The role of astrocytes in the formation of cartilage in gliomas. An immunohistochemical study of four cases.

The occasional presence of focal cartilage in gliomas is generally attributed to metaplasia of the mesenchymal supportive elements. While this mechanism undoubtedly exists, the present report describes a different mode of development of cartilage in four gliomas occurring in young individuals. Two of the tumors were pontine astrocytomas, one was a mixed ependymoma and astrocytoma involving the fourth ventricle and the brainstem, and one was an extraspinal malignant astrocytoma in the lumbar region of a young boy who earlier had been diagnosed as having a pontine glioma for which he received radiation treatment. In all four tumors, transitions from astrocytic to cartilaginous elements were seen, characterized by an increasing deposition of chondroid ground substance between the astrocytes and a gradual morphologic changes of the glial cells to more rounded forms with a vacuolated cytoplasm, indistinguishable from chondrocytes of mesenchymal origin. Many of these cells retained positive staining for glial fibrillary acidic protein by the immunoperoxidase method, attesting to their astrocytic nature. The production of cartilage by neoplastic astrocytes may be related to their ability to secrete, in certain circumstances and occasionally in large amounts, basement membrane material and other forms of mucopolysaccharides, which may become condensed to form a chondroid ground substance. The process appears analogous to that of cartilage formation by epithelial cells in pleomorphic adenomas of the salivary glands.