Scanning and transmission electron microscopy of Ewing's sarcoma of bone (typical and atypical variants). An analysis of nine cases.

Scanning electron microscopy (SEM) is of value for the differential diagnosis of Ewing's tumor of bone. Based upon 9 new cases which were observed with SEM and TEM (transmission electron microscopy), this paper puts into consideration, for the first time, the SEM ultrastructure of Ewing's sarcoma (both variants; typical Ewing's sarcoma and the large cell Ewing's sarcoma). Furthermore, a new case of vascular Ewing's sarcoma, studied with TEM, is discussed and included in the differential diagnosis with other round cell sarcomas of bone. Both Ewing's sarcoma types evidence common ultrastructural characteristics, but the atypical variant (large cell type) shows a greater variation in cell size and contour. The cell surfaces displayed smooth structures, interrupted only by clusters of short, stub-like microvilli. Isolated cilia were also observed. Variations in cell contour and size within the same tumour are also induced through intensive chemotherapy, as noted in one of our cases. SEM seems to be suitable for the differentiation of Ewing's tumours from other primary malignancies of the bone marrow, as is the case of the so-called "reticulum cell sarcoma of bone" or malignant non-Hodgkin lymphoma. SEM studies associated with TEM give further support to the mesenchymal origin of this neoplasm.