Anatomical MRI abnormalities in bipolar disorder: do they exist and do they progress?

Aim: Morphometric brain imaging studies have revealed regional brain abnormalities in patients with bipolar disorder, which may play a role in illness pathophysiology. It is not known whether such changes are of neurodevelopmental, neurodegenerative, or combined origin. We reviewed the anatomical brain imaging literature in bipolar disorder, in an attempt to determine whether there is evidence to suggest that such abnormalities are progressive. Method: Literature searches were conducted using MEDLINE for the period from 1966 to June 2004, using specific key words; bipolar disorder and the names of the individual brain structures. Papers were selected according to their salience in relation to whether reported changes are progressive. Results: Available findings suggest reduced grey matter in prefrontal brain regions such as anterior cingulate and subgenual prefrontal cortex, and abnormalities in amygdala size in adult and paediatric bipolar patients. White matter hyperintensities, which are non-specific abnormalities, are also common in bipolar patients. Bipolar patients may lose more brain grey matter by ageing. There is also evidence for impaired myelination of the corpus callosum in bipolar disorder. Lithium may reverse or prevent grey matter prefrontal cortex abnormalities in bipolar patients by its neuroprotective effects. Conclusions: Both early developmental and later neurodegenerative processes may play a role in the pathophysiology of bipolar disorder. Findings from anatomical brain imaging studies implicate key regions involved in mood regulation. The evidence for the progressive nature of this illness is tentative, as no follow-up study with bipolar patients has been reported to this date.