Primary Ewing sarcoma of rib

Clinical History

A 30-year-old-male presented with pain and swelling on the right side of chest for last 6-months. He also complained of heaviness and noticed a rapidly progressive swelling along the right lower lateral chest wall and upper abdominal wall which progressed to the present size over the last 5-months.

Imaging Findings

For the above mentioned complaints he was advised to undergo a chest radiograph. The chest radiograph showed osseous destruction of the tenth rib on the right side. This was associated with a subtle thick spiculated perisoteal reaction and a large soft tissue component, which was occupying almost the entire right hemithorax. It was displacing the mediastinum and cardia to the contralateral side. A CT scan of the thorax confirmed the lytic expansion of the right-tenth-rib with associated thick spiculated periosteal reaction. There was a disproportionately large soft tissue component seen on either side of the affected rib. This huge extraparenchymal intra-thoracic mass occupied almost the entire hemithorax and extended into the right recessus costodiaphragmaticus. At the base of the right hemithorax it was seen compressing the liver and displacing it to the left side. Laterally there was a large chest wall component, which extended caudally into the upper abdominal wall. This showed multiple tortuous and serpigeneous feeding vessels representing high vascularity of the lesion. The soft tissue component demonstrated an avid but markedly heterogeneous post contrast enhancement. A chest wall tumor of relatively short duration, demonstrating rib destruction and a disproportionately large soft tissue component raised the suspicion of Ewing's sarcoma and primitive neuroectodermal tumour (PNET). Other differentials, although less common, included chondrosarcoma and osteosarcoma. However there was no chondroid or osseous matrix calcification seen to suggest chondrosarcoma or osteosarcoma. A biopsy was performed and the histolopathology was quite characteristic of Ewing sarcoma.

Discussion

Ewing’s sarcoma (ES) has been named after Sir James Ewing who first described this entity in 1921. ES is a highly malignant small round cell tumour accounting for 5-10% of primary bone tumours. It generally arises from long bones such as tibia, femur and humerus; wherein it involves the meta-or-mid-diaphysis. ES can also arise from flat bones such as ribs, scapula and innominate bone. The majority of ES cases show the cytogenetic translocation t(11;22)-(q24;q12). ES is commonly encountered in children and young adults predominantly during first two decades of life with a slight male preponderance (male-to-female ratio 1.5:1). Although uncommonly, ES has been documented in adult patients demonstrating a similar behavior and prognosis as in children.

Approximately 10-15% of ES cases arise from the ribs. It is considered the most common malignant chest wall tumour of childhood. These patients usually present with a painful chest wall mass. Symptoms are usually of a relatively short duration. Characteristic imaging manifestation includes a chest wall tumour with associated osseous destruction. Plain radiograph findings can be highly variable ranging from a subtle rarefaction of the rib to a large soft tissue mass opacifying almost the entire hemithorax with frank rib destruction. When involving the long bones ES may demonstrate a diverse pattern of periosteal reaction ranging from onion-peel/lamellated/laminated/ sunburst/spiculated/hair-on- end/Codman’s triangle. However such an extensive periosteal reaction is not seen in ES of the rib. ES of the rib predominantly shows lytic expansion of the involved rib. Less commonly it may manifest as mixed lytic-sclerotic bone destruction or as purely sclerotic pattern. A disproportionately large soft tissue component has been described as a salient feature of ES of the rib. It has been seen that this soft tissue “engulfs” the affected rib and the intra-thoracic component is usually larger than the extra-thoracic component. The soft tissue component demonstrates smooth or lobulated margins. Cross-sectional imaging such as CT or MRI allows a superior delineation of the tumour characteristics, precise extent, relationship to the adjacent structures, intraspinal extension and metastatic spread if any to the lungs and mediastinal lymph nodes. The large overlying soft tissue can obscure the visualization of affected rib on plain radiograph, which can be better evaluated with a CT-scan. ES show a propensity for systemic spread and hence require an intensive multidrug chemotherapy. Local treatment consists of surgical resection, radiotherapy or a combination of surgery plus radiation therapy. The overall 5-10 year survival rate is approximately 50%.

Differentials include chondrosarcoma and osteosarcoma, which are relatively uncommon and demonstrate chondroid and osseous tumour matrix calcification respectively. Closest differential of thoracic ES is the primitive neuroectodermal tumour, also known as Askin tumor. Askin tumor like ES is a small round cell tumours of childhood associated with chromosome 22-translocation which is often indistinguishable from ES on imaging. Cytoplasmic glycogen at periodic-acid–Schiff staining is a feature used to differentiate Ewing sarcoma from primitive neuroectodermal tumors. Other rib lesions such as osteomyelitis, eosinophillic granuloma or leukemia do not demonstrate such an extensive soft tissue component as is seen in ES.

Differential Diagnosis List

Final Diagnosis

Primary Ewing sarcoma of rib

URL:	https://www.eurorad.org/case/8575
DOI:	10.1594/EURORAD/CASE.8575
ISSN:	1563-4086