Subtitle: A case-based pilocytic astrocytoma quiz: a cerebellar cyst with a mural nodule in a child, Rosenthal fibres, EGBs, KIAA1549::BRAF, NF1 and mimics such as haemangioblastoma, with 10 MCQs and explanations.
Author: PathologyMCQ Editorial Board
Category: Neuropathology
Last Updated: October 2026
Read Time: 5 minutes
At-a-Glance
- Pilocytic astrocytoma: CNS WHO grade 1, commonest glioma in children; cerebellum, optic pathway and brainstem.
- Classic imaging: cyst with enhancing mural nodule.
- Histology: biphasic compact and microcystic areas, Rosenthal fibres, eosinophilic granular bodies.
- Molecular: KIAA1549::BRAF fusion (most); BRAF V600E and NF1 also activate MAPK.
- Associated with NF1 (optic gliomas), not tuberous sclerosis.
Pathology MCQPathology MCQ app ยท Android
Get the Pathology MCQ app
Practise neuropathology with a new MCQ every day.
- โDaily MCQ with explanations and streaks
- ๐ฌVirtual slides you pinch-zoom, with annotations
- ๐Your courses, notes and mocks in one place
The Case
A 6-year-old child has unsteadiness and gait disturbance. Examination shows nystagmus, areflexia and hypotonia. Contrast MRI shows an enhancing nodule within the wall of a cystic cerebellar mass. The resected tumour is shown below.
Test Yourself: 10 MCQs
Pilocytic astrocytoma case: 10 MCQs
Histology, BRAF, NF1, Rosenthal fibres and mimics, with instant explanations.
More practice: the CNS tumours MCQ bank โ
Quick Review
| Feature | Key points |
|---|---|
| Age and site | Children and young adults; cerebellum, optic pathway, hypothalamus, brainstem |
| Imaging | Cyst with enhancing mural nodule |
| Histology | Biphasic; piloid cells, Rosenthal fibres, EGBs, glomeruloid vessels |
| IHC | GFAP, Olig2 and S100 positive; IDH1 R132H negative |
| Molecular | KIAA1549::BRAF fusion; BRAF V600E; NF1; FGFR1 |
| Syndrome | NF1 (optic pathway glioma) |
| Grade and outcome | CNS WHO grade 1; excellent after complete resection |
Mimics
| Mimic | Clue |
|---|---|
| Haemangioblastoma | Adults, VHL; vacuolated stromal cells, inhibin+, GFAPโ stromal cells |
| Piloid gliosis | Around craniopharyngioma, syrinx or haemangioblastoma; no tumour nodule |
| Diffuse astrocytoma | Infiltrative, IDH-mutant or H3-altered; no biphasic pattern |
| High-grade astrocytoma with piliform features | Anaplasia, CDKN2A/B deletion, ATRX loss; methylation-defined |
| Pleomorphic xanthoastrocytoma | Pleomorphic, xanthomatous cells; BRAF V600E with CDKN2A/B loss |
Related: haemangioblastoma vs metastatic RCC โ ยท WHO CNS5 glioma updates โ
Exam Pearls
- Cyst with mural nodule in a childโs cerebellum = pilocytic astrocytoma.
- KIAA1549::BRAF fusion is commonest; BRAF V600E in a minority.
- NF1, not tuberous sclerosis (SEGA).
- Rosenthal fibres: ฮฑB-crystallin + GFAP; also in piloid gliosis and Alexander disease.
More courses
Preparing for an exam?
Related reads: Cerebellar haemangioblastoma โ ยท Medulloblastoma case MCQs โ
Pathology MCQ app ยท Android
Get the Pathology MCQ app
Practise a slide and an MCQ every day, even when you are away from your desk.
- โDaily MCQ with explanations and streaks
- ๐ฌVirtual slides you pinch-zoom, with annotations
- ๐Your courses, notes and mocks in one place
References
- WHO Classification of Tumours Editorial Board. Central Nervous System Tumours. 5th ed. IARC; 2021.
- Collins VP, Jones DTW, Giannini C. Pilocytic astrocytoma: pathology, molecular mechanisms and markers. Acta Neuropathol. 2015;129:775โ88.
Leave a Reply