Medulloblastoma Case-Based MCQs: WNT, SHH, Group 3 and 4, i(17q) and IHC

Rosettes for medulloblastoma case-based MCQs

Subtitle: A case-based medulloblastoma quiz: a posterior fossa tumour in a child, Homer Wright rosettes, WNT, SHH, Group 3 and Group 4, i(17q), IHC surrogates and syndromes, with 10 MCQs and explanations.

Author: PathologyMCQ Editorial Board

Category: Neuropathology

Last Updated: October 2026

Read Time: 5 minutes

At-a-Glance

Medulloblastoma: embryonal tumour of the cerebellum, CNS WHO grade 4, mostly in children.
Four molecular groups: WNT (best), SHH (TP53 status matters), Group 3 (worst, MYC) and Group 4 (commonest).
i(17q) is the commonest cytogenetic change; monosomy 6 marks WNT tumours.
Syndromes: Turcot (APC, WNT) and Gorlin (PTCH1/SUFU, SHH); Li-Fraumeni with SHH, TP53-mutant.

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The Case

A 12-year-old boy presents with headache, projectile vomiting and blurred vision. CT shows a posterior fossa mass. The resected tumour is shown below. Answer the 10 MCQs that follow.

Medulloblastoma with Homer Wright rosettes — Case image: small round blue cells with Homer Wright rosettes. Image: Wikimedia Commons.

Test Yourself: 10 MCQs

Medulloblastoma case: 10 MCQs

Histology, molecular groups, IHC and syndromes, with instant explanations.

Score: 0 / 10

More practice: the CNS tumours MCQ bank →

Molecular Groups at a Glance

Medulloblastoma molecular groups (WHO CNS5)

Group	Age	Key alterations	Histology	Prognosis
WNT-activated	Children, teens	CTNNB1, monosomy 6	Classic	Excellent (>90%)
SHH-activated, TP53-wildtype	Infants, adults	PTCH1, SUFU, SMO	Desmoplastic/nodular, MBEN	Good to intermediate
SHH-activated, TP53-mutant	Children 5–18 y	TP53, MYCN/GLI2 amplification	Large cell/anaplastic	Poor
Group 3 (non-WNT/non-SHH)	Infants, children	MYC amplification, i(17q)	Classic or LC/A	Worst; often metastatic
Group 4 (non-WNT/non-SHH)	Children, teens	i(17q), MYCN, KDM6A	Classic	Intermediate

Full article: medulloblastoma pathology →

IHC Surrogates

IHC for molecular grouping

Marker	WNT	SHH	Group 3/4
β-catenin	Nuclear	Cytoplasmic	Cytoplasmic
GAB1	Negative	Positive	Negative
YAP1	Positive	Positive	Negative
p53 (strong diffuse)	May be positive	Positive if TP53-mutant	Negative

Exam Pearls

All medulloblastomas are CNS WHO grade 4.
WNT = best prognosis, nuclear β-catenin, monosomy 6.
Group 3 = MYC amplification, worst prognosis.
i(17q) is the commonest cytogenetic abnormality.
Gorlin (PTCH1/SUFU) → SHH; Turcot (APC) → WNT.

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References

WHO Classification of Tumours Editorial Board. Central Nervous System Tumours. 5th ed. IARC; 2021.
Taylor MD, et al. Molecular subgroups of medulloblastoma: the current consensus. Acta Neuropathol. 2012;123:465–72.