Brain and cerebrospinal fluid 3D center of mass shift after spaceflight.

A subset of long-duration spaceflight astronauts at the International Space Station has been documented to develop spaceflight associated neuro-ocular syndrome (SANS). Researchers have sought to understand SANS by quantification of ocular and brain structural changes thought to be associated with weightlessness induced headward fluid shift. Brain tissue shift and cerebrospinal fluid (CSF) redistribution has been observed as measured by MRI on return to Earth, and not fully quantified. To improve the understanding of this phenomenon, we developed and applied automated methods to quantify 3D center of mass shift within the skull of the extra-axial cerebrospinal fluid (eaCSF) and brain after long-duration spaceflight in astronauts (N = 13) and controls not exposed to microgravity (N = 10). 3D center of mass shift of brain tissue and CSF was computed based on registration of an individual skull segmentation at a baseline timepoint versus follow-up. 3D center of mass shift was quantified in the Gx, Gy, and Gz axis defined as -posterior/+anterior, -left/+right, -inferior/+superior, respectively. For astronauts, average MRI follow-up time pre- to post-flight was 697 ± 137 days (average flight duration = 179 ± 59 days with post-flight MRIs collected an average of 2.23 ± 1.64 days after return to Earth). For controls, average MRI follow-up time was 307 ± 19 days. For astronauts, a superior Gz shift in whole brain was present (+ 0.74 ± 0.28 mm, p < 0.0001) with a concomitant inferior Gz shift in eaCSF (-2.45 ± 0.99 mm, p < 0.0001). In the control cohort, brain tissue Gz shift (-0.082 ± 0.048 mm) and eaCSF Gz shift (0.096 ± 0.26 mm) were not statistically significant. Gy shift lacked significance in both controls and astronauts. These findings support that sustained exposure to weightlessness impacts the overall position of fluids and tissues within the skull.