A 13-year-old girl presents with swelling over the proximal part of the leg just below the knee, increasing in size for 3 weeks. The swelling is diffuse with dull aching pain. Superficial veins are prominent and there is a slight rise in temperature. No fever or trauma. Discuss the differential diagnosis. (
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Ewing sarcoma AND osteomyelitis
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Ewing sarcoma differential diagnosis osteomyelitis pediatric bone tumor clinical presentation
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https://www.ncbi.nlm.nih.gov/books/NBK12731
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Most likely diagnosis: osteosarcoma of the proximal tibial metaphysis.
This is a classic presentation: an adolescent with a rapidly enlarging, painful swelling near the knee, local warmth, tense skin and prominent superficial veins. Osteosarcoma most often arises in the metaphysis of long bones, commonly around the knee, including the proximal tibia. - S Das A Manual on Clinical Surgery, p. 169; Tintinalli's Emergency Medicine, p. 1001.
Differential diagnosis
| Diagnosis | Features supporting / distinguishing it |
|---|---|
| Osteosarcoma | Best fit. Age 13 years, metaphyseal site near knee, rapidly progressive deep aching pain and diffuse swelling. Local warmth and dilated superficial veins occur from a large, vascular tumour and venous compression. Pain may become constant and worse at night. |
| Ewing sarcoma | Usually affects children and adolescents and causes pain, tenderness and a rapidly growing swelling. It more often arises in the diaphysis than the metaphysis. Fever, malaise, anaemia, leukocytosis and raised ESR may mimic infection, but can be absent. Radiologically, it may show permeative destruction and lamellated ("onion-skin") periosteal reaction. |
| Acute or subacute pyogenic osteomyelitis | Proximal tibial metaphysis is a common site in children. Pain, warmth and swelling may resemble a bone tumour. Fever, toxicity, preceding infection, marked tenderness, erythema, raised leukocyte count, ESR and CRP favour infection. Their absence and the prominent veins make it less likely here, though subacute osteomyelitis remains an important exclusion. |
| Tuberculous osteomyelitis | Usually produces a slowly progressive, relatively painless "cold" swelling, often with constitutional symptoms, sinus formation or regional lymphadenopathy. The local warmth, short 3-week course and prominent veins are less typical. |
| Aneurysmal bone cyst | Occurs in children and adolescents and can cause rapidly enlarging painful expansile swelling. It is a benign but locally aggressive lesion, usually eccentric and metaphyseal. Imaging is needed to distinguish it from telangiectatic osteosarcoma. |
| Giant-cell tumour | May occur around the knee, but is usually seen after skeletal maturity, typically age 20-40 years, and is epiphyseal rather than metaphyseal. It is less likely at 13 years. |
| Osteoblastoma / osteoid osteoma | Can cause pain in young people. Osteoid osteoma typically causes small focal pain, often prominent at night and relieved by NSAIDs, rather than a large diffuse swelling. Osteoblastoma is larger but less typical at this site and presentation. |
| Langerhans-cell histiocytosis, lymphoma, adamantinoma | Less common alternatives for destructive tibial lesions. Adamantinoma has a particular tibial association but usually occurs in adults and has an indolent course. Textbook differentials for a tibial long-bone lesion also include histiocytosis, fibrous dysplasia and lymphoma. - Campbell's Operative Orthopaedics, p. 1084-1085. |
| Soft-tissue sarcoma, such as synovial sarcoma | Can present as a painful mass close to the knee in adolescents or young adults. It is primarily a soft-tissue lesion rather than a metaphyseal bony swelling; radiographs and MRI distinguish it. |
How to distinguish the leading possibilities
- Plain radiographs of the tibia and knee: osteosarcoma may show a metaphyseal mixed lytic-sclerotic lesion, cortical destruction, osteoid matrix, sunburst periosteal reaction and Codman triangle.
- Inflammatory markers and blood counts: fever, leukocytosis, high ESR/CRP support osteomyelitis but do not fully exclude Ewing sarcoma.
- MRI of the whole involved bone: defines marrow involvement, soft-tissue extension, relation to neurovascular structures and skip lesions.
- Chest CT and staging investigations if malignancy is suspected.
- Image-guided/core biopsy only after imaging and through an orthopaedic oncology team, so the biopsy tract can be removed during definitive surgery.
Thus, the clinical provisional diagnosis should be osteosarcoma of the proximal tibia, while Ewing sarcoma and osteomyelitis are the immediate high-priority alternatives to exclude.
Common 3 dd
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The common 3 differentials are:
- Osteosarcoma - most likely
- Ewing sarcoma
- Osteomyelitis - especially subacute/pyogenic osteomyelitis
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