Medulloblastoma

Epidemiology
~400 cases per year in US (15 - 20% of childhood brain tumors)
Median age 6 years; seen rarely in adults
Unknown risk factors
Associated with Gorlin syndrome (AKA basal cell nevus syndrome; association with basal cell nevi, ulcerative colitis, multiple developmental abnormalities in addition to medullo)

Pathology
Small round blue cell tumor
Homer Wright rosettes

Clinical
Primarily seen in the posterior fossa (commonly in fourth ventricle and cerebellar vermis)
CSF seeding in about 1/3 of patients

Risk groups
Standard => All of: No CSF spread, less than 1.5cm2 of residual disease, older than three years
High risk => Either + CSF disease or resection leaving more than 1.5cm2 of residual tumor
Maximal resection is critical in both groups

Treatment, standard risk
23.4Gy CSI + concurrent vincristine
55.8Gy boost to residual disease --> adjuvant cisplatin/vincristine

Treatment, high risk
36Gy CSI + concurrent vincristine
55.8Gy boost to residual tumor --> adjuvant cisplatin/vincristine

Special cases of CNS-embryonal tumors
Supratentorial PNET: clinical outcomes worse than medulloblastoma but disease is treated similarly
Medulloblastoma in infants: use chemo to defer CSI
ATRT: histologically resembles PNET but behaves much more aggressively; pts typically younger
-Molecular findings are characteristic (del chr 22 or translocation involving INI1 gene on chr 22)