This is a difficult case, due to the location of the tumour.
The finding which draws one away from the diagnosis of a GBM is the midline location and the fact that the anterior cerebral arteries are locate posterior to the mass and anterior to the corpus callosum. Thus this is not a genu mass, and one could be mistaken in thinking that it arose form the falx. One should remember that the falx, this far anteriorly, is usually a thin strip descending towards the crista galli.
The patient was taken to theatre and resection performed. The mass was more reminiscent of a glioblastoma (GBM) and frozen section confirmed the diagnosis (subsequently further confirmed with histology).
The sections show features of a densely cellular astrocytic tumour. The tumour cells show elongated, angulated and hyperchromatic nuclei. Some appear pleomorphic xanthoastrocytoma-like, being more epithelioid with abundant amounts of cytoplasm. Scattered mitotic figures are identified. There are foci of endothelial cell hyperplasia. Areas of palisaded necrosis are present. The features are those of glioblastoma multiforme. The tumour cells are GFAP and nestin positive. The Ki-67 index is about 30%.
FINAL DIAGNOSIS: Glioblastoma (WHO Grade IV).