Background: Major depression is common after epilepsy surgery. It has previously been suggested that surgical removal of limbic system structures such as the hippocampus may contribute to this co-morbidity. Recent magnetic resonance imaging studies have found smaller hippocampal volumes in depressed patients in comparison to controls.
Aims: The current study examined whether pre-operative hippocampal volumes were associated depression experienced after epilepsy surgery. Patients undergoing mesial (n=26) and non-mesial (n=16) temporal lobe resections were assessed pre-operatively, and for one year post-operatively. Assessment included a clinical interview and the Beck Depression Inventory (BDI-II). Hippocampal volumes were measured on the pre-operative T1-weighted magnetic resonance imaging scans of the patients and 41 neurologically normal controls.
Results: A similar proportion of mesial and non-mesial temporal patients had a pre-operative history of major depression. Post-operatively, 42% of mesial and 19% of non-mesial temporal patients were depressed. There was no relationship between hippocampal volume and pre-operative depression in either group. Depression after surgery was associated with significantly smaller hippocampal volumes contralateral to the resection in the mesial temporal group (p=0.005). This effect was seen in mesial temporal patients who developed de novo depression (p=0.006). Hippocampal volume was unrelated to post-operative depression in the non-mesial group.
Conclusion: This study highlights the role of neurobiological factors in the development of post-operative depression. These initial findings have implications for understanding depression following epilepsy surgery as well as the pathogenesis of depression more generally.