Glioblastoma IDH wild-type (multifocal)
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A large region of high T2 signal with positive mass effect involves a majority of the left frontal lobe, with expansion also of the caudate nucleus and lentiform nucleus and signal creeping into the corpus callosum. Superiorly within this region is vividly enhancing component, with central areas of non-enhancing suggestive of necrosis. Spectroscopic trace of this lesion demonstrates marked elevation of choline, depressed NAA, and a large lactate peak. Perfusion demonstrates markedly elevated cerebral blood volume (CBV).
In the right frontal pole is a further region of high T2 signal is demonstrated involving the anterior aspect of the superior frontal gyrus, embedded within it are two enhancing nodule. It is difficult to demonstrate convincing bridging high T2 signal across the corpus callosum between the two frontal lobes.
Involving the posterior aspect of the middle temporal gyrus on the left is a further region of high T2 signal with thickening of the cortex, without abnormal enhancement.
The remainder of the brain is unremarkable in appearance.
The presence of abnormal signal with mass effect involving three lobes, with enhancing masses in the frontal lobes as described suggests gliomatosis cerebri, with high-grade (WHO grade VI - GBM) component within the left frontal lobe and smaller also high-grade component in the right frontal lobe. There is likely unseen bridging white matter disease consistent with multifocal glioblastoma (rather than multicentric glioma).
The patient went on to have a craniotomy and debulking.
All the sections show features of a densely cellular astrocytic tumour. The tumour cells have pleomorphic and hyperchromatic nuclei. Many mitotic figures are identified. There are prominent foci of microvascular proliferation. Areas of palisaded necrosis are present.
The tumour cells extend extensively into the cerebral cortex. There is no oligodendroglial component. The features are those of glioblastoma. The tumour cells are focally p53 positive. There is weak staining in 10% of the tumour cells for MGMT immunostain. IDH-1 is negative.
DIAGNOSIS: Glioblastoma (WHO Grade IV).
Note: Although this is tumour 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 tumour 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 tumours (2016).
Multicentric vs multifocal
Multifocal glioblastoma is that where multiple areas of enhancement are connected to each other by abnormal white matter signal, which represents microscopic spread to tumour cells.
Multicentric glioblastoma on the the other hand is where no such connection can be seen.
In this case, although definite connection cannot be seen, the areas of enhancement are along large connecting white matter tracts and thus almost certainly represent multifocal disease rather than the much rarer multicentric disease.