Variation of the apparent diffusion coefficient of skull bone marrow by age group, pubertal status, and gender in a pediatric population.

Abstract

BACKGROUND: Bone marrow composition varies with stage of development. PURPOSE: To assess differences in apparent diffusion coefficient (ADC) derived from clivus bone marrow in healthy children by age, pubertal status, and gender as a benchmark when monitoring local and systemic treatment-induced effects. MATERIAL AND METHODS: Non-oncological pediatric patients (30 pre-pubertal [15 girls, 15 boys] and 30 post-pubertal [15 girls, 15 boys]) with previous normal magnetic resonance imaging (MRI) of the brain including diffusion-weighted magnetic resonance imaging (DW-MRI; 1.5-T Philips Achieva-Ingenia, b-values 0 and 1000s/mm2) were studied. A 4-6 mm diameter region of interest (ROI), drawn within the clivus on two or three DW-MRI slices, yielded mean and centile ADC values. Pubertal status was recognized from imaging appearances of the pituitary gland and from fusion of the spheno-occipital synchondrosis. Correlations between ADC and age were assessed (Pearson's coefficient). Mann-Whitney U tests compared ADC by age, pubertal status, and gender. RESULTS: Age and ADC were significantly negatively correlated (median ADC r=-0.48, mean ADC r=-0.42, P=0.0001 and 0.0008, respectively) which held true when divided by gender. Mean and median ADC differed significantly before and after puberty for the whole population (P=0.0001 and 0.0001, respectively). There was a left shift of the ADC histogram after puberty with significant differences in centile values. ADC differences before and after puberty remained when divided by gender (girls: P=0.04 and 0.009, respectively; boys: P=0.005 and 0.0002, respectively). CONCLUSION: ADC of clivus bone marrow correlates with age in children. ADC decreases significantly after puberty, likely due to replacement of hypercellular marrow with fat. There are no gender-related differences in clivus bone-marrow ADC before or after puberty.