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The focal emergence of subpopulations of tumor cells morphologically displaying some degree of neuronal commitment is being increasingly appreciated as a novel facet to the histological versatility of gliomas of adults [3]. All major histologic subtypes of the latter (i.e. astrocytomas; oligodendrogliomas; ependymomas) have been reported to occasionally involve such diVerentiation, and the epithet “glioneuronal” rather liberally conferred upon to qualify this phenomenon [7, 10, 12]. Uncommon though they obviously are, reports on detecting neuronal diVerentiation in gliomas—be it by conventional histology, immunohistochemistry or electron microscopy—do appear with suYcient regularity as for conceptual problems to become manifest. Indeed, diagnostic criteria for purported neuronal diVerentiation tend to range from expression of neuronal markers in isolated cells to dysplastic neurons, to suggestive architectural patterns [9, 13]. While the increasing sensitivity of detection methods clearly is at odds with the speciWc relevance of results thus obtained, reproducible patterns are being searched for in order for meaningful entities to be singled out. Introduced by Teo et al. in 1999, the so-called “glioneuronal tumor with neuropil-like islands” has subsequently been the subject of a handful of case studies conWrming a remarkably constant clinicopathologic presentation of this neoplasm [3 and references therein]. This includes occurrence in the cerebral hemispheres of adults, involving an inWltrating astrocytoma (WHO grade II or higher) punctuated by discreet clusters of round cells enmeshed within a Synaptophysin-immunoreactive feltwork. With but one exception—the case documented by Keyvani et al.—the cells engaged in the neuropil-like islands have been felt not to represent the most intensely proliferating moiety of the lesions [5]. Although the mere presence of neuropil-like islands does not seem to bestow a particularly favorable prognosis, the modest proliferative activity of these is likely to be intuited to connote maturation. We recently had the privilege of studying a high-grade glioma with intensely proliferating neuropil islands surgically removed from the left frontal lobe of a 59-year-old woman. By World Health Organization criteria, the major part of the tumor (approximately 70%) corresponded to conventional glioblastoma (WHO grade IV), i.e. an astrocytoma with cellular anaplasia, mitotic Wgures and microvascular proliferation as well as extensive palisading necrosis (Fig. 1a, b). In addition, several discreet aggregates of nondescript round cells with inconspicuous cytoplasm and round darkly stained, primitive-appearing nuclei were encountered (Fig. 1c). Measuring 40–350 m in diameter, the contours of each of these variably appeared as smudged to rather clear-cut (Fig. 1d, f). Within individual clusters, cells either were interwoven with delicate Wbrillary processes, or tended to haphazardly collapse to produce nuclear crowding. Irrespective of architecture, such foci stained intensely and almost exclusively for Synaptophysin as opposed to surrounding GFAP-positive astrocytes (Fig. 1e, g, h). No gangliocytic maturation or any suggestive immunoreactivity for neuroWlament proteins was found. While MIB-1 counts averaged some 9–11% in the intervening astrocytic tumor component, nuclear labeling within the neuropil-like nodules was as high as 40% (Fig. 1i). I. Vajtai (&) Section of Neuropathology, Institute of Pathology, University of Bern, Murtenstrasse 31, Postfach 62, 3010 Bern, Switzerland e-mail: istvanvajtai@yahoo.com

acta neuropathologica

Malignant glioneuronal tumor of the adult cerebrum with neuropil-like islands involving “proliferating nodules”: confirmatory report of an unusual variant