<unk>  in the frontal right lobe as seen on CT scan Sagittal MRI with contrast of a<unk>  WHO grade IV in a 15-year-old boy Axial post-contrast T1 (top) and T2 (bottom) weighted MRI showing an IDH1 mutant frontal lobe<unk>  with sparse enhancement despite large size. When viewed with MRI,<unk> s often appear as ring-enhancing lesions. The appearance is not specific, however, as other lesions such as abscess, metastasis, tumefactive multiple sclerosis, and other entities may have a similar appearance. Definitive diagnosis of a suspected<unk>  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<unk>  from secondary<unk>  is important. These tumors occur spontaneously (de novo) or have progressed from a lower-grade glioma, respectively. Primary<unk> s 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<unk> s carry a mutation in IDH1, whereas this mutation is rare in primary<unk>  (5–10%). Thus, IDH1 mutations are a useful tool to distinguish primary and secondary<unk> s, since histopathologically they are very similar and the distinction without molecular biomarkers is unreliable. File:Histopathology of<unk> , high magnification, annotated.Histopathology of<unk> , showing high grade astrocytoma features of marked nuclear pleomorphism, multiple mitoses (one at white arrow) and multinucleated cells (one at black arrow), with cells having a patternless arrangement in a pink fibrillary background on H&E stain. File:Glioblastoma (1).Lower magnification histopathology, showing necrosis surrounded by pseudopalisades of tumor cells, conferring a diagnosis of<unk>  rather than anaplastic astrocytoma.
Glioblastoma
Ameloblastoma
Glioma
Medulloblastoma
Hemangioblastoma
Gliosarcoma
Astrocytoma
Gliosis