The amygdala has gained special interest regarding the neuropathology of bipolar disorder (BD). Structural magnetic resonance imaging (MRI) studies with patients suffering from BD have yielded quite inconsistent results with respect to amygdala volume. We performed a meta-analysis of structural MRI studies that investigated right and left amygdala volume in pediatric and adult patients with BD. The aim was to assess the heterogeneous findings and to investigate whether a correlation between amygdala volume and the patient's age exists. Studies were searched for in "Pub Med" (last search June 2007), and data for right and left amygdala volume in cm(3) were extracted and combined in a meta-analysis. Thirteen studies with 389 scans of patients and 488 scans of healthy control subjects (HC) were included. The impact of age on the difference in amygdala volume between patients and HC was assessed by meta-regression. The amygdala volume was bilaterally reduced in the overall sample of patients with BD and the pediatric subsample. The results of the adult studies were less homogeneous, and on average, no significant difference between adult patients and HC was found. A meta-regression analysis revealed a positive correlation between mean age and amygdala volume in patients with BD. We speculate that amygdala volume is reduced at the onset of the disease and increases with age.
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