STEPTRACKERNERVOUS SYSTEM + ONCOLOGY | PATHOLOGY + GENETICS | HIGH-YIELD REVIEW

Pediatric Brain Tumors

The most common solid tumors of childhood — mostly in the posterior fossa, so they present with ataxia and hydrocephalus.

FOCUS ON
Children's tumors are mostly infratentorial. Pilocytic astrocytoma: cerebellar cyst with mural nodule, Rosenthal fibers, benign. Medulloblastoma: vermis, small round blue cells, Homer-Wright rosettes, drop metastases. Ependymoma: 4th ventricle, perivascular pseudorosettes, hydrocephalus. Supratentorial: craniopharyngioma (calcified suprasellar) and pineal germinoma (Parinaud).
TUMOR
ORIGIN · GENETICS
FEATURES · HISTOLOGY
CLUE
Pilocytic astrocytoma
most common primary
Low-grade astrocytoma; KIAA1549-BRAF fusion; NF1 (optic glioma)
Cerebellum: cystic mass with mural nodule; bipolar hair-like cells, Rosenthal fibers (eosinophilic corkscrews), eosinophilic granular bodies
GFAP ⁺ · cured by resection
Medulloblastoma
most common malignant
Embryonal tumor of the cerebellum; WNT (best), SHH, group 3 (MYC, worst); Gorlin, Turcot
Vermis (midline) → truncal ataxia, 4th ventricle compression → hydrocephalus; small round blue cells, Homer-Wright rosettes
Drop metastases via CSF · radiosensitive
Ependymoma
Ependymal cells lining ventricles
Usually 4th ventricle in children → hydrocephalus, vomiting; perivascular pseudorosettes, true ependymal rosettes, rod-shaped blepharoplasts
Spinal cord in adults (NF2)
Diffuse midline glioma
H3 K27M mutation; pons (DIPG), thalamus, cord
Rapid multiple cranial nerve palsies + long-tract signs
Very poor prognosis · not resectable
Craniopharyngioma
Rathke pouch remnant; adamantinomatous type: CTNNB1
Suprasellar, calcified, cystic with "machinery oil" fluid; bitemporal hemianopia, short stature, DI
Most common supratentorial pediatric tumor
Pineal germinoma
Germ cell tumor (like seminoma)
Parinaud syndrome, obstructive hydrocephalus; boys; hCG → precocious puberty
Radiosensitive
Atypical teratoid/rhabdoid tumor
Loss of SMARCB1 (INI1)
Infants < 3; aggressive; rhabdoid cells
INI1 stain negative
Choroid plexus papilloma
Choroid plexus epithelium
Infants; lateral ventricle; overproduces CSF → hydrocephalus
Li-Fraumeni (carcinoma)
Subependymal giant cell astrocytoma
Tuberous sclerosis (TSC1/2 → mTOR)
Near foramen of Monro → obstructive hydrocephalus
mTOR inhibitors (everolimus)
Optic pathway glioma
Pilocytic astrocytoma of the optic nerve/chiasm; NF1
Vision loss, proptosis
Usually indolent
Presentation in children
Posterior fossa mass blocks the 4th ventricle
Morning headache, vomiting, ataxia, head tilt, macrocephaly in infants, papilledema, CN VI palsy
Morning vomiting → think tumor

Mechanism — why kids present with hydrocephalus

Posterior fossa tumorVermis, 4th ventricle
→
4th ventricle blocked
→
Noncommunicating hydrocephalus
→
↑ ICPMorning headache, vomiting, papilledema

Medulloblastoma also seeds the CSF — image the whole spine ("drop metastases").

Posterior fossa tumors compared

FEATURE
PILOCYTIC
MEDULLOBLASTOMA
EPENDYMOMA
Site
Cerebellar hemisphere
Vermis
4th ventricle
Look
Cyst + nodule
Solid, midline
Fills ventricle
Histology
Rosenthal fibers
Homer-Wright rosettes
Perivascular pseudorosettes
Behavior
Benign
Malignant, CSF spread
Variable
Clue
Limb ataxia
Truncal ataxia
Hydrocephalus

How it's tested

COMMON CONFUSIONHomer-Wright rosettes (medulloblastoma, neuroblastoma — no central vessel) vs perivascular pseudorosettes (ependymoma — cells around a vessel).
THE TRAPA calcified suprasellar mass in a child with short stature and bitemporal field loss is craniopharyngioma, not a pituitary adenoma (rare in kids).
YOUR APPROACHInfra- vs supratentorial → hemisphere, vermis or ventricle → cystic vs solid → rosette type → syndrome (NF1, TSC, Gorlin, Li-Fraumeni) → prognosis.

If you see… think…

Child with cerebellar cyst and mural nodule, Rosenthal fibers → pilocytic astrocytoma
Child with truncal ataxia, midline cerebellar mass, small blue cells → medulloblastoma
Spinal "drop metastases" from a cerebellar tumor → medulloblastoma
4th ventricle tumor with perivascular pseudorosettes → ependymoma
Child with rapid multiple cranial nerve palsies, pontine mass → diffuse midline glioma (H3 K27M)
Calcified suprasellar cyst, short stature, bitemporal hemianopia → craniopharyngioma
Boy with upgaze palsy and early puberty → pineal germinoma
Infant with hydrocephalus from CSF overproduction → choroid plexus papilloma
Tuberous sclerosis with a tumor at the foramen of Monro → SEGA
NF1 child with proptosis and vision loss → optic pathway glioma