CHONDROID CHORDOMA - A HYALINIZED CHORDOMA WITHOUT CARTILAGINOUS DIFFERENTIATION

''Chondroid chordoma'' is a controversial and confusing entity that wa s originally described by Heffelfinger and colleagues as a biphasic ma lignant neoplasm possessing elements of both chordoma and cartilaginou s tissue. Because the premise for this distinction was based strictly on histomorphologic criteria, the light microscopic, immunohistochemic al, and electron microscopic features of the chondroid and chordoid ar eas of five chondroid chordomas of the skull base were evaluated separ ately, and compared to five typical chordomas and six low grade chondr osarcomas. Using light microscopy, chondroid chordoma revealed areas t hat resembled typical chordoma (chordoid areas) and areas that resembl ed low grade chondrosarcoma (chondroid areas). However, both the chord oid and chondroid areas had an epithelial phenotype and stained strong ly for cytokeratin and EMA as well as S-100. 5'-nucleotidase, an enzym e that has been described in chordoma but not in chondrosarcoma, was f ound in both the chordoid and chondroid areas of one chondroid chordom a. Electron microscopic studies of both the chordoid and chondroid are as in four of the tumors demonstrated both tonofibrils and desmosomes. Chordoma demonstrated immunohistochemical and electron microscopic fe atures that were nearly identical to chondroid chordoma. Chordoma was cytokeratin, EMA, S-100, and 5'-nucleotidase positive. Ultrastructural ly, chordoma exhibited variably-sized vacuoles, abundant rough endopla smic reticulum (RER), and desmosomes with tonofilaments. In contrast t o chondroid chordoma, chondrosarcoma consistently stained for only S-1 00 protein and was cytokeratin, EMA and 5'-nucleotidase negative. Ultr astructurally, chondrosarcoma demonstrated a flocculogranular matrix, glycogen, abundant RER, and scalloped cellular outlines, but lacked de smosomes with tonofilaments. These findings indicate that ''chondroid chordoma'' is a variant of chordoma with histologic features that may mimic chondrosarcoma. Despite the resemblance of these hyalinized area s to cartilaginous tissue, these tumors retain their epithelial phenot ype. Biphasic differentiation is not present. These findings undermine the original premise for distinguishing ''chondroid chordoma'' from t ypical chordoma. The authors propose that these tumors be classified a s ''hyalinized chordomas,'' rather than ''chondroid chordoma,'' to cla rify their histogenesis and avoid confusion with chondrosarcomas of th e base of the skull.