Question 1: Glioblastoma (GBM)
Stem: A 65-year-old man presents with a 2-week history of personality changes and headaches. An MRI of the brain reveals a large, poorly defined mass in the right frontal lobe that extends across the corpus callosum into the left hemisphere. The mass shows thick, irregular rim enhancement and a central area of non-enhancement consistent with necrosis.
Question: This pattern of “butterfly” extension across the midline is most characteristic of:
(A) Glioblastoma (GBM) (B) Primary CNS Lymphoma (C) Meningioma (D) Low-grade Astrocytoma (E) Cerebral Abscess
Correct Answer: (A) Glioblastoma (GBM).
Explanation:
- Why (A) is correct: Glioblastoma (WHO Grade 4) is the most common primary malignant brain tumour in adults. It is highly infiltrative and frequently crosses the midline via white matter tracts like the corpus callosum, giving the classic “butterfly glioma” appearance. Irregular rim enhancement and internal necrosis are hallmark features.
- Why (B) is wrong: While CNS lymphoma can also cross the midline, it typically presents as a more homogeneous, solid-enhancing mass without significant central necrosis in immunocompetent patients.
- Why (C) is wrong: Meningiomas are extra-axial tumours that do not infiltrate the brain parenchyma or cross the midline through the corpus callosum in this manner.
- Why (D) is wrong: Low-grade astrocytomas typically do not show necrosis or avid contrast enhancement.
- Why (E) is wrong: An abscess is a ring-enhancing lesion but is usually well-circumscribed with a smooth rim and does not typically infiltrate across the corpus callosum like a high-grade glioma.
Key Points: Glioblastoma (GBM)
- WHO Grade 4: Most aggressive primary brain tumour.
- Butterfly Glioma: Classic sign of midline extension via the corpus callosum.
- MRI Features: Irregular, “shaggy” rim enhancement with central necrosis and prominent vasogenic oedema.
- MRS Findings: High choline (cell turnover), low NAA (neuronal loss), and a lactate peak (anaerobic metabolism).
Question 2: Meningioma
Stem: A 50-year-old woman has a CT head for minor trauma, which reveals an incidental 3 cm, sharply circumscribed, hyperdense mass abutting the falx cerebri. On MRI, the mass is isointense to grey matter on all sequences and demonstrates intense, uniform enhancement with a visible “dural tail” sign.
Question: What is the most likely diagnosis?
(A) Meningioma (B) Glioblastoma (C) Metastasis (D) Schwannoma (E) Oligodendroglioma
Correct Answer: (A) Meningioma.
Explanation:
- Why (A) is correct: This is the classic description of a meningioma, the most common extra-axial tumour. Key features include the broad-based dural attachment, uniform enhancement, and the dural tail sign (thickened, enhancing dura adjacent to the mass). They are often hyperdense on CT due to calcification or dense cell packing.
- Why (B) is wrong: GBM is an intra-axial tumour with irregular margins and necrosis.
- Why (C) is wrong: Metastases are typically intra-axial, often multiple, and located at the grey-white matter junction.
- Why (D) is wrong: Schwannomas are typically associated with specific cranial nerves (e.g., CN VIII in the internal auditory canal) and are not usually dural-based in this location.
- Why (E) is wrong: Oligodendrogliomas are intra-axial, cortical-based tumours that often contain coarse calcification.
Key Points: Meningioma
- Extra-axial: Arises from arachnoid cap cells.
- Broad Dural Base: Classic attachment to the falx, tentorium, or convexity.
- Dural Tail Sign: Enhancement of the adjacent dura (not pathognomonic but highly suggestive).
- CT: Often hyperdense and can cause hyperostosis (thickening) of the adjacent bone.
Question 3: Brain Metastases
Stem: A 55-year-old smoker presents with headaches and a new-onset seizure. An MRI reveals multiple, small, well-circumscribed, ring-enhancing lesions located at the grey-white matter junction. There is a disproportionate amount of vasogenic oedema surrounding the lesions.
Question: Given the patient’s history and the imaging pattern, what is the most likely diagnosis?
(A) Brain Metastases (B) Multiple Sclerosis (C) Cerebral Abscesses (D) Meningiomatosis (E) Neurocysticercosis
Correct Answer: (A) Brain Metastases.
Explanation:
- Why (A) is correct: The presence of multiple lesions at the grey-white matter junction (where small vessels narrow, trapping emboli) is the hallmark of brain metastases. The large amount of vasogenic oedema relative to the lesion size is also a common feature.
- Why (B) is wrong: MS plaques are typically periventricular (Dawson’s fingers) and do not usually present as multiple solid, ring-enhancing masses.
- Why (C) is wrong: Multiple abscesses are possible but usually associated with systemic sepsis; metastases are more common in an older smoker.
- Why (D) is wrong: Meningiomatosis involves multiple dural-based masses, not parenchymal lesions at the grey-white junction.
- Why (E) is wrong: Neurocysticercosis typically presents with smaller, often calcified cysts in specific stages, common in endemic regions.
Key Points: Brain Metastases
- Distribution: Typically multiple and located at the grey-white matter junction.
- Top Primaries: Lung (most common), Breast, Melanoma, Renal Cell, and Colon.
- Melanoma: Known for being T1-bright on MRI due to melanin or haemorrhage.
- Oedema: Often show disproportionate vasogenic oedema.
Question 4: Medulloblastoma
Stem: A 5-year-old boy presents with progressive ataxia and vomiting. A CT head shows a hyperdense midline mass arising from the roof of the fourth ventricle and causing obstructive hydrocephalus. MRI reveals the mass has restricted diffusion on DWI.
Question: What is the most likely diagnosis?
(A) Medulloblastoma (B) Pilocytic Astrocytoma (C) Ependymoma (D) Brainstem Glioma (E) Haemangioblastoma
Correct Answer: (A) Medulloblastoma.
Explanation:
- Why (A) is correct: Medulloblastoma is the most common malignant brain tumour in children. It classically arises from the roof of the fourth ventricle (vermis), is midline, and appears hyperdense on CT due to dense cell packing. The restricted diffusion on MRI is a key diagnostic feature.
- Why (B) is wrong: Pilocytic astrocytoma is typically cystic with an enhancing mural nodule and is usually located in the cerebellar hemisphere, not the midline vermis.
- Why (C) is wrong: Ependymomas arise from the floor of the fourth ventricle and often “squeeze” through the exit foramina of Luschka and Magendie.
- Why (D) is wrong: Brainstem gliomas primarily involve the pons and are typically hypodense and infiltrative.
- Why (E) is wrong: Haemangioblastomas are rare in children and typically present as a cyst with a highly vascular nodule.
Key Points: Medulloblastoma
- WHO Grade 4: Highly malignant embryonal tumour.
- Location: Midline (vermis), arising from the roof of the 4th ventricle.
- Imaging Hallmarks: Hyperdense on CT and shows restricted diffusion on MRI.
- Seeding: High propensity for leptomeningeal spread (“drop metastases”) throughout the spinal cord.
Question 5: Pilocytic Astrocytoma
Stem: An 8-year-old girl is found to have a well-defined mass in the left cerebellar hemisphere. MRI shows a large cyst with a small, intensely enhancing mural nodule. There is no associated calcification.
Question: What is the most likely diagnosis?
(A) Pilocytic Astrocytoma (B) Medulloblastoma (C) Ependymoma (D) Brain Abscess (E) Haemangioblastoma
Correct Answer: (A) Pilocytic Astrocytoma.
Explanation:
- Why (A) is correct: This is the classic “cyst with a nodule” appearance of a pilocytic astrocytoma (WHO Grade 1), the most common paediatric glioma. It is typically located in the cerebellum.
- Why (B) is wrong: Medulloblastoma is a solid, midline mass that is hyperdense on CT.
- Why (C) is wrong: Ependymomas are usually heterogeneous solid masses within the 4th ventricle.
- Why (D) is wrong: A brain abscess would have a smooth, enhancing ring, not a discrete solid nodule, and would be associated with clinical infection.
- Why (E) is wrong: While it also presents as a “cyst with a nodule,” haemangioblastoma is very rare in children (typically seen in young adults with VHL).
Key Points: Pilocytic Astrocytoma
- WHO Grade 1: Benign, slow-growing tumour.
- Classic Appearance: Cyst with an intensely enhancing mural nodule.
- Location: Most common in the cerebellum, followed by the optic pathway (especially in NF-1).
Question 6: Brain Abscess
Stem: A 33-year-old man presents with severe headache and confusion. An MRI reveals a ring-enhancing lesion in the left frontal lobe. On Diffusion-Weighted Imaging (DWI), the central fluid portion of the lesion shows intense hyperintensity (restricted diffusion) with corresponding low signal on the ADC map.
Question: The finding of restricted diffusion in the central core is highly specific for:
(A) Pyogenic Brain Abscess (B) Necrotic Glioblastoma (C) Necrotic Metastasis (D) Resolving Haemorrhage (E) Arachnoid Cyst
Correct Answer: (A) Pyogenic Brain Abscess.
Explanation:
- Why (A) is correct: DWI is the critical sequence for differentiating an abscess from a necrotic tumour. The viscous pus in an abscess significantly restricts the motion of water, appearing very bright on DWI and dark on ADC.
- Why (B) & (C) are wrong: Necrotic or cystic tumours contain serous fluid or liquefied necrosis, which typically does not restrict diffusion (it will be dark on DWI and bright on ADC).
- Why (D) is wrong: Resolving blood has variable signal but doesn’t typically show this “bright core” on DWI like pus.
- Why (E) is wrong: Arachnoid cysts follow CSF signal and show no restricted diffusion.
Key Points: Brain Abscess
- MRI Hallmark: Restricted diffusion (DWI bright, ADC dark) within the central cavity.
- Ring Enhancement: Typically a smooth, regular, thin enhancing rim.
- Spectroscopy: May show an amino acid peak, which is specific for infection.
Question 7: Herpes Simplex Encephalitis (HSV-1)
Stem: A 40-year-old woman presents with acute fever, headache, and olfactory hallucinations. MRI shows increased T2/FLAIR signal and swelling in the medial temporal lobes and limbic system bilaterally. The basal ganglia are notably spared.
Question: This specific distribution of brain involvement is most characteristic of:
(A) Herpes Simplex Encephalitis (HSV-1) (B) Toxoplasmosis (C) Japanese Encephalitis (D) Hypoxic-Ischaemic Encephalopathy (E) Limbic Paraneoplastic Syndrome
Correct Answer: (A) Herpes Simplex Encephalitis (HSV-1).
Explanation:
- Why (A) is correct: HSV-1 encephalitis has a pathognomonic predilection for the limbic system (medial temporal lobes, insular cortex, cingulate gyrus). The sparing of the basal ganglia is a classic feature that helps differentiate it from other conditions like stroke or other viral encephalitides.
- Why (B) is wrong: Toxoplasmosis presents as multiple ring-enhancing lesions, often in the basal ganglia.
- Why (C) is wrong: Japanese encephalitis characteristically involves the thalami and substantia nigra.
- Why (D) is wrong: Hypoxic injury typically involves the basal ganglia and cortex, not the isolated limbic system.
- Why (E) is wrong: Limbic paraneoplastic syndrome can look identical, but HSV is a medical emergency and the most common cause of this pattern in an acute febrile setting.
Key Points: HSV-1 Encephalitis
- Medical Emergency: Most common cause of sporadic fatal encephalitis.
- Location: Medial temporal lobes, insula, and cingulate gyrus.
- Key Sign: Often bilateral but asymmetric; spares the basal ganglia.
- Complication: Haemorrhage in the temporal lobes is common.
Question 8: CNS Toxoplasmosis
Stem: A 35-year-old patient with AIDS (CD4 count < 100) presents with a right-sided hemiparesis. MRI shows multiple ring-enhancing lesions in the basal ganglia and at the grey-white matter junction. A Thallium-201 SPECT scan shows no uptake in the lesions.
Question: What is the most likely diagnosis?
(A) Toxoplasmosis (B) Primary CNS Lymphoma (C) Progressive Multifocal Leukoencephalopathy (PML) (D) Cryptococcosis (E) HIV Encephalitis
Correct Answer: (A) Toxoplasmosis.
Explanation:
- Why (A) is correct: Toxoplasmosis is the most common cause of multiple mass lesions in AIDS patients. It classically involves the basal ganglia. The lack of Thallium-201 uptake is a key nuclear medicine finding that points to infection (Toxo) rather than a hypermetabolic tumour (Lymphoma).
- Why (B) is wrong: Primary CNS lymphoma also causes mass lesions in AIDS, but it is typically a solitary lesion and would show intense Thallium-201 uptake.
- Why (C) is wrong: PML causes white matter signal changes without mass effect or enhancement.
- Why (D) is wrong: Cryptococcus often presents with “gelatinous pseudocysts” in the Virchow-Robin spaces of the basal ganglia, but not ring-enhancing masses.
- Why (E) is wrong: HIV encephalitis causes diffuse atrophy and symmetrical white matter T2 high signal without enhancement.
Key Points: Toxoplasmosis vs. Lymphoma
- Toxoplasmosis: Multiple lesions, basal ganglia, Thallium negative, responds to anti-parasitic treatment.
- Primary CNS Lymphoma: Often solitary, periventricular, Thallium positive.
Question 9: Neurocysticercosis
Stem: A 28-year-old man from Central America presents with a new-onset seizure. An MRI shows multiple, small (5-10 mm) cysts scattered throughout the brain. One of the cysts shows a small, eccentric, T2-dark nodule within it, resembling a “hole-with-a-dot”.
Question: The “dot” in the “hole-with-a-dot” sign represents the:
(A) Scolex (head of the parasite) (B) Calcified wall (C) Feeding artery (D) Area of necrosis (E) Haemorrhagic core
Correct Answer: (A) Scolex (head of the parasite).
Explanation:
- Why (A) is correct: This is the pathognomonic sign of the vesicular stage of neurocysticercosis (infection by the pork tapeworm Taenia solium). The cyst is the fluid sac, and the eccentric nodule (the “dot”) is the scolex (the head) of the parasite.
- Why (B) is wrong: Calcification is seen in the final “nodular calcified” stage.
- Why (C), (D), (E) are wrong: These are not features of neurocysticercosis cysts.
Key Points: Neurocysticercosis
- Most common parasitic infection of the brain.
- Classic Sign: “Scolex” seen as an eccentric nodule within a cyst.
- Stages:
- Vesicular (scolex visible, no enhancement).
- Colloidal (cyst wall enhances, scolex dies).
- Granular nodular (cyst shrinks).
- Nodular calcified (final stage, small calcified “grain of rice” dots).
Question 10: Oligodendroglioma
Stem: A 40-year-old man presents with long-standing epilepsy. A CT head reveals a peripheral, cortical-based mass in the left frontal lobe. The mass shows coarse, irregular calcifications and has caused some thinning/scalloping of the adjacent inner table of the skull.
Question: Given the cortical location and the calcification, what is the most likely diagnosis?
(A) Oligodendroglioma (B) Glioblastoma (C) Meningioma (D) Cerebral Abscess (E) Central Neurocytoma
Correct Answer: (A) Oligodendroglioma.
Explanation:
- Why (A) is correct: Oligodendrogliomas are WHO Grade 2 tumours that classically occur in the cortex of the frontal lobes. They are notorious for containing calcification (90% of cases) and often cause expansion of the cortex and scalloping of the overlying bone due to their slow growth.
- Why (B) is wrong: GBM is an infiltrative, malignant tumour that rarely calcifies.
- Why (C) is wrong: Meningiomas are extra-axial and arise from the dura, not from within the cortex.
- Why (D) is wrong: Abscesses are fluid collections with a ring of enhancement and no coarse calcification.
- Why (E) is wrong: Central neurocytoma is a tumour located within the lateral ventricles, attached to the septum pellucidum.
Key Points: Oligodendroglioma
- Genetic Marker: 1p/19q codeletion (implies better prognosis and response to chemotherapy).
- Imaging: Peripheral, cortical-based mass.
- CT Sign: Coarse calcifications are highly suggestive (90%).
- Bone sign: Inner table scalloping is common.
Question 11: Acoustic Neuroma (Vestibular Schwannoma)
Stem: A 30-year-old woman is found to have bilateral, intensely enhancing masses in the internal auditory canals and cerebellopontine angles.
Question: This finding is essentially diagnostic of which neurocutaneous syndrome?
(A) Neurofibromatosis Type 2 (NF-2) (B) Neurofibromatosis Type 1 (NF-1) (C) Tuberous Sclerosis (D) Von Hippel-Lindau (VHL) (E) Sturge-Weber Syndrome
Correct Answer: (A) Neurofibromatosis Type 2 (NF-2).
Explanation:
- Why (A) is correct: The presence of bilateral vestibular schwannomas is the defining hallmark of NF-2.
- Why (B) is wrong: NF-1 is associated with optic nerve gliomas, not acoustic neuromas.
- Why (C) is wrong: Tuberous sclerosis is associated with cortical tubers, subependymal nodules, and SEGA.
- Why (D) is wrong: VHL is associated with haemangioblastomas of the cerebellum and spinal cord.
- Why (E) is wrong: Sturge-Weber is associated with a pial angioma (leptomeningeal enhancement).
Key Points: NF-2 (Mnemonic: MISME)
- M – Meningiomas.
- I – Intracranial.
- S – Schwannomas (specifically bilateral acoustic neuromas).
- M – Multiple.
- E – Ependymomas.
Question 12: Primary CNS Lymphoma
Stem: An 80-year-old woman presents with rapid cognitive decline. MRI reveals a solitary, intensely and homogeneously enhancing mass in the periventricular white matter. The mass shows restricted diffusion on DWI.
Question: In an immunocompetent elderly patient, this appearance is most suggestive of:
(A) Primary CNS Lymphoma (B) Glioblastoma (GBM) (C) Brain Metastasis (D) Cerebral Abscess (E) Multiple Sclerosis
Correct Answer: (A) Primary CNS Lymphoma.
Explanation:
- Why (A) is correct: In immunocompetent patients, primary CNS lymphoma classically presents as a solitary, dense, homogeneously enhancing mass in a periventricular location. Because it is a highly cellular tumour, it shows significant restricted diffusion on MRI.
- Why (B) is wrong: GBM typically shows ring enhancement and central necrosis, not homogeneous enhancement.
- Why (C) is wrong: Metastases are often multiple and at the grey-white junction.
- Why (D) is wrong: Abscesses show ring enhancement and a “bright core” on DWI, but the enhancement pattern is different.
- Why (E) is wrong: MS is usually a demyelinating process, not a solid enhancing mass in an 80-year-old.
Key Points: Primary CNS Lymphoma
- Histology: Usually Diffuse Large B-Cell Lymphoma.
- Imaging (Immunocompetent): Solitary, periventricular, homogeneous enhancement, and restricted diffusion.
- Imaging (AIDS/Immunocompromised): Often multiple and can show ring enhancement (mimicking Toxo).
Question 13: Subependymal Giant Cell Astrocytoma (SEGA)
Stem: A 12-year-old boy with known Tuberous Sclerosis presents with a headache and new-onset hydrocephalus. An MRI reveals a large, enhancing mass at the foramen of Monro. Multiple calcified subependymal nodules are also seen.
Question: What is the most likely diagnosis for the mass at the foramen of Monro?
(A) Subependymal Giant Cell Astrocytoma (SEGA) (B) Choroid Plexus Papilloma (C) Colloid Cyst (D) Ependymoma (E) Central Neurocytoma
Correct Answer: (A) Subependymal Giant Cell Astrocytoma (SEGA).
Explanation:
- Why (A) is correct: SEGA is a hallmark tumour of Tuberous Sclerosis. It is a WHO Grade 1 tumour that classically arises near the foramen of Monro and can cause obstructive hydrocephalus. Its origin from a degenerating subependymal nodule is a characteristic feature.
- Why (B) is wrong: Choroid plexus tumours arise from the choroid plexus, typically in the trigone of the lateral ventricle or the 4th ventricle.
- Why (C) is wrong: A colloid cyst is a non-neoplastic cyst in the same location but is typically hyperdense on CT and does not occur specifically in TS.
- Why (D) is wrong: Ependymomas typically arise in the 4th ventricle.
- Why (E) is wrong: Central neurocytoma is an intraventricular tumour attached to the septum pellucidum but not specifically associated with TS.
Key Points: SEGA
- Classic Association: Tuberous Sclerosis Complex (TSC).
- Location: Near the foramen of Monro.
- Clinical Significance: Can cause acute obstructive hydrocephalus.
- Imaging: Avidly enhancing mass > 1 cm in a patient with other signs of TS (tubers, nodules).
Question 14: Cerebral Cryptococcosis
Stem: An AIDS patient presents with headache and lethargy. An MRI shows multiple, small, non-enhancing, fluid-filled “pseudocysts” along the Virchow-Robin spaces in the basal ganglia.
Question: This “gelatinous pseudocyst” appearance is highly suggestive of:
(A) Cryptococcosis (B) Toxoplasmosis (C) Primary CNS Lymphoma (D) HIV Encephalitis (E) Neurocysticercosis
Correct Answer: (A) Cerebral Cryptococcosis.
Explanation:
- Why (A) is correct: Cryptococcus neoformans is a common fungal infection in AIDS. It travels through the perivascular (Virchow-Robin) spaces, filling them with fungal mucin. This creates the classic “gelatinous pseudocyst” appearance (small CSF-like cysts in the basal ganglia). They typically do not enhance.
- Why (B) & (C) are wrong: These present as ring-enhancing masses.
- Why (D) is wrong: HIV encephalitis causes diffuse atrophy, not focal basal ganglia cysts.
- Why (E) is wrong: Neurocysticercosis has a specific scolex and different clinical context.
Key Points: Cerebral Cryptococcosis
- Pathogen: Cryptococcus neoformans (yeast).
- Imaging Hallmarks:
- Gelatinous Pseudocysts: Small, non-enhancing cysts in the basal ganglia Virchow-Robin spaces.
- Meningitis (often no enhancement).
- Cryptococcomas (enhancing masses, less common).
Question 15: Progressive Multifocal Leukoencephalopathy (PML)
Stem: An HIV-positive patient presents with progressive ataxia. MRI reveals multiple, asymmetric areas of T2/FLAIR high signal in the subcortical white matter, involving the U-fibres. There is no mass effect and no enhancement post-contrast.
Question: This appearance is most characteristic of:
(A) Progressive Multifocal Leukoencephalopathy (PML) (B) HIV Encephalitis (C) Multiple Sclerosis (D) Toxoplasmosis (E) CMV Encephalitis
Correct Answer: (A) Progressive Multifocal Leukoencephalopathy (PML).
Explanation:
- Why (A) is correct: PML is caused by the reactivation of the JC virus in immunocompromised patients. Its hallmarks are: 1) Subcortical white matter involvement, 2) Involvement of the U-fibres (unlike HIV encephalitis, which spares them), and 3) Absence of mass effect or contrast enhancement.
- Why (B) is wrong: HIV Encephalitis is typically symmetric, involves the deep white matter, and characteristically spares the subcortical U-fibres.
- Why (C) is wrong: MS plaques are smaller, ovoid, and typically show some mass effect or enhancement in the acute phase.
- Why (D) is wrong: Toxo causes enhancing mass lesions.
- Why (E) is wrong: CMV encephalitis in AIDS typically presents as ventriculitis (thin, linear periventricular enhancement).
Key Points: PML
- Cause: JC Papovavirus.
- Clinical: Rapidly progressive neurological deficits.
- Imaging Hallmark: Asymmetric, subcortical white matter lesions that involve the U-fibres, with no enhancement or mass effect.
- Prognosis: Very poor (death within 2-5 months).
