Cerebral Parenchymal Lesions: II. Primary Tumors

The most common primary tumor of the central nervous system is astrocytoma, and in particular glioblastoma. The focus of this chapter is to discuss tumors that are most likely to arise in the cerebral hemispheres (in addition to metastatic neoplasms which were addressed in Chap. 4) (Table 5.1). Most of these tumors represent fibrillary or diffuse astrocytomas. These lesions can arise at any age; most present in adults between the third and seventh decades of life. These tumors are notoriously heterogeneous in nature, which means that different areas of the tumor may have a different histologic appearance. Features that are used to grade a diffuse astrocytoma include the degree of cellularity, mitotic activity, vascular proliferative changes, and necrosis. Currently, the World Health Organization (WHO) grading system is the most widely employed. Attempts at providing some information regarding possible tumor grade should be made at the time of frozen section consultation. Any grade that is assigned, of course, is preliminary and hinges on the evaluation of the permanent sections.