Teaching Case

A 23-year-old man presented with severe pain at the right chest wall for more than a month. There was no history of trauma.

Plain films of the right rib cage (Fig. 1) showed a subtle triangular opacity projecting underneath the anterior aspect of the right diaphragm.

A subsequent CT examination of the chest (Fig. 2) confirmed an extrapleural, sharply lineated soft-tissue mass encasing the seventh right rib. There was an associated aggressive periosteal reaction (sunburst type) at the inner border of the seventh rib. There was heterogeneous enhancement of the lesion.

MR-imaging (Fig. 3) showed lesion extension into the muscles of the right chest wall. The lesion was of high signal on T2-weighted images and was iso-intense to muscle on the T1-WI. After intravenous administration of gadolinium contrast, there was a heterogeneous enhancement.

Based on the age of the patient and the imaging features, the lesion was very suspicious for Ewing’s sarcoma of the chest wall or Askin tumour. This was confirmed after histopathological examination of a biopsy of the lesion.

Ewing’s sarcoma is the second most common malignant bone tumour in young adults. Occasionally the lesion is located extra-skeletally, aka soft-tissue Ewing’s sarcoma or primitive neuroectodermal tumours (PNET). The peak incidence is the second decade of life. The male-to-female ratio is 1.5:1. The clinical presentation of Ewing’s sarcoma is nonspecific and includes pain and swelling at the affected site. Fever, weight loss, cough, anaemia and leukocytosis are less frequently seen. The most frequent locations are the pelvis, femur, tibia, humerus, fibula and ribs. [1, 2]

Askin tumours are soft-tissue Ewing’s sarcomas of the chest wall and are histologically similar to PNET and Ewing’s sarcomas of the bone. Cytogenetic and molecular evaluation techniques showed that all these tumours have the same genetic lineage, having a translocation between chromosomes 11 and 22. Most authors agree that Ewing’s sarcoma, PNET and Askin tumour are closely related and might even be identical lesions. Therefore, they are referred to as the Ewing sarcoma family of tumours. [2, 3]

Plain films show bone destruction, which is often associated with an aggressive periosteal reaction. Bone sclerosis may also be seen. A large associated soft-tissue mass is common. CT may be useful for detection of the lesion in complex anatomical areas, where there is a lot of superposition such as the skull base, pelvis and chest wall. [2, 4] MRI is superior to CT to assess bone marrow replacement and any associated soft-tissue component. The signal intensity is usually intermediate and inhomogeneous on T1-WI. On T2-WI the signal intensity varies from low (68%) to high (32%). Ewing’s sarcomas of the soft tissues are usually of high signal on T2-WI. There is always (heterogeneous) contrast enhancement. [1, 2]

Subtle cortical involvement can be seen as linear intermediate signal intensity channels permeating the cortex between the bone marrow and the soft-tissue component. This represents tumour extension along the Haversian canals and the neurovascular channels. In most soft-tissue Ewing’s sarcomas, there is usually no bone marrow extension but reactive periosteal reaction can be present if the lesion is adjacent to bone. Askin tumours -however- present often with rib destruction. [2]

The final diagnosis is made by histopathology. Treatment is multidisciplinary and involves (neo)adjuvant chemotherapy, surgical resection and radiation therapy. The prognosis of Askin tumour is poor compared to Ewing’s sarcoma at other sites. Two-year and 6-year survival rates of only 38% and 14% respectively have been reported. [2, 3]