Glioblastoma

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Diagnosis Definition

Glioblastomas are classified by the World Health Organization (WHO) as grade IV malignant astrocytomas
They are the most common type of adult primary brain tumor and have a poor prognosis, with a 10-20% 5-year survival
Most occur in the supratentorial cerebral hemispheres, commonly involving the subcortical and periventricular white matter and crossing white matter tracts; they are occasionally multicentric

Imaging Findings

CT of glioblastomas usually shows an avidly enhancing heterogeneous mass with hemorrhage and necrosis, significant mass effect, and marked surrounding vasogenic edema
MRI shows a poorly defined mass with mixed heterogeneous signal intensity (indicative of hemorrhage, necrosis, cyst formation, and contrast enhancement), mass effect, and surrounding edema
Most high grade astrocytomas show restricted diffusion in the non-necrotic portion, have elevated perfusion, and reduced NAA/Choline ratios
Thick irregular enhancement surrounding a central necrotic focus is the most common MRI finding and necrosis is the sina qua non of high grade astrocytomas

Pearls

Involvement of both sides of the corpus callosum is described as a “butterfly” appearance
The solid portions of glioblastoma may be densely cellular and show restricted diffusion
Glioblastomas can infiltrate to other brain structures via the white matter tracts and disseminate along the ependyma and via the cerebrospinal fluid (CSF)
The differential diagnosis of a glioblastoma includes other high grade neoplasms, CNS lymphoma, single large metastasis, and brain abscess
MR spectroscopy and perfusion can help differentiate between a glioblastoma and a single large metastasis

References

Okamoto K, Ito J, Takahashi N, et al. MRI of high-grade astrocytic tumors: early appearance and evolution. Neuroradiology 2002; 44:395–402
Felix R, Schorner W, Laniado M, et al. Brain tumors: MR imaging with gadolinium-DTPA. Radiology 1985; 156:681-688
Law M, Yang S, Wang H, et al. Glioma grading: sensitivity, specificity, and predictive values of perfusion MR imaging and proton MR spectroscopic imaging compared with conventional MR imaging. AJNR Am J Neuroradiol 2003; 24(10):1989-1998

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