Ewing's Sarcoma

This tumour occurs at a younger age than osteosarcoma and its range of incidence is primarily between 5 - 30 yrs. The patient usually presents with pyrexia pain and may have an elevated ESR. The tumour involves a long bone, particularly the diaphysis. 40% of cases of Ewings sarcoma are found in the axial skeleton, usually pelvis. With large tumours, the site of origin is inferred from the centre of radius of the mass. The tumour is primarily destructive, ill-defined and erodes the cortex of the bone. Its cellular origin is obscure, but is thought to be derived from undifferentiated mesenchymal cells in the medulla of the bone. There is an early periosteal reaction and a classical appearance of this tumour is of a lamellated series of periosteal reactions showing an onion skin appearance. The elevation of the periosteum gives rise to the Codman's triangle appearance.

Ewing's sarcoma is very vascular and its extent of spread down the bone through the medulla is greater than indicated on the plain films and the tumour is usually staged with MRI. Under microscopy the appearance is of undifferentiated small round or spindle cells with predominent nuclei. Metastasis occurs frequently and early.