Osteosarcoma is the most common primary malignant bone tumor, arising from malignant mesenchymal cells that produce osteoid matrix. It predominantly occurs in the metaphysis of long bones, especially the distal femur and proximal tibia. Peak incidence is in adolescents and young adults (10-25 years). It is an aggressive tumor with a tendency for early hematogenous metastasis (particularly to the lungs). Radiologically, it is characterized by osteoid matrix production, aggressive periosteal reaction, and soft tissue mass.
Age Range
10-25
Peak Age
15
Gender
Male predominant
Prevalence
Uncommon
Osteosarcoma is a malignant neoplasm arising from mesenchymal stem cells in the bone marrow, where tumor cells directly produce osteoid or immature bone. The tumor's osteoid matrix production manifests on imaging as cloud-like or ivory-like mineralization; this mineralization pattern is the direct radiological correlate of the tumor's osteoblastic activity. The tumor starts from the medullary cavity, destroys the cortex, and invades soft tissues by breaching the periosteal barrier; the elevation of the periosteum by the tumor creates the Codman triangle and sunburst periosteal reaction. Due to rapid proliferation, the tumor contains areas of necrosis and hemorrhage; this heterogeneity is observed as mixed signal intensity on MRI. T2-weighted sequences help differentiate the tumor's solid components, edema, and necrotic areas because tissues with increased free water content exhibit prolonged T2 relaxation time and increased signal.
Sunburst pattern aggressive periosteal reaction in a cortex-destructing metaphyseal mass and Codman triangle formed by tumor elevation of the periosteum, together with osteoid matrix mineralization, constitute the most characteristic radiological triad of osteosarcoma.
Cloud-like or ivory-like dense osteoid matrix mineralization within an irregularly marginated metaphyseal lesion. This mineralization, also visible on conventional radiography, is much better characterized on CT. Mineralization density varies depending on the histological subtype: dense in osteoblastic type, minimal or absent in fibroblastic/telangiectatic types.
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Cloud-like osteoid matrix mineralization is seen within the metaphyseal lesion, consistent with osteosarcoma.
Aggressive sunburst pattern periosteal reaction formed by the tumor breaching the cortex and elevating the periosteal barrier. Spiculated radially oriented new bone formation extends outward from the cortex. This finding, visible on conventional radiography, is evaluated three-dimensionally on CT multiplanar reformats. This periosteal reaction is an indicator of high-grade malignancy.
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Sunburst pattern aggressive periosteal reaction accompanying cortical destruction is seen, consistent with high-grade malignant bone tumor.
Triangular periosteal reaction formed at the point where the periosteum separates from the cortex due to tumor elevation of the periosteal barrier. The Codman triangle is a classic radiological sign of aggressive tumor growth and, while not pathognomonic for osteosarcoma, is strongly suggestive. It appears as triangular ossification at the cortex-periosteum junction on CT.
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Codman triangle is seen at the cortex-periosteum junction, consistent with an aggressive bone lesion.
Mass lesion filling the medullary cavity and extending through the cortex into soft tissue demonstrates low-to-intermediate signal intensity on T1-weighted sequences. The normal high T1 signal of fatty bone marrow is lost due to tumor infiltration. T1 sequence is critically important for evaluating intramedullary extent of the tumor and is the gold standard for detecting skip metastases (distant medullary metastases within the same bone) for surgical planning.
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A metaphyseal mass lesion with low signal intensity on T1-weighted sequences, filling the medullary cavity and showing extraosseous extension, is identified.
The tumor shows heterogeneous high signal on T2-weighted sequences. Solid tumor components demonstrate intermediate-to-high T2 signal while necrotic/cystic areas show markedly high T2 signal. Mineralized osteoid matrix areas remain low in signal intensity on all sequences. Perifocal bone marrow and soft tissue edema appear as high T2 signal and require careful evaluation in determining the true tumor boundaries.
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The mass demonstrates heterogeneous high signal intensity on T2-weighted sequences with areas of necrosis and foci of low-signal mineralized matrix.
Tumor and peritumoral edema are seen with markedly high signal on STIR sequence. Normal fatty bone marrow signal is suppressed, allowing clearer assessment of the true intramedullary extent of tumor infiltration. Perifocal soft tissue edema and reactive bone marrow edema become more conspicuous on STIR. STIR provides complementary information to T1 for detection of skip metastases.
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Intramedullary extent of the lesion and perifocal edema are clearly assessed on STIR, and the entire bone should be evaluated for skip metastases.
Solid tumor components demonstrate marked restricted diffusion on diffusion-weighted imaging (DWI) (high signal on DWI, low values on ADC map). Necrotic areas do not show diffusion restriction. DWI plays an important role in treatment response assessment (after neoadjuvant chemotherapy) for determining necrosis rate and distinguishing viable tumor tissue.
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Marked restricted diffusion is seen in solid tumor components, consistent with high cellularity; necrotic areas do not show diffusion restriction.
Solid tumor components show marked heterogeneous enhancement on post-gadolinium sequences. Necrotic and cystic areas do not enhance. Mild enhancement may be seen in perifocal reactive edema areas. Contrast-enhanced MRI is particularly valuable for evaluating the tumor's relationship with vascular structures (neurovascular bundle involvement) and joint invasion.
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Marked heterogeneous enhancement in solid components with non-enhancement in necrotic areas on post-contrast sequences.
The osteosarcoma primary tumor shows intense FDG uptake (SUVmax usually >5-10). FDG uptake is low in necrotic areas. PET-CT plays an important role in detection of distant metastases (especially lung and bone metastases) and staging. Reduction in FDG uptake after neoadjuvant chemotherapy is an indicator of treatment response.
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Intense FDG uptake is seen in the primary tumor; whole body should be evaluated for distant metastases.
Criteria
Most common subtype (75%). Characterized by dense osteoid matrix production. Metaphyseal location, prominent matrix mineralization.
Distinct Features
Dense cloud-like/ivory mineralization on CT, sunburst periosteal reaction. Low signal in mineralized matrix areas on all MRI sequences.
Criteria
Significant portion of tumor shows cartilaginous differentiation. Arcs and rings calcification and osteoid matrix coexist.
Distinct Features
Chondroid matrix (arcs and rings calcification) and osteoid matrix coexisting on CT. Chondroid component shows high T2 signal on MRI (hyaline cartilage). Differential diagnosis with chondrosarcoma may be challenging.
Criteria
Characterized by prominent cystic/hemorrhagic components. Minimal or no matrix mineralization. May be confused with aneurysmal bone cyst.
Distinct Features
Lytic, expansile lesion on CT with minimal mineralization. Fluid-fluid levels on MRI, areas of high T1 signal due to methemoglobin. Enhancement in solid components on contrast MRI — distinguishing feature from aneurysmal bone cyst.
Criteria
Low-grade surface osteosarcoma. Arises from the bone surface (periosteum). Posterior distal femur predilection. Slow growth, late metastasis.
Distinct Features
Densely mineralized, lobulated mass on the bone surface on CT. No medullary invasion initially (may occur in late stages). Low signal in mineralized areas on T1 and T2 MRI. Significantly better prognosis than conventional osteosarcoma.
Distinguishing Feature
Ewing sarcoma is diaphyseal, shows permeative destruction and onion-skin periosteal reaction; no osteoid matrix mineralization. Osteosarcoma is metaphyseal and produces osteoid matrix.
Distinguishing Feature
Chondrosarcoma produces chondroid matrix (arcs and rings calcification) and typically occurs in older patients. Osteosarcoma produces osteoid matrix (cloud-like) and is common in young patients.
Distinguishing Feature
Osteomyelitis is typically characterized by sinus tracts, sequestrum, and involucrum. Matrix mineralization and aggressive periosteal reaction are expected in osteosarcoma. Clinical context (fever, elevated CRP) supports osteomyelitis.
Distinguishing Feature
Osteoblastoma typically locates in posterior vertebral elements or long bone diaphysis, is larger than 2 cm but well-circumscribed without prominent aggressive periosteal reaction. Osteosarcoma shows more aggressive growth, periosteal reaction, and soft tissue mass.
Distinguishing Feature
Aneurysmal bone cyst is an expansile lytic lesion showing fluid-fluid levels but no solid enhancing component. Telangiectatic osteosarcoma has fluid-fluid levels but also contains enhancing solid nodules.
Urgency
highManagement
Neoadjuvan kemoterapi + cerrahi rezeksiyon (uzuv kurtarıcı cerrahi veya amputasyon) + adjuvan kemoterapi. Multidisipliner yaklaşım (ortopedik onkoloji, medikal onkoloji, radyoloji) zorunludur.Biopsy
NeededFollow-up
Tedavi sonrası ilk 2 yıl 3 ayda bir MR + akciğer BT, 2-5 yıl arası 6 ayda bir, 5 yıl sonrası yıllık takip. Neoadjuvan kemoterapi yanıtı cerrahi sonrası histolojik nekroz oranı ile değerlendirilir (>%90 iyi yanıt).Osteosarcoma is a high-grade malignant bone tumor requiring urgent multidisciplinary evaluation. Staging (chest CT, whole bone MRI/scintigraphy, PET-CT) should be performed rapidly after diagnosis, and neoadjuvant chemotherapy should be initiated. Surgical margin adequacy and chemotherapy response (histological necrosis rate) are the most important prognostic factors. 5-year survival is 60-70% for localized disease and 20-30% for metastatic disease.
Osteosarcoma is an aggressive malignant bone tumor. With early diagnosis and neoadjuvant chemotherapy + surgical resection, 5-year survival can reach 60-70%. Lung metastasis is the most common distant metastatic site. Skip metastases are critical for local staging.