Ewing Sarcoma

  • Etiology: malignant small round blue cell tumor, family of tumors – Ewing sarcoma of bone / extraskeletal Ewing sarcoma / peripheral primitive neuroectodermal tumor / Askin tumor
  • Imaging:
    — Location: diametaphyseal or diaphyseal
    — Lytic or blastic:
    — Matrix: (chondroid, osteoid, fibrous)
    — Zone of transition: wide
    — Periosteal new bone or cortical destruction: lamellated or sunburst periosteal reaction and permeative / lytic-sclerotic / sclerotic cortical destruction
    — Additionally: most common sites: axial skeleton (54%) and appendicular skeleton (42%), occurs in both long + flat bones, in spine mimics other vertebral body tumors with vertebral body collapse and intradural and extradural spinal extension
  • Radiograph: diametaphyseal or diaphyseal, poorly marginated, intramedullary, permeative / lytic-sclerotic / sclerotic, lamellated (onion skin) or sunburst periosteal reaction, + or – soft tissue mass
  • MRI: T1WI – heterogenous and hypointense, T2WI – heterogenous and hyperintense, heterogenous enhancement, look for skip metastases in bone
  • DDX: osteomyelitis, osteosarcoma
    — Can mimic osteomyelitis + be associated with leukocytosis / fever / increased sedimentation rate
    — Periosteal reaction is sunburst in osteosarcoma vs. onion skin in Ewing sarcome
    — Tumor margins on MRI are sharp in osteosarcoma vs. infiltrative in Ewing sarcoma
    — Focal bone metastases in osteosarcoma vs. bone marrow involvement in Ewing sarcoma
  • Complications: 25% have metastases at diagnosis to lung / bone / bone marrow / skip metastasis to bone, presence of overt metastatic disease at diagnosis is strongest adverse clinical prognostic indicator, but is almost always micrometastatic at diagnosis
  • Clinical: occurs in 10-20 year olds, second most common primary bone tumor and soft tissue tumor in children
  • Note: Askin tumor
    — Ewing sarcoma arising from chest wall, rib, lung parenchyma
    — Imaging: large intra and extrathoracic mass, rib destruction, pleural thickening and effusions, rarely calcified, heterogenous due to necrosis and hemorrhage

Radiology Cases of Ewing Sarcoma

Radiograph and CT of Ewing sarcoma of the spine
Lateral radiograph of the spine shows collapse of the T12 vertebral body. Sagittal 2D reconstruction and axial CT without contrast of the T12 vertebral body in bone windows shows a permeative destructive process affecting it. Axial CT without contrast of the abdomen at the T12 level shows a large left-sided paraspinal soft tissue mass.
Radiograph of Ewing Sarcoma
AP radiograph of the right hip shows a permeative appearance to the medullary portion of the proximal femur with cortical destruction and diffuse periosteal reaction.
CT of Ewing sarcoma of the rib
Axial CT with contrast of the chest shows a large heterogenous non-enhancing soft tissue mass centered around the posterior aspect of the right 11th rib. 3D CT reconstruction better demonstrates the lesion’s origin from the right 11th rib.

Gross Pathology Cases of Ewing Sarcoma

Pathological image of Ewing sarcoma of the rib
Pathological image shows a tumor which was brown and grossly necrotic and was seen to be located predominantly in the soft tissues and not in the rib.