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Aims: Intraoperative consultation using frozen sections (FSs) is an integral component of clinical practice. As a quality control measure, FS diagnosis is subsequently compared with the findings on a FS control slide. These control slides can be used for immunohistochemistry, and the immunohistochemical performance in FS controls is known to be antibody‐dependent. Isocitrate dehydrogenase (IDH) is mutated in >80% of lower‐grade infiltrating gliomas in adults and in ~10% of glioblastomas, with IDH1 (R132H) being the most common mutation. IDH status is used as a major classifier of glioma. An IDH1 (R132H)‐specific antibody (H09) has been accepted as a robust surrogate for genetic testing. In this study, we aimed to determine how previous freezing and thawing affects IDH1 immunohistochemistry. Methods and results: Thirty cases of IDH1 (R132H)‐mutant diffuse glioma, which were originally assessed on FSs, were retrieved. The positive IDH1 (R132H) status of each case was previously determined with pyrosequencing and H09 immunohistochemistry on permanent sections. The FS control tissue of each case was immunostained with H09 antibody. Among 30 gliomas, 25 showed negative reactivity on FS control slides, whereas, in the remaining five, the staining was uninterpretable, owing to a high diffuse background. Of the former 25 specimens, 20 showed at least focal areas with variably increased levels of background staining, whereas the remaining five specimens showed a relatively pristine background. Conclusions: We conclude that IDH1 (R132H)‐specific (H09) immunohistochemistry often results in false‐negative reactions on FS controls with focally increased background staining, and this application should be avoided in clinical practice. [ABSTRACT FROM AUTHOR]

Primitive polar spongioblastoma was first described by Russell and Cairns in 1947. However, the polar spongioblastoma pattern is often seen in many neuroepithelial tumors, and this category was deleted in the previous World Health Organization (WHO) classification. In 2010, Nagaishi et al. reported on a case involving a neuroepithelial tumor with the typical histological pattern of polar spongioblastoma and suggested that this tumor might not be suited to any of the neuroepithelial tumors in the current WHO classification. We report on an autopsy case involving an unclassified high-grade glioma with polar spongioblastoma pattern that was very similar to the case described by Nagaishi et al. A 44-year-old man who presented with a headache exhibited a tumor of the right frontal lobe on MRI. Histological diagnosis of the tumor obtained by gross total resection was high-grade glioma, which was composed of the parallel palisading of spindle tumor cells expressing GFAP, without microvascular proliferation (MVP) and necrosis. Conventional chemoradiotherapy was performed, but the case was complicated by cerebrospinal fluid (CSF) dissemination that resulted in multiple extraneural metastases through systemic diversionary CSF shunting. Finally, the patient died approximately 13 months after the initial treatment. Both the cerebral and Douglas pouch tumors that were obtained at autopsy were diagnosed as typical glioblastomas, and they were composed of the proliferation of atypical astrocytes with MVP and pseudopalisading necrosis without the formation of rhythmic palisading. Although the histological findings were different from that of the first operation, immunohistochemical and genetic profiles demonstrated almost the same results. This tumor was not classified as a typical glioblastoma by the initial findings, but it had the nature of a glioblastoma. These findings suggest that the tumor might be classified as a new subset of glioblastoma called glioblastoma with polar spongioblastoma pattern. [ABSTRACT FROM AUTHOR]