Longitudinal MRI reveals adolescent pituitary growth patterns linked to puberty and environmental exposures.

Puberty is a period of profound behavioral reorganization that recalibrates social motivation, risk-taking, and sexual behavior in ways that shape lifelong human health. Yet its characterization in population-based studies relies largely on self-report, which reflects perceived physical changes rather than the neuroendocrine substrates driving the transition. The pituitary gland sits at the center of this reorganization, coordinating hypothalamic-pituitary axes that orchestrate puberty. Leveraging 11,818 adolescents (ABCD Study; 30,276 MRI observations), we show that pituitary volume is a precise, scalable marker of pubertal progression carrying non-redundant information beyond chronological age, salivary hormones, and self-reported stage. Sex-specific non-linear trajectories, accelerated expansion anchored to menarche, and distinct patterns across menarche timing subgroups capture both the timing and tempo of puberty at population scale. Pituitary volume was further associated with ACEs and decreased within-person growth following hormonal contraception initiation, positioning it as a sensitive index of the biological embedding of exogenous exposures known to influence pubertal maturation.