[Primary angiosarcoma of the thyroid. Presentation of a case (epithelioid type) and nosological problems].

There is a great deal of confusion in the literature as to whether or not true angiosarcomas of the thyroid exist or whether these are all anaplastic carcinomas of the thyroid which have an angiosarcomatoid appearance. Due to the fact that undifferentiated carcinomas of this organ can strikingly resemble various sarcomas it is recommended that great care should be taken prior to qualify as an angiosarcoma a malignant thyroid tumor. A lot of viewpoints have been expressed so far in literature concerning this theme, and they can be summarized as follows. On one side and not admitting the existence of angiosarcoma in this location there are opinions which think of it as a "variant" of undifferentiated carcinoma (a pure carcinoma with a pseudovascular pattern or a carcinoma with an intermingled non-neoplastic reactive vascular component), or as a neoplasm in transition from epithelial to endothelial differentiation ("mesenchymal neometaplasia"), or as a carcinoma with aberrant expression of endothelial markers, or as a carcinoma with a non-specific uptake of endothelial antigens(e.g. from serum in case of F-VIII R-Ag positivity). On the other side there are opinions in favor of the existence of such an entity, based upon light microscopy features coupled with immunocytochemical results (endothelial antigens expression without or with cytokeratins expression) and with the possible support of electron microscopy. Anyway ultrastructural findings of specific markers (Weibel-Palade bodies, pericellular basal lamina, tight junctions, subplasmalemmal pinocytotic vesicles) according to some authors are not a prerequisite: so poorly differentiated neoplasma can fail to show those histogenetic markers.(ABSTRACT TRUNCATED AT 250 WORDS)