Neuropathology plays very important role in dealing with patients who underwent surgery for the central nervous lesion. Diagnosis and treatment depend on the result of pathological examination. If neuropathologists can be called producers of the pathological diagnosis, we neurosurgeons are consumer because they use the diagnosis for the patient. In this paper we described our personal experiences how Kinki brain tumor pathology conference（KBTC）helped us with treating patients with correct diagnosis. Six representative cases of above mentioned example were presented. Their initial pathological diagnoses and final ones made at　KBTC were astrocytoma grade II – dysembryoplastic neuroepithelial tumor（DNT）, undetermined – cysticercosis, astrocytoma – acute disseminated encephalomyelitis（ADEM）, gemistocytic astrocytoma －mitochondrial encephomyopathy lactic acidosis and stroke like syndrome（MELAS）, cavernous angioma – angioglioma, xanthoma – Erdheim-Chester disease respectively. 　Those cases indicate that there are many diseases which mimic brain tumor and also many rare diseases which most of us are unfamiliar with. Systemic regional cooperation of neuropathologists, neurosurgeons and neuroradiologists are necessary for making correct diagnosis for difficult neuropathological cases.

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We clinicopathologically analyzed 12 cases who were initially diagnosed as malignant brain tumor, but were difficult to diagnose after surgery. Finally, 4 cases were diagnosed as malignant brain tumors, and 8 as nonneoplastic disease. By unusual clinical course, four patients were changed their preoperative diagnosis to nonneoplstic disease and surgery was performed to rule out tumor. Craniotomies were performed in 9cases, and stereotactic biopsies in 3. In five cases, inflammatory changes were seen and we diagnosed these cases as multiple sclerosis, vasculitis or encephalitis. In two cases, pathological findings supported cerebral infarction. There were no pathological findings in four cases, The reasons that surgical specimen did not give diagnostic yield were that they were too small or obtained from unappropriate resion. We also found malignant lymphoma, （especially intravascular lymphoma）is the most difficult to be distinguished from other disease such as inflammatory processes without histopathological examintaion. There has been no patient whose diagnosis changed again due to clinical course after treatments. These results suggested that if surgical specimen had sufficient pathological yields, they bring us some clues to decide clinical diagnosis and exact treatment strategy.

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The current practice of relying solely on microscopic examinations for histological classification of gliomas and, consequentially, determination of optimal treatment, appears to be insufficient. As a result of the increasing use of molecular markers in tumor classification, there is an emerging emphasis in the genetic profiles of distinct subtypes of glioma. These subtypes of glioma constitute distinct disease entities that evolve through different genetic pathways, and are likely to differ in prognosis and response to therapy. Status of O⁶-methylguaninemethyltransferase（O⁶-MGMT） gene is associated with the resistance to temozolomide（TMZ）. We have previously found methylation or expression mosaicism of O⁶-MGMT in gliomas, resulting in problems on tumor sampling and respose to TMZ. An assessment of O⁶-MGMT methylation mosaicism in heterogeneous glioma may provide a more accurate assessment for the response to TMZ. Oligodendroglioma is recognized as a particular subtype of gliomas that shows remarkable response to chemotherapy（procarbazine + CCNU + vincristine（PCV）, making their correct diagnosis important. Loss of heterozygosity（LOH） on chromosomes 1p and 19q is correlated with sensitivity to PCV chemotherapy with increased survival in anaplastic oligodendroglioma cases（WHO grade III）. This article reviews biological and molecular approaches to glioma classification that have the potential to increase the efficacy of treatments for these tumors.

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Medulloblastoma is defined as a malignant, invasive embryonal tumor of　the cerebellum in children, predominantly neuronal differentiation and inherent tendency to metastasize via CNS pathways. Cerebellar neuroblastoma, albeit very rare, is subclassifed in medulloblastoma with extensive nodularity and advanced neuronal differentiation. We have encountered these rare cerebellar neuroblastomas, many cases of which have been examined ultrastrlucturally for more than thirty years. Given hallmarks of neuronal differentiation is the presence of developing axons and synapse devices, cerebellar neuroblastoma is very rare, and most cases are equivocal neuroblastoma or medulloblastoma. Glial differentiation is none or minimal. Central neurocytoma is a well defined tumor but it should be born in mind that this tumor contains immature neuronal cells, that is neuroblasts, and “some cases are called neurocytoma-neuroblastoma”, I consider personally.

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The first case of clear cell ependymoma is introduced with the episodes how the author struggled and managed to reach a right diagnosis of the tumor. In 1982, a 22 years old man was revealed to have a calcified tumor with ring enhancement by CT scan within the right frontal lobe. At operation, the tumor was well demarcated from the surrounding brain tissue as if it had a capsule and it adhered to the wall of lateral ventricle. Histologically, as the major part of the tumor tissue was composed of clear round tumor cells with chicken wire appearance, a diagnosis of oligodendroglioma was given by the pathology department. On the other hand, the author recognized that the tumor cells had fine processes and formed epithelial lining in a limited area. GFAP (glial fibrillary acidic protein) immunostaining and electron microscopy were performed and they showed that all the tumor cells were neoplastic ependymal cells, namely it was ependymoma entirely. As this histological pattern of ependymoma has not been recognized in the past, the case was reported as a " Clear Cell Variant of Ependymoma " in 1983, and later its name was changed to " Clear Cell Ependymoma " in 1989. The author wishes to thank several doctors who offered invaluable advices in the study of this case. They are late Dr. Y. Nishiyama, Dr. Saburo Yagishita, late Dr. E. Alvord, and Dr. D. Horoupian.

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Glioneuronal tumors （GNT） are mixed glial and neuronal tumors of the central nervous system and are essentially benign neoplasms. In the WHO 2007 Classification, the category of GNT contains 12 entities, three of which, extraventricular neurocytoma, papillary glioneuronal tumor （PGNT）, rosette-forming glioneuronal tumor （RGNT）, were new additions to the current edition. PGNT is comprised of two microscopic components: 1） compact pseudopapillae composed of hyalinized vessels covered by a single layer of GFAPpositive astrocytes; 2） synaptophysin-positive neuronal cells of varying size, including neurocytic, ganglioid and ganglion cells within neuropil. RGNT is also comprised of two microscopic components: 1） synaptophysinpositive neurocytes forming neurocytic and/or perivascular pseudorosettes in a fibrillary, partly microcystic matrix; 2） the component resembling pilocytic astrocytoma, which consisted of fibrillated spindle cells with oval nuclei associated with occasional Rosenthal fibers,and oligodendrocyte-like cells （OLC）. In that their clinical, radiographic, and morphologic characteristics are distinctive, PGNT and RGNT represent heretofore undescribed forms of GNT. Recent development of highly sensitive immunohistochemistly certainly aids a daily practice but also arouse unexpected controversies in an identification of neuronal phenotype as well as tumor entities of GNT. These include the presence of neuronal immuno-phenotype in malignant gliomas. The presence of OLC in PGNT as well as RGNT further suggest their derivation from neuronal-oligodendrocytic progenitor cells.

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[in Japanese]

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The lack of reliable immunohistochemical markers available for specific and sensitive recognition of human oligodendrocytes and their neoplasms was a big issue for neuropathology for a long time. Nowadays, anti-Olig2 antibody has partially settled the problem. It faithfully immunolabels nuclei of oligodendrocytes on formalinfixed, paraffin-embedded tissue section. This is a personal history on establishment of anti-human Olig2 antibody covering from the initial concept through commercialization.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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