In summary, male adolescents, as a group, have larger brain volumes than females. The longitudinal data show that adolescent males reach their peak volumes later than females, such that volumes become increasingly divergent as males and females reach adulthood, particularly for WM. Assessing regional differences is complicated by the observation that scaling with increased volume is not necessarily linear, leading to regional differences that could be attributable to variations in brain size alone (Im et al., 2007b; Leonard et al., 2008). The complexities of comparing brain measurements in cross-sectional data across development are highlighted by findings in the hippocampus and the corpus callosum, in which studies done at different ages have found different patterns of sex differences (Giedd et al., 1997; Lenroot et al., 2007; Suzuki et al., 2005). If brain regions are growing at different rates, the size or even direction of the difference between them could depend on the age at which measurements are made.
