Reply to Liu et al.: Visualization of cerebral perivascular spaces following administration of intrathecal contrast

We read Haitao Liu and collaborators' letter to the PNAS editor ( 1 ) regarding our paper "The perivascular space is a conduit for cerebrospinal fluid flow in humans: A proof-of-principle report."( 2 ) We offer the following clarifying points.First, the authors state that "it is unclear if [visualization of gadoliniumenhanced perivascular spaces] is specific to meningiomas.Thus, a larger sample size is needed for further experiments to confirm these results' reliability."We agree with the authors regarding the need for confirmatory studies using larger sample sizes and different disease mechanisms.Our initial study was a proof of concept using a convenience sample, given that intrathecal gadolinium injection is invasive.Second, the authors state, "it is important to investigate whether [visualization of contrast-enhanced perivascular spaces] occurs in patients with other diseases, particularly Alzheimer's disease" We agree with the authors regarding the need for further research investigating the effect of diseases such as Alzheimer's dementia on perivascular space flow.Last, the authors mention the importance of studying the relation between perivascular space flow and meningeal