Neuroimaging of delirium

Neuroimaging is routinely used in the investigation of delirium in clinical practice as a means of detecting primary central nervous system causes, for example, stroke and tumors. Yet there are very few studies which can inform the clinician which patients should undergo imaging. Neuroimaging has also been used in a small number of studies as a research tool to help improve understanding of the predisposing factors, acute mechanisms, and consequences of delirium. Currently there are fewer than 20 studies which have explicitly sought to study delirium with neuroimaging. This lack likely reflects the practical and ethical challenges involved in imaging in patients with active delirium. Additionally, to measure change resulting from delirium, or to assess putative neuroimaging predictors of delirium, longitudinal studies incorporating analysis of pre-delirium abnormalities are required. Such studies are costly and challenging and to date have involved recruiting patients undergoing high-risk elective surgery. The currently available research literature has yielded a mixed set of results. Although there are no truly definitive studies, it appears that vascular pathology, as indicated by lacunar infarcts and other white matter lesions, is the finding most consistently found in delirium. This pathology may be important through its role in disrupting fronto-subcortical attentional networks. Some structural studies also suggest an association between various markers of cerebral atrophy and delirium, but no specific brain regions have reliably been implicated. Functional neuroimaging studies of delirium have shown some abnormalities, but the evidence base is not large enough to draw conclusions on which brain areas or systems may be involved. The wider neuroimaging literature provides an extensive array of promising avenues for delirium research. Multiple parameters indicating the volume, integrity, and biochemistry of gray and white matter are now available. There is also scope for more studies on the effective use of neuroimaging in investigating delirium in the clinical setting. This is important in terms of rational use of resources – an important issue given that one in eight hospital inpatients develop delirium, and many undergo neuroimaging as part of their diagnostic work-up. There may also be value in evaluating the clinical value of certain more advanced techniques, such as diffusion tensor imaging, in determining acute causes of delirium. In summary, the field of the neuroimaging of delirium is at a very early stage, but the existing evidence base provides useful early indications of the large potential of neuroimaging to improve our understanding of delirium and also to care for patients more effectively.