White matter abnormalities as a risk factor for postoperative delirium revealed by diffusion tensor imaging.

OBJECTIVE: Delirium is a common and critical clinical syndrome in older persons. The authors examined whether any abnormalities in the white matter (WM) assessed by diffusion tensor imaging (DTI) predisposes patients to develop delirium after cardiac surgery and also analyzed other risk factors for delirium.
METHOD: In 116 consecutive patients who underwent scheduled cardiac operations, fractional anisotropy (FA) values obtained by DTI before the surgery and pre-, peri-, and postoperative factors were evaluated. The postoperative delirium was diagnosed according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, criteria for delirium.
RESULTS: Delirium developed in 19 of 116 patients (16.4%). Eighteen of the patients with delirium (94.7%) were older than 60 years. A multivariate logistic regression analysis showed that advanced age and poor performance on a semantic fluency task (the Word Fluency test animal) were important predictive indicators of the delirium. In addition, a voxel-by-voxel analysis using the Statistical Parametrical Mapping 2 revealed that the FA values of the patients with postoperative delirium were significantly lower than those of the nondelirium patients in the bilaterally widespread deep WMs and bilateral thalamus, whereas the analysis treating age as a nuisance variable indicated a significant change in only four clusters of the brain areas, e.g., the left frontal lobe WM, and left thalamus, when compared with the nondelirium group.
CONCLUSION: The abnormalities in the deep WMs and thalamus that were mainly accelerated by aging may account for the vulnerability to postoperative delirium, and the semantic word fluency could be a useful predictive indicator of delirium.