Pathology of midline brain tumors. Immunocytochemical tumor markers and classificatory aspects

Our understanding of the pathology of human brain tumors has considerably increased in recent years thanks to investigation of nervous tissue markers which can be demonstrated by immunocytochemical techniques in sections of neurosurgical tissue specimens. This development is presented here in a review of the most important entities among midline brain tumors. Detection of neural differentiation markers such as glial fibrillary acidic protein (GFAP), S 100 protein (S 100 p), neurofibrillary proteins and neuron-specific enolase (NSE) greatly contributed to clarifying the histogenesis and differentiation potential of undifferentiated small-cell tumors grouped as primitive neuroectodermal tumors (PNETs) which include cerebellar medulloblastomas and pinealoblastomas as well as neuroblastomas and ependymoblastomas. Among medulloblastomas, the desmoplastic variety (formerly called by some "arachnoidal sarcoma of the cerebellum") shows frequent glioneuronal differentiation. Monoclonal antibodies recognizing antigenic determinants specific for tumor types and grades of malignancy/differentiation will gain significance in brain tumor diagnosis, as demonstrated in some examples. Despite the development of more objective ("scientific") criteria for typing human brain tumors, the "art" of classical histopathologic evaluation is not replaced but supplemented by the wealth of data supplied by such modern accomplishments.