Extraskeletal Ewing sarcoma

Clinical History

A 23-year-old man presented with a 3-month history of right lower extremity paresis and sensory disturbances. Two weeks before he noticed a right inguinal mass and decided to consult us.

Imaging Findings

After clinical examination an ultrasound was performed first. B mode US showed a nodular, lobed and hypoechoic right inguinal mass with an approximated size of 55x43x25 mm (Fig. 1 a). US Power Doppler demonstrated hypervascularization (Fig. 1 b). For further characterization an MR was made. MR-T1 weighted images (Fig. 2 a) located an hypointense mass above the psoas muscle, between the iliac-femoral veins and the sartorius muscle. On MR-T2 weighted images (Fig. 2 b) the mass appeared hyperintense. Diffusion WI sequences showed restriction of the water movement that indicated malignancy (Fig. 2 c). After the injection of gadolinium a heterogeneous and centripetal enhancement was demonstrated, suggesting necrotic areas inside the mass (Fig. 2 d). PET-CT indicated hypercaptation of the inguinal lesion without systemic extension (Fig. 3). The histopathological analysis demonstrated a round, small cell sarcoma. Finally FISH study showed translocation 11;22. The immunohistochemical test with Ki67 showed nuclear immunoreactivity of 70 % of the tumoural cells.

Discussion

Ewing sarcoma is an aggressive malignant tumour with a neuroectodermal origin. It primarily affects young people during the first two decades of life, usually as a pelvic or long bone tumour [1].

Extraskeletal Ewing sarcoma is an uncommon variant which develops from soft tissue instead of bone. It is part of a group of tumours called the Ewing sarcoma family, which have karyotype abnormalities and histological findings in common. It usually appears as a rapidly growing and painless mass. The most common sites of presentation include paravertebral region, lower extremities and chest wall [2]. Clinical manifestations will depend on the localization of the mass. Paravertebral extraskeletal Ewing sarcoma may present as back or radicular pain, while sensory disturbances may manifest in the extremities [1].

Imaging features of extraskeletal Ewing sarcoma are nonspecific. In ultrasound images lesions are most frequently hypoechoic. Some anechoic areas may also be present, as a sign of haemorrhage or necrosis. Colour Doppler US usually demonstrates an increased blood flow inside the mass. CT can show a hypodense soft tissue mass adjacent to muscle. Hypodense areas are frequent inside large masses and are due to intratumour necrosis. On MR T1-weighted images, the tumour shows low to intermediate signal intensity. On T2-weighted images malignant sarcomas are hyperintense with heterogeneous contrast enhancement after gadolinium injection. If the mass is located near bone, it might result in cortical erosion and/or a periosteal reaction. PET-CT may be useful for detecting lymph nodes and bone metastases involvement [1].

The final diagnosis is histological and shows the characteristic small and round cells. A specific antigen, CD99/MIC2, 12-14 and the t(11;22)(q24;q12), 15 chromosomal translocation allow to differentiate skeletal and extraskeletal Ewing sarcoma from other small, round cell tumours [3].

There is not yet a strong consensus on the treatment of extraskeletal Ewing sarcoma, but multidisciplinary management offers the best prognosis. To reduce the size of the tumour and the risk of metastatic disease and recurrence, chemotherapy is required as neoadjuvant as well as adjuvant therapy. Surgical resection and/or irradiation follow [2, 4].

Differential Diagnosis List

Final Diagnosis

Extraskeletal Ewing sarcoma

URL:	https://www.eurorad.org/case/11296
DOI:	10.1594/EURORAD/CASE.11296
ISSN:	1563-4086