Medulloblastoma is the most common malignant posterior fossa tumor in children and the second most common of all pediatric central nervous system cancers (about 20% of the total). It has a bimodal peak at age 3 to 4 years and at age 8 to 10 years but can occur throughout childhood. Medulloblastoma is a type of primitive neuroectodermal tumor (PNET).
Etiology of medulloblastoma is unknown in most patients, but medulloblastoma may occur with certain syndromes (eg, Gorlin syndrome, Turcot syndrome).
MRI with gadolinium contrast is the test of choice for initial evaluation of possible medulloblastoma. Definitive diagnosis is made using tumor tissue obtained by biopsy or ideally by gross total resection of the tumor at initial presentation.
Once the initial diagnosis is established, staging and risk group determination are critical in medulloblastoma.
Staging tests include
Risk assessment is based on amount of residual tumor, and evidence of spread of disease:
Molecular subgrouping is also part of the diagnostic evaluation, and treatments are evolving based on these subgroups. The major molecular subgroups for medulloblastoma are WNT, SHH, group 3, and group 4.
Prognosis depends on the stage, on the histologic, cytogenetic, and molecular parameters of the tumor, and on patient age but generally
Age > 3 years: Likelihood of 5-year disease-free survival is 50 to 60% if the tumor is high risk and 80% if the tumor is average risk.
Age ≤ 3 years: Prognosis is more problematic, in part because up to 40% of children have disseminated disease at diagnosis. Children who survive are at risk of severe long-term neurocognitive deficits (eg, in memory, verbal learning, and executive function).
Molecular subgroup WNT has the best prognosis with 90 to 100% overall survival. Ongoing pediatric clinical trials are being done to determine whether therapy can be reduced in these patients.
Treatment of medulloblastoma includes surgery, radiation, and chemotherapy. Cure with chemotherapy alone has been shown in some children < 3 years of age. Autologous hematopoietic stem cell transplantation may also be used to treat certain patients. Combination therapy typically provides the best long-term survival.