HEAD AND NECK FIBROMYXOID SARCOMA - CLINICOPATHOLOGICAL CORRELATION WITH EMPHASIS ON PECULIAR ULTRASTRUCTURAL FEATURES RELATED TO COLLAGEN PROCESSING

A fibromyxoid sarcoma of the jaw of a young patient is described. The tumor recurred and was locally aggressive but displayed mostly a low-g rade morphology with only a few areas showing undifferentiated (high-g rade) appearance. An isolated lung metastasis was identified 15 years after the original presentation. Ultrastructurally, the tumor cells sh owed features of partial fibroblastic differentiation, with abundant a nd often markedly dilated rough endoplastic reticulum cisternae, but a lso interrupted segments of basal lamina. The cytoplasm contained nume rous large, spindle-shaped, membrane bound inclusions of collagen that showed a complex triple periodicity. A distinct cell polarity was see n, with the nucleus at one end of the cell and the collagenous inclusi ons at the other. All of these features indicate a tumor with signific ant cytodifferentiation, correlating with the relatively protracted cl inical course. The intercellular space contained mature collagen fiber s and scattered aggregates of delicate, slender fibers embedded in mod erately electron-dense granular matrix (fibril-logranular aggregates). The results suggest that based on its morphology and clinical present ation this tumor represents an unusual Variant in the spectrum of fibr omyxoid sarcomas.