What are the most common posterior‑fossa brain tumors in children?

Most Common Posterior Fossa Brain Tumors in Children

The most common posterior fossa tumors in children are medulloblastoma (accounting for 10-20% of all pediatric brain tumors), pilocytic astrocytoma, and ependymoma, with medulloblastoma being the single most frequent malignant posterior fossa tumor in the pediatric population 1.

Primary Tumor Types

Medulloblastoma

• Most common malignant posterior fossa tumor in children with an incidence of 0.47 per 100,000 children aged 0-14 years 1
• Predominantly located in the cerebellum, typically appearing as a large heterogeneous posterior fossa mass occupying either the fourth ventricle or cerebellar hemisphere 1
• Comprises four distinct molecular subtypes with vastly different prognoses 1:
  • WNT-activated tumors (10% of cases): Most common in children aged 7-14 years with excellent prognosis (>90% long-term survival)
  • SHH-activated tumors (10-20% of cases): Prognosis depends on TP53 mutation status
  • Group 3 tumors (25-35% of cases): Poor prognosis with 5-year survival rates of 20-30%
  • Group 4 tumors (25-35% of cases): Better prognosis with overall survival rates of 75-90%

Pilocytic Astrocytoma

• Second most common posterior fossa tumor in children 2, 3
• Typically located in the cerebellar hemispheres
• Generally has a favorable prognosis compared to other posterior fossa malignancies

Ependymoma

• Third most common posterior fossa tumor 2, 3, 4
• Often arises from the fourth ventricle
• Requires molecular characterization for optimal treatment planning

Other Important Posterior Fossa Tumors

Additional tumors that occur less frequently but require consideration include 2, 3:

• Atypical teratoid/rhabdoid tumors (ATRT): Highly aggressive, more common in very young children
• Diffuse midline gliomas: Poor prognosis, often involving the brainstem
• Brainstem gliomas: Location-specific challenges for surgical management

Clinical Context

Posterior fossa tumors account for 45-60% of all pediatric brain tumors 5, despite the posterior fossa representing only 10% of intracranial volume. This concentration makes them the predominant location for pediatric CNS malignancies, contrasting sharply with adults where supratentorial tumors predominate 2.

The most common anatomical locations within the posterior fossa are 4:

1. Cerebellar vermis (most common)
2. Cerebellar hemispheres
3. Fourth ventricle
4. Brainstem

Key Diagnostic Considerations

Peak incidence occurs in the first decade of life 4, with presenting symptoms typically including:

• Raised intracranial pressure
• Headache and vomiting
• Cerebellar signs

Molecular classification has become essential for accurate diagnosis, risk stratification, and treatment planning, particularly for medulloblastoma where molecular subtype dramatically impacts both treatment approach and prognosis 1.