Eighteen children previously treated surgically and with craniospinal irradiation for medulloblastoma (MED), and matched with a group having low-grade posterior fossa tumors with surgery alone, received neuropsychological testing and quantitative magnetic resonance imaging for white matter loss at St Jude Children’s Research Hospital, Memphis, TN. Normal white matter (NWM) volume and Full Scale IQ values were significantly lower among survivors of MED compared to controls. Irradiation (with or without chemotherapy)-induced destruction of NWM may explain the intellectual and academic deficits associated with MED survival. 
COMMENT. A lowered IQ in children treated for medulloblastoma is correlated with a loss of normal cerebral white matter. Diffuse and multifocal white matter hyperintensities demonstrated on MRI, and calcifications in cortical gray matter and basal ganglia have been correlated with the dose of cranial radiation therapy (CRT).
Younger patients and those receiving standard dose CRT are at greater risk of cognitive deficits than older children or those receiving reduced dose CRT . If dose of CRT cannot be lowered and white matter cannot be protected during irradiation treatment, children surviving MED should receive early cognitive intervention therapy.
Packer RJ in a review article, “Childhood medulloblastoma: progress and future challenges“  comments that recent treatment trials have attempted to reduce the amount of craniospinal radiation therapy. In older children, the outcome may be good following reduced-dose CRT with adjuvant chemotherapy. For children with poor risk, intensification of chemotherapy during and after CRT is being explored. Treatment of infants and young children with MED remains a problem.