Radiology Corner – Ewing’s Sarcoma

By: Terry R. Yochum, D.C., D.A.C.B.R., Fellow, A.C.C.R., and Chad J. Maola, D.C.

Case History: This 21 year old male complains of lateral ankle pain of one month duration.

Diagnosis: Observer the lytic moth-eaten (permeative) destruction of the distal diametaphysis of the fibula. The initial differential diagnosis was osteomyelitis versus primary malignant tumor. Biopsy confirmed the diagnosis of “Ewing’s tumor”.

Discussion

Ewing’s sarcoma represents approximately 7% of all primary malignant bone tumors and is the fourth most common primary malignant bone tumor, with myeloma, osteosarcoma and chondrosarcoma occurring more frequently (in decreasing order of incidence). (1)

Age and Sex Distribution

Ewing’s sarcoma is found most commonly in the 10 to 25 year age range, with a peak at 15 years. It is rare before the age of 5 and after the age of 30; 50% of cases occur before the age of 20. Patients in the younger age range (5 to 20 years) usually have lesions in the peripheral skeleton, while those older patients (age 20 to 35) present with axial lesions. There is a 2:1 male to female ratio.

Signs and Symptoms

Localized pain with swelling at the site of the lesion is a consistent presenting complaint. Often, a soft tissue mass is palpable. The pain initially is dull in nature; however, it usually becomes severe and persistent a few months prior to diagnosis. Systemic symptoms of slight to moderate fever, secondary anemia, leukocytosis and increased ESR are common in Ewing’s sarcoma. Ewing’s tumor seems to be the only primary malignant bone tumor with symptoms simulating an infection. Local temperature elevation with dilated veins and associated tenderness accompanies the lesion, thereby suggesting an inflammatory condition. The inflammatory-like symptoms of Ewing’s sarcoma may be explained by the fact that the tumor characteristically outgrows its blood supply, resulting in extensive degeneration and necrosis. With such a clinical presentation, biopsy may be the only means of diagnosis. (1)

Location

Ewing’s sarcoma is seen most frequently in the long tubular bones (50%) and in the flat bones (40%). The lower extremity encompasses the largest portion of the tubular involvement. The femur is most commonly involved (23%) with the tibia, fibula and humerus following (9%). The diaphysis is the classic location for these tumors; however, more cases are being seen affecting the metaphysis and metadiaphyseal region (as seen in this case). (1)

Radiological Features

The classic presentation is that of a diaphyseal lesion (usually in the lower extremity), permeative in its appearance, with a wide zone of transition. A delicate, laminated, onion skin or onion peel periosteal response is noted in only 25 to 50% of cases. Cortical saucerization is an early and characteristic sign. This irregular defect effaces the outside of the bone occasionally, exhibiting a marginal scalloping effect. It occurs when the tumor grows through the haversian system and presents subperiosteally. Purely lytic lesions are uncommon, with a mixed lytic and sclerotic pattern predominating in the tubular bones. Approximately 1/3rd of the cases affecting flat bones demonstrate diffuse sclerosis. This diffuse sclerosis represents normal bone formed as a reaction to the tumor cells rather than actual tumor bone. Pathologic fracture is noted in approximately 5% of cases (1)

Periosteal Bone Formation

The delicate parallel, laminated, onion skin or onion peel radiographic presentation is quite striking in its appearance when present. This appearance is caused by the splitting and thickening of the cortex by the tumor cells. The layering is continuous, with reactive ossification in the form of Codman’s triangles occurring frequently. Osteomyelitis, traumatic periostitis, osteosarcoma and malignant lymphoma may also show a Codman’s reactive triangle; therefore, it is not pathognomonic. (1)

Metastases

Skeletal metastases occur frequently and early, leading to extensive bone destruction. Ewing’s sarcoma is the most common primary malignant bone tumor to metastasize to bone. The spine is a common site for metastasis. Multiple lesions in the one bone occur and are described as skip lesions, a phenomenon also seen in osteosarcoma. Secondary spread to the lungs is also a very common occurrence, with the lung parenchyma and pleura being the favored locations. (1)

Treatment and Prognosis 

The 5-year survival rate has been approximately 5% for Ewing’s sarcoma. Radiation therapy rendered in conjunction with effective chemotherapy in lesions detected early is increasing the survival rate. Amputation may still be used in lesions around the knee. A recent study reports a 35% 5-year survival rate in 107 patients. Early detection remains the key to effective treatment and improved prognosis. (1)

References

  1. 1. Yochum TR, Rowe LJ: Essentials of Skeletal Radiology, ed 3. Baltimore, Williams & Wilkins, 2005.