Brain Tumour Imaging

A high-yield neuroradiology topic where the exam tests pattern recognition: location (intra- vs extra-axial), MRI signal, and enhancement pattern are the three discriminators that crack almost every image-based MCQ. Master the classic appearances and the eponymous signs, and you convert "hard" questions into instant answers.

Why imaging dominates the diagnosis

Intracranial tumours are increasingly asked as image-based or "best investigation" questions. The single most important first decision on any brain MRI is intra-axial (within brain parenchyma) vs extra-axial (outside brain, from meninges, nerves, skull). This narrows the differential dramatically before you even look at signal.

High-yield: MRI with contrast (gadolinium) is the investigation of choice for almost all brain tumours. CT is used for emergency screening, detecting calcification, bony involvement, and acute haemorrhage. MR spectroscopy helps differentiate tumour from abscess and grades gliomas.

Intra-axial vs extra-axial — the master table

Feature	Intra-axial	Extra-axial
Origin	Brain parenchyma	Meninges, nerves, skull, pituitary
Grey–white junction	Expanded/effaced	Preserved, displaced inward
CSF cleft sign	Absent	Present (CSF rim between mass & brain)
Dural tail	Usually absent	Often present (meningioma)
Buckling of white matter	No	Yes (white matter buckled away)
Examples	Glioma, metastasis, lymphoma	Meningioma, schwannoma, pituitary adenoma

High-yield: The CSF cleft sign and buckling of grey–white matter are the hallmarks of an extra-axial mass. A broad dural base also favours extra-axial.

MRI sequences — what each tells you

• T1: anatomy. CSF dark, fat/melanin/subacute blood bright. Used post-gadolinium for enhancement.
• T2/FLAIR: oedema and most tumours are bright (hyperintense). FLAIR suppresses CSF, highlighting peritumoral oedema.
• DWI/ADC: restricted diffusion (bright DWI, dark ADC) seen in abscess, lymphoma, hypercellular high-grade tumours, epidermoid.
• MR spectroscopy: ↑choline (membrane turnover), ↓NAA (neuronal loss), ↑choline/NAA ratio in tumour; lactate/lipid peak in necrosis/high grade.
• Perfusion (rCBV): raised in high-grade gliomas; helps distinguish radiation necrosis (low rCBV) from recurrence (high rCBV).

High-yield: Choline up, NAA down = tumour. A lipid–lactate peak suggests necrosis (high-grade glioma or abscess). Succinate/amino-acid peak suggests abscess, not tumour.

Glioblastoma (GBM, Glioblastoma multiforme — WHO grade 4 astrocytoma)

The commonest primary malignant brain tumour in adults, peaking in the 5th–7th decades. Arises from astrocytes; spreads along white matter tracts.

Imaging

• Butterfly pattern: crosses the corpus callosum to involve both cerebral hemispheres — the classic "butterfly glioma."
• Thick, irregular ring enhancement around a central necrotic core on post-contrast T1.
• Marked surrounding vasogenic oedema (bright on T2/FLAIR) that itself contains infiltrating tumour cells.
• Heterogeneous signal with haemorrhage and necrosis; high rCBV on perfusion; high choline on spectroscopy.

High-yield: GBM = butterfly glioma crossing corpus callosum + irregular (thick, shaggy) ring enhancement + central necrosis. Other lesions that cross the corpus callosum: lymphoma and demyelination (Marburg).

Ring-enhancing lesion differential — "MAGIC DR"

Metastasis, Abscess, Glioblastoma, Infarct (subacute), Contusion, Demyelination, Radiation necrosis / Resolving haematoma. (Add lymphoma and toxoplasmosis in immunocompromised.)

High-yield: Abscess shows smooth, thin, regular ring with restricted diffusion (bright DWI/dark ADC) — versus tumour's thick, irregular ring with facilitated central diffusion. This DWI distinction is heavily tested.

Meningioma

The commonest extra-axial and the commonest overall benign intracranial tumour. Arises from arachnoid cap (meningothelial) cells. Female predominance; associated with neurofibromatosis type 2 (NF2) and prior radiation. Express progesterone receptors.

Imaging

• Extra-axial, broad dural-based mass, often isointense to grey matter on T1 and T2.
• Intense, homogeneous enhancement after gadolinium.
• Dural tail sign: linear enhancement of thickened dura tapering away from the mass — characteristic but not entirely pathognomonic.
• Hyperostosis of adjacent bone on CT; psammomatous calcification common.
• CSF cleft and buckled white matter confirm extra-axial location.

Common sites: parasagittal/falcine, convexity, sphenoid wing, olfactory groove (→ anosmia, Foster–Kennedy syndrome), cerebellopontine angle.

High-yield: Dural tail + extra-axial + homogeneous enhancement + isointense to grey matter = meningioma. Most are WHO grade 1 and managed by surgical excision (Simpson grading predicts recurrence). Calcification is best seen on CT.

Acoustic neuroma (Vestibular schwannoma)

The commonest cerebellopontine angle (CPA) tumour and commonest extra-axial posterior-fossa mass in adults. Arises from Schwann cells of the vestibular division of CN VIII. Bilateral acoustic neuromas are pathognomonic of NF2.

Clinical features

Sensorineural hearing loss (earliest, asymmetric), tinnitus, imbalance; later trigeminal (corneal reflex loss) and facial nerve involvement as it enlarges in the CPA.

Imaging

• "Ice-cream cone" appearance: the rounded cisternal component (ice cream) with a tail extending into a widened internal acoustic meatus (the cone).
• Avidly enhancing; may show cystic change.
• Best detected on thin-section contrast MRI of the IAM.

High-yield: CPA mass + ice-cream-cone shape + widening of internal acoustic meatus = vestibular schwannoma. The chief differential at the CPA is meningioma (broad dural base, no IAM widening, dural tail) and epidermoid (restricted diffusion, insinuates around vessels).

CPA mass differential

Tumour	Key clue	DWI
Vestibular schwannoma	Ice-cream cone, IAM widening	Variable
Meningioma	Dural tail, broad base, no IAM widening	No restriction
Epidermoid	"Insinuating", follows CSF, bright on DWI	Restricts
Arachnoid cyst	Follows CSF on all sequences, no enhancement	No restriction

Craniopharyngioma

A benign but locally aggressive suprasellar tumour arising from remnants of Rathke's pouch (squamous epithelial rests). Bimodal age: children (adamantinomatous type, 5–14 yrs) and older adults (papillary type).

Clinical features

• Bitemporal hemianopia (compresses optic chiasm).
• Hypopituitarism, growth failure in children, diabetes insipidus.

Imaging

• Suprasellar location, frequently with calcification (≈90% in children) — best seen on CT.
• Cystic + solid components; cyst classically contains "machinery/crankcase oil" cholesterol-rich fluid → T1 hyperintense cyst.
• Solid portions and cyst wall enhance.

High-yield: Suprasellar + calcified + cystic in a child = craniopharyngioma. Differentials in the suprasellar region: Rathke cleft cyst (no calcification, non-enhancing), pituitary macroadenoma ("snowman/figure-of-8", arises from sella, rarely calcifies), meningioma, and hypothalamic glioma.

Sella vs suprasellar quick logic

Mass centred in sella → pituitary adenoma. Mass above sella + calcification + cyst → craniopharyngioma. Mass with dural tail → meningioma.

Brain metastases

The commonest intracranial tumours overall in adults (outnumber primaries). Primary sources: lung > breast > melanoma > renal > GI/colon. Melanoma, renal, choriocarcinoma and thyroid mets are classically haemorrhagic.

Imaging

• Multiple, well-circumscribed, rounded lesions at the grey–white junction (where vessels narrow and emboli lodge).
• Ring or nodular enhancement with disproportionately large vasogenic oedema relative to lesion size.
• Melanoma metastasis may be T1 hyperintense (melanin/haemorrhage).

High-yield: Multiple ring-enhancing lesions at the grey–white junction with marked oedema = metastases until proven otherwise. A solitary met can mimic GBM; MR spectroscopy/perfusion of the peritumoral zone helps (GBM has tumour cells in oedema → raised choline; mets do not).

Other classic patterns worth knowing

• CNS lymphoma: periventricular, homogeneous enhancement, restricted diffusion (very cellular); in immunocompromised may show ring enhancement (mimics toxoplasmosis). Melts away with steroids ("ghost tumour"). Low rCBV vs GBM.
• Pilocytic astrocytoma (child, posterior fossa): cyst with an enhancing mural nodule; WHO grade 1, best prognosis. Commonest paediatric glioma.
• Medulloblastoma: midline vermian mass in a child, hyperdense on CT, restricts diffusion (small round blue cell tumour); drop metastases in CSF.
• Ependymoma: fourth ventricle mass that is "plastic", extending out of the foramina (of Luschka/Magendie).
• Haemangioblastoma: cyst + mural nodule in adult cerebellum, associated with von Hippel–Lindau; polycythaemia (EPO).
• Colloid cyst: third ventricle at foramen of Monro → intermittent positional headache and acute hydrocephalus.

High-yield: Cyst + enhancing mural nodule → pilocytic astrocytoma (child) or haemangioblastoma (adult, cerebellum). Fourth ventricle child → medulloblastoma (midline) vs ependymoma (extends through foramina).

Diagnostic flow

Step 1 — Localise: Intra-axial or extra-axial? (CSF cleft, buckling, dural base) → Step 2 — Single or multiple? Multiple at grey–white junction → metastases/abscesses → Step 3 — Enhancement: thick irregular ring → GBM; thin smooth ring + DWI restriction → abscess; homogeneous + dural tail → meningioma → Step 4 — Special signal: calcification (CT) → craniopharyngioma/oligodendroglioma; T1 bright cyst → craniopharyngioma; T1 bright solid → melanoma met → Step 5 — Problem solving: MR spectroscopy/perfusion/DWI to separate tumour vs abscess vs necrosis.

Management & investigation of choice

• Investigation of choice (all): contrast-enhanced MRI. CT for calcium, bone, acute bleed, or when MRI contraindicated.
• GBM: maximal safe surgical resection + radiotherapy + temozolomide (Stupp protocol). MGMT promoter methylation predicts temozolomide response; IDH-mutant tumours have better prognosis.
• Meningioma: observation if small/asymptomatic; surgical excision (Simpson grade) ± radiosurgery.
• Vestibular schwannoma: observation, stereotactic radiosurgery (gamma knife), or microsurgery depending on size/hearing.
• Craniopharyngioma: surgical resection ± radiotherapy; manage endocrine deficits and DI.
• Metastases: treat primary; whole-brain RT / stereotactic radiosurgery, surgery for solitary accessible lesions; steroids for oedema.

Complications

• Raised intracranial pressure, herniation syndromes (uncal, subfalcine, tonsillar).
• Obstructive hydrocephalus (posterior fossa & third ventricular tumours, colloid cyst).
• Seizures, focal neurological deficits, endocrine failure (sellar/suprasellar).
• Intratumoral haemorrhage (GBM, melanoma/renal/thyroid mets, pituitary apoplexy).
• Leptomeningeal/CSF spread ("drop metastases" — medulloblastoma, ependymoma, germinoma).

Key differentials at a glance

Pattern on MRI	First think of	Clinching feature
Butterfly, crosses callosum, thick ring	GBM	Central necrosis, high rCBV
Thin smooth ring, DWI bright	Abscess	Restricted diffusion, succinate peak
Extra-axial, dural tail, homogeneous	Meningioma	Isointense to GM, hyperostosis
CPA, ice-cream cone, IAM widening	Vestibular schwannoma	Bilateral → NF2
Suprasellar, calcified, cystic, child	Craniopharyngioma	T1-bright "oil" cyst
Sella, snowman shape	Pituitary macroadenoma	Cavernous sinus invasion
Multiple, grey–white junction, oedema	Metastases	Known/occult primary
Periventricular, restricts, melts on steroids	CNS lymphoma	Immunocompromised
Cyst + mural nodule, child cerebellum	Pilocytic astrocytoma	WHO grade 1
Cyst + mural nodule, adult cerebellum	Haemangioblastoma	VHL, polycythaemia

Recently asked / exam angle

• Image-based: "butterfly appearance crossing corpus callosum" → answer glioblastoma.
• Dural tail sign → meningioma (also asked: which sign indicates extra-axial → CSF cleft).
• Ice-cream cone at CPA / widened internal acoustic meatus → acoustic neuroma; bilateral → NF2.
• Suprasellar calcified cystic mass in a child → craniopharyngioma; from Rathke's pouch.
• Best investigation for brain tumour → contrast MRI; calcification best seen → CT.
• Restricted diffusion ring lesion → abscess (vs GBM); MR spectroscopy lactate/lipid interpretation.
• Commonest CPA tumour → vestibular schwannoma; commonest extra-axial tumour → meningioma; commonest primary malignant → GBM; commonest intracranial tumour overall → metastasis.
• Cyst with mural nodule → pilocytic astrocytoma (child) / haemangioblastoma (adult).
• Spectroscopy: choline up, NAA down; succinate in abscess.

Rapid revision

1. MRI with contrast = investigation of choice for brain tumours; CT for calcification, bone and acute bleed.
2. CSF cleft + buckled white matter + dural tail = extra-axial mass.
3. Butterfly glioma crossing corpus callosum + thick irregular ring + necrosis = glioblastoma (commonest primary malignant).
4. Dural tail + homogeneous enhancement + isointense to grey matter = meningioma (commonest extra-axial; NF2).
5. Ice-cream cone at CPA + widened internal acoustic meatus = vestibular schwannoma; bilateral = NF2.
6. Suprasellar + calcified + cystic + child = craniopharyngioma (Rathke's pouch; bitemporal hemianopia).
7. Multiple lesions at grey–white junction + marked oedema = metastases (commonest overall; lung #1).
8. Thin smooth ring + DWI restriction = abscess, not tumour; succinate/amino-acid peak confirms.
9. MR spectroscopy: choline ↑, NAA ↓ in tumour; lactate/lipid peak = necrosis/high grade.
10. Cyst + enhancing mural nodule: pilocytic astrocytoma (child) or haemangioblastoma (adult cerebellum, VHL).
11. Fourth-ventricle child tumour: medulloblastoma (midline vermis, hyperdense) vs ependymoma (extends through foramina).
12. CNS lymphoma: periventricular, restricts diffusion, homogeneous, "melts" with steroids, low rCBV.