Specific Imaging Findings

Glioblastoma multiforme (GBM) usually presents as a heterogenous enhancing mass. It is frequently hypodense on CT and with high T2 signal on MRI. The T2 hyperintense/CT hypodense area with the appearance of vasogenic edema surrounding the enhancing lesion is almost always present, but its size varies. A characteristic of gliomas is the infiltrative edema with signal abnormality not being limited to the white matter but extending to involve the cortex and/or deep gray matter. This feature is almost always present along at least a portion of the abnormality. Although frank intratumoral hematomas are not common, multiple areas of signal loss caused by susceptibility effects from small amounts of blood products are almost always detected onT2* MR imaging. Gadolinium-enhanced T1WI most commonly demonstrates a necrotic mass with thick, irregular predominantly peripheral enhancement. Nodular or ring-like enhancement may also be present, and enhancement is absent in rare cases. Solid portions of the neoplasm commonly show low diffusion with reduced ADC values, while necrotic areas are bright on ADC maps. Increased choline, decreased NAA and elevated lactate/lipid peak will be detected on MRS. Very high rCBV of solid tumor areas is a hallmark of GBM on perfusion studies. Analysis of the signal intensity curve on susceptibility-weighted post-contrast perfusion studies shows return to the baseline value following the first pass of contrast medium. In around 10% of cases GBM presents as multifocal lesions on initial imaging studies.