Astrocytomas: old and newly recognized variants, their spectrum of morphology and antigen expression

The relationship between the morphology of astrocytomas and their prognosis is complex, with the localization of the tumour, the predominant cell type and the degree of anaplasia all playing an important part in determining the patient's future. Since many astrocytomas have a diversity of patterns, small needle biopsies taken from just one or a few areas may fail to elucidate the principal features of a given tumour. In addition to the astrocytoma subtypes listed in the WHO's International Histological Classification of brain tumours, new entities have been observed in the last few years. These include lipidized forms, such as the relatively benign pleomorphic xanthoastrocytoma and the highly malignant lipidized glioblastoma. Neoplastic astrocytes are capable of forming basal laminae and of phagocytosis, and often contain alpha-1-antitrypsin, features that may lead to confusing them with histiocytes. They may be arranged in a whorled pattern imitating meningiomas, their myxoid intercellular stroma may assume the morphology of cartilage and closely packed tumour cells in "epithelioid" astrocytomas come close to imitate metastatic carcinoma. Some astrocytomas contain cells indistinguishable from those of granular cell tumours of other tissues. The presence of reactive lymphocytes in astrocytomas and reactive astrocytes in malignant lymphomas can be the source of confusion between those two kinds of neoplasms.