19 CNS TUMOURS & DISEASE

# 20 CNS TUMOURS & DISEASE

👩‍⚕️ Why this matters for MRCS Part A. CNS tumour questions almost always follow the same recipe: a vignette pairing age + location + imaging signature + a classic clinical sign. If you can match those four together for the high-yield tumours below, you will pick up every mark. Examiners are not testing molecular subtypes — they are testing pattern recognition.

How to think about a brain tumour vignette

Ask three questions, in order:

1. Adult or child? Adults skew supratentorial; children skew infratentorial (posterior fossa). This single fact answers half the questions.

2. Intra-axial or extra-axial? Intra-axial = within brain parenchyma (gliomas, metastases, lymphoma). Extra-axial = outside the brain, pushing it inward (meningioma, schwannoma, pituitary adenoma).

3. What is the imaging giveaway? Ring enhancement, dural tail, calcification, cerebellopontine angle (CPA), cystic-with-mural-nodule — each points to one diagnosis.

➡ Most common primary brain tumour overall (benign + malignant) = meningioma.

➡ *Most common primary malignant brain tumour in adults = glioblastoma multiforme (GBM).*

➡ Most common brain tumour in children overall = pilocytic astrocytoma.

➡ Most common brain mass lesion of all = metastasis (outnumbers primary tumours roughly 10:1).

Adult brain tumours

Gliomas

Gliomas arise from glial cells — the supporting cells of the CNS. The WHO grades them I–IV by aggressiveness.

Astrocytoma — Glioblastoma multiforme (GBM). WHO Grade IV. The classic adult vignette: middle-aged or older patient, progressive headache, focal deficit and personality change. Imaging shows a heterogeneous lesion with central necrosis and ring enhancement and surrounding vasogenic oedema. Spread across the corpus callosum gives the "butterfly glioma" pattern. Histology: pseudopalisading necrosis — tumour cells lining up around necrotic foci — and microvascular proliferation. Median survival is roughly 15 months even with surgery, radiotherapy and temozolomide.

Oligodendroglioma. Slower-growing, typically frontal lobe, adults 40–50. Calcification on CT is the classic clue. Histology shows the "fried egg" appearance (perinuclear haloes) and a "chicken-wire" capillary pattern. 1p/19q co-deletion carries better prognosis and chemosensitivity — a popular MRCS factoid.

Meningioma

Most common extra-axial tumour, most common primary intracranial tumour overall, female predominance. Arises from arachnoid cap cells of the arachnoid mater, so it sits on the dura, not in the brain.

Imaging: well-circumscribed, homogeneously enhancing, dural-based mass with a dural tail and sometimes hyperostosis of the overlying skull. Histology: whorls of meningothelial cells and psammoma bodies (laminated calcifications).

Classic sites: parasagittal (along the falx), convexity, sphenoid wing, olfactory groove. Risk factors: prior cranial irradiation, NF2, female sex hormones (progesterone receptor positive — can grow in pregnancy).

Pituitary adenoma

Arises from the anterior pituitary. Two patterns to know:

- Functioning — most commonly a prolactinoma (galactorrhoea, amenorrhoea, infertility). Others: GH (acromegaly), ACTH (Cushing's disease).

- Non-functioning — present by mass effect: bitemporal hemianopia from compression of the optic chiasm above, and hypopituitarism.

Pituitary apoplexy (haemorrhage into the adenoma) is a neurosurgical emergency: sudden headache, visual loss, ophthalmoplegia, collapse.

Vestibular schwannoma (acoustic neuroma)

Benign tumour of Schwann cells of the vestibular division of CN VIII, sitting in the cerebellopontine angle (CPA). Despite the name "acoustic neuroma," it arises from the vestibular fibres — but presents with cochlear symptoms because the cochlear nerve runs alongside.

Triad: unilateral sensorineural hearing loss, tinnitus, imbalance. Larger tumours compress CN V (facial numbness, absent corneal reflex) and CN VII (facial weakness).

Histology: alternating Antoni A (compact, palisading Verocay bodies) and Antoni B (loose, myxoid) areas. Bilateral vestibular schwannomas are diagnostic of Neurofibromatosis type 2 (NF2).

➡ CPA mass differential: schwannoma (~80%) > meningioma (~10%) > epidermoid cyst.

Brain metastases

The most common intracranial mass lesion overall. Typically multiple, located at the grey–white matter junction, often ring-enhancing — a key GBM mimic but distinguished by being multiple and having a known primary.

Top primaries (memorise the order):

➡ Lung > Breast > Melanoma > Renal > Colorectal

Melanoma and renal/choriocarcinoma mets characteristically bleed.

Paediatric brain tumours

Children: think posterior fossa first. The vignette usually includes morning headache, vomiting and ataxia — features of obstructive hydrocephalus.

Pilocytic astrocytoma. Most common paediatric brain tumour overall. WHO Grade I, benign, usually cerebellar hemisphere. Imaging: cystic lesion with an enhancing mural nodule. Histology: Rosenthal fibres (eosinophilic corkscrew fibres). Excellent prognosis after resection.

Medulloblastoma. Most common malignant posterior fossa tumour in children. Arises from the cerebellar vermis (midline), so causes truncal ataxia rather than limb ataxia. A primitive neuroectodermal tumour (PNET) of small round blue cells with Homer-Wright rosettes. Characteristically seeds via CSF — "drop metastases" down the spinal cord, so staging requires whole-neuraxis MRI.

Ependymoma. Arises from the ependymal lining of the ventricles, most often the floor of the 4th ventricle in children. Can extrude through the foramina of Luschka and Magendie ("plastic" tumour). Histology: perivascular pseudorosettes. Causes obstructive hydrocephalus.

Craniopharyngioma. Arises from remnants of Rathke's pouch in the suprasellar region. Bimodal age peaks (children and older adults). Calcified, cystic suprasellar mass that compresses the optic chiasm (bitemporal hemianopia) and pituitary stalk (growth failure, diabetes insipidus). Cyst fluid is famously "machine oil" or "crankcase oil."

Posterior fossa tumour	Origin	Key clue
Pilocytic astrocytoma	Cerebellar hemisphere	Cyst + mural nodule, Rosenthal fibres
Medulloblastoma	Cerebellar vermis (midline)	Truncal ataxia, CSF drop mets
Ependymoma	Floor of 4th ventricle	Perivascular pseudorosettes
Brainstem glioma	Pons	Cranial nerve palsies, long-tract signs

👩‍⚕️ Mnemonic for paediatric posterior fossa tumours — "MEGA": Medulloblastoma, Ependymoma, Glioma (brainstem), Astrocytoma (pilocytic).

Raised intracranial pressure and herniation

The skull is a closed box (Monro–Kellie doctrine: brain + blood + CSF = fixed volume). Any added mass eventually pushes brain across a fixed dural edge — a herniation.

Herniation	Direction	Classic finding
Subfalcine (cingulate)	Cingulate gyrus under falx cerebri	Compresses anterior cerebral artery → contralateral leg weakness
Uncal (transtentorial)	Medial temporal lobe over tentorium	CN III palsy (fixed dilated pupil ipsilateral to lesion) ± contralateral hemiparesis (or ipsilateral via Kernohan's notch — "false localising sign")
Central (transtentorial)	Diencephalon downward	Progressive coma, small reactive pupils
Tonsillar (coning)	Cerebellar tonsils through foramen magnum	Brainstem compression, Cushing's reflex, respiratory arrest, death
Upward cerebellar	Cerebellum up through tentorium	Caused by overdraining a posterior fossa lesion; midbrain compression

Cushing's reflex

The brainstem's last-ditch response to critically raised ICP. A triad:

➡ Hypertension + Bradycardia + Irregular (Cheyne–Stokes) respiration.

Mechanism: rising ICP throttles cerebral perfusion, so sympathetic outflow drives systemic BP up to maintain it; the baroreceptor reflex then triggers vagal bradycardia; brainstem ischaemia disrupts respiratory centres. Cushing's reflex is a pre-terminal sign — do not wait for it before treating raised ICP.

Signs of raised ICP — "HOVA": Headache (morning, worse with cough/straining), Optic disc swelling (papilloedema), Vomiting (often projectile), Altered consciousness.

In infants, the open fontanelle absorbs early pressure rises, so the signs are different: bulging fontanelle, rapidly increasing head circumference, sutural diastasis, sunset eyes (forced downgaze from dorsal midbrain compression — Parinaud syndrome).

──────────────────────────────

Meningitis

Inflammation of the meninges (pia + arachnoid). The clinical triad is fever, headache, neck stiffness, with photophobia, vomiting and altered mental state.

Meningism on examination:

- Kernig's sign — with hip flexed to 90°, passive knee extension causes pain/resistance (stretches inflamed lumbosacral roots).

- Brudzinski's sign — passive neck flexion causes involuntary hip and knee flexion.

- Non-blanching petechial/purpuric rash — points to meningococcal septicaemia.

Causative organisms by age

Age group	Common bacterial causes
Neonates (<3 months)	Group B Streptococcus, E. coli, Listeria monocytogenes
Children & adults	Neisseria meningitidis, Streptococcus pneumoniae
Elderly / immunocompromised	S. pneumoniae, Listeria, Gram-negatives

CSF findings on lumbar puncture

Parameter	Bacterial	Viral	TB / Fungal
Appearance	Cloudy / turbid	Clear	Fibrin web, clear/opaque
Opening pressure	↑↑	Normal or mild ↑	↑↑
Cells	↑↑ Neutrophils	↑ Lymphocytes	↑ Lymphocytes
Protein	↑↑	Normal or mild ↑	↑↑↑
Glucose (CSF:plasma)	↓↓ (<0.4)	Normal	↓

👩‍⚕️ Do not delay antibiotics for the LP. Empirical IV ceftriaxone goes in first; CSF samples can be taken once the patient is stable and a CT has excluded contraindications (focal deficit, GCS <12, seizure, papilloedema — anything that raises suspicion of a mass lesion and risk of coning).

Other CNS disease for MRCS

Multiple sclerosis (MS)

A chronic autoimmune demyelinating disease of the CNS — T-cell mediated attack on oligodendrocytes (which myelinate CNS axons; Schwann cells do the equivalent in the PNS — important MCQ distinction).

Typical patient: young woman, 20–40, higher latitudes. Presentations: optic neuritis (painful monocular visual loss with afferent pupillary defect), internuclear ophthalmoplegia, sensory disturbances, limb weakness, bladder dysfunction, Lhermitte's sign (electric shock down the spine on neck flexion), Uhthoff's phenomenon (symptoms worse with heat).

Diagnosis requires lesions disseminated in time and space: MRI shows periventricular and juxtacortical plaques (T2/FLAIR hyperintense, often Dawson's fingers radiating from ventricles); CSF shows oligoclonal bands not present in serum.

Motor neurone disease (MND)

Progressive degeneration of motor neurones — both upper and lower — with sensation completely spared and eye movements typically preserved. The commonest variant is amyotrophic lateral sclerosis (ALS).

Hallmark: mixed UMN + LMN signs in the same limb — e.g. wasting and fasciculations (LMN) coexisting with brisk reflexes and upgoing plantars (UMN). Bulbar onset: dysarthria, dysphagia, tongue fasciculations. Median survival ~3 years from diagnosis; death usually from respiratory failure. Only disease-modifying drug: riluzole (modest survival benefit).

Feature	UMN lesion	LMN lesion
Tone	↑ (spastic)	↓ (flaccid)
Reflexes	Brisk	Reduced/absent
Plantars	Upgoing (Babinski +)	Downgoing
Wasting	Minimal (disuse only)	Marked
Fasciculations	Absent	Present

![MCQs banner]

Test yourself

A 60-year-old man presents with headache, confusion and right hemiparesis. CT shows a 4 cm left frontal lesion with central necrosis crossing the midline via the corpus callosum and extensive surrounding oedema. What is the most likely diagnosis?

• ((Central neurocytoma::Intraventricular tumour near the foramen of Monro; does not cross the corpus callosum.))
• ((Ependymoma::Arises from ependymal lining of ventricles, most often 4th in children.))
• ((Meningioma::Extra-axial, dural-based, homogeneously enhancing — no central necrosis.))
• ((Oligodendroglioma::Frontal calcified tumour with fried-egg cells; slower growing, no butterfly pattern.))
• ((Glioblastoma multiforme::☑️ Grade IV astrocytoma; ring-enhancing necrotic mass crossing the corpus callosum — the "butterfly glioma."))

👩‍⚕️ GBM is the most common primary malignant adult brain tumour; meningioma is the most common primary brain tumour overall.

A 7-year-old presents with early-morning headaches, vomiting and truncal ataxia. MRI shows a midline posterior fossa mass arising from the cerebellar vermis with CSF dissemination. What is the most likely diagnosis?

• ((Pilocytic astrocytoma::Cerebellar hemisphere, cyst with mural nodule; benign and does not seed via CSF.))
• ((Ependymoma::Arises from the floor of the 4th ventricle, not the vermis; perivascular pseudorosettes.))
• ((Haemangioblastoma::Vascular posterior fossa tumour of adults; associated with von Hippel-Lindau.))
• ((Choroid plexus papilloma::Lateral ventricle tumour causing CSF overproduction, not a vermis mass.))
• ((Medulloblastoma::☑️ Midline vermis PNET; truncal ataxia and CSF drop metastases are classic.))

👩‍⚕️ Medulloblastoma — the four Ms: Midline, Malignant, Most common malignant paediatric posterior fossa tumour, Metastasises via CSF.

A 45-year-old woman presents with progressive unilateral sensorineural hearing loss and tinnitus. MRI shows an enhancing mass at the cerebellopontine angle. What is the most likely diagnosis?

• ((Meningioma::Second most common CPA mass; dural-based with a dural tail rather than centred on CN VIII.))
• ((Epidermoid cyst::CPA lesion that follows CSF on MRI and does NOT enhance; restricted diffusion on DWI.))
• ((Glomus jugulare tumour::Jugular foramen tumour with pulsatile tinnitus and lower cranial nerve palsies.))
• ((Medulloblastoma::Midline paediatric vermis tumour, wrong age and wrong location.))
• ((Vestibular schwannoma::☑️ Commonest CPA tumour; Schwann cells of CN VIII vestibular division — bilateral lesions = NF2.))

👩‍⚕️ CPA tumours by frequency: schwannoma (~80%) > meningioma (~10%) > epidermoid cyst.

A 55-year-old woman has a well-defined, homogeneously enhancing extra-axial mass attached to the falx cerebri with adjacent hyperostosis of the skull. What is the most likely diagnosis?

• ((Glioblastoma multiforme::Intra-axial ring-enhancing necrotic tumour; does not arise from dura.))
• ((Cerebral metastasis::Intra-axial, usually multiple, grey–white junction; no dural attachment.))
• ((Meningioma::☑️ Arachnoid cap cell tumour — dural-based, homogeneous enhancement, hyperostosis, psammoma bodies.))
• ((Haemangiopericytoma (solitary fibrous tumour)::Dural mimic of meningioma but no hyperostosis and higher recurrence.))
• ((Primary CNS lymphoma::Periventricular intra-axial mass in immunocompetent patients; no dural attachment.))

👩‍⚕️ Meningioma associations: prior cranial radiation, NF2, female sex hormones (can enlarge in pregnancy).

A 3-year-old presents with increasing head circumference, vomiting and upgaze palsy (setting sun sign). MRI shows hydrocephalus from a tumour obstructing the aqueduct of Sylvius. Where does this lesion most likely sit?

• ((Cerebral hemisphere::Supratentorial paediatric tumours rarely obstruct the aqueduct.))
• ((Cerebellar hemisphere::Pilocytic astrocytomas here cause limb ataxia, not aqueductal block.))
• ((Cerebellopontine angle::CPA masses compress CN VII/VIII — they don't obstruct the aqueduct.))
• ((Tectal plate / dorsal midbrain::☑️ Obstructs the aqueduct (non-communicating hydrocephalus) and compresses the dorsal midbrain → Parinaud syndrome (upgaze palsy, setting sun sign).))
• ((Spinal cord::Causes segmental motor/sensory deficits, not hydrocephalus.))

👩‍⚕️ Cushing's triad (hypertension, bradycardia, irregular respiration) is a late, pre-terminal sign of raised ICP — treat well before it appears.

A 19-year-old student is brought to A&E with fever, headache, photophobia and a non-blanching purpuric rash. LP shows cloudy CSF with neutrophils, high protein and low glucose. What is the most likely organism?

• ((Streptococcus pneumoniae::Common bacterial meningitis cause, but the petechial rash points elsewhere.))
• ((Neisseria meningitidis::☑️ Gram-negative diplococcus; classic non-blanching purpuric rash from septicaemia in young adults.))
• ((Listeria monocytogenes::Neonates, pregnant women, elderly and immunocompromised — not healthy students.))
• ((Haemophilus influenzae type b::Now rare in vaccinated populations; previously unvaccinated children.))
• ((Enterovirus::Viral meningitis gives lymphocytes, normal glucose and a clear CSF — not this picture.))

👩‍⚕️ Give IV ceftriaxone before the LP — antibiotics save lives, the LP can wait.

A 28-year-old woman has had two episodes of painful monocular visual loss and one of right-sided limb numbness, separated by months. MRI shows multiple periventricular T2 hyperintensities. Which cell is the primary target of the disease process?

• ((Astrocytes::Provide structural support and form the blood–brain barrier; not the target in MS.))
• ((Schwann cells::Myelinate peripheral nerves — target in Guillain-Barré and CIDP, not MS.))
• ((Oligodendrocytes::☑️ Myelinate CNS axons; destroyed by T-cell-mediated autoimmunity in MS.))
• ((Microglia::Resident CNS macrophages — activated in MS but not the primary target.))
• ((Ependymal cells::Line the ventricles and central canal; unrelated to demyelination.))

👩‍⚕️ Schwann cells = PNS myelin; oligodendrocytes = CNS myelin. A favourite MCQ distractor.

A 62-year-old man has progressive limb weakness with wasting and fasciculations of the hands, brisk knee jerks and upgoing plantars. Sensation and eye movements are entirely normal. What is the most likely diagnosis?

• ((Multiple sclerosis::Demyelinating disease with sensory symptoms, optic neuritis and relapsing course — not pure motor.))
• ((Guillain-Barré syndrome::Acute ascending LMN weakness with areflexia; no UMN signs.))
• ((Myasthenia gravis::Fatigable weakness affecting ocular and bulbar muscles; no UMN/LMN mixture.))
• ((Motor neurone disease (ALS)::☑️ Mixed UMN and LMN signs in the same limb with sensory and ocular sparing — pathognomonic.))
• ((Cervical myelopathy::Can mix UMN and LMN signs but produces sensory level and sphincter symptoms.))

👩‍⚕️ MND's signature is UMN + LMN signs in the same limb with sensation completely spared.

Revision summary

➡ Commonest tumours: mets > meningioma (primary, all) > GBM (primary malignant adult) > pilocytic astrocytoma (paediatric).

➡ GBM: Grade IV astrocytoma, butterfly glioma, ring enhancement, pseudopalisading necrosis.

➡ Meningioma: extra-axial, dural tail, hyperostosis, psammoma bodies; NF2 and prior radiation.

➡ Vestibular schwannoma: CPA, CN VIII, unilateral SNHL + tinnitus; bilateral = NF2; Antoni A/B.

➡ Oligodendroglioma: frontal, calcified, fried egg cells, 1p/19q co-deletion = better prognosis.

➡ Metastases order: Lung > Breast > Melanoma > Renal > Colorectal.

➡ Paediatric posterior fossa "MEGA": Medulloblastoma (vermis, CSF drop mets), Ependymoma (4th ventricle, pseudorosettes), brainstem Glioma, pilocytic Astrocytoma (cyst + mural nodule, Rosenthal fibres).

➡ Craniopharyngioma: Rathke's pouch remnant, calcified suprasellar cyst, bitemporal hemianopia, "machine oil" fluid.

➡ Pituitary adenoma: prolactinoma commonest; bitemporal hemianopia from optic chiasm compression; apoplexy = emergency.

➡ Raised ICP — "HOVA": Headache, Optic disc swelling, Vomiting, Altered consciousness. Cushing's triad (HTN + bradycardia + irregular respiration) is pre-terminal.

➡ Herniations: subfalcine (ACA), uncal (CN III palsy), tonsillar (coning → death), upward cerebellar.

➡ Bacterial meningitis CSF: cloudy, neutrophils, ↑protein, ↓glucose. Viral: clear, lymphocytes, normal glucose.

➡ Empirical antibiotics before LP if any sign of raised ICP.

➡ MS: young women, oligodendrocyte demyelination, dissemination in time and space, oligoclonal bands.

➡ MND: UMN + LMN signs in the same limb, sensation spared, riluzole only DMT.