Chordoma with osseous element in a F344 rat.

Chordoma occurred in the sacrococcygeal region of the vertebral column of a 97-week old male control F344 rat. Macroscopically, it was a mass (20 mm in diameter) protruding into the retroperitoneum and the cut surface was white to dark-reddish and showed a gelatinous appearance. Histologically, the tumor was composed of physaliphorous and stellate cells growing in nests or cords and divided into lobules by a thin fibrous stroma. The tumor cells locally invaded adjacent tissues, but no metastasis to other organs was noted. Centrally, the tumor often had islands of bone that entrapped physaliphorous cells and the bone tissue consisted of well-differentiated osteocytes. Based on these findings, this tumor was diagnosed as chordoma with osseous element.