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Brain tumors

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I am Radiology resident I am having seminar on topic of Intra axial brain tumors ,so provide in depth knowledge about intra axial tumours,what to add in intraaxial tumours and explain all in depth,add extra other things as you think if needed

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intra-axial brain tumors MRI imaging classification

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glioblastoma MRI brain tumor imaging

This diagnostic comparison chart displays multi-modal brain imaging for a high-grade glioblastoma (upper row) and a low-grade glioma (lower row) across four modalities: contrast-enhanced T1-weighted MRI (T1ce), amide proton transfer-weighted (APTw) MRI, FET PET, and normalized cerebral blood volume (nCBV) maps. Column (a) shows T1ce MRI with segmentation overlays: red indicates contrast-enhancing tumor (CET) and green highlights FLAIR hyperintense tumor (FHT). In the glioblastoma, CET and FHT are more extensive and irregular compared to the circumscribed regions in the low-grade glioma. Column (b) presents APTw imaging, where the glioblastoma exhibits higher yellow-green signal intensity, signifying increased endogenous protein/cellularity. Column (c) FET PET images demonstrate significantly higher amino acid uptake (red hot spots) in the glioblastoma, indicating higher metabolic activity. Column (d) nCBV maps show increased perfusion (red/yellow areas) in the glioblastoma, reflecting higher vascularity. This comparison highlights how multi-parametric advanced imaging differentiates tumor grades based on cellularity, metabolism, and hemodynamics.

This diagnostic comparison chart displays multi-modal brain imaging for a high-grade glioblastoma (upper row) and a low-grade glioma (lower row) across four modalities: contrast-enhanced T1-weighted MRI (T1ce), amide proton transfer-weighted (APTw) MRI, FET PET, and normalized cerebral blood volume (nCBV) maps. Column (a) shows T1ce MRI with segmentation overlays: red indicates contrast-enhancing tumor (CET) and green highlights FLAIR hyperintense tumor (FHT). In the glioblastoma, CET and FHT are more extensive and irregular compared to the circumscribed regions in the low-grade glioma. Column (b) presents APTw imaging, where the glioblastoma exhibits higher yellow-green signal intensity, signifying increased endogenous protein/cellularity. Column (c) FET PET images demonstrate significantly higher amino acid uptake (red hot spots) in the glioblastoma, indicating higher metabolic activity. Column (d) nCBV maps show increased perfusion (red/yellow areas) in the glioblastoma, reflecting higher vascularity. This comparison highlights how multi-parametric advanced imaging differentiates tumor grades based on cellularity, metabolism, and hemodynamics.

This Comparison Chart displays serial axial T1-weighted post-contrast MRI slices (Slices 15–18) of a patient with glioblastoma, comparing two clinical time points: 'Within 90 days after completing CRT' and 'At the progression state'. The layout is organized into three columns for each state: 'Brain MRI' (standard imaging), 'Brain tissue' (segmented parenchyma), and 'Tumor area' (isolated segmentation of the lesion).

This Comparison Chart displays serial axial T1-weighted post-contrast MRI slices (Slices 15–18) of a patient with glioblastoma, comparing two clinical time points: 'Within 90 days after completing CRT' and 'At the progression state'. The layout is organized into three columns for each state: 'Brain MRI' (standard imaging), 'Brain tissue' (segmented parenchyma), and 'Tumor area' (isolated segmentation of the lesion).

This diagnostic image displays axial 18F-FDOPA PET/MRI scans of the brain, comparing two patients with IDH-wildtype glioblastoma to demonstrate the effect of carbidopa premedication on image contrast. The visualization uses two imaging metrics: Standardized Uptake Value (SUV) and Tumor-to-Healthy-Brain Ratio (TBR). Row A (no carbidopa) shows a localized high-intensity SUV signal in the left hemisphere glioblastoma with low background uptake in healthy brain tissue. Row B (with carbidopa) illustrates significantly increased background SUV throughout the striatum and cortex, which reduces the visual contrast between the tumor and healthy tissue on the SUV parametric map. The corresponding TBR parametric images (right column) demonstrate how normalizing the signal to healthy brain tissue improves tumor definition and contrast, particularly in the premedicated patient (B) where the tumor otherwise blends with the elevated background. A color scale indicates SUV values from 0 to 4. This comparison is clinically relevant for neuro-oncology imaging protocols, highlighting how carbidopa increases tracer availability and the necessity of TBR maps for accurate tumor delineation.

This diagnostic image displays axial 18F-FDOPA PET/MRI scans of the brain, comparing two patients with IDH-wildtype glioblastoma to demonstrate the effect of carbidopa premedication on image contrast. The visualization uses two imaging metrics: Standardized Uptake Value (SUV) and Tumor-to-Healthy-Brain Ratio (TBR). Row A (no carbidopa) shows a localized high-intensity SUV signal in the left hemisphere glioblastoma with low background uptake in healthy brain tissue. Row B (with carbidopa) illustrates significantly increased background SUV throughout the striatum and cortex, which reduces the visual contrast between the tumor and healthy tissue on the SUV parametric map. The corresponding TBR parametric images (right column) demonstrate how normalizing the signal to healthy brain tissue improves tumor definition and contrast, particularly in the premedicated patient (B) where the tumor otherwise blends with the elevated background. A color scale indicates SUV values from 0 to 4. This comparison is clinically relevant for neuro-oncology imaging protocols, highlighting how carbidopa increases tracer availability and the necessity of TBR maps for accurate tumor delineation.

A multi-panel diagnostic imaging series demonstrating tumor microenvironment (TME) mapping across four brain tumor types: (A) Glioblastoma WHO grade 4, (B) Brain metastasis from breast cancer, (C) Primary central nervous system lymphoma (PCNSL), and (D) Meningioma. For each entity, axial MRI slices are presented across five modalities: Conventional CE T1w, FLAIR, tissue oxygen tension (PO2) maps, neovascularization activity (MTI) maps, and color-coded TME maps. Corresponding radar charts quantify metabolic compartments: Glycolysis (blue), Oxidative Phosphorylation (OxPhos, green), Necrosis (black), and Hypoxia (red/yellow). Glioblastoma (A) shows high heterogeneity with central necrosis and a significant hypoxic rim. The metastasis (B) shows a larger necrotic center compared to hypoxia. PCNSL (C) and Meningioma (D) exhibit metabolic dominance in aerobic glycolysis (65-71%) with higher oxygen tension and functional neovascularization, showing minimal necrosis. This visual data illustrates how advanced MRI mapping can differentiate tumor physiology based on metabolic signatures and vascular integrity.

A multi-panel diagnostic imaging series demonstrating tumor microenvironment (TME) mapping across four brain tumor types: (A) Glioblastoma WHO grade 4, (B) Brain metastasis from breast cancer, (C) Primary central nervous system lymphoma (PCNSL), and (D) Meningioma. For each entity, axial MRI slices are presented across five modalities: Conventional CE T1w, FLAIR, tissue oxygen tension (PO2) maps, neovascularization activity (MTI) maps, and color-coded TME maps. Corresponding radar charts quantify metabolic compartments: Glycolysis (blue), Oxidative Phosphorylation (OxPhos, green), Necrosis (black), and Hypoxia (red/yellow). Glioblastoma (A) shows high heterogeneity with central necrosis and a significant hypoxic rim. The metastasis (B) shows a larger necrotic center compared to hypoxia. PCNSL (C) and Meningioma (D) exhibit metabolic dominance in aerobic glycolysis (65-71%) with higher oxygen tension and functional neovascularization, showing minimal necrosis. This visual data illustrates how advanced MRI mapping can differentiate tumor physiology based on metabolic signatures and vascular integrity.

This diagnostic imaging panel provides a comparative analysis of positron emission tomography (PET) and magnetic resonance imaging (MRI) in a rat brain glioblastoma model. The top row displays axial PET scans using two different radiopharmaceuticals: O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET), which targets amino acid transport, and [18F]fluoroazomycin arabinoside ([18F]FAZA), which targets tissue hypoxia. Both tracers show increased focal uptake (indicated by red/yellow pseudocoloring) within the tumor region. [18F]FET exhibits higher overall brain background and more uniform tumor delineation, whereas [18F]FAZA shows a more speckled, heterogeneous distribution reflecting hypoxic sub-volumes. The bottom row consists of corresponding contrast-enhanced T1-weighted MRI scans. These scans show a focal region of hyperintensity (gadolinium enhancement) indicative of blood-brain barrier disruption. A white boundary line is used across all modalities to delineate the anatomical extent of the rat brain. The image illustrates the clinical utility of multi-modal imaging to identify different physiological characteristics of glioblastoma, such as metabolic activity versus hypoxia, which is critical for targeted radiotherapy planning.

This diagnostic imaging panel provides a comparative analysis of positron emission tomography (PET) and magnetic resonance imaging (MRI) in a rat brain glioblastoma model. The top row displays axial PET scans using two different radiopharmaceuticals: O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET), which targets amino acid transport, and [18F]fluoroazomycin arabinoside ([18F]FAZA), which targets tissue hypoxia. Both tracers show increased focal uptake (indicated by red/yellow pseudocoloring) within the tumor region. [18F]FET exhibits higher overall brain background and more uniform tumor delineation, whereas [18F]FAZA shows a more speckled, heterogeneous distribution reflecting hypoxic sub-volumes. The bottom row consists of corresponding contrast-enhanced T1-weighted MRI scans. These scans show a focal region of hyperintensity (gadolinium enhancement) indicative of blood-brain barrier disruption. A white boundary line is used across all modalities to delineate the anatomical extent of the rat brain. The image illustrates the clinical utility of multi-modal imaging to identify different physiological characteristics of glioblastoma, such as metabolic activity versus hypoxia, which is critical for targeted radiotherapy planning.

This composite of six axial brain MRI scans demonstrates a glioblastoma (GBM) and its progression over a 7-month interval. (A) T2-FLAIR image shows a hyperintense mass involving the septum pellucidum and corpus callosum with associated perilesional edema. (B) Contrast-enhanced T1-weighted (CE T1W) image displays the primary tumor's heterogeneous enhancement, signifying blood-brain barrier disruption. (C) A Ve map (extracellular extravascular volume fraction) highlights increased vascular permeability, with arrows pointing to focal areas of elevated Ve. (D) A predictive MRI model overlay identifies a high-risk region (red) for local recurrence within the non-enhancing T2 hyperintense zone. (E, F) Longitudinal follow-up CE T1W scans at 7 months confirm disease progression, evidenced by a new, measurable enhancing lesion at the genu of the corpus callosum. This sequence illustrates the clinical utility of combining conventional imaging with physiological MRI parameters (like Ve maps) and predictive modeling to anticipate sites of glioblastoma recurrence beyond the initial contrast-enhancing tumor margins.

This composite of six axial brain MRI scans demonstrates a glioblastoma (GBM) and its progression over a 7-month interval. (A) T2-FLAIR image shows a hyperintense mass involving the septum pellucidum and corpus callosum with associated perilesional edema. (B) Contrast-enhanced T1-weighted (CE T1W) image displays the primary tumor's heterogeneous enhancement, signifying blood-brain barrier disruption. (C) A Ve map (extracellular extravascular volume fraction) highlights increased vascular permeability, with arrows pointing to focal areas of elevated Ve. (D) A predictive MRI model overlay identifies a high-risk region (red) for local recurrence within the non-enhancing T2 hyperintense zone. (E, F) Longitudinal follow-up CE T1W scans at 7 months confirm disease progression, evidenced by a new, measurable enhancing lesion at the genu of the corpus callosum. This sequence illustrates the clinical utility of combining conventional imaging with physiological MRI parameters (like Ve maps) and predictive modeling to anticipate sites of glioblastoma recurrence beyond the initial contrast-enhancing tumor margins.

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brain tumor MRI classification types low grade high grade glioma lymphoma metastasis

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medulloblastoma posterior fossa MRI cerebellum child

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primary CNS lymphoma PCNSL MRI basal ganglia periventricular

This composite diagnostic image displays MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography) scans for six different patients, illustrating various manifestations of hematologic Central Nervous System (CNS) disease. The top row primarily features axial and sagittal MRI views, while the bottom row includes complementary coronal MRI and PET fusion images. Patient 1 shows secondary CNS lymphoma (SCNSL) with an intramedullary lesion in the cervical spinal cord on sagittal MRI, matched with focal hypermetabolism on a PET/CT neck axial slice. Patients 2 and 3 demonstrate parenchymal SCNSL; Patient 2 exhibits a contrast-enhancing mass in the right basal ganglia/thalamic region, and Patient 3 shows a left frontal lobe lesion with surrounding vasogenic edema. Patients 4 and 5 illustrate Primary CNS Lymphoma (PCNSL), showing periventricular and multifocal enhancing masses respectively. Patient 6 depicts leptomeningeal diffuse infiltration associated with leukemia, showing less focal mass effect but subtle enhancement patterns. The images serve as an educational comparison of intracranial and intraspinal lymphoproliferative involvement, highlighting differing morphologies such as focal parenchymal masses, leptomeningeal spread, and spinal cord expansion.

This composite diagnostic image displays MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography) scans for six different patients, illustrating various manifestations of hematologic Central Nervous System (CNS) disease. The top row primarily features axial and sagittal MRI views, while the bottom row includes complementary coronal MRI and PET fusion images. Patient 1 shows secondary CNS lymphoma (SCNSL) with an intramedullary lesion in the cervical spinal cord on sagittal MRI, matched with focal hypermetabolism on a PET/CT neck axial slice. Patients 2 and 3 demonstrate parenchymal SCNSL; Patient 2 exhibits a contrast-enhancing mass in the right basal ganglia/thalamic region, and Patient 3 shows a left frontal lobe lesion with surrounding vasogenic edema. Patients 4 and 5 illustrate Primary CNS Lymphoma (PCNSL), showing periventricular and multifocal enhancing masses respectively. Patient 6 depicts leptomeningeal diffuse infiltration associated with leukemia, showing less focal mass effect but subtle enhancement patterns. The images serve as an educational comparison of intracranial and intraspinal lymphoproliferative involvement, highlighting differing morphologies such as focal parenchymal masses, leptomeningeal spread, and spinal cord expansion.

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oligodendroglioma calcification MRI CT brain

Imaging modality and technique: Non-contrast CT of the brain is the primary image, with axial sections demonstrating a well circumscribed, extra-axial mass located at the anterior cranial fossa near the frontal convexity. The lesion is markedly hyperdense due to dense calcification, with coarse calcifications producing bright foci that obscure the underlying cortex. The mass abuts the dura and appears to cause mild mass effect on the adjacent frontal lobes, but there is no midline shift or intraventricular hemorrhage. The appearance is classic for a calcified meningioma; the tumor originates from the dura and demonstrates dural-based expansion, with a possible dural tail on the MRI counterpart. The MRI image (not shown here) would typically show a lesion with variable T1/T2 signal and strong, homogeneous enhancement after gadolinium, consistent with meningioma and predominance of calcified components. Clinically, incidental discovery of a calcified meningioma aligns with a slow-growing, benign meninges-derived neoplasm. Differential considerations include psammomatous meningioma, calcified oligodendroglioma (intra-axial), calcified metastasis, and dural-based schwannoma; however, location and extra-axial behavior with dense calcifications favor meningioma. Diagnostic significance is that surgical resection often yields cure; prognosis depends on size, location, edema, and invasion; radiologic monitoring is advised.

Imaging modality and technique: Non-contrast CT of the brain is the primary image, with axial sections demonstrating a well circumscribed, extra-axial mass located at the anterior cranial fossa near the frontal convexity. The lesion is markedly hyperdense due to dense calcification, with coarse calcifications producing bright foci that obscure the underlying cortex. The mass abuts the dura and appears to cause mild mass effect on the adjacent frontal lobes, but there is no midline shift or intraventricular hemorrhage. The appearance is classic for a calcified meningioma; the tumor originates from the dura and demonstrates dural-based expansion, with a possible dural tail on the MRI counterpart. The MRI image (not shown here) would typically show a lesion with variable T1/T2 signal and strong, homogeneous enhancement after gadolinium, consistent with meningioma and predominance of calcified components. Clinically, incidental discovery of a calcified meningioma aligns with a slow-growing, benign meninges-derived neoplasm. Differential considerations include psammomatous meningioma, calcified oligodendroglioma (intra-axial), calcified metastasis, and dural-based schwannoma; however, location and extra-axial behavior with dense calcifications favor meningioma. Diagnostic significance is that surgical resection often yields cure; prognosis depends on size, location, edema, and invasion; radiologic monitoring is advised.

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brain tumor MRI perfusion DWI spectroscopy advanced imaging

This composite of six diagnostic images illustrates the multidimensional MRI and spectroscopic profile of a localized lesion in the left parietal lobe, characteristic of epithelioid glioblastoma (eGBM). (a) Axial T2-weighted imaging (T2WI) shows a hyperintense lesion involving the cortical and subcortical white matter with clear boundaries and minimal peritumoral edema. (b) Diffusion-weighted imaging (DWI) reveals high signal intensity, which corresponds to low signal intensity on the (d) Apparent Diffusion Coefficient (ADC) map, indicating restricted diffusion within the tumor parenchyma. (c) Coronal contrast-enhanced T1-weighted imaging demonstrates obvious, uniform enhancement of the lesion and a visible 'meningeal tail sign' (white arrow), suggesting dural involvement. (e) MR perfusion imaging (PWI) shows significantly increased cerebral blood flow (rCBF) in the lesion area (red/warm colors), reflecting high vascularity. (f) MR spectroscopy (MRS) graph displays an elevated Choline (Cho) peak and a markedly reduced N-acetylaspartate (NAA) peak, resulting in a high Cho/NAA ratio characteristic of high-grade malignancy. This multimodal presentation is a key educational example of how advanced imaging sequences differentiate aggressive brain tumors from other cerebral pathologies.

This composite of six diagnostic images illustrates the multidimensional MRI and spectroscopic profile of a localized lesion in the left parietal lobe, characteristic of epithelioid glioblastoma (eGBM). (a) Axial T2-weighted imaging (T2WI) shows a hyperintense lesion involving the cortical and subcortical white matter with clear boundaries and minimal peritumoral edema. (b) Diffusion-weighted imaging (DWI) reveals high signal intensity, which corresponds to low signal intensity on the (d) Apparent Diffusion Coefficient (ADC) map, indicating restricted diffusion within the tumor parenchyma. (c) Coronal contrast-enhanced T1-weighted imaging demonstrates obvious, uniform enhancement of the lesion and a visible 'meningeal tail sign' (white arrow), suggesting dural involvement. (e) MR perfusion imaging (PWI) shows significantly increased cerebral blood flow (rCBF) in the lesion area (red/warm colors), reflecting high vascularity. (f) MR spectroscopy (MRS) graph displays an elevated Choline (Cho) peak and a markedly reduced N-acetylaspartate (NAA) peak, resulting in a high Cho/NAA ratio characteristic of high-grade malignancy. This multimodal presentation is a key educational example of how advanced imaging sequences differentiate aggressive brain tumors from other cerebral pathologies.

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WHO 2021 CNS tumor classification 5th edition intra-axial brain tumors radiology updates

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Here is a comprehensive, seminar-level guide to Intra-Axial Brain Tumors for your radiology presentation:

INTRA-AXIAL BRAIN TUMORS

A Comprehensive Radiology Seminar Guide

1. DEFINITION AND FUNDAMENTAL CONCEPT

Intra-axial tumors arise from within the brain parenchyma itself - from the neurons, glial cells, ependymal cells, or any tissue intrinsic to the brain substance. This distinguishes them fundamentally from extra-axial tumors (meningiomas, schwannomas, epidermoids), which arise outside the brain but compress or displace it.

Key Radiological Signs That Confirm Intra-Axial Origin:

  • No CSF cleft between lesion and brain
  • No buckling/displacement of gray-white matter interface
  • No broad dural base
  • Epicenter within brain parenchyma
  • Surrounding infiltrative edema rather than compressed cortex

2. WHO CNS CLASSIFICATION - UNDERSTANDING THE EVOLUTION

This is the single most important conceptual shift for any modern neuroradiology seminar.

WHO 2016 (4th Edition - Major Paradigm Shift)

Introduced molecular markers into diagnosis for the first time - the "layered diagnosis":
  • IDH mutation status
  • 1p/19q codeletion
  • MGMT promoter methylation
Tumor TypeICD-O Code
Glioblastoma, IDH-wildtype9440/3
Glioblastoma, IDH-mutant9445/*
Diffuse astrocytoma, IDH-mutant9400/3
Oligodendroglioma, IDH-mutant AND 1p/19q-codeleted9450/3
Diffuse midline glioma, H3 K27M-mutant9385/*

WHO 2021 (5th Edition - Current Standard)

The 2021 WHO CNS5 classification introduced several major updates:
  • Arabic numerals replace Roman numerals for grading (Grade 4, not Grade IV)
  • Within-type grading - grade is assigned within a tumor type, not across all CNS tumors
  • DNA methylation profiling added as a diagnostic tool
  • 22 newly recognized tumor entities added
  • Greater separation between pediatric-type and adult-type diffuse gliomas
  • Astrocytoma, IDH-mutant is now graded 2, 3, or 4 (previously only grade 2-3 for astrocytoma; grade 4 was called GBM)

3. CLASSIFICATION OF INTRA-AXIAL TUMORS

A. Diffuse Glial Tumors (Most Common - 50-70% are high grade)

  1. Glioblastoma, IDH-wildtype (Grade 4)
  2. Astrocytoma, IDH-mutant (Grade 2, 3, 4)
  3. Oligodendroglioma, IDH-mutant + 1p/19q codeleted (Grade 2, 3)
  4. Diffuse midline glioma, H3 K27M-mutant (Grade 4)
  5. Diffuse hemispheric glioma, H3 G34-mutant (Grade 4) - NEW in 2021

B. Circumscribed Gliomas

  1. Pilocytic astrocytoma (Grade 1)
  2. Pleomorphic xanthoastrocytoma (PXA) (Grade 2, 3)
  3. Subependymal giant cell astrocytoma (SEGA) (Grade 1)

C. Glioneuronal & Neuronal Tumors

  1. Ganglioglioma (Grade 1-3)
  2. Dysembryoplastic neuroepithelial tumor (DNET) (Grade 1)
  3. Central neurocytoma
  4. Cerebellar liponeurocytoma

D. Ependymal Tumors

  1. Ependymoma (Grade 2-3)
  2. Myxopapillary ependymoma (Grade 2)
  3. Subependymoma (Grade 1)
  4. Ependymoma, RELA-fusion positive (now called supratentorial ependymoma, ZFTA fusion-positive in WHO 2021)

E. Embryonal Tumors (predominantly pediatric)

  1. Medulloblastoma (all grades)
  2. CNS embryonal tumor (Grade 4)

F. Other Intra-Axial Entities (non-primary)

  1. Brain metastases
  2. Primary CNS Lymphoma (PCNSL)
  3. Tumefactive MS (mimicker)
  4. Brain abscess (mimicker)

4. GLIOBLASTOMA (GBM) - THE MOST IMPORTANT TUMOR

Epidemiology

  • Most common primary malignant brain tumor in adults
  • Peak incidence: 55-75 years
  • Median survival: 12-14 months even with maximal treatment (surgery + RT + TMZ)
  • M:F ratio approximately 1.6:1

Molecular Biology (Critical for Radiology Reports)

MarkerSignificance
IDH statusWild-type = primary GBM (>90%), worst prognosis
MGMT methylationPredicts response to temozolomide; better prognosis
EGFR amplificationCommon in IDH-wt GBM
TERT mutationCommon in IDH-wt GBM

Imaging Features

CT:
  • Heterogeneous hypodense mass with irregular peripheral hyperdense rim (blood)
  • Surrounding vasogenic edema
  • Mass effect, midline shift
  • Avid, irregular ring enhancement
MRI - Conventional:
  • T1: Heterogeneous, central hypointensity (necrosis)
  • T2/FLAIR: Extensive surrounding hyperintensity - the T2/FLAIR halo ALWAYS contains infiltrating tumor cells (not just edema)
  • T1+Gd: Thick, nodular, irregular ring enhancement - hallmark
  • DWI/ADC: Restricted diffusion in solid components (high cellularity); low ADC in enhancing margins
GBM MRI: T2 heterogeneous mass with surrounding edema, post-Gd ring enhancement, ADC restricted diffusion - Grainger & Allison's Radiology
Classic GBM: (A) T2 - heterogeneous right hemisphere mass with surrounding edema; (B) Post-Gd T1 - no enhancement in this IDH-wt case (note: non-enhancing GBMs exist!); (C) ADC - restricted diffusion within the solid component
MRI - Advanced/Functional:
ModalityGBM FindingSignificance
DSC Perfusion (rCBV)Markedly elevated (>1.75 cutoff)Neovascularity / angiogenesis
MRSElevated Cho, reduced NAA, Cho/NAA >2, lipid/lactate peaksHigh cellularity + necrosis
DWIRestricted diffusion in cellular areasHigh tumor grade
fMRIMaps eloquent cortexPre-surgical planning
DTIWhite matter tract displacement vs. infiltrationSurgery planning

Butterfly GBM - High Yield Pattern

Bilateral hemispheric involvement crossing the corpus callosum. The CC is involved in 5% of GBMs at presentation. Differential: PCNSL, tumefactive MS, lymphoma.

GBM Treatment Response Monitoring

A critical concept for radiologists:
  • Pseudoprogression: Apparent increase in enhancement within 3 months of RT + TMZ - represents treatment effect, not true progression. More common with MGMT-methylated tumors.
  • Pseudoresponse: Apparent decrease in enhancement with anti-VEGF therapy (bevacizumab) - the tumor shrinks its enhancement but continues growing as non-enhancing T2/FLAIR disease.
  • RANO criteria: Standardized bidirectional measurements for treatment response; requires combining enhancing AND non-enhancing T2/FLAIR changes.

5. IDH-MUTANT GLIOMAS (Lower Grade)

The IDH Mutation - Why It Matters

IDH1 (R132H, found in ~90% of IDH-mutant gliomas) and IDH2 mutations produce the oncometabolite 2-hydroxyglutarate (2-HG). Despite being "mutant," IDH-mutant gliomas have significantly better prognosis (survival often 5-10+ years vs. 12-14 months for GBM).
IDH-mutant gliomas are divided by 1p/19q codeletion:
  • 1p/19q codeleted → Oligodendroglioma (best prognosis, ~8 years mean survival)
  • No 1p/19q codeletion → Astrocytoma, IDH-mutant (intermediate prognosis)

Imaging Features of IDH-Mutant Low-Grade Gliomas

General Features:
  • Young adults (mean age 30-40 years)
  • Often cortically based, frontal lobe predominance
  • Seizures as presenting symptom
  • Well-defined, non-enhancing (usually)
  • T2/FLAIR hyperintense without much surrounding edema (unlike GBM)
Oligodendroglioma (IDH-mutant, 1p/19q codeleted):
  • Cortically based, frequently frontal lobe (70%)
  • Calcification in ~70-90% (coarse, irregular) - best seen on CT
  • T2 heterogeneous with cysts
  • Enhancement variable
  • Can have paradoxically elevated rCBV despite low grade (due to branching "chicken-wire" vasculature)
Astrocytoma, IDH-mutant:
  • Diffuse, infiltrating
  • T2/FLAIR homogeneous hyperintensity
  • Usually non-enhancing at Grade 2; enhancement signals Grade 3-4
  • Lower rCBV than oligodendroglioma
IDH-wt astrocytoma MRI: T2, post-Gd T1, DWI, ADC - Grainger & Allison's
IDH-wildtype astrocytoma (WHO Grade 3): (A) T2 hyperintense; (B) Post-Gd - no enhancement (note non-enhancing GBMs are more common than thought); (C) DWI - no significant restriction; (D) ADC - elevated signal

6. DIFFUSE MIDLINE GLIOMA (H3 K27M-Mutant) - HIGH YIELD

  • WHO Grade 4 - all cases, regardless of histology
  • Predominantly pediatric/young adults
  • Location: Brainstem (especially pons = DIPG), thalamus, spinal cord
  • The H3 K27M mutation (histone mutation) is the defining molecular feature
  • Imaging: Diffuse, infiltrating pontine/thalamic mass, variable enhancement, often no necrosis
  • Prognosis: Median survival ~10-12 months despite treatment
Radiological tip: A child with a diffuse, infiltrative pontine mass that wraps around the basilar artery and does NOT enhance dramatically = DIPG until proven otherwise.

7. CIRCUMSCRIBED GLIOMAS

Pilocytic Astrocytoma (Grade 1)

  • Most common brain tumor in children overall
  • Location: Cerebellum (most common), optic pathway, hypothalamus, brainstem
  • Classic MRI: Cyst with enhancing mural nodule - "cyst + nodule" pattern
  • The cyst wall does NOT enhance; the mural nodule enhances avidly
  • Leptomeningeal spread is rare despite WHO Grade 1 - excellent prognosis after surgery

Pleomorphic Xanthoastrocytoma (PXA)

  • Young adults, temporal lobe
  • Classic: Cortically based, superficial, cyst + nodule; dural involvement/tail may be seen (but it's intra-axial!)
  • Can mimic meningioma due to dural contact
  • Often presents with chronic epilepsy
  • May dedifferentiate to anaplastic PXA (Grade 3) or GBM

Subependymal Giant Cell Astrocytoma (SEGA)

  • Virtually pathognomonic of tuberous sclerosis
  • Location: Foramen of Monro (causes obstructive hydrocephalus)
  • CT: Hyperdense, calcified; MRI: Heterogeneous with avid enhancement
  • Treatment: Surgical or mTOR inhibitor (everolimus)

8. EPENDYMOMAS

Key Facts

  • Arise from ependymal cells lining the ventricles and central canal
  • Bimodal distribution: Children (posterior fossa) and adults (spinal cord)
  • The WHO 2021 classification now defines ependymomas by molecular subtypes, not just location

Intracranial Ependymoma Locations

LocationAge GroupMolecular Subtype
4th ventricleChildrenPF-EPN-A or PF-EPN-B
SupratentorialOlder children/YAZFTA fusion-positive (formerly RELA)
SpinalAdultsNOS or myxopapillary

Imaging Features

  • 4th ventricle ependymoma: Classically "squeezing" through the foramina of Luschka/Magendie (plastic/insinuating growth) - high yield!
  • Heterogeneous: cysts, calcification, hemorrhage ("salt and pepper")
  • Moderate to marked enhancement
  • Leptomeningeal drop metastases occur - must image the whole spine

9. MEDULLOBLASTOMA

Epidemiology

  • Most common malignant brain tumor in children
  • Peak age 5-7 years; second peak in adults 20-40 years
  • Location: Cerebellar vermis (children, arising from 4th ventricle roof) vs. cerebellar hemisphere (adults)

WHO 2021 Molecular Subgroups (High Yield for Modern Practice)

SubgroupMolecular FeatureAgePrognosis
WNT-activatedCTNNB1 mutationOlder childrenBest (>90% survival)
SHH-activatedPTCH1, SMO, SUFUInfants + adultsIntermediate
Group 3MYC amplificationYoung childrenWorst
Group 4CDK6 amplificationAll agesIntermediate

Imaging Features

  • CT: Hyperdense vermian mass (highly cellular - high nuclear:cytoplasmic ratio causes T2 hypointensity and CT hyperdensity)
  • MRI T2: Isointense to hypointense - differentiates from pilocytic astrocytoma (T2 bright)
  • DWI: Markedly restricted diffusion (ADC very low) - key feature
  • Heterogeneous enhancement
  • Obstructive hydrocephalus common
  • Drop metastases along the spinal axis in ~30-40% - MRI whole spine mandatory at staging

10. BRAIN METASTASES - A RADIOLOGIST'S DAILY BREAD

Epidemiology

  • 10x more common than primary brain tumors in adults
  • Most common in adults >40 years
  • Common primaries: Lung (most common, ~50%), Breast, Melanoma, Renal cell, Colorectal

Distribution Pattern

  • 80% supratentorial (proportional to blood flow)
  • Predilection for gray-white matter junction (embolic trapping at small vessel branching)
  • 15% infratentorial (cerebellum)

Imaging Features

CT: Hypo/isodense mass + ring or solid enhancement + surrounding edema
MRI:
  • T1: Hypointense (or hyperintense if melanoma/hemorrhage)
  • T2: Hypointense to isointense solid portions; extensive surrounding vasogenic edema (often disproportionately large edema relative to the small metastatic nodule)
  • T1+Gd: Ring or solid enhancement; small metastases may be invisible without contrast - always use Gd-enhanced MRI
  • DWI: Variable (usually no restriction, unlike abscess which restricts)
  • SWI: Look for blooming artifact - melanoma, choriocarcinoma, thyroid metastases are hemorrhage-prone

Special Cases - High Yield for Radiology

Primary TumorSpecial Imaging Clue
MelanomaT1 hyperintense (melanin/hemorrhage); hemorrhagic
LungMost common; solitary or multiple
Renal cell carcinomaHypervascular, cystic, hemorrhagic
BreastLeptomeningeal spread common
ChoriocarcinomaHighly hemorrhagic

Solitary Metastasis vs. GBM - The Classic Differential

FeatureMetastasisGBM
LocationGM-WM junctionDeep white matter/basal ganglia
EdemaVasogenic, largeInfiltrative T2 halo
EnhancementClean ring/solidIrregular, nodular rim
MultiplicityOften multipleUsually solitary
ADC inner cavityUnrestrictedMay show restricted areas in necrotic core
MRSElevated Cho (if solid)Cho/NAA markedly elevated + lipid/lactate

11. PRIMARY CNS LYMPHOMA (PCNSL)

Overview

  • B-cell NHL confined to the CNS (usually diffuse large B-cell)
  • Increasing incidence in immunocompetent patients (not just AIDS)
  • Highly aggressive but steroid-sensitive and chemosensitive (HD-MTX based)

Imaging Features - "The Ghost Tumor"

  • Location: Deep gray matter (basal ganglia, thalamus), periventricular white matter, corpus callosum
  • CT: Hyperdense (due to high cellular density, nuclear:cytoplasm ratio)
  • MRI T2: Iso to hypointense (unlike most tumors - this is a key teaching point)
  • T1+Gd: Homogeneous, avid enhancement in immunocompetent patients
  • DWI: Markedly restricted diffusion (ADC very low) - due to hypercellularity
  • Immunocompromised patients (HIV/AIDS): Ring-enhancing; must differentiate from toxoplasmosis (toxo responds to empirical treatment; PCNSL does not)

The Ghost Tumor Sign

When steroids are given empirically before biopsy, PCNSL can literally disappear on MRI within days. This is pathognomonic - "the ghost tumor." Always avoid steroids before biopsy unless there is life-threatening herniation.
PCNSL and other CNS lymphoproliferative disease: Periventricular and multifocal enhancing masses in PCNSL; comparison with GBM, metastasis, and meningioma

12. GLIONEURONAL TUMORS

Ganglioglioma

  • Most common cause of chronic temporal lobe epilepsy in young patients
  • Location: Temporal lobe (>70%)
  • MRI: Cortically based, cyst + enhancing nodule (similar to pilocytic)
  • Calcification frequent
  • Usually Grade 1-2, excellent prognosis after surgery

DNET (Dysembryoplastic Neuroepithelial Tumor)

  • Young patients, intractable partial seizures
  • Supratentorial cortex (temporal, frontal)
  • "Bubbly" multicystic appearance - T1 hypointense, T2 bright
  • Classic: No edema, no mass effect, no enhancement (in most cases)
  • Cortical location, may have pseudogyral expansion

13. INTRAVENTRICULAR TUMORS (Technically Intra-Axial or Periventricular)

TumorAgeLocationKey Feature
Central neurocytomaYoung adultLateral ventricles, septum pellucidum"Bubbly," calcified, heterogeneous enhancing
SubependymomaMiddle-aged adults4th ventricle, lateral ventriclesNon-enhancing, very indolent
Choroid plexus papillomaChildren (<5 yrs)Lateral ventricle trigoneCauliflower, intense enhancement, hydrocephalus
EpendymomaChildren4th ventricleSqueezes through foramina
SEGAChildren/adolescentsForamen of MonroTuberous sclerosis
Colloid cystMiddle-agedForamen of MonroHyperdense CT; blocks CSF → acute hydrocephalus

14. ADVANCED MRI TECHNIQUES IN BRAIN TUMOR IMAGING

This section is what elevates a radiology seminar:

A. Diffusion-Weighted Imaging (DWI) / ADC

  • Low ADC (restricted diffusion) = high cellularity = high grade
  • Clinically key differentials:
    • Ring-enhancing lesion + restricted center → Abscess (pus restricts)
    • Ring-enhancing lesion + non-restricted center → GBM/metastasis (necrotic core = unrestricted)
    • Solid homogeneous lesion + markedly restricted → PCNSL (hypercellular)

B. Perfusion MRI (DSC, DCE, ASL)

  • DSC (Dynamic Susceptibility Contrast) - T2 perfusion*: Most validated; gives rCBV
    • rCBV >1.75 → High grade glioma (sensitivity 95%)
    • rCBV elevated in oligodendroglioma despite low grade (chicken-wire vasculature)
    • rCBV low → PCNSL, metastasis (despite enhancement), radiation necrosis
  • DCE (Dynamic Contrast-Enhanced) - T1 perfusion: Gives Ktrans, Ve (vessel permeability)
  • ASL (Arterial Spin Labeling): No contrast; good for pediatric patients

C. MR Spectroscopy (MRS)

MetaboliteSignificance
Choline (Cho)Membrane turnover; elevated in high-grade tumor
NAA (N-acetylaspartate)Neuronal marker; reduced in tumor
Creatine (Cr)Reference metabolite
Lipid/LactateNecrosis/anaerobic metabolism
2-HG peak at 2.25 ppmSpecific for IDH-mutant gliomas
  • Key ratios: Cho/NAA > 2 = malignant; Cho/NAA > 3 = highly malignant
  • MRS can detect tumor outside the enhancing margin

D. MR Perfusion + DWI + Spectroscopy Combined

Advanced MRI multiparametric imaging: DWI restriction, PWI elevated rCBF, MRS elevated Cho/NAA - epithelioid GBM example
Multiparametric MRI profile: (a) T2WI, (b) DWI with restricted diffusion, (c) CE T1 with dural tail sign (arrow), (d) ADC low signal, (e) PWI with elevated rCBF in red, (f) MRS showing elevated Cho and markedly reduced NAA

E. Tumor Microenvironment Mapping (Emerging)

Tumor Microenvironment comparison: GBM vs Metastasis vs PCNSL vs Meningioma - CE T1, FLAIR, O2 tension, neovascularization maps
Advanced TME mapping differentiating GBM (high hypoxia/necrosis), Metastasis (large necrotic center), PCNSL (dominant glycolysis, low hypoxia), and Meningioma (extra-axial, high OxPhos)

F. Radiogenomics / Radiomics

  • AI-based texture analysis can predict IDH status, MGMT methylation, 1p/19q codeletion non-invasively
  • T2/FLAIR mismatch sign: T2 homogeneous high signal WITH FLAIR isointense "mismatch" = highly specific for IDH-mutant, 1p/19q intact astrocytoma (specificity >90%)
  • Growing role in clinical practice and the 2021 WHO update has increased demand for radiomic biomarker integration

15. IMPORTANT DIFFERENTIAL DIAGNOSIS PEARLS

Ring-Enhancing Brain Lesion (RING)

CauseKey Clue
GlioblastomaIrregular ring, T2 halo, solitary, WM
Radiation necrosisPrevious RT history; MRS lipid/lactate no Cho
Infection (abscess)Thin smooth ring + DWI restricted center + fever
Neoplasm (metastasis)GM-WM junction, multiple, known primary
Granuloma (TB/Toxo)Smooth ring; contact history; HIV status
Demyelination (tumefactive MS)Open ring (horseshoe) enhancement; white matter lesions elsewhere; young woman

T2/FLAIR Mismatch Sign (High Yield)

  • T2 bright + FLAIR relatively dark/isointense within the same lesion
  • Specificity >90% for IDH-mutant, non-codeleted astrocytoma
  • Easy to use, no contrast needed

Corpus Callosum Involvement

Bilateral CC lesionDiagnosis
"Butterfly" mass, heterogeneousGBM
Periventricular, homogeneous, restricted DWIPCNSL
Multiple ovoid lesionsTumefactive MS (Dawson fingers)
Bilateral thalamic involvementDiffuse midline glioma

16. PEDIATRIC vs. ADULT BRAIN TUMORS - KEY DIFFERENCES

FeatureChildrenAdults
Most common locationPosterior fossa (infratentorial)Supratentorial
Most common tumorPilocytic astrocytomaGlioblastoma
Most common malignantMedulloblastomaGlioblastoma
Common entitiesDIPG, ependymoma, ATRTGBM, metastases, PCNSL
Molecular classificationNow critical (WHO 2021)IDH, MGMT, 1p/19q

17. IMAGING PROTOCOL RECOMMENDATION (For Your Department)

Standard Brain Tumor MRI Protocol:

  1. T1 3D (pre-contrast) - Anatomy baseline
  2. T2 Axial - Tumor delineation
  3. FLAIR Axial - Perilesional edema/infiltration
  4. DWI - Cellularity, abscess vs. tumor
  5. SWI/GRE - Hemorrhage, calcification, vessels
  6. T1+Gd 3D - Enhancement pattern (axial, coronal, sagittal)
  7. DSC Perfusion - rCBV for grading
  8. MRS (single or multivoxel) - Metabolite profile
Advanced/Research additions: DCE perfusion, ASL, DTI, fMRI (pre-surgical), sodium MRI, CEST, PET (FET, FDG, FDOPA)

18. TREATMENT RESPONSE CRITERIA - RANO

The Response Assessment in Neuro-Oncology (RANO) working group criteria incorporate:
  • Bidirectional enhancement measurements
  • Non-enhancing T2/FLAIR changes
  • Treatment timing context (pseudoprogression window = first 12 weeks post-RT)
  • Modified RANO-HGG for high-grade, RANO-LGG for low-grade
Volumetric imaging is increasingly favored over 2D bidirectional measurements for more accurate serial comparisons.

19. SUMMARY TABLE - INTRA-AXIAL TUMOR AT A GLANCE

TumorAgeLocationCTT2EnhancementDWIrCBVKey Feature
GBM55-75WM/deepHypodense+ringHeterogeneousIrregular ring+ restrictedHighNecrosis, T2 halo with tumor
Astrocytoma IDH-mut30-40Frontal WMHypodenseHomogeneous brightNone/faint-Low-modT2/FLAIR mismatch
Oligodendroglioma35-45Frontal cortexCalcifiedHeterogeneousVariable-ElevatedCalcification + cortical
Pilocytic<20CerebellumCyst+noduleCyst T2 brightNodule avid-LowCyst+nodule pattern
DNET<30Temporal cortexHypodenseBubbly brightNone-LowNo edema, no mass effect
Medulloblastoma5-7Vermis/4th VHyperdenseIso/hypointenseModerateModVery restrictedDrop mets, hyperdense CT
Ependymoma5-104th ventricleCalcifiedHeterogeneousModerate-LowSqueezes through foramina
PCNSL50-70BG/periventriculHyperdenseIso/hypointenseHomogeneous++ restrictedLow-modGhost sign, steroids
Metastasis>40GM-WM junctionVariableVasogenic edemaRing/solid- (center)VariableMultiple, known primary
GCT/Ganglioglioma10-30TemporalCalcifiedHeterogeneousVariableLowLowChronic epilepsy

20. EXTRA TOPICS TO INCLUDE IN YOUR SEMINAR

A. Leptomeningeal Disease

  • Tumors that spread via CSF: Medulloblastoma, ependymoma, GBM (rare), PCNSL, breast/lung mets
  • MRI: Leptomeningeal enhancement on post-Gd T1 FLAIR sequence
  • Post-Gd FLAIR is more sensitive than post-Gd T1 for leptomeningeal mets

B. Stereotactic Biopsy Targeting

  • Avoid the necrotic center - biopsy the enhancing rim or highest rCBV area
  • Perfusion-guided biopsy improves diagnostic yield

C. Post-Treatment Imaging Challenges

  • Pseudoprogression vs. true progression: MRS (low Cho = necrosis, high Cho = tumor), DSC perfusion (low rCBV = treatment effect)
  • LITT (Laser Interstitial Thermal Therapy): New ablative technique; post-treatment MRI shows a "treatment zone" with rim enhancement and central necrosis - recent AJNR review (2025) covers what the neuroradiologist should know

D. Functional Imaging for Pre-Surgical Planning

E. PET Imaging in Brain Tumors

  • FDG-PET: Limited due to high background glucose uptake in brain
  • FET-PET (fluoroethyl-tyrosine): Amino acid PET - excellent for tumor delineation, recurrence vs. necrosis
  • FDOPA-PET: Best for differentiating recurrence from treatment effects; note carbidopa effect on background
  • PET/MRI fusion gives best of both worlds

KEY TAKE-HOME MESSAGES FOR YOUR SEMINAR

  1. WHO 2021 changed everything - molecular markers are now primary, histology is secondary. Reports must mention IDH, 1p/19q, MGMT.
  2. Enhancement does NOT equal malignancy - 30-40% of GBMs may not enhance early; IDH-mutant Grade 2 gliomas rarely enhance. - Grainger & Allison's Diagnostic Radiology
  3. The T2/FLAIR halo of GBM always contains infiltrating tumor cells - surgical margins must extend beyond enhancement.
  4. T2/FLAIR mismatch sign = IDH-mutant non-codeleted astrocytoma with >90% specificity.
  5. PCNSL disappears with steroids - the "ghost tumor" - never give steroids before biopsy.
  6. DWI is your grading tool: PCNSL (most restricted) > Medulloblastoma > GBM solid areas > Low-grade glioma.
  7. rCBV > 1.75 = high grade (except oligodendroglioma which is falsely elevated).
  8. Medulloblastoma in the vermis + T2 hypointense + restricted DWI + drop mets = diagnosis.
  9. Gray-white matter junction + multiple lesions + vasogenic edema = Metastases until proven otherwise.
  10. Pseudoprogression and pseudoresponse are the radiologist's biggest challenge in neuro-oncology follow-up.
Sources: Grainger & Allison's Diagnostic Radiology (Textbook of Medical Imaging), Robbins & Kumar Basic Pathology, Goldman-Cecil Medicine 26E, Adams & Victor's Principles of Neurology 12E, Bradley & Daroff's Neurology in Clinical Practice; WHO CNS5 2021 Classification [PMC8328013]; AJNR WHO CNS5 Review; Radiopaedia WHO CNS Classification
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