Quantitative magnetic resonance image assessment of the optic nerve and surrounding sheath after spaceflight

• Type of Material: Article
• Authors: Jesse J. Rohr, University of Idaho; Stuart Sater, University of Idaho; Austin M. Sass, University of Idaho; Karina Marshall-Goebel, KBR; Robert J. Ploutz-Snyder, University of Michigan; Ross Ethier, Emory University; Michael B. Stenger, NASA; Bryn A. Martin, University of Idaho; Brandon R. Macias, KBR
• Language: English
• Date: 2020-10-08
• Publisher: NATURE PORTFOLIO
• Publication Version: Final Published Version
• Copyright Statement: © The Author(s) 2020
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1038/s41526-020-00119-3
• Title of Journal or Parent Work: NPJ MICROGRAVITY
• Volume: 6
• Issue: 1
• Start Page: 30
• End Page: 30
• Grant/Funding Information: This study was funded by NASA Idaho Space Grant Consortium grant NNX10AM75H, NASA grant NNX16AT06G, National Institute of Neurological Disorders, and Stroke grant 1R01NS11128301, the Georgia Research Alliance, and the NASA Human Research Program.
• Keywords: DISC EDEMA; Multidisciplinary Sciences; IDIOPATHIC INTRACRANIAL HYPERTENSION; VISUAL IMPAIRMENT; ULTRASOUND; Science & Technology - Other Topics; DEFORMATION; Science & Technology
• Research Categories: Health Sciences, Radiology; Health Sciences, Opthamology

Abstract

A subset of long-duration spaceflight astronauts have experienced ophthalmic abnormalities, collectively termed spaceflight-associated neuro-ocular syndrome (SANS). Little is understood about the pathophysiology of SANS; however, microgravity-induced alterations in intracranial pressure (ICP) due to headward fluid shifts is the primary hypothesized contributor. In particular, potential changes in optic nerve (ON) tortuosity and ON sheath (ONS) distension may indicate altered cerebrospinal fluid dynamics during weightlessness. The present longitudinal study aims to provide a quantitative analysis of ON and ONS cross-sectional areas, and ON deviation, an indication of tortuosity, before and after spaceflight. Ten astronauts undergoing ~6-month missions on the International Space Station (ISS) underwent high-resolution magnetic resonance imaging (MRI) preflight and at five recovery time points extending to 1 year after return from the ISS. The mean changes in ON deviation, ON cross-sectional area, and ONS cross-sectional area immediately post flight were −0.14 mm (95% CI: −0.36 to 0.08, Bonferroni-adjusted P = 1.00), 0.13 mm2 (95% CI −0.66 to 0.91, Bonferroni-adjusted P = 1.00), and −0.22 mm2 (95% CI: −1.78 to 1.34, Bonferroni-adjusted P = 1.00), respectively, and remained consistent during the recovery period. Terrestrially, ONS distension is associated with increased ICP; therefore, these results suggest that, on average, ICP was not pathologically elevated immediately after spaceflight. However, a subject diagnosed with optic disc edema (Frisen Grade 1, right eye) displayed increased ONS area post flight, although this increase is relatively small compared to clinical populations with increased ICP. Advanced quantitative MRI-based assessment of the ON and ONS could help our understanding of SANS and the role of ICP.