The relationship between T2 weighted MRI images (T2H) and cognitive functioning in a cohort of 76 children with neurofibromatosis type 1 (NF1) was determined in a study at Children's Hospital at Westmead, University of Sydney, Australia. Patients ranged in age from 8.0 to 16.75 (mean 11.63). NF1 was sporadic in 61% and familial in 39%. One-half were macrocephalic. Ninety percent had T2H, and 71% had discrete T2H lesions. Those with T2H lesions were slightly younger than those without (11.4 vs 13.3 yrs; p=0.029), and a greater number of T2H were found in younger children. Discrete lesions were usually located in the basal ganglia and cerebral hemispheres, whereas diffuse lesions involved the thalamus, cerebellum and brainstem. T2H in general were not associated with cognitive dysfunction, specific learning disabilities or ADHD, but patients with discrete thalamic lesions showed lower levels of cognitive functioning than those without lesions or with lesions elsewhere (Full scale IQ 72.8 vs 91.4). Thalamic lesions were also associated with lower performance on Verbal IQ, Performance IQ, Processing Speed Index, spelling, sustained attention, fine motor coordination, and motor speed. More diffuse lesions in the thalamus were also associated with reductions in IQ but less marked than those with discrete lesions. 
COMMENT. Thalamic lesions, particularly when discrete, are associated with cognitive impairment in children with NF1. Previous studies have shown that high-signal MRI lesions in NF1 evolve over time. They either increase or decrease in size or number, dependent on their location. Lesions in the thalamus, brainstem and cerebellar peduncles expand whereas those in cerebral hemispheres and cerebellum regress. Surgery or radiotherapy was required for mass lesions in 3 patients followed for a mean time of 2 to 3 years.