Extraskeletal Ewing sarcoma

Extraskeletal Ewing sarcoma (EES) is included in the Ewing sarcoma family of tumors (ESFT) along with Ewing sarcoma of bone, peripheral primitive neuroectodermal tumor (pPNET), peripheral neuroepithelioma, and Ewing sarcoma of the chest wall (previously known as Askin tumor). When compared with Ewing sarcoma of bone, extraskeletal Ewing sarcoma is rare.

Epidemiology

Extraskeletal Ewing sarcoma is generally found in younger patients (85% between the age of 20 months and 30 years). Osseous Ewing sarcoma is estimated to be about 5 to 6 times more prevalent than extraskeletal Ewing sarcoma ², however, in adults, at least half of primary cases are extraskeletal ¹.

When compared with Ewing sarcoma of bone, extraskeletal Ewing sarcoma displays several differences ^8-11:

• no distinct male predilection, but instead a more equal distribution between sexes

• slightly older age group than found in osseous Ewing sarcoma by 5-10 years, the average age is 20 years of age

• the trunk is affected more frequently than the lower extremities

Clinical presentation

A rapidly growing, solitary, superficial or deep mass in the soft tissues is generally seen between 5 and 10 cm at the initial presentation ⁸. Depending on where the tumor is located, adult patients generally present with a painless mass or vague abdominal or chest pain ¹. If the mass is seen to be paravertebral, the patient can present with symptoms of cord compression ¹⁰. Between 35% and 43% of adult patients have metastatic disease at presentation ^3,5. The lung is the most common site of metastasis ⁴.

Pathology

Location

• paravertebral region (~30%)

• lower extremities (~25%)

• chest wall (~20%)

• retroperitoneum (~10%)

• pelvis and hip (~10%)

• upper extremities (3%) ^6,8,10,12,13

• intracranial ¹⁸

Radiographic features

Extraskeletal Ewing sarcoma imaging features are generally non-specific.

Ultrasound

• most frequently hypoechoic ¹⁵

• increased Doppler blood flow ¹⁴

Plain radiograph

• normal appearance

• large soft-tissue mass (50%)

• calcification (25%)

• presence of adjacent bone erosion, cortical thickening, osseous invasion, or periosteal reaction ²

CT

• nonspecific soft-tissue mass of similar attenuation to the muscle (87%)

• low attenuation can be due to hemorrhage or necrosis

• calcification (25-30%)

• osseous involvement of bone surface with cortical erosion or periosteal reaction (40%) ¹⁴

MRI

A common feature is disorganized high-flow vascular channels with low signal intensity with all pulse sequences (90%). Additionally, a pseudocapsule with somewhat well-defined margins can be seen (36%) ¹⁴.

• T1

  • soft tissue mass with heterogeneous signal intensity (~90%)

  • similar intensity to skeletal muscle

• T1 C+ (Gd)

  • heterogeneous but prominent enhancement

• T2

  • intermediate to high signal intensity (100%)

  • fluid levels may be evident

Nuclear medicine

Bone scintigraphy and FDG-PET both show increased radionuclide uptake ¹².

Treatment and prognosis

Management of local disease starts with neoadjuvant chemotherapy as the standard of care before definitive radiation or surgery. Extraskeletal Ewing sarcoma is aggressive with a high propensity for local recurrence and distant metastasis. Recurrence occurs in ~30% (range 22-36%) ^3,4.  Adult outcomes may be worse than in children, because of the inability of adults to tolerate aggressive chemotherapy ^16,17.

Differential diagnosis

General imaging differential considerations include:

• higher grade vascular lesions (hemangioendothelioma, hemangiopericytoma, angiosarcoma)

• rhabdomyosarcoma

• synovial sarcoma

• alveolar soft-part sarcoma