Medial temporal lobe abnormalities in pediatric unipolar depression

In vivo anatomical magnetic resonance imaging (MRI) studies in adults with major depressive disorder (MDD) have implicated neurocircuitries involved in mood regulation in the pathophysiology of mood disorders. Specifically, abnormalities in the medial temporal lobe structures have been reported. This study examined a sample of children and adolescents with major depressive disorder to investigate anatomical abnormalities in these key medial temporal brain regions. Nineteen children and adolescents with DSM-IV major depression (mean age ± S.D. = 13.0 ± 2.4 years; 10 unmedicated) and 24 healthy comparison subjects (mean age ± S.D. = 13.9 ± 2.9 years) were studied using a 1.5 T Philips MRI scanner. We measured hippocampus and amygdala gray matter volumes. MRI structural volumes were compared using analysis of covariance with age and total brain volumes as covariates. Pediatric depressed patients had significantly smaller left hippocampal gray matter volumes compared to healthy controls (1.89 ± 0.16 cm³ versus 1.99 ± 0.18 cm³, respectively; F = 5.0, d.f. = 1/39, p = 0.03; effect size: η_p² = 0.11). Unmedicated depressed patients showed a trend towards smaller left hippocampal volumes compared to medicated patients and healthy subjects (F = 2.8, d.f. = 2/38, p = 0.07; effect size: η_p² = 0.13). There were no statistically significant differences in mean volumes for left or right amygdala. Smaller left hippocampal volumes in children and adolescents with MDD are in agreement with findings from adult studies and suggest that such abnormalities are present early in the course of the illness. Amygdala volumes are not abnormal in this age group. Smaller hippocampal volumes may be related to an abnormal developmental process or HPA axis dysfunction.