Prospective investigation of the neural risk factors for postoperative delirium using magnetic resonance imaging

Abstract

Delirium is an acute confusional state that is characterized by sudden alteration and fluctuation in consciousness and cognition associated with impaired attention. Delirium frequently occurs after surgery, particularly in patients undergoing hip fracture, however, the underlying neural mechanism remains uncertain. The present study aimed to investigate predictive neural correlates of postoperative delirium. Before surgery, patients with hip fracture were assessed for cognitive impairment and scanned using magnetic resonance imaging. After surgery, they were evaluated for postoperative delirium for 7 successive days and additional functional scans were performed on postoperative delirium onset or the end of assessment day according to postoperative delirium occurrence. Then anatomical and functional data were analyzed with voxel based morphometry, diffusion tensor imaging, and functional connectivity analysis. Patients with postoperative delirium had bigger total intracranial volume and ventricle volume, and smaller volume in the medial frontal gyrus, cingulate/precuneus, superior and transverse temporal gyrus, and caudate nucleus. These changes of brain areas were similar with Alzheimer's disease. In particular, the frontal areas, temporal areas, and caudate nucleus were more associated with MMSE scores. Patients with postoperative delirium also showed broadly reduced fractional anisotropy across the brain, including the superior and longitudinal fasciculus, corpus callosum, and external capsule. In functional connectivity, patients on delirious state showed greater association in the caudate nucleus and insula with the superior and transverse temporal regions, and there were negative correlations between Korean-Delirium Rating Scale and connectivity strength of the superior temporal gyrus and inferior frontal gyrus (r = -0.672, p = 0.048), and connectivity strength of the caudate nucleus and inferior frontal gyrus (r = -0.633, p = 0.067), respectively. This study suggests that cortical atrophy, particularly in the temporal areas and caudate nucleus, and overall impairment of cortical connections may be involved in postoperative delirium occurrence; nevertheless, increased connectivity of the bilateral temporal brain regions with the thalamo-cortical brain regions on delirious state could be interpreted as efforts to prevent persistent postoperative delirium and promote restoration of altered consciousness.