Ewing’s sarcoma is a highly malignant tumor that is a type of peripheral
primitive neuroectodermal tumor (PNET). Ewing’s sarcoma is found in the lower extremity more than the upper extremity,
but any long tubular bone may be affected. The most common sites are the metaphysis and diaphysis of the femur
followed by the tibia and humerus. Ewing’s sarcoma is most common in the first and second decade but may affect
persons from age 2 to 80. This tumor preferentially affects whites more than blacks and Asians. The ratio of male to
female is 3:2.
The
clinical presentation of Ewing’s sarcoma includes pain and swelling of weeks or months duration. Erythema and warmth
of the local area are sometimes seen. Osteomyelitis is often the initial diagnosis based on intermittent fevers,
leukocytosis, anemia and an increased ESR.
Radiologically,
Ewing’s sarcoma is often associated with a lamellated or “onion skin” periosteal reaction. This appearance
is caused by and splitting and thickening of the cortex by tumor cells. The lesion is usually lytic and central.
Endosteal scalloping is often present. The “onion-skin” appearance is often followed with a
“moth-eaten” or mottled appearance and extension into soft tissue. Bone marrow infiltration is not obvious
on plain x-ray. While Ewing’s sarcoma is usually lytic it may present as a sclerotic lesion with bone expansion. CT
is helpful in defining bone destruction. MRI is essential to elucidate the soft tissue involvement because with
TI-weighted images the tumor has low intensity compared to the normal high intensity of bone marrow. On :1 2
-weighted images the tumor is hyper intense compared to muscle. Ewing’s sarcoma has increased uptake on bone
scan.
Grossly,
the tumor is gray to white in color and poorly demarcated. The consistency is soft and gray and sometimes semi-liquid
especially after breaking through the cortex. Areas of hemorrhage and necrosis are common. The destruction is often
greater on gross appearance than was visible on radiographs. Under the microscope, Ewing’s sarcoma consists of
densely packed uniform small cells in sheets. The cells have scant cytoplasm without distinct borders. The cells are
two to three times as big as lymphocytes and have a single oval or round nucleus without prominent nucleoli. The
tumor spreads through Haversian canals which cause the appearance of permeative margins on x-ray. Glycogen is present
within the cells causing a positive reaction to periodic acid-schiff (PAS) stain. Most Ewing’s sarcomas are positive
with HBA-71 or 0-13 stain which is an antibody to the protein product of myc 2. The microscopic differential includes
lymphoma and metastatic neuroblastoma which must be excluded by reticulin stain and urine vanillyl mandelic acid and
homovanillic acid respectively. Rhabdomyosarcoma is ruled out if the specimen stains negatively with desmin,
myoglobin and actin stains.A neural origin is supported by electron microscope findings of pseudorosettes. This is
further supported by the common finding in Ewing’s sarcoma and primitive neuroectodermal tumors of choline
acetyltransferase and the translocation t(11:22)(q24;ql2). It is thought that Ewing’s sarcoma with its few organelles
is the poorly differentiated end of the spectrum of PNET. Neuroepithelioma is an example of well differentiated PNET
and has neurosecretory granules and neuritic processes.
Treatment
for Ewing’s sarcoma includes surgery, radiation and multi-drug chemotherapy. Radiation or chemotherapy with
vincristine, dactinomycin and cyclophophamide (VAC) are used preoperatively. Adjuvant chemotherapy follows surgery
and decreases recurrences.i The tumor metastasizes to lungs and lymph nodes. Poor prognostic signs include increased
age, increased ESR and leukocytosis at presentation.
References
Eggli,
KD et al., Ewing’s Sarcoma, Radiologic Clinics of North America, 31(2):325-337, March, 1994.
Bulloughs,
Peter, Orthopaedic Pathologv (third edition), Times Mirror International Publishers Limited, London,
1997.
Fletcher, Christopher, Diagnostic Histopathology of Tumors, Churchill Livingstone:New York, 1990.
Huvos,
Andrew, Bone Tumors:Diagnosis Treatment and Prognosis, W.B.Saunders, Co.,
1991.
Adapted, with permission from bonetumor.com By Henry DeGroot III, M.D.
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