• bipolar disorder;
  • cerebellar vermis;
  • cerebellum;
  • sex difference;
  • structural MRI

Objectives:  The cerebellar vermis is increasingly implicated in bipolar disorder (BD). In this study, we investigated vermis morphology in BD using a quantitative volumetric analysis.

Methods:  Volumes for total vermis and vermis subregions V1 (lobules I–V), V2 (lobules VI–VII), and V3 (lobules VIII–X) were calculated using high-resolution structural magnetic resonance imaging obtained from 44 individuals with BD (25 females and 19 males) and 43 healthy comparison (HC) subjects (26 females and 17 males). Total vermis volumes were compared between the BD and HC groups. Potential effects of vermis subregions and clinical features were explored.

Results:  Total vermis volumes were significantly larger in the BD group than in the HC group (p = 0.02). There was a significant group-by-sex interaction (p = 0.02). Total vermis volumes were significantly larger in males with BD than HC males (p = 0.004); vermis volumes did not differ significantly between females with and without BD (p = 0.95). Subregion analyses showed a trend-level interaction between diagnosis and subregion (p = 0.07) in which subregion V1 volumes were significantly larger in BD participants (p = 0.001), with differences primarily driven by males (p = 0.001).

Conclusions:  Our findings demonstrate increases in cerebellar vermis volumes in males with BD. These findings support the presence of structural alterations in the cerebellar vermis in BD and furthermore the influence of sex on such changes.