Magnetic Resonance Derived CSF Production Rate as a Predictor of Orbital Abnormalities after Exposure to Microgravity Courtesy of NASA
Disclosure Information 84th Annual AsMA Scientific Meeting Larry A. Kramer I have no financial relationships to disclose. I will not discuss off-label use and/or investigational use in my presentation
Background Information In 2009 an astronaut was experiencing vision problems after a mission in space. Optic disc edema and choroidal folds. Etiology unknown? High resolution MR imaging of the orbits was requested to evaluate the abnormalities.
Choroidal folds? Retin al Pig me nt E p itheliu m Chor o id www.oculist.net/downaton502/prof/ebook/duanes/pages/v3/v3c036.html
Retinal Pigment Epithelium Melanoma Choroid http://80.36.73.149/almacen/medicina/oftalmologia/enciclopedias/duane/pages/v3/ch036/004f.html
Vitreous S P S CSF CSF S N O * * ON
Normal
Normal
Additional astronauts were studied which eventually resulted in a retrospective analysis June 2012 Radiology, 263, 819827.
Hypothesis Based on Imaging Evidence Orbital abnormalities are in part related to intracranial hypertension.
Modulators of ICH Intracranial Reserve: Intracranial reserve is the capacity to absorb intracranial fluid before pressure increases. CSF Production rate: ICP = Pressure Sagittal Sinus + CSF production rate x R(CSF outflow)
Secondary Hypothesis Above average baseline CSF production rate may reduce intracranial reserve and increase the risk of intracranial hypertension in microgravity.
Methods CSF production rate was non-invasively measured with MRI using a cardiac-gated phase-contrast sequence. Posterior globe flattening was qualitatively assessed on both axial and sagittal oblique T2weighted sequences. Why? Because posterior globe flattening has 100% specificity for idiopathic intracranial hypertension and would suggest exposure to elevated CSF pressures. Time to imaging was recorded for each astronaut based on the most recent mission.
All imaging was performed at 3 Tesla Axial T2 Sagittal Oblique T2
Pre Post Only astronauts with baseline normal posterior globe convexity were used in the final analysis.
cc/s
Results 27 astronauts (2009-2010) Average age = 48 years ± 4.3 All astronauts had microgravity exposure
Result Breakdown A total of 43 exams were performed 16 astronauts with a repeat mission 14 with an initial normal posterior globe 12 with flattening after repeat mission 2 with no flattening after repeat mission
CSF Production Rate=microliter/min P>0.45
P>0.2 pre (ave=911 days after mission) post (ave=8 ± 6 days after mission)
Limitations Fundamental causal hypothesis of intracranial hypertension and visual impairment remains unproven. CSF production rate in microgravity is unknown.
Conclusion Astronauts that developed globe flattening on repeat mission in space did not show evidence of increased baseline CSF production rates. So the secondary hypothesis is false.
Conclusion Several questions however remain: Is the trend to increased CSF production rate post-flight a possible rebound phenomenon? Does the rebound phenomenon then indicate CSF down regulation in microgravity?
Final Thought Is the rebound phenomenon observed in some astronauts indirect evidence of the development of intracranial hypertension in microgravity?
Kramer, Sargsyan, Hasan, Polk, Hamilton, Tarver, Powers, Straube, Shimadas Thanks