Medulloblastoma is one of those “classic USMLE posterior fossa tumors” that shows up everywhere—peds headaches + vomiting, cerebellar signs, and a very specific imaging/histology vibe. If you can lock down where it is, what it looks like, and how it spreads, you’ll grab easy points on Step 1 and Step 2.
The Quick Mnemonic: “MEDULLO = MIDline, Embryonal, Drops, Under 10, Little blue, Obstructs”
Think: MEDULLO as a checklist you can run in 5 seconds.
| Letter | High-yield hook | What to remember |
|---|---|---|
| M | MIDline | Cerebellar vermis tumor (classically midline in kids) |
| E | Embryonal | Highly malignant primitive neuroectodermal tumor (PNET)-type |
| D | Drops | Drop metastases via CSF seeding (spreads through CSF) |
| U | Under 10 | Most common in children |
| L | Little blue | Histology: small round blue cells + Homer Wright rosettes |
| O | Obstructs | Obstructive hydrocephalus → headache, vomiting, papilledema |
One-liner:
Medulloblastoma = malignant midline cerebellar (vermis) embryonal tumor in kids that seeds the CSF (“drop mets”) and causes obstructive hydrocephalus.
Visual Device (mental picture you’ll actually recall)
Picture a kid on a merry-go-round (cerebellum) with a “MEDULLO” medal pinned to their shirt:
- The medal sits on the MIDline of the shirt (vermis).
- It’s made of blue beads (small round blue cells).
- Blue beads form little circles (Homer Wright rosettes).
- The medal drips blue paint down the back (CSF drop metastases down the spinal cord).
- The kid looks nauseated and holds their head (↑ ICP from 4th ventricle obstruction).
How it presents (USMLE-style)
Common symptoms/signs
- Headache + morning vomiting (increased ICP)
- Papilledema
- Ataxia, gait instability (cerebellar dysfunction)
- Hydrocephalus from obstruction of 4th ventricle
Classic location (test favorite)
- Children: midline cerebellar vermis
- (Sometimes cerebellar hemispheres in adults, but Step tends to emphasize the pediatric midline pattern.)
Imaging & pathology pearls
Imaging
- Posterior fossa mass; often described as hyperdense on CT (high cellularity) and enhancing on MRI
- Causes compression/obstruction of the 4th ventricle → hydrocephalus
Histology
- Small round blue cells
- Homer Wright rosettes (tumor cells arranged around neuropil)
The metastasis detail you can’t miss: “Drop mets”
Medulloblastoma characteristically spreads through CSF pathways, leading to spinal “drop metastases.”
USMLE clue: back pain, neurologic deficits, or imaging showing spinal seeding in a child with posterior fossa tumor.
Rapid differential: medulloblastoma vs other posterior fossa tumors
| Tumor | Age | Location | Key clue |
|---|---|---|---|
| Medulloblastoma | Children | Midline vermis | CSF seeding (“drop mets”), Homer Wright rosettes |
| Pilocytic astrocytoma | Children | Cerebellar hemispheres | Cystic with mural nodule, Rosenthal fibers |
| Ependymoma | Children | 4th ventricle | Can extend through foramina (Luschka/Magendie); perivascular pseudorosettes |
Exam-day “if you see this, think medulloblastoma”
- Child + posterior fossa mass + hydrocephalus symptoms
- Midline cerebellar vermis
- Small round blue cells / Homer Wright rosettes
- CSF seeding / drop metastases