Ewing sarcoma is the second most common primary malignant bone tumor and belongs to the small round blue cell tumor group. It predominantly occurs in the diaphysis or metadiaphysis of long bones, and flat bones (pelvis, scapula, ribs) are also frequently affected. Peak incidence is in the pediatric and adolescent age group (5-15 years). Radiologically, it is characterized by permeative bone destruction, onion-skin periosteal reaction, and disproportionately large soft tissue mass. EWS-FLI1 gene fusion is a diagnostic marker.
Age Range
5-25
Peak Age
12
Gender
Male predominant
Prevalence
Uncommon
Ewing sarcoma is a malignant neoplasm arising from neural crest-derived mesenchymal stem cells, and tumor cells do not produce any matrix (osteoid or chondroid) — this feature forms the basis for the radiological appearance of lytic destruction without matrix mineralization. Tumor cells start from the bone marrow and permeatively infiltrate the cortex along Haversian and Volkmann canals; this permeative spread manifests radiologically as moth-eaten or permeative destruction pattern. The tumor's spread beneath the periosteum after breaching the cortex causes repeated cycles of periosteal elevation and ossification, creating the onion-skin periosteal reaction. In Ewing sarcoma, a soft tissue mass disproportionately large relative to the bone component forms; this reflects the tumor's early and aggressive extraosseous spread and appears on MRI as a large extraosseous component showing homogeneous high signal on T2-weighted sequences — the T2 signal is relatively homogeneous compared to other bone tumors due to the tumor's high cellularity and small round cell morphology.
Lamellar (onion-skin) periosteal reaction accompanying permeative bone destruction in diaphyseal location with a disproportionately large soft tissue mass without matrix mineralization — in a pediatric/adolescent patient, this combination is the most characteristic radiological appearance of Ewing sarcoma.
Aggressive bone destruction with moth-eaten or permeative pattern in diaphyseal or metadiaphyseal location. This finding, also visible on conventional radiography, is superior on CT for evaluating the full extent of cortical destruction and soft tissue component. No matrix mineralization — this feature is the most important distinguishing finding from osteosarcoma.
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Permeative pattern bone destruction without matrix mineralization in diaphyseal location, consistent with aggressive bone lesion.
Lamellar (onion-skin) periosteal reaction formed by repeated tumor spread beneath the periosteum. Multiple thin layers of periosteal bone are arranged concentrically over the cortex. This periosteal reaction pattern is characteristic of Ewing sarcoma but not pathognomonic; it can also be seen in other aggressive processes such as osteomyelitis and lymphoma. CT multiplanar reformats are superior to conventional radiography for evaluating periosteal reaction.
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Lamellar (onion-skin) pattern periosteal reaction is seen around the cortex, consistent with Ewing sarcoma.
Disproportionately large, homogeneous-to-moderate enhancing soft tissue mass relative to the bone lesion. Contrast-enhanced CT is important for evaluating the tumor's relationship with vascular structures and compartment invasion. Areas of necrosis may be seen in large tumors but it is less heterogeneous compared to osteosarcoma.
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A large, moderately homogeneously enhancing soft tissue mass disproportionate to the bone lesion is identified.
Tumor infiltration replaces the high T1 signal of normal fatty bone marrow on T1-weighted sequences. The tumor shows homogeneous low-to-intermediate signal intensity. T1 sequence is critically important for assessing medullary extent and surgical planning. The soft tissue mass also shows low-to-intermediate T1 signal.
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Low signal intensity lesion infiltrating bone marrow on T1-weighted sequences with accompanying soft tissue mass is identified.
Both intramedullary component and soft tissue mass show high signal on T2-weighted sequences. The T2 signal in Ewing sarcoma is more homogeneous compared to osteosarcoma — this feature reflects the tumor's uniform small round cell structure. Areas of necrosis and hemorrhage may create heterogeneity in large tumors. Perifocal edema appears as high T2 signal.
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Large soft tissue mass and intramedullary component showing homogeneous high signal on T2-weighted sequences.
Tumor infiltration and surrounding tissue edema show markedly high signal on STIR sequence. Normal bone marrow fat signal is suppressed, allowing clear assessment of intramedullary tumor extent. The full extent of periosteal reaction and soft tissue mass boundaries in Ewing sarcoma are best seen on STIR.
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Intramedullary extent, periosteal reaction, and soft tissue mass boundaries of the tumor are clearly assessed on STIR.
Solid tumor components demonstrate marked diffusion restriction on DWI (high signal on DWI, low values on ADC map). Diffusion restriction is prominent due to high cellularity and small round cell morphology in Ewing sarcoma. ADC values are generally lower than osteosarcoma. Increase in ADC values during treatment response assessment indicates response to therapy.
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Marked diffusion restriction in solid tumor components consistent with high cellularity; ADC values are markedly low.
Solid tumor components show diffuse, relatively homogeneous enhancement on post-gadolinium sequences. Unlike osteosarcoma, enhancement is more homogeneous — this feature reflects the tumor's uniform cellular structure. No enhancement in necrotic areas. Contrast-enhanced MRI plays a critical role in evaluating neurovascular bundle involvement and compartment boundaries.
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Diffuse homogeneous enhancement in solid tumor components on post-contrast sequences; neurovascular bundle and compartment boundaries should be evaluated.
Ewing sarcoma shows intense FDG uptake (SUVmax usually >5). PET-CT plays an important role in detection of distant metastases (bone, lung, bone marrow) and staging. PET-CT is superior to conventional bone scintigraphy for detection of bone marrow metastases. Decrease in FDG uptake after neoadjuvant chemotherapy (especially SUVmax change) is an important indicator of treatment response.
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Intense FDG uptake is seen in the primary tumor and metastatic foci; baseline SUVmax value should be noted for treatment response assessment.
Criteria
Most common form. Primary bone location. Long bone diaphysis or flat bone (pelvis, scapula, rib) involvement. CD99 positive, EWS-FLI1 fusion.
Distinct Features
Typical permeative destruction and onion-skin periosteal reaction. Large soft tissue mass. Diaphyseal predilection. No matrix mineralization on conventional radiography and CT.
Criteria
Primary soft tissue location. No or secondary bone involvement. May occur in older patient group. Same histology and genetic profile (EWS-FLI1).
Distinct Features
Presents as soft tissue mass, bone destruction and periosteal reaction may be absent. Homogeneous T2 high signal and marked enhancement on MRI. Marked diffusion restriction on DWI. Requires differential diagnosis with rhabdomyosarcoma and lymphoma.
Criteria
Neural differentiation-showing member of Ewing sarcoma family. Same genetic translocation (t(11;22)). Radiologically indistinguishable from classic Ewing. Immunohistochemically positive for neural markers (NSE, S-100, synaptophysin).
Distinct Features
Radiologically same findings as classic Ewing sarcoma. Distinction is made histopathologically and immunohistochemically. Treatment and prognosis are similar.
Criteria
Located in pelvis, scapula, rib, or vertebra. Typical diaphyseal periosteal reaction may not be seen in flat bones. Large soft tissue mass may be the dominant finding.
Distinct Features
Large destructive mass in pelvic location with prominent soft tissue extension. Onion-skin periosteal reaction is absent. Permeative destruction on CT and large soft tissue mass on MRI direct the diagnosis. Pelvic location is associated with worse prognosis.
Distinguishing Feature
Osteosarcoma is metaphyseal and produces osteoid matrix mineralization (cloud-like). Ewing sarcoma is diaphyseal, lacks matrix mineralization, and shows onion-skin periosteal reaction.
Distinguishing Feature
Osteomyelitis may also show lamellar periosteal reaction but is characterized by sequestrum, involucrum, and sinus tracts. Clinical context (fever, elevated CRP/ESR) and penrose-type peripheral enhancement on contrast MRI support osteomyelitis.
Distinguishing Feature
Langerhans cell histiocytosis is usually a well-defined lytic lesion with less aggressive periosteal reaction. More common in younger age group (1-5 years). Soft tissue mass is small or absent. Large soft tissue mass and more aggressive destruction are expected in Ewing sarcoma.
Distinguishing Feature
Multiple myeloma typically occurs in adults over 50 and is characterized by multiple lytic lesions. Ewing sarcoma is a solitary aggressive lesion in pediatric/adolescent age group. Periosteal reaction is rare in myeloma, characteristic in Ewing.
Distinguishing Feature
Bone metastases in children usually originate from neuroblastoma, in adults from various primary tumors. Multiple lesions and known primary tumor history support metastasis. Ewing sarcoma is usually a solitary lesion without known primary focus.
Urgency
highManagement
Neoadjuvan kemoterapi (vincristin, doxorubisin, siklofosfamid, ifosfamid, etoposid) + lokal kontrol (cerrahi rezeksiyon veya radyoterapi) + adjuvan kemoterapi. Radyoterapiye duyarlı bir tümördür. Multidisipliner yaklaşım zorunludur.Biopsy
NeededFollow-up
Tedavi sonrası ilk 2 yıl 3 ayda bir MR + akciğer BT + kemik sintigrafisi/PET-BT, 2-5 yıl arası 6 ayda bir, 5 yıl sonrası yıllık takip. Kemoterapi yanıtı MR (özellikle DWI/ADC) ve PET-BT ile değerlendirilir.Ewing sarcoma is a high-grade malignant bone tumor requiring urgent multidisciplinary evaluation. Staging (chest CT, whole-body MRI/PET-CT) should be performed rapidly after diagnosis, and neoadjuvant chemotherapy should be initiated. Ewing sarcoma is radiosensitive — radiotherapy is an alternative for local control in surgically unresectable cases. 5-year survival is 65-70% for localized and 20-30% for metastatic disease. Pelvic location and large tumor size are poor prognostic factors.
Ewing sarcoma is an aggressive small round blue cell tumor. With chemotherapy + surgery/radiotherapy, 5-year survival for localized disease is 65-75%. Prognosis is significantly worse for metastatic disease (20-30%). Early diagnosis and multidisciplinary approach are critical.