A transmission electron microscopic study of two cases of oral smooth muscle neoplasm.

Two cases of smooth muscle tumors that had appeared in the oral regions were examined by means of histopathology and electron microscopy. One was a case of angiomyoma that appeared in the lip of a 33-year-old man, and the other was a case of leiomyosarcoma in the maxilla of a 63-year-old woman. The results of the examination of both cases were as follows: the benign tumor (angiomyoma) was composed of mainly mature smooth muscle cells having dark cytoplasm, and the malignant tumor (leiomyosarcoma) consisted mainly of two types of cells, undifferentiated mesenchymal cells or fibroblast-like cells (type I) and myofibroblast-like cells (type II). Based upon these results, the relationship between the myogenous differentiation and the component cell types, and biological behavior of these smooth muscle tumors was discussed.