CNS

Question 1

Name the layers of the cerebellum

Answer 1

Molecular layer

Granular layer

Purkinje layer

White matter tracts

Question 2

Describe the Classification of Medulloblastoma

Answer 2

Histologic variants:

Classic; desmoplastic / nodular; extensive nodularity; anaplastic / large cell

Molecular classification:

WnT activated

SHH activated

Group 3 / 4

Ancillary tests: Beta catenin / LEF1, YAP1 / GAB1 / p53, MYCN amplification

Question 3

Cyst with Mural Nodule on Imaging

Answer 3

Pilocytic astrocytoma

Pleomorphic xanthoastrocytoma

Ganglioglioma

Desmoplastic infantile astrocytoma / ganglioglioma

Question 4

Algorithim for Diagnosing Adult Gliomas

Answer 4

IDH mutant, ATRX retained - 1p/19q co-deleted = Oligo

IDH mutant, ATRX lost, 1p/19q intact = Astrocytoma, grade based on presence / absence of CDKN2A/B and/or histology

IDH WT, ATRX retained, H3.3 G34 mutant = Diffuse hemispheric glioma, H3.3 G34 mutant WHO 4

IDH WT, ATRX retained, H3.3 G34 wild type = GBM WHO 4 based on TERT mutant, EGFR amplified, +7/-10 or histology

Midline, IDH WT, ATRX retained, H3K27M positive, H3K27me loss = Diffuse midline glioma, H3K27M WHO 4

Question 5

Macrophage Rich Lesions

Answer 5

Infectious:

Abscess: fungal, parasitic, mycobacterial

Non Infectious:

Demyelinating disease

Leukoencephalopathy (toxic, metabolic, vascular)

Subacute infarct

Histiocytoses and neoplasms (e.g. lymphoma post steroids)

Question 6

DDx Sellar Lesions

Answer 6

Pituitary Tumours:

Anterior pituitary adenomas, posterior pituitary tumours

Other tumours:

Craniopharyngioma, germ cell tumour, meningioma, chordoma, met

Cysts:

Rathke cleft cyst, arachnoid cyst, epidermoid and dermoid cysts

Inflammatory Lesions:

LCH, Lymphocytic hypophysitis, sarcoidosis

Infections:

TB, syphilis, bacteria, fungal

Other:

ICA aneurysm, hypothalamic hamartoma, pituitary hyperplasia

Question 7

DDx Vascular Nested Tumours in CNS

Answer 7

Haemangioblastoma (Inhibin, CAIX+)

Metastatic RCC (PAX8+, Inhibin -)

Angiomatous meningioma (EMA, SSTR2 +)

Question 8

DDx Dural Based Spindle Cell Tumours

Answer 8

Meningioma (fibrous) (SSTR2 +)

SFT (STAT6 +)

Melanocytoma (melanocytic markers +)

Question 9

DDx Myxoid / Chondromyxoid Lesions of CNS

Answer 9

Chordoma (CK, S100 Brachyury+)

Myxoid chondrosarcoma (S100, D240+)

Myxopapillary ependymoma (GFAP+)

Chordoid meningioma (EMA, SSTR2+)

Chordoid glioma (CK, EMA, GFAP, S100+, always 3rd ventricle)

Question 10

Grading of Meningiomas

Answer 10

Grade I - lack of higher grade features

Grade II - clear cell or chordoid

• > 4 mitoses per 2 mm ²
• brain invasion
• 3 of the following features: sheet-like growth, prominent nucleoli, hypercellularity, small cell change, spontaneous necrosis

Grade III - papillary or rhabdoid, frankly malignant cytology (resemble melanoma, carcinoma or UPS) > 20 mitoses per 2mm²

Question 11

Classification of Ependymomas

Answer 11

Divided into 3 compartments: supratentorial, posterior fossa and cord

In each compartment there is subependymoma CNS WHO 1

In the cord there is myxopapillary ependymoma CNS WHO 2

All others ependymomas are subdivided based on their genetics:

Supratentorial = ZFTA fusion positive, YAP1 positive, NOS

Posterior fossa = PFA, PFB, NOS

Spinal cord = MYCN amplified, NOS