title: Orbital and intracranial effects of microgravity: findings at 3-T MR imaging.
abstract: OBJECTIVE
  To identify intraorbital and intracranial abnormalities in astronauts previously exposed to microgravity by using quantitative and qualitative magnetic resonance (MR) techniques.
  
  
  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.
  
  
  CONCLUSIONS
  Exposure to microgravity can result in a spectrum of intraorbital and intracranial findings similar to those in idiopathic intracranial hypertension.
authors.affiliation: Department of Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, 6431 Fannin St, MSB 2.100, Houston, TX 77030, USA. Larry.A.Kramer@uth.tmc.edu
authors.forename: Larry A
authors.initials: LA
authors.lastname: Kramer
authors.forename: Ashot E
authors.initials: AE
authors.lastname: Sargsyan
authors.forename: Khader M
authors.initials: KM
authors.lastname: Hasan
authors.forename: James D
authors.initials: JD
authors.lastname: Polk
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Hamilton
mesh_terms: D018480:Astronauts; D001927:Brain Diseases / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007427:Intracranial Pressure / Q000502:physiology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000473:pathology*; D009915:Orbit / Q000473:pathology*; D010902:Pituitary Gland / Q000473:pathology*; D012189:Retrospective Studies; D018709:Statistics, Nonparametric; D014893:Weightlessness