Author: Michael Kadoch
NECT CECT MRI - T1 MRI - T2 MRI - FLAIR MRI - Diffusion/ADC MRI - Postcontrast T1 Gross Pathology Histology Additional comments
Pilocytic astrocytoma Well-marginated round cystic mass with mural nodule or soft tissue component (s); most frequently seen in cerebellar hemisphere Almost always shows enhancement, which can vary from heterogeneous to homogenous enhancement (of the solid components; no image shown). Solid-portions are usualy iso- or hypo-intense to normal brain tissue Hyperintense compared to normal brain; contents of cyst similar to CSF intensity No diffusion restriction (no image shown) Intense enhancement of the solid portions Well-circumscribed, smooth mass usually located in cerebellar hemispheres Classic "biphasic" appearance with a loose glial component (g) with microcysts & EG bodies & a more compact component (p) of bipolar cells Most common pediatric CNS glial neoplasm & most common pediatric cerebellar tumor. Associated with NF1.
Glioblastoma multiforme Heterogeneous hypo- or iso-dense mass with central hypodensity from necrosis (no image shown) Strong, usually heterogeneous rim enhancement, often with a shaggy inner margin & a thicker margin on the cortical side of the lesion Iso- or hypo- intense heterogeneous mass Heterogeneous, hyperintense mass with adjacent edema +/- necrosis & hemorrhage Heterogeneous, hyperintense mass (seen here in the posterior left temporal lobe) with a large amount of surrouding T2 hyperintensity suggestive of edema Usually do not display diffusion restriction; hyperintense areas seen on the ADC map here of a left temporal GBM suggest absence of diffusion restriction Thick, irregular enhancement surrounding central necrosis Ill-defined, heterogeneous mass with areas of hemorrhage & necrosis Pleomorphic astrocytes (black arrows) surrounded by regions of necrosis (white arrows) & vascular hyperplasia (arrowheads) Most common of all primary intracranial neoplasms
Lymphoma Hyperdense lesion usually located in deep gray matter or periventricular white matter which shows less mass effect than expected given the size of the lesion +/- hemorrhage or necrosis; may be multifocal or irregularly shaped (as in this case, which demonstrates the lesion encasing the right ventricle with surrounding vasogenic edema) Most commonly shows dense homogenous enhancement, but can also display ringlike enhancement or no enhancement Iso- or hypo-intense to surrounding brain Usually iso- to hypo-intense lesions, here seen in the bilateral basal ganglia & thalamus, with extensive adjacent edema Image 1 (Diffusion): Frequently shows diffusion restriction

Image 2 (ADC): which is confirmed by ADC mapping on this image
Marked enhancement, either homogenous or in a ring-like pattern Single or multiple homogenous circumscribed mass(es) with firm consistency & granular surface Predominately B-cell; see sheets of closely packed cells which surround & cluster around vascular channels Usually in basal ganglia or periventriucular white matter
Mets Lesions most frequently at GWM junction; often iso- or hypo-dense to surrounding parenchyma & therefore may not be visualized; hemorrhagic mets (here from malignant melanoma) can be hyperattenuating & more conspicuous Strong enhancement which may be homogenous, nodular, or rim-enhancing; delayed imaging may help bring out more conspicuous mets (a ring-enhancing met is seen here from a renal cell carcinoma primary) Most frequently iso- or hypo-intense lesions at the GWM junction; hyperintensity suggests hemorrhagic metastases or melanoma Variable intensity depending on cellular content of metastasis; multiple hyperintense mets from unknown primary seen here Image 1: Variable diffusion characteristics of the non-necrotic components of metastasis (most frequently do not restrict diffusion, as seen on this DWI & corresponding ADC map); necrotic components show suppressed DWI signal & increased ADC values

Image 2: Rim of hyperintensity seen here on DWI shows corresponding high ADC value suggesting T2 shine-through from vasogenic edema
Usually intense enhancement Usually well-circumscribed round lesions near GWM junction (no image shown) Displays same histology as primary neoplasm (no image shown) Can arise from malignancies outside the CNS (usually via hematogenous spread) or from spread of primary CNS neoplasms; represent > 50% of all brain tumors
Medulloblastoma Hyperdense, well-defined cerebellar mass usually with compression of 4th ventricle (arrowheads), +/- calcifications (10%), +/- heterogeneity from necrosis >90% show enhancement, classically homogenous (no image shown) Hypointense compared to adjacent gray matter Isointense to mildly hyperintense compared to surrounding gray matter Mass shows diffusion restriction Intense enhancement Usually round, well-circumsized mass most frequently arising from the floor of the 4th ventricle in the midline cerebellar vermis Four histologic subtypes; most common type displays densely-packed small cells with high nuclear:cytoplasm ratio PNET most frequently arising from midline cerebellar vermis; Peak age <10 years & 2nd most common neoplasm in children; WHO grade IV
Ganglioglioma Classically a cystic mass with mural nodule, but often solid of varying density +/- calcifications +/- erosion of adjacent calcarium Variable enhancement pattern (~50% enhance; no image shown) Mass is often iso- to hypo-intense; often cystic with mural nodule (40%) Heterogeneous hyperintense mass or mural nodule without significant surrounding edema Variable enhancement of mass or mural nodule Well-circumscribed mass, often cystic with mural nodule (image shows bulging of the cortical surface from the tumor) Mixture of neoplastic ganglion cells (arrowheads) & glial cells (often astrocytomas) of varying levels of differentiation 80% occur in patients younger than 30 years old. Prediliction for cerebral hemispheres, temporal > frontal > parietal. Low grade (I or II)/well-differentiated. Frequently present with history of seizures.
Dysembryoplastic neuroepithelial tumor Frequently wedge-shaped hypodense region in a cortical or subcortical location Usually nonenhancing (no image shown) Sharply-marginated hypointense mass High signal intensity; often multinodular or septated Mass generally doesn't enhance Lesion near the cortex, often with a gelatinous consistency Neuronal elements surrounded by prominent vacuoles, called "floating neurons" (arrows) Most frequently in temporal lobe & strongly associated with seizures; usually in patients <20
Oligodendroglioma Mixed density (hypo- or iso-dense) mass usually arising from cortical or subcortical frontal lobe, +/- calcifications (70%); can cross corpus callosum as in this image Variable enhancement pattern (~50% enhance) Hypo- or iso-intense heterogeneous mass, usually cortical or subcortical Hyperintense mass; heterogeneity due to calcium Heterogeneous, hyperintense mass ADC shows hyperintense signal in the region of the mass, which indicates absence of diffusion restriction ~50% enhance, usually heterogeneously; no enhancement seen with this image Solid, well-defined, encapsulated mass which causes expansion of the cortex & gyri Two main subtypes:
Well-differentiated oligodendroglioma, which displays rounded homogenous nuclei with clear cytoplasm

Anaplastic oligodendroglioma, which shows increased cellularity & marked atypia
Most commonly in frontal lobe of middle-age adults.
Desmoplastic infantile ganglioglioma Heterogeneous cystic (c) & solid (s) mass; solid component usually cortically-based Marked enhancement of solid component of mass (no image shown) Hypointense cyst, often multiloculated, with a heterogeneous solid component often abutting the dura High intensity cystic component with heterogeneous low-intensity solid component Marked enhancement of solid tumor component Cortically-based solid tumor component with adjacent dural thickening associated with large cystic component Dense desmoplastic tissue (arrow) with mix of glial & neuronal cells (arrowheads) Location: Frontal > Parietal > Temporal. Majority of cases reported in children < 1 year old. Usually present due to rapidly increasing head size.
Pleomorphic xanthoastrocytoma Cystic supratentorial mass with a mural nodule which is adjacent to the leptomeninges (can also appear solid or heterogeneous) Strong enhancement of the mural nodule or entire tumor mass Solid portions are iso- or hypo-intense to surrounding gray matter Solid portions are iso- or hyper-intense to surrounding gray matter Cystic portion is iso-intense to CSF (no image shown) Strong enhancement of solid portion or mural nodule as well as rim enhancement of the cystic portion; may see enhancement of a dural tail Pleomorphic astrocytic cells with intracytoplasmic lipid (xanthomatous change, arrow), usually superficial & attached to the meninges Rare tumors occuring in adolescents or young adults, often with a history of seizures. Suratentorial tumor most commonly in temporal lobes.
Gliomatosis cerebri Vague hypodense assymetry involving multiple lobes (no image shown) Usually nonenhancing (no image shown) Iso- or hypo-intense infiltrating mass involving at least 3 lobes (no image shown) Hyperintense infiltrating mass involving at least 3 lobes, with expansion of the involved lobes (here seen involving multiple areas of the bilateral periventricular white matter) Hyperintense, involving multiple lobes Usually no or minimal patchy enhancement; this image shows no enhancement of a hypointense lesion in the right frontal centrum semiovale & a patchy enhancing area in the left centrum semiovale Blurring of gray-white junctions, heterogeneous discoloration, +/- distinct tumor nodules Glial cells (most commonly astrocytes) which demonstrate pleomorphism & invasion of parenchyma in a parallel orientation to myelinated tracts Infiltrative tumor involving at least 3 lobes; differentiated from multifocal gliomas by lack of clear distinction from adjacent normal brain tissue, as well as by continuity of the cellular infiltration.
Hemangioblastoma Isodense mass moss frequently in posterior fossa +/- hypodense cystic component (no image shown) Intense enhancement of solid components (no image shown) Nodule/solid components are iso- or hypo-intense to brain (seen here in the hypothalamus); cystic components mildly hyperintense to CSF Hyperintense mass in posterior fossa; 60% are cystic with mural nodule, both of which are hyperintense on T2 Solid components of tumor are hyperintense, cystic components show same signal intensity as CSF (seen here is hippocampal hemangioblastoma in a patient with vHL) Strong enhancement of entire solid tumor or mural nodule of a cystic tumor Vascular, well-circumscribed, unencapsulated mass (no image shown) Proliferation of neoplastic fusiform stromal cells (arrow) with adjacent blood material (arrowheads) Classically cystic mass with mural nodule in the posterior fossa (~60% are actually cystic; ~95% are in the posterior fossa); WHO grade I tumors; Strong association with vHL (often occur supratentorially)