Patient Data
4.5cm heterogeneous mass arising from the genu and body of the corpus callosum. There is associated minor bilateral superior frontal vasogenic edema. The ventricles are age appropriate. Basal cisterns are not effaced.
Mild enhancement is noted of the corpus callosum mass.
The patient went on to have an MRI (movement degraded, not shown) and a craniotomy and debulking of the tumor.
Histology
MICROSCOPIC DESCRIPTION:
Paraffin sections show fragments of a densely hypercellular astrocytic glioma. Tumor cells show marked nuclear and cellular pleomorphism. Frequent mitotic figures are identified. There is multifocal microvascular proliferation with accumulation of endothelial-like cells in vessel walls. Foci of necrosis are also identified. Tumourcells show patchy strong immunostaining for GFAP and strong diffuse staining for nestin. No staining for IDH-1 is seen. The features are of glioblastoma multiforme. The topoisomerase labeling index is >50%.
FINAL DIAGNOSIS: Glioblastoma (WHO Grade IV)
Note: Although this tumor is entirely consistent with IDH wild-type molecular subtype, strictly speaking, to conclusively establish this, IDH would need to be sequenced to ensure that a non-IDH1 R132H mutation was present. In practice, an IDH1 R132H negative tumor in an individual over 55-years-of-age makes the possibility of this being IDH mutant remote (<1%), and sequencing is not felt to be necessary by many institutions, and not recommended by the WHO classification of CNS tumors (2016).
Case Discussion
Involvement of the corpus callosum is rare in metastases, and the vast majority of such cases represent high grade gliomas or CNS lymphoma. Central necrosis / non-enhancement is uncommon in lymphoma in the absence of treatment or immunosuppression (e.g. AIDS) and as such one can be confident in the diagnosis of high grade glioma on imaging grounds alone.
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