444 Quantitative Mapping of Cerebral Blood Flow and Blood-Brain Barrier Water Exchange Rate (Kw) Reveals the Mechanobiological Impact of Cranioplasty: A Magnetic Resonance Imaging Study of Patients With Cranial Defects

Abstract

INTRODUCTION: Large cranial defects may cause neurological decline due to brain shift, while cranioplasty may improve cognitive function, although the underlying mechanisms remain poorly understood. Blood-brain barrier (BBB) water exchange rate (Kw) is a novel magnetic resonance imaging (MRI) method which provides insights into the processes underlying the effects of cranioplasty. METHODS: Adult patients with cranial defects who were candidates for elective cranioplasty were consented and enrolled. Using a 3T MRI, we conducted baseline imaging on all patients, and repeated the imaging during the early post-cranioplasty period. The Kw and CBF were quantified, and asymmetry was calculated as the difference between the values on the ipsilateral and contralateral hemispheres relative to the cranial defect, divided by the sum of those values. Pairwise comparisons of the changes from baseline to post-cranioplasty period were performed using Wilcoxon signed-rank test. RESULTS: A total of 10 patients were enrolled (mean age: 35.4 ± 9.49, 9/10 men). The global CBF showed significant improvements after cranioplasty. There was a remarkable Kw asymmetry in the caudate area at baseline (low on defect side), which significantly improved post-operatively (median: -0.077 vs. 0.021, p = 0.049), while the changes in CBF in this area were not significant (median: -0.002 vs. 0.014, p = 0.160). Other brain regions yielded no significant changes in Kw asymmetry. CONCLUSIONS: Reduced Kw has been reported in cognitive decline and cerebral small vessel diseases, and may be related to impaired water circulation in the brain. We observed increased global CBF and Kw asymmetry in caudate which may reflect improved brain physiology and water circulation following cranioplasty. Kw is a non-invasive and non-contrast method that offers an opportunity to understand the intricate changes in brain homeostasis following reconstruction surgery.