island (osteoma) |
Enchondroma |
Feature | Nonaggressive | Aggressive/undetermined |
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Type of lysis | Geographic | Moth-eaten/permeative |
Margins | Well defined | Ill defined |
Zone of transition to normal bone | Narrow | Wide |
Bone contour | Expansion from slow growth | Destruction |
Periosteal reaction | Smooth, uninterrupted | Aggressive types (sunburst, hair-on-end, linear interrupted, Codman triangle) |
Soft-tissue mass | Absent | Present |
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Whenever a finer, more detailed characterisation of the cortical changes, bone matrix alteration and periosteal reaction is necessary, CT is the adequate technique. It offers a more detailed “radiological” view of the lesion and completes the findings of the X-ray related to bone changes.
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MRI is more appropriate to identify the presence of bone oedema as well as identify and quantify infiltration, extraosseous masses and soft tissue changes. As such it is essential in the characterisation of malignant lesions. However, an important caveat must be kept in mind: some very typical radiological lesions, such as nonossifying fibroma, may have nonspecific and sometimes challenging aspects on MRI. Thus, MRI is not adequate as an initial imaging technique, and problematic focal bone lesions incidentally found on MRI require a complementary X-ray.
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Even though it lacks specificity, a bone scan is especially useful to demonstrate whether a lesion is uni- or multifocal, an important element in the differential diagnosis. It may also have more specific applications, such as identifying the nidus of an osteoid osteoma in doubtful cases.
Most common benign tumours in children
Tumour | Most common locations | Location in long bones |
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FCD/NOF | Around the knee joint (distal femur/proximal tibia) | Metaphysis |
Exostosis (osteochondroma) | Long bones, pelvis, ribs | Metaphysis |
Enchondroma | Phalanges hands/feet | Metaphysis, diaphysis |
Chondroblastoma | Around the knee joint (distal femur/proximal tibia), proximal humerus | Epiphysis |
Simple bone cyst | Proximal humerus, proximal femur | Metaphysis |
Aneurysmal bone cyst | Long bones, pelvis, posterior elements of vertebrae | Metaphysis |
Osteoid osteoma | Neck of femur, other long bones (especially lower limbs) | Diaphysis, metaphysis |