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    Original Research

    Orbital and Intracranial Effects of Microgravity: Findings at 3-T MR Imaging

    Published Online:Jun 1 2012https://doi.org/10.1148/radiol.12111986

    Abstract

    Retrospective MR analysis of 27 astronauts exposed to microgravity revealed various combinations of optic nerve sheath distention, posterior globe flattening, optic disc protrusion, increased optic nerve diameter, and moderate concavity of the pituitary gland with posterior stalk displacement, which are hypothesized to be related to intracranial hypertension and represent a potential limitation to long-duration space travel.

    Purpose

    To identify intraorbital and intracranial abnormalities in astronauts previously exposed to microgravity by using quantitative and qualitative magnetic resonance (MR) techniques.

    Materials and Methods

    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.

    Results

    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.

    Conclusion

    Exposure to microgravity can result in a spectrum of intraorbital and intracranial findings similar to those in idiopathic intracranial hypertension.

    ©RSNA, 2012

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    Article History

    Received September 23, 2011; revision requested November 9; revision received January 9, 2012; accepted January 13; final version accepted February 1.
    Published online: June 2012
    Published in print: June 2012