Ewing sarcoma of the chest wall

Last revised by Joshua Yap on 26 Apr 2023

Ewing sarcomas of the chest wall are malignant tumors affecting children and young adults, originating either from the osseous structures or the soft tissues of the chest wall. 

On imaging, they are usually characterized as large extrapulmonary invasive soft tissue masses that are heterogeneous due to the presence of hemorrhage, necrosis, or cystic changes. Enhancement is intense and there is increased uptake in nuclear medicine studies. Calcifications are uncommon and a small pleural effusion is frequently present. 

Originally, a small round blue cell tumor of the soft tissues of the chest was described and became known as an Askin tumor or peripheral primitive neuroectodermal tumor (pPNET). All these entities are now thought to belong to the same tumor family, now referred to as Ewing sarcoma family of tumors (ESFT) 1-3.

Not surprisingly, the demographics of these chest wall tumors are similar to those of Ewing sarcomas elsewhere, seen predominantly in children and young adults 4. Ewing sarcomas account for 10-15% of all primary chest wall tumors 6.

These tumors may either arise in the osseous structures of the chest wall (rib, scapula, sternum, or clavicle) or less frequently in the soft tissues of the chest (it was these latter lesions that were first described as Askin tumors/pPNET) 3. They can either be single or multiple masses and present as rapidly growing masses.

Typically they present as rapidly growing, often painful, warm soft tissue masses 6.

The Ewing sarcoma family of tumors share common cytogenetic and microscopic features. They demonstrate non-random t(11;22)(q24;q12) chromosome rearrangement resulting in the formation of the EWS-ETS fusion gene, with variable degrees of differentiation (e.g. Homer Wright rosettes) 1-3. As the tumor progresses, cystic degeneration can occur.

Despite their aggressive nature, these tumors tend to (at least initially) displace adjacent structures (e.g. lung, diaphragm). Direct invasion is however seen especially in larger tumors 3. They may cause rib destruction.

On CT, these tumors are typically ill-defined with heterogeneous attenuation and multiple areas of cystic degeneration. Solid components demonstrate enhancement following the administration of contrast. Pleural effusions are common but are usually small 4. Calcification is uncommon 4.

When these tumors arise in bone, onion skin periosteal reaction may be evident.

Typically these masses are heterogeneous on MRI as well as CT on account of numerous areas of necrosis, degenerative cystic change and hemorrhage 3,4. Smaller tumors are more likely to be homogeneous 4.

  • T1: iso- or hyperintense to muscle 3

  • T2: heterogeneous high signal

  • T1 C+ (Gd): prominent heterogeneous enhancement

When tumors arise in the paravertebral region, direct extension through the neural exit foramen may be seen 3.

Treatment involves surgical resection and neoadjuvant chemotherapy +/- radiotherapy. The strongest predictor of outcome is the presence or development of distant metastases 5,6. In patients whose tumor is confined to the chest, long-term survival is achievable. Overall 5-year survival is between 15-48% 6.

The differential is that of other tumors of the chest wall, especially other sarcomas, including: 

  • osteosarcoma 

    • tumor matrix ossification/calcification

    • the thorax is an atypical location

  • chest wall and pleural metastases 

    • usually the most common primary tumors are themselves located in the chest: lung cancer and breast cancer 

  • lymphoma

    • homogeneous, vividly enhancing mass without rib destruction

  • solitary fibrous tumor of the pleura

    • chest wall involvement rare

  • rhabdomyosarcoma

    • usually indistinguishable

    • the thorax is a rare location

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