Magnetic resonance imaging defines structural brain injury acquired during critical illness

Introduction

Patients with non-neurological critical illness commonly develop cerebral dysfunction, which may take the form of delirium, coma, and long-term cognitive impairment. Delirium in the ICU is associated with increased mortality and prolonged mechanical ventilation and hospital stay, and is commonly attributed to metabolic derangements. Tests such as brain computed tomography (CT) and cerebrospinal fluid analysis are frequently nondiagnostic. We hypothesized that brain magnetic resonance imaging (MRI) is a valuable tool in the diagnosis of delirium and coma acquired in the ICU.

Methods

Patients who underwent brain MRI for the evaluation of delirium or coma while in the adult medical or surgical ICUs were identified through an institutional database. Subjects with brain disorders diagnosed before their admission to the ICU and those admitted to the neurological ICU were excluded. Patients were classified into two groups according to whether or not MRI identified an acute pathological process.

Results

Over a 2-year period, 158 critically ill patients underwent brain MRI, among whom 96 were being evaluated for unexplained delirium or coma. In this group, MRI revealed an acutely evolving structural abnormality in 45 patients (47%), including cerebral infarction in 33, intracerebral hemorrhage in seven, posterior reversible leukoencephalopathy in three, and meningitis in two. Demographic characteristics, admission diagnoses, SAPS II, cardiovascular risk factors, and prevalence of sepsis, acute lung injury, acute renal failure, and acute hepatic failure were not significantly different between patients with and without acute changes on MRI. The ICU length of stay and mortality were also the same in both groups. MRI results led to a modification in presumptive diagnosis in 46 patients (48%), and altered the management plan in 17 (18%). No adverse events were noted in relation to MRI and patient transfer to the radiology suite. When compared with MRI, the sensitivity, specificity, positive predictive value and negative predictive value of CT for detecting acute cerebral changes were 44%, 57%, 42% and 48%, respectively.

Conclusion

In ICU patients with delirium or coma, brain MRI reveals an underlying acute structural abnormality in nearly one-half of cases, while the diagnostic impact of CT appears more limited. Occult brain injury may contribute significantly to the pathogenesis of cerebral dysfunction acquired during critical illness.