Medulloblastoma

Medulloblastoma is the most common malignant pediatric brain tumor. These tumors respond well to modern treatments when managed by an experienced team. Treatment typically involves surgery followed by radiation and chemotherapy. The molecular characteristics of the tumor are essential for determining the specific care plan.

What Is Medulloblastoma?

Medulloblastoma is a fast-growing tumor that starts in the cerebellum — the part of the brain that controls balance, coordination and fine movement. It's the most common malignant brain tumor in children, making up about 20% of pediatric brain cancers. It peaks between ages 3 and 8 but can appear in infants, teenagers, and adults.

Because of where it grows, medulloblastoma often blocks the normal circulation of cerebrospinal fluid, causing pressure to build up inside the skull. It can also shed cells into the spinal fluid, which is why treatment has to cover the entire central nervous system.

At a Glance

Medulloblastoma is the most common malignant brain tumor in children and also occurs, more rarely, in adults
It grows in the cerebellum and often blocks the flow of spinal fluid, causing headaches and vomiting
Treatment almost always involves surgery, craniospinal radiation and several months of chemotherapy
Modern pathology divides medulloblastoma into four molecular subgroups — WNT, SHH, Group 3, and Group 4
With modern risk-adapted therapy, more than 80% of children with average-risk disease are alive and disease-free five years after diagnosis

Symptoms

Signs of rising pressure

Morning headaches that improve after getting up
Vomiting, especially first thing in the morning
Unusual sleepiness or fatigue

Signs the cerebellum is affected

Clumsiness or a wide, unsteady walk
Trouble with handwriting, reaching for objects, or climbing stairs
Slurred or jerky speech; uncontrolled eye movements (nystagmus)

Signs of brainstem involvement

Double vision or a new eye turn
Trouble swallowing or a weak voice

Diagnosis

MRI of the brain with contrast

Typically shows a bright mass in the middle of the cerebellum, often pushing on or filling the fourth ventricle. MRI of the entire spine also required for staging.

Spinal fluid sampling

Lumbar puncture done 10-14 days after surgery to check whether tumor cells have spread into the CSF.

Pathology and molecular testing

Every medulloblastoma is assigned to one of four molecular subgroups — WNT, SHH, Group 3, or Group 4 — using DNA methylation arrays, targeted sequencing, and immunohistochemistry. Risk classification (average-risk vs high-risk) drives treatment intensity.

Types

WNT-activated (~10% of cases)

Excellent prognosis — >95% of patients are cured with standard therapy. Current trials testing whether therapy can be safely reduced.

SHH-activated (~30% of cases)

Outlook depends on TP53 status. TP53 wild-type: ~80% five-year survival. TP53-mutant: ~40% five-year survival.

Group 3 (~25% of cases)

Most aggressive subgroup. Mostly infants and young children. MYC-amplified Group 3 has historically the worst outcomes. Five-year survival ~40-60%.

Group 4 (~35% of cases)

Most common subgroup. Intermediate prognosis — roughly 75% five-year survival overall.

Treatment

Surgery first — maximal safe resection

Goal is maximal safe resection — stopping short of chasing small amounts of tumor stuck to the brainstem. A landmark 2016 analysis showed survival difference between gross total and near-total resection disappears once molecular subgroup is accounted for.

Cerebellar mutism syndrome

Happens to about 1 in 4 children after medulloblastoma surgery. Children can suddenly stop speaking, become emotionally fragile, and develop difficulty swallowing. Speech usually returns over weeks to months.

Radiation therapy

Craniospinal irradiation to entire brain and spine. Average-risk: 23.4 Gy; high-risk: 36 Gy, with tumor-bed boost to ~54 Gy. Proton beam therapy preferred for children when available.

Chemotherapy

About 9-12 months of chemotherapy after radiation. Standard backbone: cisplatin, lomustine (CCNU) or cyclophosphamide, and vincristine (based on COG trial A9961).

For infants under 3

Goal is to delay or avoid radiation to protect the developing brain — intensive chemotherapy with stem-cell rescue.

Outcomes

Subgroup / Risk	5-Year EFS	5-Year OS	What to Know
WNT-activated	~90%	~95%	Excellent; trials now testing reduced therapy
SHH, TP53 wild-type	~75%	~80%	Favorable
SHH, TP53-mutant	~30%	~40%	Aggressive; intensified therapy often needed
Group 3 (non-MYC-amplified)	~60%	~70%	Intermediate outlook
Group 3, MYC-amplified	~30%	~40%	Highest-risk subgroup
Group 4	~75%	~80%	Intermediate; metastatic cases fare worse
Average-risk (overall)	~83%	~87%	From SJMB03 and A9961 trials

Long-term side effects (hearing loss, hormone deficiencies, cognitive changes) are a major focus of modern trials, which aim to reduce therapy for favorable subgroups.

References

Louis DN, et al. The 2021 WHO Classification of Tumors of the Central Nervous System. Neuro-Oncology. 2021;23(8):1231-1251. PMID: 34185076
Taylor MD, et al. Molecular subgroups of medulloblastoma: the current consensus. Acta Neuropathologica. 2012;123(4):465-472. PMID: 22134537
Gajjar A, et al. Outcomes by clinical and molecular features in children with medulloblastoma (SJMB03). J Clin Oncol. 2021;39(7):822-835. PMID: 33405951
Thompson EM, et al. Prognostic value of medulloblastoma extent of resection after accounting for molecular subgroup. Lancet Oncol. 2016;17(4):484-495. PMID: 26976201
Yock TI, et al. Long-term toxic effects of proton radiotherapy for paediatric medulloblastoma. Lancet Oncol. 2016;17(3):287-298. PMID: 26830377
Robertson PL, et al. Incidence and severity of postoperative cerebellar mutism syndrome. J Neurosurg. 2006;105(6 Suppl):444-451. PMID: 17184075

Our Specialists

Arthur DiPatri, MD

Pediatric Neurosurgery

Bakhtiar Yamini, MD

Neurosurgery

Peter Warnke, MD

Neurosurgery

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