Chordoma: Ultrastructural, Biochemical and Cytophotometric Findings

Abstract

Introduction: Chordoma is a rare tumor originating from the residuum of the chorda dorsalis and only a few reports of ultrastructural appearance of chordomas have been published up to now (Cancilla et al., 1964; Friedman et al., 1962; Spjut and Luse, 1964; Peña et al., 1970; Murad and Murthy, 1970; Kay and Schatzki, 1972; Mikuz and Mydla, 1974). In the present paper we report the results of ultrastructural, cytophotometric and biochemical investigations of two chordomas. Special emphasis is given to the proliferative behaviour of the cell type.

Material and Methods: Two chordomas, one of the sacrococcygeal (57 years ♂ and one of the spheno occipital (38 years ♂ region were investigated. For light microscopy specimens were fixed in 4% formaldehyde, embedded in paraffin and stained with hematoxylin-eosin, PAS and Astra-blue.

For electron microscopy, specimens were fixed with phosphate buffered (0.1 M; pH 7.2) 6,5% glutaraldehyde, followed by postfixation with Dalton's chrome-osmium tetroxide. The specimens were dehydrated with acetone, embedded in Durcopan and sectioned on a Reichert ultramicrotome OMU2. Thin sections were stained with uranyl acetate, lead citrate, and examined with a Zeiss electron-microscope EM 9 A. Imprint preparations from biopsy specimens of the tumors were fixed immediately in 96% ethanol; after Feulgen staining according to Sandritter et al. (1958), the DNA content of tumor cell nuclei was determined with an integrating microdensitometer (GN 2, Barr & Stroud, Glasgow, Scotland).

Biochemical Investigations: Acid mucopolysaccharides were isolated from the tumor and for comparison also from a nucleus pulposus of a premature infant by the method of Svejcar and Robertson (1967). TLC was carried out following the modified method of Marzullo and Lash (1967) as follows: chromatography was done on Merck DC-Alufolie Cellulose (Nr. 5552) and was carried out twice in the same direction, thereby improving separation. The spots were visualised by heating the plate for a short time up to 180° C.

Results and Discussion: By the means of electron microscopy three different cell types could be differentiated: the indifferent stellate cells, the high differentiated physaliferous and the intermediate (or transitional) cells. These types of chordoma cells represent different functional stages relative to mucopolysaccharide production and storage as well as to proliferation. The stellate cells are poorly differentiated, fibroblast-like and spindle-shaped, with a prominent nucleus and a very well developed coarse ER. The intermediate cells are characterised by many small and big vesicles, communicating with the cisternae of the RER, and suggesting transformation of the stellate cells. The physaliferous cells are filled with such vesicles, in which mucous substances are stored but not produced. Secretion of such vesicles can be observed and the authors suppose, that in this way the intercellular matrix (“mucous lakes”) is produced. A very interesting feature of this tumor is the selfdestruction of the physaliferous cells that has already been described by Kay and Schatzki (1972).

Cytophotometric investigation indicated that only the stellate cells are proliferating whereas the physaliferous cells do not proliferate and correspond to a GO population. There was a difference of about 25% in the DNA content of physaliferous cells and the mean DNA content of the tumor stem line, i.e. the stellate cell population, which may have been due to decrease of Feulgen DNA content during nuclear pyknosis (Lederer, 1966) in the nuclei of physaliferous cells.

Biochemical investigations did not reveal any difference between the acid mucopolysaccharides in tumor and in nucleus pulposus, but the storage capacity of individual tumor cells seems to be enhanced. These investigations suggest that in chordoma self-preserving proliferating (stellate cells) and selfdestroying (physaliferous) cell systems exist. When the proliferating stellate cells prevail rapid growth and aggressive behaviour can be inferred.