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E1625. Intracranial Changes Related to Long Duration Microgravity Exposure: 2020 Update
Authors
  1. Larry Kramer; University of Texas Health Science Center-Houston
  2. Khader Hasan; University of Texas Health Science Center-Houston
  3. Karina Marshall-Goebel; NASA
  4. Steven Laurie; NASA
  5. Brandon Macias; NASA
Background
Approximately 60% astronauts with long duration exposure to microgravity have reported altered visual acuity (1). Chronic elevation of intracranial pressure (ICP) is hypothesized to be the underlying cause induced by natural headward shift of lower extremity body fluid in microgravity. The purpose of this educational exhibit is to demonstrate how changes in brain morphology and aqueductal cerebral spinal fluid (CSF) flow characteristics determined non-invasively by quantitative magnetic resonance imaging (MRI) obtained pre-to-postflight helps to support the ICP hypothesis. A method to reduce headward shift in body fluid will be discussed.

Educational Goals / Teaching Points
1. Review the pathophysiology of microgravity and how it potentially relates to altered visual acuity in astronauts. 2. Review the Monro-Kellie hypothesis and how it relates to ICP and intracranial compliance. 3. Review changes in intracranial morphology and how it impacts ICP and intracranial compliance. 4. Review changes in aqueductal flow CSF and describe how it indicates changes in intracranial compliance and ICP pulsatility. 5. Review current method to reduce headward shift of lower extremity body fluid.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
1. Quantitative MRI is an essential tool in evaluating the intracranial effects of microgravity. 2. Spaceflight enlarges the ventricular system and expands white matter volume. 3. The summation of total CSF and total brain tissue volume demonstrates a significant increase in intracranial volume pre-to-postflight. 4. Spaceflight causes acquired flattening/concavity of the pituitary dome and decreased height of the pituitary gland. 5. Lower extremity negative pressure reduces cross-sectional area of internal jugular veins.

Conclusion
Intracranial volume expansion within the semi-rigid cranial compartment due to microgravity exposure, has the potential to decrease intracranial compliance and increase ICP when the intracranial capacitance is exceeded (2). Quantitative changes in aqueductal CSF flow support altered ICP pulsatility and decreased intracranial compliance. Acquired pituitary deformity in astronauts is similar to that found in patients with idiopathic intracranial hypertension supporting the hypothesis of inflight exposure to elevated ICP. Lower body negative pressure has the potential to reverse these changes during spaceflight by reducing headward shift in lower extremity body fluid.