Brain Tumours - Comprehensive Neuroradiology Reference

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PART 1: SYSTEMATIC APPROACH TO BRAIN TUMOURS

1. Patient age - determines the differential diagnosis fundamentally
2. Location - intra vs. extra-axial, anatomical compartment, midline vs. lateral
3. Number - solitary vs. multifocal
4. Tissue characteristics - T1/T2 signal, calcification, fat, cysts, necrosis
5. Enhancement pattern - homogeneous, ring, nodular, absent
6. Advanced imaging - DWI/ADC, perfusion, MR spectroscopy

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PART 2: CLASSIFICATION BY AGE

Paediatric (0-18 years)

Adults (18-60 years)

• Glioblastoma (most common intraaxial primary)
• Oligodendroglioma (IDH-mutant, 1p/19q-codeleted)
• Astrocytoma (IDH-mutant)
• Metastases
• Meningioma (most common intracranial tumour overall)
• Primary CNS lymphoma
• Pituitary adenoma
• Craniopharyngioma (papillary type - adults)

Elderly (>60 years)

• Glioblastoma (IDH-wildtype, WHO grade 4)
• Metastases (most common intraaxial in adults)
• Primary CNS lymphoma (immunocompromised but also de novo elderly)
• Meningioma

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PART 3: CLASSIFICATION BY CELL ORIGIN

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PART 4: CLASSIFICATION BY LOCATION

Supratentorial

• Frontal: Glioblastoma, Oligodendroglioma, Lymphoma, DNET (temporal > frontal for DNET)
• Temporal: DNET, Ganglioglioma, Low-grade glioma, Herpes encephalitis mimic
• Parietal/Occipital: Metastases, High-grade glioma
• Intraventricular (lateral): Subependymoma, SEGA (foramen of Monro), Ependymoma, Central neurocytoma, Colloid cyst (3rd ventricle)
• Sellar/Parasellar: Pituitary adenoma, Craniopharyngioma, Rathke cleft cyst, Meningioma, Germinoma

Infratentorial

• Cerebellar hemisphere: Pilocytic astrocytoma, Metastases, Hemangioblastoma
• Cerebellar vermis: Medulloblastoma (children), DNET
• Fourth ventricle: Ependymoma (children), Subependymoma (adults), Choroid plexus papilloma
• Brainstem (pons): DIPG, Glioma
• Cerebellopontine angle (CPA): Schwannoma (VS), Meningioma, Epidermoid

Midline / Deep

• Corpus callosum: Glioblastoma (butterfly), Lymphoma, Lipoma, Lymphoma
• Thalamus: Glioma, ASTROBLASTOMA
• Pineal region: Germinoma, Pineal parenchymal tumour, Dermoid/Epidermoid

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PART 5: INTRA-AXIAL vs. EXTRA-AXIAL

Extra-axial Signs

• CSF cleft between lesion and brain parenchyma
• Buckling of cortex (white matter pushed inward)
• Grey matter displaced away from lesion (not surrounding it)
• Dural attachment / dural tail
• Hyperostosis of adjacent bone
• Homogeneous enhancement (no BBB)
• Expanded subarachnoid space adjacent to lesion

Intra-axial Signs

• Grey matter surrounding the lesion (engulfed, not displaced)
• White matter oedema radiating from the lesion
• No CSF cleft
• Heterogeneous enhancement (BBB disruption)

Most Common Extra-axial Tumours

• Meningioma (80% of extra-axial) - broad dural base, homogeneous enhancement, dural tail
• Schwannoma (vestibular, trigeminal) - CPA cistern, "ice cream cone" through IAM
• Note: 80% of extra-axial lesions = meningioma or schwannoma

Extra-axial Pitfall

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PART 6: IMPORTANT SPREADING PATTERNS

Midline Crossing

• Glioblastoma: "Butterfly glioma" - crosses corpus callosum
• Lymphoma: periventricular, can cross midline
• Lymphoma vs GBM: Lymphoma - homogeneous solid enhancement, restricted diffusion (high DWI, low ADC), no necrosis. GBM - heterogeneous ring enhancement with central necrosis.

Subarachnoid / Leptomeningeal Seeding

• Medulloblastoma (most common paediatric CNS tumour to seed) - "sugar coating" of spinal cord
• Ependymoma (posterior fossa)
• GBM (rare)
• PNET, Pineal tumours, Choroid plexus carcinoma
• Imaging: Nodular or linear enhancing deposits on surface of brain/cord on post-contrast T1. Whole spine MRI mandatory at staging.

Ependymal Seeding (Subependymal / Periventricular Spread)

• GBM - subependymal tumour spread
• Lymphoma - classically periventricular/subependymal
• Medulloblastoma - ventricular system seeding
• Pineal tumours / Germinoma
• Ependymoma
• Imaging: Enhancing nodular deposits lining ventricles on post-contrast T1

Cortical-Based Tumours

• DNET (dysembryoplastic neuroepithelial tumour)
• Ganglioglioma
• PXA (pleomorphic xanthoastrocytoma)
• Low-grade oligodendroglioma
• LEAT group (long-term epilepsy associated tumours)
• Imaging feature: Cortical involvement, pseudostratified bubbly appearance, minimal oedema, no/faint enhancement

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PART 7: SIGNAL CHARACTERISTICS

T1 Hyperintense Lesions (Bright on T1)

T2 Hypointense Lesions (Dark on T2)

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PART 8: TUMOURS WITH CALCIFICATIONS

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PART 9: LOW GRADE vs. HIGH GRADE TUMOURS

Low Grade Features (WHO 1-2)

• T2/FLAIR hyperintense, well-circumscribed or infiltrative
• No contrast enhancement (with exceptions: pilocytic astrocytoma, ganglioglioma DO enhance despite being low grade)
• No necrosis
• No haemorrhage
• Minimal or no oedema
• High ADC (low cellularity)
• Low rCBV on perfusion
• MRS: mild Cho elevation, NAA preserved or mildly reduced

High Grade Features (WHO 3-4)

• Heterogeneous signal, irregular enhancement (often ring)
• Central necrosis
• Haemorrhage
• Surrounding vasogenic oedema
• Low ADC (high cellularity)
• High rCBV on perfusion (>2 x contralateral white matter)
• MRS: high Cho, low NAA, lipid/lactate peaks

Important Exceptions

• Pilocytic astrocytoma (WHO 1): vivid cyst-with-mural-nodule enhancement - DO NOT misgrade
• Ganglioglioma (WHO 1-2): cortical enhancement, calcification
• DNET (WHO 1): no enhancement (bubbly cortical lesion)
• PXA (WHO 2-3): may show meningeal contact, cyst + nodule, BRAF V600E

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PART 10: CONTRAST ENHANCEMENT PATTERNS

No Enhancement

• Low-grade astrocytoma (WHO 2, IDH-mutant)
• DNET
• Arachnoid cyst
• Epidermoid cyst
• Dermoid cyst

Homogeneous Enhancement

• Metastases (small, solid)
• Lymphoma (periventricular, homogeneous, ice-ball appearance)
• Germinoma / Pineal tumours
• Pituitary macroadenoma
• Pilocytic astrocytoma (solid component)
• Ganglioglioma
• Meningioma (extra-axial, homogeneous)
• Schwannoma

Ring Enhancement

• GBM (thick, irregular ring)
• Metastases (thin, regular ring)
• Brain abscess (thin, smooth, regular ring - "rim sign"; inner dark rim on T2)
• Tumefactive MS (incomplete/open ring - "horseshoe" opens toward grey matter)
• Radiation necrosis (ring-like)
• Lymphoma in immunocompromised (ring) vs immunocompetent (solid)

Cyst + Mural Nodule Enhancement

• Pilocytic astrocytoma (classic)
• Hemangioblastoma (solid enhancing nodule + large cyst, posterior fossa adults, VHL)
• Ganglioglioma
• PXA

Dural Tail Enhancement

• Meningioma (classic)
• Also seen in: Lymphoma, Sarcoidosis, Chloroma, some metastases - NOT specific

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PART 11: MR SPECTROSCOPY FINDINGS

Tumour-Specific MRS Patterns

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PART 12: PERFUSION MRI FINDINGS

DSC (Dynamic Susceptibility Contrast) - rCBV

Leakage Correction

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PART 13: DWI / ADC FINDINGS

• Low ADC = high cellularity = high-grade or lymphoma
• Epidermoid vs Arachnoid cyst: Epidermoid restricts (bright DWI, dark ADC); Arachnoid does NOT restrict
• Abscess vs GBM: Abscess has very low ADC in core; GBM necrotic core has HIGH ADC

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PART 14: CT vs. MRI APPEARANCE SUMMARY

CT Density Rules

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PART 15: WHO 2021 CNS TUMOUR CLASSIFICATION (5th Edition)

1. Molecular markers are now required for classification (integrated diagnosis)
2. Glioblastoma is now EXCLUSIVELY IDH-wildtype (previously IDH-mutant GBM reclassified as astrocytoma grade 4)
3. Diffuse gliomas separated into adult-type and paediatric-type
4. Grading: now uses Arabic numerals (1, 2, 3, 4) instead of Roman (I, II, III, IV)
5. New entities: Diffuse midline glioma H3K27-altered, Diffuse hemispheric glioma H3G34-mutant

WHO 2021 Adult Diffuse Glioma Groups

Paediatric-Type Diffuse Gliomas

• Diffuse low-grade glioma, MAPK-altered
• Diffuse high-grade glioma, H3-wildtype, IDH-wildtype
• Infant-type hemispheric glioma (NTRK/ALK/ROS/MET fusions)

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PART 16: T2/FLAIR MISMATCH SIGN

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PART 17: SPECIFIC TUMOURS - IMAGING & ASSOCIATIONS

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GLIOBLASTOMA (GBM, WHO Grade 4, IDH-wildtype)

• T1: Hypointense core (necrosis), T1-bright haemorrhage may be present
• T2/FLAIR: Heterogeneous; central hypointense necrosis; surrounding FLAIR bright oedema
• DWI: Solid component intermediate-restricted; necrosis = facilitated diffusion
• ADC: Necrosis >1000; solid component ~745 ± 135 x10⁻⁶ mm²/s
• Post-contrast: Thick, irregular ring enhancement
• Perfusion: Very high rCBV
• MRS: Very high Cho, very low NAA, lipid/lactate

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OLIGODENDROGLIOMA (IDH-mutant, 1p/19q-codeleted, WHO 2-3)

• T2/FLAIR: Hyperintense, may involve cortex
• No T2/FLAIR mismatch (unlike astrocytoma)
• ADC: High (facilitates diffusion)
• Enhancement: 20-30% (grade 2); more in grade 3
• Perfusion: rCBV elevated (more than astrocytoma of same grade - due to "chicken wire" vasculature)
• MRS: Elevated Cho/NAA

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DIFFUSE MIDLINE GLIOMA, H3K27-ALTERED (WHO Grade 4)

• T2/FLAIR: Diffuse hyperintensity engulfing and expanding the pons
• Basilar artery "engulfed" by tumour (classic pontine sign)
• Minimal or no contrast enhancement (may enhance at recurrence)
• Diffuse, poorly defined borders

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PILOCYTIC ASTROCYTOMA (WHO Grade 1)

• Classic: Cyst with enhancing mural nodule (60%)
• Solid with central necrosis (25%)
• Purely solid (15%)
• T2: Very hyperintense
• T1 post-contrast: Vivid nodule enhancement
• ADC: High (low cellularity)
• Perfusion: Low rCBV despite enhancement
• MRS: Mildly elevated Cho

• Cyst + brightly enhancing mural nodule in cerebellum of child
• KIAA1549-BRAF fusion (most common molecular marker)
• Rosenthal fibres + eosinophilic granular bodies on histology

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PLEOMORPHIC XANTHOASTROCYTOMA (PXA, WHO Grade 2-3)

• Cyst with enhancing mural nodule (leptomeningeal contact - KEY feature)
• T2 hyperintense
• Superficial/cortical location
• Enhancement: Solid nodule and meningeal enhancement
• Young adults, chronic epilepsy history

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DNET (Dysembryoplastic Neuroepithelial Tumour, WHO Grade 1)

• T2: "Bubbly" multicystic cortical lesion with pseudostratified appearance
• FLAIR: "Bright rim sign" - peripheral FLAIR hyperintensity, central FLAIR suppression (like T2/FLAIR mismatch in cortex)
• DWI: No restriction
• Enhancement: None or very faint (< 30%)
• No oedema, no mass effect (despite large size)
• Scalloping of overlying calvarium (chronic pressure)
• T1: Hypointense

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GANGLIOGLIOMA (WHO Grade 1-2)

• T2: Hyperintense, well-circumscribed, cortical/subcortical
• Mixed solid-cystic
• Enhancement: Variable - mural nodule or solid enhancement (30-50%)
• Calcification: 30-50%
• DWI: No restriction
• Low ADC (variable)
• No significant oedema

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ROSETTE-FORMING GLIONEURONAL TUMOUR (RGNT, WHO Grade 1)

• Mixed cystic-solid lesion in fourth ventricle/aqueduct
• Enhancement: Nodular within the solid component
• T2: Hyperintense cystic component
• Young adults (20-30s)

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SUBEPENDYMOMA (WHO Grade 1)

• T2: Hyperintense, lobulated intraventricular mass
• T1: Hypointense
• Enhancement: None or minimal (KEY - distinguishes from ependymoma)
• DWI: No restriction
• Calcification: Possible
• Incidental finding in middle-aged/older adults

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EPENDYMOMA (WHO Grade 2-3)

• Children: Fourth ventricle (intracranial) - "squeezes" through foramina
• Adults: Spinal cord (most common site in adults), filum terminale (myxopapillary)
• Supratentorial: RELA fusion type (now WHO molecular classification)

• T2: Heterogeneous, intermediate-high signal
• T1 post-contrast: Moderate heterogeneous enhancement
• DWI: Variable
• Calcification, cysts, haemorrhage - "heterogeneous" = classic
• Fourth ventricle tumour that "squeezes" through foramen of Magendie into cervical canal = PATHOGNOMONIC
• Haemosiderin capping (on spine): "cap sign" - haemosiderin at superior and inferior poles

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MEDULLOBLASTOMA (WHO Grade 4)

• T2: Isointense to hypointense (dense cells)
• DWI: RESTRICTED (bright DWI, dark ADC) - KEY feature
• T1 post-contrast: Moderate-vivid heterogeneous enhancement
• Cysts, calcification, haemorrhage possible
• Hydrocephalus (obstructs 4th ventricle)
• Perfusion: High rCBV

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SEGA (Subependymal Giant Cell Astrocytoma, WHO Grade 1)

• T2: Heterogeneous, mixed signal
• T1 post-contrast: Vivid, heterogeneous enhancement
• Large (>1 cm) enhancing intraventricular nodule at foramen of Monro
• May cause obstructive hydrocephalus

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CENTRAL NEUROCYTOMA (WHO Grade 2)

• T2: Heterogeneous, "soap bubble" or sponge-like cystic areas
• T1 post-contrast: Moderate, heterogeneous enhancement
• Calcification common
• DWI: May show mild restriction
• MRS: Glycine peak at 3.55 ppm (characteristic)

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MENINGIOMA (WHO Grade 1-3)

• T1: Isointense to grey matter
• T2: Variable (isointense to hypointense in fibrotic types)
• Post-contrast: Vivid homogeneous enhancement
• Dural tail sign (reactive dural thickening - NOT tumour itself)
• Restricted diffusion in atypical/malignant meningioma

• Fibroblastic/transitional: T2 hypointense (collagen)
• Meningothelial: T2 isointense
• Secretory: T2 hypointense

• Grade 1 (benign, 80%): Surgical cure, low recurrence
• Grade 2 (atypical, 18%): Brain invasion, mitoses >4/10 HPF
• Grade 3 (anaplastic, 2%): Sarcomatous, high recurrence

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SOLITARY FIBROUS TUMOUR (SFT) / Haemangiopericytoma (WHO Grade 2-3)

• T2: "Yin-yang" or "flip-flop" sign - heterogeneous T2 signal (mix of high and low)
• Post-contrast: Vivid heterogeneous enhancement
• May have prominent flow voids (vascular)
• Narrow dural base (vs meningioma which has broad dural base)
• Can erode bone (vs meningioma which causes hyperostosis)

• Heterogeneous T2 (meningioma is more homogeneous)
• Bone erosion not hyperostosis
• Narrower base
• NAB2-STAT6 fusion (molecular diagnosis)

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PITUITARY TUMOURS (PitNETs - Pituitary Neuroendocrine Tumours)

• Microadenoma: < 10mm
• Macroadenoma: ≥ 10mm
• Giant adenoma: > 40mm

• T1: Hypointense relative to normal pituitary (KEY)
• T2: Variable
• Dynamic contrast: Enhances LATER than normal pituitary (normal gland enhances first)
• Stalk deviation away from lesion

• T1 pre/post: "Snowman" or "figure-of-8" appearance through diaphragma sellae
• Suprasellar extension - "waist" at diaphragma
• T2: Heterogeneous (haemorrhage = pituitary apoplexy)
• Enhancement: Moderate, heterogeneous
• Optic chiasm compression (superior)
• Cavernous sinus invasion (lateral) - Knosp grading

• Prolactinoma (most common): Medical treatment (dopamine agonists)
• GH-secreting: Acromegaly/gigantism
• ACTH-secreting: Cushing disease (often very small - needs dynamic study)
• TSH-secreting: Central hyperthyroidism
• Non-functioning: Headache, visual field defects

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CRANIOPHARYNGIOMA (WHO Grade 1)

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RATHKE CLEFT CYST (RCC)

• T1: Variable (depends on protein content) - 60% T1 bright, 40% T1 dark
• T2: Variable
• No enhancement of cyst wall (KEY distinguishing feature)
• Intracystic nodule (T1 dark, T2 dark): Floating debris = pathognomonic - "pea in a pod" appearance
• No calcification (vs craniopharyngioma)

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PINEAL GLAND TUMOURS

1. Germinoma (most common, 50-60% of pineal tumours)
2. Pineal parenchymal tumour (pineocytoma vs pineoblastoma)
3. Glioma
4. Dermoid/Epidermoid/Teratoma
5. Benign pineal cyst (incidental)

Germinoma

• Young males (peak 10-25 years)
• T1: Isointense; T2: Isointense; Vivid homogeneous enhancement
• "Engulfs" pre-existing pineal calcification (calcium within tumour)
• Can seed ventricles and subarachnoid space
• Parinaud syndrome (upgaze palsy - dorsal midbrain compression)
• HCG and AFP can be elevated (non-germinomatous GCT)

Pineocytoma (WHO Grade 1)

• Mature pineal cells
• "Exploded" pineal calcification - calcification displaced to periphery
• Small, well-circumscribed, homogeneous enhancement

Pineoblastoma (WHO Grade 4)

• Highly cellular, aggressive embryonal tumour
• T2: Hypointense (dense cells)
• DWI: Restricted
• Heterogeneous enhancement
• Leptomeningeal seeding common
• Associated with germline RB1 mutation ("trilateral retinoblastoma")

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PART 18: PRIMARY and SECONDARY CNS LYMPHOMA

Primary CNS Lymphoma (PCNSL)

• T1: Isointense to hypointense
• T2: Isointense to hypointense (DARK on T2 relative to white matter) - KEY
• DWI: RESTRICTED (bright DWI, low ADC) - KEY
• Post-contrast:
  • Immunocompetent: Solid, homogeneous, vivid enhancement ("ice ball")
  • Immunocompromised (HIV/AIDS): Ring enhancement (may look like toxoplasmosis)
• Perfusion: Elevated Cho, BUT rCBV paradoxically LOW compared to GBM
• MRS: High Cho, high lipid

• Periventricular/subependymal hyperdense mass
• T2 DARK (not T2 bright like most tumours)
• Restricted diffusion
• Solid homogeneous enhancement
• Dramatic response to steroids ("ghost tumour" - may disappear on steroids - do NOT give steroids before biopsy)

Secondary CNS Lymphoma

• From systemic B-cell or T-cell lymphoma
• Leptomeningeal involvement more common
• Dural deposits
• Intraparenchymal rarer

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PART 19: CYSTIC TUMOURS OF THE BRAIN

Intra-axial Cystic Tumours

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PART 20: BENIGN CYSTS OF THE BRAIN

Extra-axial Benign Cysts

Arachnoid Cyst

• Content: CSF - identical signal to CSF on all sequences
• T1: Hypointense (CSF); T2: Hyperintense (CSF)
• FLAIR: Suppressed (CSF signal nulled)
• DWI: NO restriction (unlike epidermoid!)
• Enhancement: None
• Scallops adjacent bone (pressure effect)
• Location: Middle cranial fossa (most common), CPA, suprasellar, posterior fossa
• Key differentiator from epidermoid: Arachnoid = no DWI restriction; Epidermoid = DWI BRIGHT

Epidermoid Cyst

• Content: Desquamated keratin from ectoderm
• T1: Hypointense (slightly higher than CSF)
• T2: Hyperintense (similar to CSF)
• FLAIR: Incomplete suppression (slightly higher than CSF)
• DWI: RESTRICTED (bright DWI, dark ADC) - KEY distinguishing feature from arachnoid cyst
• Enhancement: None (smooth capsule)
• Location: CPA cistern (most common), parasellar, fourth ventricle
• "Cauliflower" or "frond-like" insinuating margins - wraps around neurovascular structures
• Trigeminal neuralgia if CPA location

Dermoid Cyst

• Content: All three germ layers - hair, sebaceous glands, fat
• T1: Very hyperintense (fat!) - BRIGHT on T1
• T2: Heterogeneous
• Fat-suppressed sequences: Fat signal suppressed
• Ruptured dermoid: Fat droplets scattered throughout subarachnoid space - pathognomonic
• Enhancement: None
• DWI: Bright (lipid signal, not true restriction)
• Location: Midline - posterior fossa, suprasellar

Neurenteric / Neuroenteric Cyst

• Rare; spinal > intracranial
• Contents = CSF signal or higher protein
• T1: Variable; T2: Hyperintense

Intra-axial Benign Cysts

Ependymal Cyst (also called "neuroepithelial cyst")

• Lined by ependymal cells
• Within brain parenchyma or ventricles
• CSF-identical signal on ALL sequences including FLAIR
• No restriction, no enhancement
• Incidental; near trigone of lateral ventricle

Choroid Plexus Cyst

• Small cysts within choroid plexus; incidental; may relate to aneuploidy (trisomy 18) in fetal context

Pineal Cyst

• Very common (up to 40% of population)
• Simple: < 10mm, no internal septae, thin wall
• Enhancement: Thin peripheral rim (normal ependyma enhances)
• T1: Slightly higher than CSF (protein)
• FLAIR: Incomplete suppression
• If > 10mm, thick wall, internal nodule, or septa - consider tumour

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PART 21: SCHWANNOMA

• Vestibular schwannoma (acoustic neuroma) - CN VIII, CPA cistern, IAC
• Trigeminal schwannoma - CN V, Meckel cave / middle cranial fossa
• Facial schwannoma - CN VII
• Less common: IX, X, XI, XII

Vestibular Schwannoma

• T1: Isointense to hypointense
• T2: Hyperintense (high fluid-content microcysts)
• Post-contrast: Vivid, homogeneous enhancement
• "Ice cream cone" shape - bulb in CPA cistern + cone into IAM
• Widening of IAC (vs meningioma at CPA which does NOT widen IAC)
• Cystic change in larger tumours

• Meningioma (no IAC widening, broad dural base, hyperdense CT, dural tail)
• Epidermoid (no enhancement, DWI bright)
• Facial nerve schwannoma (follows CN VII)

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PART 22: BRAINSTEM GLIOMA - TYPES

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PART 23: MENINGIOMA - COMPLETE

1. Cerebral convexity
2. Parasagittal / falcine
3. Sphenoid wing (inner - cavernous sinus; outer - "en plaque")
4. Olfactory groove
5. Planum sphenoidale
6. Suprasellar / tuberculum sellae
7. Posterior fossa / CPA
8. Foramen magnum
9. Intraventricular
10. Orbital

• T2 signal correlates with subtype: Secretory (very T2 bright) vs Fibroblastic (T2 dark)
• Perfusion: Very high rCBV
• MRS: Alanine peak (1.47 ppm) + absent NAA = classic for meningioma
• ADC: Intermediate; Grade 2/3 = lower ADC (more restricted)

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PART 24: TUMOUR MIMICS

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PART 25: RADIATION NECROSIS vs. PSEUDOPROGRESSION

Background

• After treatment of GBM with radiation + temozolomide, new or enlarged enhancement can be seen
• Must distinguish TRUE progression from treatment-related changes

Pseudoprogression

• Definition: Treatment-related enhancement increase at 1-3 months post-chemoradiation (early) that RESOLVES spontaneously
• More common in MGMT-methylated tumours (~50% of MGMT-methylated vs 20% unmethylated)
• Timing: Within 3 months of completing radiation

Radiation Necrosis

• Definition: Late treatment effect (months to years post-radiation)
• Can look identical to tumour recurrence on conventional MRI

Imaging Differentiation

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PART 26: SUBEPENDYMAL SEEDING / EPENDYMAL SPREAD - Summary

• GBM (subependymal spread along ventricles)
• Lymphoma (classically periventricular)
• Medulloblastoma (CSF seeding to ventricles)
• Germinoma (ventricles)
• Ependymoma

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PART 27: QUICK REFERENCE - PATHOGNOMONIC FEATURES

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SUMMARY APPROACH ALGORITHM

INTRACRANIAL MASS
│
├── EXTRA-AXIAL? (CSF cleft, buckling, no grey matter engulfment)
│   ├── CPA → Schwannoma vs Meningioma vs Epidermoid
│   ├── Dural → Meningioma vs SFT vs Metastasis vs Sarcoidosis
│   └── Sellar → Pituitary vs Craniopharyngioma vs RCC vs Meningioma
│
└── INTRA-AXIAL?
    ├── AGE: Paediatric?
    │   ├── Posterior fossa → Pilocytic vs Medulloblastoma vs Ependymoma
    │   └── Supratentorial → DNET vs Ganglioglioma vs PXA vs SEGA(TS)
    │
    └── AGE: Adult?
        ├── Enhancement + Ring → GBM vs Metastasis vs Abscess vs Lymphoma (HIV)
        ├── Homogeneous + periventricular → Lymphoma
        ├── No enhancement + diffuse → Low-grade glioma (IDH-mutant)
        ├── T2/FLAIR mismatch → IDH-mutant astrocytoma
        ├── DWI bright + low ADC → Lymphoma / Medulloblastoma / Abscess (check MRS)
        └── Perfusion high + necrosis → GBM

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