| Unipolar depression is a common, debilitating mental illness affecting more than 12% of Canadians. The hippocampus appears to be a key structure in the pathogenesis of depression and has received much attention. Despite the number of magnetic resonance imaging (MRI) studies that have examined structural abnormalities in the hippocampus with relation to unipolar depression findings are inconclusive. Evidence derived from previous studies indicates that the hippocampus is divided into functionally and anatomically distinct regions. Using an adapted MRI volumetric approach, total as well as subregional potential volume abnormalities of the hippocampus were studied in young female patients. No evidence for total hippocampal or subregional abnormalities was found. Factors that may contribute to these findings include the relatively young ages of the patients, possible 'protective' effects of antidepressant medications, circulating hormone levels such as estrogens, lack of stressors during development and in adulthood, including childhood trauma, or comorbid disorders, respectively. The present study supports the 'combined insults hypothesis' that proposes that cumulative effects of several insults together can contribute to MRI-detectable hippocampal abnormalities. To address the question of whether hippocampal structural abnormalities may represent a risk factor for developing the disorder, a consequence of the disorder, or perhaps a way of contributing to differential diagnosis of subtypes of depression, there is a need for further studies with more homogeneous patient populations. |
