Question 1: Medulloblastoma
Stem: A 5-year-old boy presents with ataxia and signs of increased intracranial pressure. A CT head shows a midline, hyperdense mass in the posterior fossa arising from the cerebellar vermis, causing obstructive hydrocephalus. On MRI, the mass shows significant restricted diffusion.
Question: Which of the following is the most likely diagnosis?
(A) Pilocytic Astrocytoma (B) Ependymoma (C) Medulloblastoma (D) Brainstem Glioma (E) Atypical Teratoid Rhabdoid Tumour (ATRT)
Correct Answer: (C) Medulloblastoma
Explanation:
- Why (C) is correct: Medulloblastoma is a highly cellular “small round blue cell” tumour. This dense cell packing results in its classic CT hyperdensity and restricted diffusion (DWI bright, ADC dark). Its midline location (vermis) is typical for the paediatric population.
- Why (A) is wrong: Pilocytic astrocytoma is typically a cyst with an enhancing mural nodule and is usually located in the cerebellar hemisphere, not the midline. It does not restrict diffusion.
- Why (B) is wrong: Ependymomas arise from the floor of the 4th ventricle and are “plastic,” squeezing through the foramina of Luschka and Magendie. They are usually heterogeneous with calcifications.
- Why (D) is wrong: Brainstem gliomas cause diffuse expansion of the pons (“bulbous pons”) and are not discrete intraventricular masses.
- Why (E) is wrong: ATRT is seen in younger children (< 3 years) and is highly heterogeneous/aggressive, often off-midline.
Key Points:
- WHO Grade 4.
- Most common malignant brain tumour in children.
- Imaging: Hyperdense (CT), Restricted Diffusion (MRI).
- Complication: Check the entire spine for “drop metastases” (leptomeningeal seeding).
Question 2: Neurofibromatosis Type 1 (NF1)
Stem: A 7-year-old girl with multiple café-au-lait spots undergoes an MRI for progressive vision loss. Imaging shows a fusiform, tortuous enlargement of the right optic nerve which is T2-hyperintense and enhances mildly.
Question: This finding is a hallmark of which condition?
(A) Neurofibromatosis Type 1 (NF1) (B) Neurofibromatosis Type 2 (NF2) (C) Tuberous Sclerosis (D) Von Hippel-Lindau (VHL) (E) Sturge-Weber Syndrome
Correct Answer: (A) Neurofibromatosis Type 1 (NF1)
Explanation:
- Why (A) is correct: Optic pathway gliomas (usually pilocytic astrocytomas) are a primary diagnostic criterion for NF1. They appear as fusiform expansion of the optic nerves.
- Why (B) is wrong: NF2 is characterized by MISME (Meningiomas, Intracranial Schwannomas—especially bilateral acoustics, and Ependymomas).
- Why (C) is wrong: TSC is associated with subependymal nodules, tubers, and SEGAs.
- Why (D) is wrong: VHL is associated with haemangioblastomas.
- Why (E) is wrong: Sturge-Weber involves pial angiomas and facial port-wine stains.
Key Points:
- NF1 MRI findings: Optic gliomas and FASI (Foci of Abnormal Signal Intensity)—T2 bright spots in the basal ganglia/cerebellum that do not enhance or cause mass effect.
Question 3: Tuberous Sclerosis (SEGA)
Stem: A 12-year-old boy with a known neurocutaneous syndrome presents with a new headache. MRI reveals an enlarging, avidly enhancing 1.5 cm mass at the Foramen of Monro, causing unilateral ventriculomegaly.
Question: What is the most likely diagnosis?
(A) Subependymal Nodule (SEN) (B) Choroid Plexus Papilloma (C) Subependymal Giant Cell Astrocytoma (SEGA) (D) Colloid Cyst (E) Ependymoma
Correct Answer: (C) Subependymal Giant Cell Astrocytoma (SEGA)
Explanation:
- Why (C) is correct: SEGAs are characteristic of Tuberous Sclerosis. They are defined as an enhancing lesion at the Foramen of Monro measuring > 1 cm or showing interval growth.
- Why (A) is wrong: SENs are small (< 1 cm) nodules along the ventricular walls that frequently calcify but do not typically grow or cause obstruction.
- Why (B) is wrong: While intraventricular, they usually arise from the glomus of the choroid plexus in the trigone.
- Why (D) is wrong: Colloid cysts are also at the Foramen of Monro but are non-enhancing and hyperdense on CT; they are not associated with TSC.
- Why (E) is wrong: These are typically 4th ventricle tumours.
Key Points:
- TSC Triad: Adenoma sebaceum, seizures, and mental retardation.
- SEGA = Enhancing, > 1 cm, near Foramen of Monro.
Question 4: Dandy-Walker Malformation
Stem: A neonatal ultrasound shows a large posterior fossa fluid collection. MRI confirms a hypoplastic cerebellar vermis that is rotated superiorly, and a cystic dilatation of the fourth ventricle that fills the enlarged posterior fossa. The torcula is elevated.
Question: What is the diagnosis?
(A) Mega Cisterna Magna (B) Arachnoid Cyst (C) Dandy-Walker Malformation (D) Blake Pouch Cyst (E) Joubert Syndrome
Correct Answer: (C) Dandy-Walker Malformation
Explanation:
- Why (C) is correct: The Dandy-Walker triad is: 1. Vermian agenesis/hypoplasia, 2. Cystic dilatation of the 4th ventricle, 3. Enlarged posterior fossa with high torcula (Torcular-lambdoid inversion).
- Why (A) is wrong: Mega cisterna magna has a normal vermis and 4th ventricle.
- Why (B) is wrong: Retro-cerebellar arachnoid cysts cause mass effect and flatten/displace a normal vermis.
- Why (D) is wrong: Blake Pouch Cyst shows a posterior cyst and a normal (but rotated) vermis; the posterior fossa is usually not enlarged.
- Why (E) is wrong: Joubert syndrome has a “molar tooth sign” due to elongated superior cerebellar peduncles.
Question 5: Germinal Matrix Haemorrhage (GMH)
Stem: A premature infant (28 weeks) has a cranial ultrasound on Day 3. There is hyperechoic blood filling the lateral ventricles. The ventricles are dilated, but the brain parenchyma is normal.
Question: What is the Papile Grade?
(A) Grade I (B) Grade II (C) Grade III (D) Grade IV (E) Grade V
Correct Answer: (C) Grade III
Explanation:
- Why (C) is correct: Grade III involves intraventricular haemorrhage with ventricular dilatation.
- Why (A) is wrong: Grade I is confined to the germinal matrix (caudothalamic groove).
- Why (B) is wrong: Grade II is intraventricular blood without dilatation.
- Why (D) is wrong: Grade IV involves intraparenchymal haemorrhage (usually a venous infarct).
- Why (E) is wrong: There is no Grade V in the Papile system.
Question 6: Sturge-Weber Syndrome
Stem: A child with a facial port-wine stain presents with seizures. CT shows “tram-track” calcifications in the cortex of the left occipital lobe. MRI shows pial enhancement in the same region.
Question: What is the underlying pathology of the brain findings?
(A) Cortical Hamartomas (B) Leptomeningeal Capillary-Venous Malformation (C) Arteriovenous Malformation (AVM) (D) Cavernoma (E) Gliosis
Correct Answer: (B) Leptomeningeal Capillary-Venous Malformation
Explanation:
- Why (B) is correct: Sturge-Weber is characterized by a leptomeningeal angioma (pial angiomatosis). This leads to chronic ischaemia of the underlying brain, causing the classic tram-track calcifications and cortical atrophy.
- Why (A) is wrong: This is a TSC finding.
- Why (C), (D) are wrong: These are discrete vascular malformations, not diffuse pial angiomatosis.
Question 7: Chiari II Malformation
Stem: A newborn with a lumbar myelomeningocele has an MRI brain. Findings include a small posterior fossa, a “beaked” tectum, and downward displacement of the vermis and medulla through the foramen magnum.
Question: Which of the following is also frequently seen in this condition?
(A) Enlarged interthalamic adhesion (massa intermedia) (B) Small interthalamic adhesion (C) Absent pituitary gland (D) Large posterior fossa (E) Normal sized ventricles
Correct Answer: (A) Enlarged interthalamic adhesion (massa intermedia)
Explanation:
- Why (A) is correct: An enlarged interthalamic adhesion is a very common supratentorial finding in Chiari II (>90% of cases).
- Why (B) is wrong: The adhesion is classically large, not small.
- Why (D) is wrong: Chiari II always has a small posterior fossa (due to premature closure of sutures).
- Why (E) is wrong: Almost all have hydrocephalus and “colpocephaly” (dilated occipital horns).
Question 8: Holoprosencephaly
Stem: An antenatal ultrasound shows a single, large “monoventricle” and fused thalami. The facial features show cyclopia.
Question: What is the most severe form of this spectrum?
(A) Lobar (B) Semilobar (C) Alar (D) Alobar (E) Septo-optic dysplasia
Correct Answer: (D) Alobar
Explanation:
- Why (D) is correct: Alobar is the most severe form: monoventricle, fused thalami, absent falx, and absent corpus callosum.
- Why (A), (B) are wrong: These are less severe forms (partial separation of hemispheres).
- Why (E) is wrong: This is a different entity involving absent septum pellucidum and optic nerve hypoplasia.
Question 9: Vein of Galen Malformation
Stem: A neonate presents with high-output congestive heart failure. Ultrasound of the brain shows a large, midline, cystic structure posterior to the third ventricle with high-velocity turbulent flow on Doppler.
Question: This structure is actually a dilated:
(A) Vein of Galen (B) Median prosencephalic vein (C) Internal cerebral vein (D) Straight sinus (E) Basal vein of Rosenthal
Correct Answer: (B) Median prosencephalic vein
Explanation:
- Why (B) is correct: This is a classic “trick” question. The “Vein of Galen Malformation” is actually an aneurysmal dilatation of the embryonic precursor, the median prosencephalic vein of Markowski.
- Why (A) is wrong: The true Vein of Galen is never actually formed in this condition.
Question 10: Periventricular Leukomalacia (PVL)
Stem: A 2-year-old child born very prematurely has spastic diplegia. MRI shows periventricular white matter volume loss, especially near the trigones, with associated “squaring” of the posterior horns of the lateral ventricles.
Question: What is the characteristic early ultrasound finding for this condition?
(A) Ventricular haemorrhage (B) Periventricular echogenicity persisting > 7 days (C) Choroid plexus cysts (D) Dilated 3rd ventricle (E) Midline shift
Correct Answer: (B) Periventricular echogenicity persisting > 7 days
Explanation:
- Why (B) is correct: Early PVL appears on US as “flaring”—increased echogenicity in the periventricular white matter. If this persists beyond a week and later turns into cysts (cystic PVL), it is diagnostic.
- Why (A) is wrong: Haemorrhage is a different entity (GMH).
Question 11: Joubert Syndrome
Stem: An MRI of a child with hypotonia and “panting” breathing shows a “molar tooth sign” on axial images through the midbrain.
Question: The “molar tooth” appearance is caused by the elongation and lack of decussation of which structure?
(A) Superior cerebellar peduncles (B) Middle cerebellar peduncles (C) Inferior cerebellar peduncles (D) Corticospinal tracts (E) Corpus callosum
Correct Answer: (A) Superior cerebellar peduncles
Explanation:
- Why (A) is correct: The molar tooth sign is formed by thickened, elongated, and horizontal superior cerebellar peduncles and a deep interpeduncular fossa.
- Why (B), (C) are wrong: These do not contribute to the molar tooth sign.
Question 12: Septo-optic Dysplasia (De Morsier)
Stem: MRI shows an absent septum pellucidum and small, hypoplastic optic nerves. The pituitary gland is also small.
Question: Which of the following is most commonly associated with this triad?
(A) Schizencephaly (B) Schizencephaly (often bilateral) (C) Encephalocele (D) Chiari III (E) Dandy-Walker
Correct Answer: (B) Schizencephaly (often bilateral)
Explanation:
- Why (B) is correct: Septo-optic dysplasia is associated with schizencephaly (clefts in the brain) in up to 50% of cases.
Question 13: Rhombencephalosynapsis
Stem: MRI shows a small posterior fossa with fusion of the cerebellar hemispheres across the midline and an absent cerebellar vermis. The 4th ventricle is diamond-shaped.
Question: This is the pathognomonic appearance of:
(A) Dandy-Walker (B) Joubert Syndrome (C) Rhombencephalosynapsis (D) Chiari IV (E) Lhermitte-Duclos
Correct Answer: (C) Rhombencephalosynapsis
Explanation:
- Why (C) is correct: This is a rare anomaly where the cerebellar hemispheres fail to separate and the vermis is absent.
- Why (A), (B) are wrong: These have vermian hypoplasia, but the hemispheres are not fused.
Question 14: Craniosynostosis (Apert Syndrome)
Stem: A child presents with a high, peaked skull (turricephaly) and syndactyly (fused fingers/toes).
Question: What is the most likely syndrome?
(A) Crouzon Syndrome (B) Apert Syndrome (C) Pfeiffer Syndrome (D) Carpenter Syndrome (E) Treacher Collins
Correct Answer: (B) Apert Syndrome
Explanation:
- Why (B) is correct: Apert = Craniosynostosis + Syndactyly (“mitten hands”).
- Why (A) is wrong: Crouzon has craniosynostosis but no limb abnormalities.
Question 15: Neuroblastoma Metastases (Orbits)
Stem: A 2-year-old presents with “raccoon eyes” (periorbital ecchymosis) and proptosis. CT shows aggressive bony destruction of the orbital walls with an associated “hair-on-end” periosteal reaction.
Question: What is the most likely primary tumour?
(A) Wilms’ Tumour (B) Neuroblastoma (C) Rhabdomyosarcoma (D) Retinoblastoma (E) Lymphoma
Correct Answer: (B) Neuroblastoma
Explanation:
- Why (B) is correct: Neuroblastoma is notorious for metastasizing to the orbits (bone and retro-orbital soft tissue), leading to the clinical “raccoon eyes” and aggressive bony changes.
- Why (C) is wrong: Rhabdomyosarcoma is a primary orbital tumour, not a metastatic deposit from an abdominal primary.
- Why (D) is wrong: This is an intra-ocular tumour.
