Brain ventricular volume changes induced by long-duration spaceflight

Abstract

Long-duration spaceflight induces detrimental changes in human physiology. Its residual effects and mechanisms remain unclear. We prospectively investigated the changes in cerebrospinal fluid (CSF) volume of the brain ventricular regions in space crew by means of a region of interest analysis on structural brain scans. Cosmonaut MRI data were investigated preflight (n = 11), postflight (n = 11), and at long-term follow-up 7 mo after landing (n = 7). Post hoc analyses revealed a significant difference between preflight and postflight values for all supratentorial ventricular structures, i.e., lateral ventricle (mean % change ± SE = 13.3 ± 1.9), third ventricle (mean % change ± SE = 10.4 ± 1.1), and the total ventricular volume (mean % change ± SE = 11.6 ± 1.5) (all P < 0.0001), with higher volumes at postflight. At follow-up, these structures did not quite reach baseline levels, with still residual increases in volume for the lateral ventricle (mean % change ± SE = 7.7 ± 1.6; P = 0.0009), the third ventricle (mean % change ± SE = 4.7 ± 1.3; P = 0.0063), and the total ventricular volume (mean % change ± SE = 6.4 ± 1.3; P = 0.0008). This spatiotemporal pattern of CSF compartment enlargement and recovery points to a reduced CSF resorption in microgravity as the underlying cause. Our results warrant more detailed and longer longitudinal follow-up. The clinical impact of our findings on the long-term cosmonauts' health and their relation to ocular changes reported in space travelers requires further prospective studies.

Keywords: CSF; brain; microgravity; spaceflight; ventricles.

Fig. 1.

Percentage volume change for each ventricular CSF compartment, as well as total ventricular volume change given for comparisons postflight vs. preflight (dark colored bar) and follow-up vs. preflight (light colored bar). The percentage volume difference between the two time points for the controls is also given (diagonal stripes). The bar colors represent each ventricular ROI, as also indicated on the sagittal slice. A positive value indicates an increase in ventricular volume at postflight compared with preflight or at follow-up compared with preflight. A negative value indicates a decrease in ventricular volume at postflight compared with preflight or at follow-up compared with preflight. ***P < 0.0001 (Bonferroni-corrected) and *P < 0.017 (Bonferroni-corrected), from post hoc tests of the linear mixed model. Bars indicate SE.

Fig. 2.

Scatter plots showing the relationship between total relative brain ventricular volume change for preflight and postflight (in 11 cosmonauts) with respect to (A) mission duration (in days), (B) age at launch (in years), (C) previous space experience (in days), and (D) total intracranial volume (in milliliters). No significant correlations were found. Results in A, B, and C are blurred to guarantee anonymity of the cosmonauts, given the fact that most of the information is publicly available. The masking cloud follows the actual data distribution pattern, but is modified to disguise individual data points.

Fig. 3.

Scatter plots showing the relationship between (A) total and (B) lateral relative brain ventricular volume change for preflight and postflight (in 11 cosmonauts) with respect to visual acuity difference. No significant correlation was found for total ventricular volume difference and visual acuity difference, while a marginally significant correlation was found for lateral ventricular volume change and visual acuity difference for the left eye only.

Fig. 4.

Overview of the changes occurring in the subarachnoid and intracerebral CSF spaces [including the superior sagittal sinus (area 1) and the ventricles (area 2) of the cosmonauts across the different time points. (A−C) Schematic coronal visualization, taking together the current findings as well as an overview of previously described changes in previous studies of long-duration space travelers (6, 7). (D−F) Exemplary individual raw data on similar coronal slices, from which, especially, the ventricular enlargement is visible to the untrained, naked eye. (A and D) Baseline status, i.e., the preflight situation. (B and E) Postflight situation (on average, 9 d after returning to Earth). Cerebral ventricular enlargement, widening of the subarachnoid CSF space around the temporal and parietal lobes (7), and a compression of the superior sagittal sinus (6, 7) and a narrower longitudinal fissure can be noted. (C and F) Illustrations of the situation at follow-up (on average, 7 mo after returning to Earth). They show a partial normalization of ventricular CSF volumes and rewidening of the superior sagittal sinus.