lesions such as abscess, metastasis, tumefactive multiple sclerosis, and other entities may have a similar appearance. Definitive diagnosis of a suspected GBM on CT or MRI requires a stereotactic biopsy or a craniotomy with tumor resection and pathologic confirmation. Because the tumor grade is based upon the most malignant portion of the tumor, biopsy or subtotal tumor resection can result in undergrading of the lesion. Imaging of tumor blood flow using perfusion MRI and measuring tumor metabolite concentration with MR spectroscopy may add diagnostic value to standard MRI in select cases by showing increased relative cerebral blood volume and increased choline peak, respectively, but pathology remains the gold standard for diagnosis and molecular characterization. Distinguishing primary glioblastoma from secondary glioblastoma is important. These tumors occur spontaneously (de novo) or have progressed from a lower-grade glioma, respectively. Primary glioblastomas have a worse prognosis and different tumor biology, and may have a different response to therapy, which makes this a critical evaluation to determine patient prognosis and therapy. Over 80% of secondary glioblastomas carry a mutation in IDH1, whereas this mutation is rare in primary glioblastoma (5–10%). Thus, IDH1 mutations are a useful tool to distinguish primary and secondary glioblastomas, since histopathologically they are very similar and the distinction without molecular biomarkers is unreliable. Prevention There are no known methods to prevent glioblastoma. It is the case for most gliomas, unlike for some other forms of cancer, that they happen without previous warning and there are no known ways to prevent them. Treatment Treating glioblastoma is difficult due to several complicating factors: The tumor cells are resistant to conventional therapies. The brain is susceptible to damage from conventional therapy. The brain has a limited capacity to repair itself. Many drugs cannot cross the blood–brain barrier to act on the tumor. Treatment of primary brain tumors consists of palliative (symptomatic) care and therapies intended to improve survival. Symptomatic therapy Supportive treatment focuses on relieving symptoms and improving the patient's neurologic function. The primary supportive agents are anticonvulsants and corticosteroids. Historically, around 90% of patients with glioblastoma underwent anticonvulsant treatment, although only an estimated 40% of patients required this treatment. Recently, neurosurgeons have been recommended that anticonvulsants not be administered prophylactically, and should wait until a seizure occurs before prescribing this medication. Those receiving phenytoin concurrent with radiation may have serious skin reactions such as erythema multiforme and Stevens–Johnson syndrome. Corticosteroids, usually dexamethasone, can