Myxoid lipoma of oral soft tissue. A clinical and ultrastructural study.

Myxoid lipoma is an unusual histologic type of lipoma. This article reports four cases of myxoid lipoma that arose in the mouth. In frozen sections stained with oil red O, the cytoplasm of tumor cells stained strongly positive. Intercellular mucoid material was PAS-positive and diastase-resistant. It also stained positively with alcian blue. Electron microscopic observations revealed that adipocytes were in different stages of differentiation, with lipid globules of variable size observed in the cytoplasm. Many pinocytotic vesicles appeared at the plasma membrane. Mature adipocytes were surrounded by a basal lamina. Fibroblasts, collagen fibers, and mucoid material were scattered among adipocytes. It appears possible that, in the histogenesis of myxoid lipoma, multipotent mesenchymal cells undergo multidirectional differentiation. Some cells differentiate to produce mucosubstance, while others differentiate to become adipocytes.