Central nervous system tumors

Electron microscopy has been extensively applied to normal tissues as well as to reactive processes and neoplasms of the central nervous system. In recent years, its diagnostic role has been partly supplanted by advances in immunocytochemistry. In view of the expense of routine electron microscopy and with the currently limited health-care budget, the full potential of routine histochemistry and immunocytochemistry should be exploited. Nonetheless, there remain a variety of recurring clinicopathologic problem situations wherein electron microscopy makes a valuable contribution in differential diagnosis; these include the characterization of small-cell tumors of the central nervous system, poorly differentiated gliomas, unusual meningeal tumors, anaplastic metastatic neoplasms, pituitary adenomas and sellar lesions, metabolic diseases and dementias, and viral and other infections. The scope of this article will be restricted to a discussion of the morphology of primary tumors of the central nervous system and its coverings. Tumors of cranial and peripheral nerves are discussed elsewhere, as are melanocytic, soft-tissue, germ-cell and, hemopoietic tumors. Pituitary adenomas and tumors of the sellar region will not be discussed here; the reader is referred to several recent publications on the subject. General references regarding the ultrastructure of the lesions under discussion are supplemented within the text by more specific citations.