MRI changes in the cerebellum and cognitive function of 13 survivors of childhood acute lymphoblastic leukemia (ALL) treated with cranial radiation of 24 Gy and intrathecal methotrexate were studied at the University of New Mexico, Albuquerque, Manitoba Cancer Foundation, Winnipeg, and University of Alberta, Edmonton. Age at diagnosis was a mean of 3 yrs 3 mos (range, 2 yrs - 4 yrs 10 mos), and age at testing was 11 yrs 8 mos (9 - 14 yrs). Hypoplasia of the cerebellar vermis and cognitive deficits involving visual-spatial-motor coordination and memory were observed in patients compared to controls. 
COMMENT. The neurotoxic effects of prophylactic cranial irradiation in children with acute lymphoblastic leukemia are well documented. As in this study, deficits in visual-motor skills and right brain involvement have been more pronounced than language and verbal deficits - evidence of left brain sparing. A causal relationship between the structural cerebellar abnormalities and the neuropsychological dysfunction is unproven. Children treated before 5 years of age are more susceptible to post-irradiation cognitive deficits than those diagnosed at or later than 5 years. Children in families of higher educational status who receive more attention and academic stimulation have a lower incidence of cognitive deficit than those with sensory-motor learning deprivation.
The dose of cranial irradiation, 2400 rads, used in this study is highly toxic in young patients. In the 1980s, most leukemia protocols limited the prophylactic dose to 1800 rads for use only in high risk patients. Reliance on intrathecal methotrexate chemotherapy for the majority of ALL patients is not known to result in significant intellectual or coordination deficits. (Personal communication: Dr David O. Walterhouse, Oncology Service, Children’s Memorial Hospital, Chicago).