Ewing's Tumor
Pre-test and tutorial

Frank J. Frassica, MD
Franklin H. Sim, MD

• Presentation
• Radiographic features
• Histologic features
• Treatment
• References

Ewing's tumor is a primitive small blue cell tumor that most commonly affects young patients. The exact cell of origin is not known. James Ewing believed that the tumor arose from endothelium within the osseous system. Ewing's tumor can virtually involve any bone in the skeleton. Common sites include:

• Femur
• Pelvis
• Humerus
• Scapula
• Sacrum
• Tibia
• Ribs

This tumor usually involves young patients age 5 to 20 years (about 75% of cases).¹ The disease may affect adults up the age of 60 years; however, the frequency rapidly decreases after the age of 40 years.

Presentation

Patients almost always present with severe bone pain. The most important aspect of the presentation is to remember that it may be insidious and non-specific.

Patients may present with symptoms and signs of infection, such as:

• Fever
• Pain
• Elevated white blood cell count
• Single destructive bone lesion

The clinician must be careful to distinguish Ewing tumor from infection. Despite the appearance of all the classic signs of infection, the clinician should always have Ewing tumor in the differential of a destructive bone lesion.

Patients may also present with pain after minor trauma. A child or young adolescent may be injured while engaged in sports activity and present with extremity pain. There is usually an antecedent history of pain at rest.

The most common presentation is pain. The pain is typical of the pain seen with malignant bone tumors: intermittent at the start then constant; pain at rest and at night; pain that is not responsive to aspirin or anti-inflammatory medications. The initial radiograph may be normal or show only subtle changes. If the clinician suspects a malignant bone tumor and the radiographs are normal, one should obtain a technetium bone scan to help localize the abnormal area.

Radiographic features

The radiographic features of Ewing tumor may be very variable. The tumor may resemble a cyst, osteomyelitis, osteosarcoma or the radiographic may actually look normal or only have minimal abnormalities.

The hallmark finding is bone destruction. Usually the lesion is completely lytic; however, many lesions will have a lytic-blastic appearance secondary to new bone formation (Slide 4). In contrast to many other primary malignant bone tumors Ewing's tumor tends to involve large segments (Slide 5) of the bone (often greater than 50% of the length of the medullary cavity). The cortex may show no changes, be destroyed, or show some thickening secondary to the periosteal reaction (Slide 5).

Slide 4


Slide 5

In some patients the bone destruction is so prominent that the lesion appears like a cyst as the entire bone is destroyed and the periosteal reaction symmetrically expands the bone (Slide 6). Usually when this occurs there will not be any matrix mineralization within the lesion. When there is lytic expansion the lesion may mimic an aneurysmal bone cyst or a bone cyst.

Slide 6

Ewing's tumor have a particular ability to permeate through the cortical bone and centripetally expand into the soft tissues. The periosteally reaction may be in the form of multiple small layers (onion skinning), streaky perpendicular layers, or a sunburst arrangement similar to osteosarcoma. The streaky periosteal bone is a non specific finding and may also be seen in osteomyelitis and other bone tumors (Slide 7). The sunburst pattern is often extensive (Slide 8).

Slide 7


Slide 8

One of the most deceptive presentations is a pathologic fracture. One must be careful to check the fracture ends for lytic bone destruction (Slide 9).

Slide 9

Histologic features

Histologically, Ewing tumor is a small blue cell tumor. On low power, there is a monotonous collection of similar appearing blue cells (Slide 10). The shape of the nuclei is round or oval. On higher power one can see the small blue cells and in some areas there are fine strands of reticulum (Slide 11).

Slide 10


Slide 11

On high power, the cell borders are indistinct and the cells look smudged together (Slide 12). On higher power, one can see that the cells are round and uniform (Slide 13). In contrast, in osteomyelitis, the histologic picture is one of a mixed cell population and the cells are spread apart by edema fluid (Slide 14). On even higher power, there are polymorphonuclear leukocytes and plasma cells (Slide 15).

Slide 12


Slide 13


Slide 14


Slide 15

Interestingly, there is a characteristic 11-22 chromosomal translocation in patients with Ewing tumor. In some patients, the cells may from rosettes and the lesion is called a primitive neuroectodermal tumor (PNET) rather than Ewing tumor. All the other clinicopathologic features are similar and the treatment is exactly the same.

Treatment

The treatment of Ewing tumor is multi-disciplinary: multi-agent chemotherapy, external beam irradiation and surgery in selected cases. In the past, the mortality rate for Ewing tumor without chemotherapy was greater than 80%. In contrast with today’s regimens greater than 60% of patients are long-term survivors.

External beam irradiation has been the main modality for local control. Typical doses are 4500 cGy to 5000 cGy. When the lesion can be precisely identified with MRI then only the lesion and a limited amount of normal tissue is treated.

The role of surgery is controversial. In the past, only expendable bones were removed, such as the fibula, ribs and wing of the ilium. There is a definite trend toward a more prominent role of surgery. Unfortunately, there are no prospective randomized studies comparing surgery and chemotherapy to external beam irradiation and chemotherapy.

References

1. Unni KK. Dahlin’s Bone Tumors: General Aspects and Data on 11,087 Cases. Philadelphia, Pa: Lippincott-Raven; 1996; chap 9:121-130; chap 10:131-142