To identify intraorbital and intracranial abnormalities in astronauts previously exposed to microgravity by using quantitative and qualitative magnetic resonance (MR) techniques. The institutional review board approved this HIPAA-compliant, retrospective review and waived the requirement for informed consent. Twenty-seven astronauts (mean age ± standard deviation, 48 years ± 4.5) underwent 3-T MR imaging with use of thin-section, three-dimensional, axial T2-weighted orbital and conventional brain sequences. Eight astronauts underwent repeat imaging after an additional mission in space. Optic nerve sheath diameter (ONSD) and optic nerve diameter (OND) were quantified in the retrolaminar optic nerve. OND and central optic nerve T2 hyperintensity were quantified at mid orbit. Qualitative analysis of the optic nerve sheath, optic disc, posterior globe, and pituitary gland morphology was performed and correlated for association with intracranial evidence of hydrocephalus, vasogenic edema, central venous thrombosis, and/or mass lesion. Statistical analyses included the paired t test, Mann-Whitney nonparametric test for group comparisons, Cronbach α coefficient for reproducibility, and Pearson correlation coefficient. All astronauts had previous exposure to microgravity and, thus, control data were not available for comparison. The ONSD and OND ranged from 4.7 to 10.8 mm (mean, 6.2 mm ± 1.1) and from 2.4 to 4.5 mm (mean, 3.0 mm ± 0.5), respectively. Posterior globe flattening was seen in seven of the 27 astronauts (26%), optic nerve protrusion in four (15%), and moderate concavity of the pituitary dome with posterior stalk deviation in three (11%) without additional intracranial abnormalities. Retrolaminar OND increased linearly relative to ONSD (r = 0.797, Pearson correlation). A central area of T2 hyperintensity was identifiable in 26 of the 27 astronauts (96%) and increased in diameter in association with kinking of the optic nerve sheath. Exposure to microgravity can result in a spectrum of intraorbital and intracranial findings similar to those in idiopathic intracranial hypertension.

After long-duration exposure to microgravity, most crewmembers on the International Space Station showed MRI evidence of pituitary gland deformation, suggesting elevated intracranial pressure durin... Background Astronauts on long-duration spaceflight missions may develop changes in ocular structure and function, which can persist for years after the return to normal gravity. Chronic exposure to...

To improve the pathophysiological understanding of visual changes observed in astronauts, we aimed to use quantitative MRI to measure anatomic and physiological responses during a ground-based spaceflight analog (head-down tilt, HDT) combined with increased ambient carbon dioxide (CO₂). Six healthy, male subjects participated in the double-blinded, randomized crossover design study with two conditions: 26.5 h of −12° HDT with ambient air and with 0.5% CO₂, both followed by 2.5-h exposure to 3% CO₂. Volume and mean diffusivity quantification of the lateral ventricle and phase-contrast flow sequences of the internal carotid arteries and cerebral aqueduct were acquired at 3 T. Compared with supine baseline, HDT (ambient air) resulted in an increase in lateral ventricular volume ( P = 0.03). Cerebral blood flow, however, decreased with HDT in the presence of either ambient air or 0.5% CO₂( P = 0.002 and P = 0.01, respectively); this was partially reversed by acute 3% CO₂exposure. Following HDT (ambient air), exposure to 3% CO₂increased aqueductal cerebral spinal fluid velocity amplitude ( P = 0.01) and lateral ventricle cerebrospinal fluid (CSF) mean diffusivity ( P = 0.001). We concluded that HDT causes alterations in cranial anatomy and physiology that are associated with decreased craniospinal compliance. Brief exposure to 3% CO₂augments CSF pulsatility within the cerebral aqueduct and lateral ventricles.NEW & NOTEWORTHY Head-down tilt causes increased lateral ventricular volume and decreased cerebrovascular flow after 26.5 h. Additional short exposure to 3% ambient carbon dioxide levels causes increased cerebrovascular flow associated with increased cerebrospinal fluid pulsatility at the cerebral aqueduct. Head-down tilt with chronically elevated 0.5% ambient carbon dioxide and acutely elevated 3% ambient carbon dioxide causes increased mean diffusivity of cerebral spinal fluid within the lateral ventricles.

Neuro-ocular changes during long-duration space flight are known as spaceflight-associated neuro-ocular syndrome (SANS). The ability to detect, monitor, and prevent SANS is a priority of current space medicine research efforts. Optic nerve sheath diameter (ONSD) measurement has been used both terrestrially and in microgravity as a proxy for measurements of elevated intracranial pressure. ONSD shows promise as a potential method of identifying and quantitating neuro-ocular changes during space flight. This review examines 13 studies measuring ONSD and its relationship to microgravity exposure or ground-based analogs, including head-down tilt, dry immersion, or animal models. The goal of this correspondence is to describe heterogeneity in the use of ONSD in the current SANS literature and make recommendations to reduce heterogeneity in future studies through standardization of imaging modalities, measurement techniques, and other aspects of study design.

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.