Primary malignant myxoid fibrous histiocytoma of the lung. Light and ultrastructural examination with review of the literature.

We studied primary pulmonary malignant myxoid fibrous histiocytoma (MFH) by light and electron microscopy. Our ultrastructural examination supports the concept that MFH arises from a primitive mesenchymal cell that is able to differentiate toward fibroblastic and histiocytic lines. In the myxoid variant these cells produce a fine intracellular and extracellular amorphous material, probably representing mucopolysaccharide, which accounts for the myxoid stroma. We believe this is the first reported example of this rare but probably underreported sarcoma of the lung.