Decreased pituitary volume in patients with bipolar disorder

Background: Neuroendocrinologic investigations in bipolar disorder have suggested abnormalities in pituitary function. However, few imaging studies have evaluated possible anatomical differences in this brain structure in mood disorder patients. Our aim was to examine potential abnormalities in pituitary volume in patients with bipolar and in a comparison group of patients with unipolar disorder. Methods: We measured the volumes of the pituitary gland in 23 patients with bipolar disorder (mean ± s.d. = 34.3 ± 9.9 years) and 13 patients with unipolar disorder (41.2 ± 9.6 years), and 34 healthy control subjects (36.6 ± 9.6 years) using 1.5 mm thick T1-weighted coronal 1.5 T MRI images. All measurements were done blindly by a trained rater. Results: Patients with bipolar disorder had significantly smaller pituitary volumes than healthy control subjects (mean volume ± s.d. = 0.55 ± 0.15 ml and 0.68 ± 0.20 ml, respectively; ANCOVA, F = 8.66, p = 0.005), and than patients with unipolar disorder (0.70 ± 0.12 ml, F = 5.98, p = 0.02). No differences were found between patients with unipolar disorder and healthy control subjects (F = 0.01, p = 0.91). Conclusions: To our knowledge, this is the first study that reports smaller pituitary volumes in bipolar disorder. Our findings suggest that detectable abnormalities in pituitary size are present in patients with bipolar disorder, which may reflect a dysfunctional HPA axis.