Principles of diagnostic imaging
Plain radiography is always the first step in diagnosing bone tumors. Evaluating the appearance of the defect, its precise localization, and the child's age often allows for a well-founded assumption about the nature of the disease.
Further tactics are based on cross-sectional imaging:
- Magnetic resonance imaging (MRI): Essential for local staging. MRI allows assessment of the spread of pathological tissue into the medullary canal and soft tissues, joint involvement, and the relationship of the tumor to neurovascular bundles.
- Computed tomography (CT) and scintigraphy: When a malignant neoplasm is suspected, chest CT and bone scintigraphy (or whole-body MRI) are used to search for distant metastases.
The final diagnosis is established by a multidisciplinary team. Biopsy must be carefully planned together with the operating surgeon: it is important to consider tissue planes to minimize the risk of tumor seeding (tumour seeding) into uninvolved fascial compartments.
Classification of bone tumors
Classification is based on the type of tissue forming the pathological focus. All neoplasms are divided into benign and malignant forms.
| Tissue type | Benign | Malignant |
|---|---|---|
| Bone-forming | Osteoid osteoma, osteoblastoma, enostosis | Osteosarcoma |
| Fibro-osseous | Non-ossifying fibroma, fibrous dysplasia | Fibrosarcoma |
| Cartilage-forming | Enchondroma, osteochondroma, chondroblastoma | Chondrosarcoma |
| Vascular | Hemangioma, lymphangioma, Gorham disease | Hemangiopericytoma |
| Cystic | Simple and aneurysmal bone cysts | No |
| Small round cell | No | Ewing sarcoma, lymphoma |
Malignant neoplasms
The peak incidence of malignant bone tumors occurs between 10 and 20 years of age.
Osteosarcoma (Osteosarcoma) This is the most common malignant bone tumor in children. Often detected after a history of trauma. Radiographs reveal a destructive lesion with indistinct margins in the metaphysis of a long tubular bone, which may cross the growth plate. Characterized by osteoid formation, aggressive periosteal reaction, and the presence of a soft tissue component. Wide-field-of-view MRI is used to search for specific skip (skip) metastases. There are special pediatric variants: telangiectatic, periosteal, and high-grade surface osteosarcomas.
Ewing sarcoma family of tumors Most commonly occur in children under 9 years of age. Preferred localization is flat bones (ribs, pelvis). The clinical picture is nonspecific (pain, fever) and can mimic osteomyelitis. They metastasize hematogenously to the lungs and bone marrow. Radiographs show a permeative destructive defect with an onion-skin (onion skin) periosteal reaction.
Benign lesions
Benign lesions include bone-forming, fibrous, and cartilaginous tumors.
- Osteoid osteoma: Typical night pain relieved by NSAIDs. CT visualizes a central nidus (nidus) with a prominent surrounding sclerotic reaction. Modern treatment methods include radiofrequency ablation or focused ultrasound.
- Osteoblastoma: A rare tumor frequently affecting the posterior elements of the vertebrae. Unlike osteoid osteoma, the nidus measures greater than 1.5–2 cm. May cause painful scoliosis.
- Non-ossifying fibroma (NOF): The most common benign tumor. Appears as a multilocular osteolytic defect in the metaphysis with marginal sclerosis (diameter greater than 2 cm).
- Osteochondroma: Arises from the displacement of physeal cartilage into the metaphysis. A pathognomonic MRI sign is the presence of a cartilage cap (cartilage cap) and the continuity of the medullary cavity between the parent bone and the tumor.
- Gorham disease: A rare condition of massive osteolysis in which bone (e.g., the mandible) is replaced by lymphovascular tissue, yielding the radiographic "vanishing bone" or "floating teeth" sign.
Cystic bone lesions
Cysts are tumor-like lesions and often present with pathological fractures.
Simple bone cyst is located in the center of the metaphysis and moderately expands the bone. As the child grows, the cyst may migrate toward the diaphysis. Fluid levels may be visualized inside it following a fracture.
Aneurysmal bone cyst (ABC) is a multilocular expansile lesion containing areas of hemorrhage. Unlike a simple cyst, it grows eccentrically and does not cross the growth plate. MRI reveals characteristic internal fluid-fluid levels of varying density. It may develop primarily or secondarily in association with other bone tumors.
Briefly: answers to topical questions
What radiographic features are characteristic of Ewing sarcoma?
Ewing sarcoma is characterized by a permeative destructive bone lesion with a wide zone of transition and multiple small areas of osteolysis.
- Onion-skin periosteal reaction (onion skin) — a multi-layered reaction, occurs infrequently
- Codman triangle (Codman triangle) — elevated interrupted periosteum, in 27% of cases
- Hair-on-end spiculated reaction (hair-on-end) — a classic sign, occurs in 50% of cases
- Large soft tissue component — soft tissue extension is evident in 80% of cases
- Cortical saucerization — erosion of the cortical layer forming a saucer-like defect
Which bones and bone segments are most commonly affected in pediatric Ewing sarcoma?
Ewing sarcoma most frequently affects the diaphysis or metadiaphysis of long tubular bones, with a typical central/medullary origin of the tumor.
| Localization | Frequency |
|---|---|
| Femur and humerus | 31% |
| Pelvic bones (most commonly the ilium) | 21% |
| Distal parts of the appendicular skeleton (hands, feet) | 27% |
| Ribs | <8% |
By bone segment: the diaphysis is affected in 35% of cases, the metadiaphysis in 60% of cases. Flat bones (ribs, ilium) are also classically affected, with 50% of all cases originating in the femur or pelvic bones.
What types of periosteal reactions are characteristic of osteosarcoma?
Osteosarcoma is characterized by the following types of periosteal reaction:
- Codman triangle (Codman triangle) — elevated interrupted periosteum, a classic sign of osteosarcoma
- Sunburst spiculation (sunburst spiculation) — characteristic of high-grade surface osteosarcoma
- Hair-on-end reaction (hair-on-end) — a fine vertical periosteal reaction described in periosteal osteosarcoma
In osteosarcoma, mineralization can occur perpendicular to the cortical bone layer, forming a spiculated periosteal reaction. This reaction is a sign of a fast-growing malignant tumor, specifically osteosarcoma.
What are the stages of malignant bone tumors according to the Enneking surgical staging system?
Bone tumor staging according to the Enneking system is based on histological grade, anatomical site, and the presence of metastases.
- IA — low grade (low grade), intra-compartmental (intra-compartmental)
- IB — low grade (low grade), extra-compartmental (extra-compartmental)
- IIA — high grade (high grade), intra-compartmental (intra-compartmental)
- IIB — high grade (high grade), extra-compartmental (extra-compartmental)
- III — any grade, presence of metastases
For the differential diagnosis of bone cysts, remember: a simple cyst is centrally located (unilocular, "quiescent"), whereas an aneurysmal bone cyst is eccentric, causes marked expansion, and contains fluid-blood levels.
Class and exam questions
What is the main clinical distinction of osteoid osteoma?
The patient complains of night pain that is quickly and effectively relieved by taking regular aspirin or other NSAIDs.
How to differentiate osteofibrous dysplasia from malignant adamantinoma on X-ray?
In dysplasia, the cortical layer is intact and there is no periosteal reaction. Moth-eaten margins and involvement of the medullary cavity indicate malignant adamantinoma.
Which symptom occurs in Gorham's disease with jaw involvement?
Massive osteolysis occurs with the loss of bony support, leading to the radiographic "floating teeth" sign.
What else to study on this topic
- Pediatric variants of osteosarcoma (telangiectatic, periosteal)
- MRI patterns and fluid levels in aneurysmal bone cyst
- Radiological differentiation of osteoid osteoma from osteoblastoma
- Osteochondroma: criteria for medullary canal continuity
- Differential diagnosis of non-ossifying fibroma and fibrous cortical defect
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