The differential includes viral (herpes) encephalitis, progressive multifocal leukoencephalopathy (PML), lymphoma, demyelination and infarction. The patient underwent craniotomy and biopsy by which the diagnosis of gliomatosis cerebri WHO grade III was made.

Importantly, whereas gliomatosis was previously considered a distinct entity, since the 2016 update to the WHO classification of CNS tumors it is now merely thought of as a growth pattern.