Aintablian, Haig

Brunstetter, Tyson

Fleischer, Jennifer

Tarver, William J.

NASA Technical Reports Server

Haig Aintablian1, Jennifer Fleischer2, Tyson Brunstetter3, William J. Tarver4
1University of Arizona - College of Medicine, Phoenix, AZ; 2Geisel School of Medicine, 
Dartmouth, NH; 3U.S. Navy, Houston, TX; 4NASA Johnson Space Center, Houston, TX 
A MECHANISM FOR THE UNILATERAL TENDENCIES
SPACEFLIGHT ASSOCIATED NEURO-OCULAR SYNDROME
https://ntrs.nasa.gov/search.jsp?R=20190014042 2019-08-31T13:37:59+00:00Z
DISCLOSURE INFORMATION
89TH ANNUAL SCIENTIFIC MEETING
HAIG AINTABLIAN, MD
CAPT TYSON BRUNSTETTER, MSC (ASO), USN
I have no financial relationships to disclose. I will not discuss off label use and/or investigational use 
in my presentation.
DoD Disclaimer: The views expressed in this presentation are those of the author and do not 
necessarily reflect the official policy or position of the Department of the Navy, Department of 
Defense, nor the U.S. Government.
UNILATERAL TENDENCIES
Many of the reported cases of Spaceflight Associated Neuro-Occular Syndrome 
(SANS) show a bias toward the right side. (Wall et al., 1998, Mitchell et al., 1992, Lepore et al., 1992, Alperin et al., 
2013, Sher et al., 1983, King et al., 1990, Huno-Baron et al., 2001, Sedwick et al., 1983)
When reviewing these cases, it becomes apparent that SANS is biased toward 
the right orbit about 45-75% of the time.
45-75%
THEORY 1
Asymmetric bias is also often found in Idiopathic Intracranial 
Hypertension (which has some similarities to SANS).
Bidot et al.’s suggestion for IIH is that the asymmetry in IIH may be 
due to asymmetric optic canal diameter.
This is plausible, but unlikely, at least when it comes to SANS (Bidot
et al., 2015) since IIH asymmetry can be either left or right sided, 
but SANS asymmetry most affects the right side.
Mader et al. suggests that finding this consistency (of asymmetric 
optic canal diameter) in astronauts is unlikely for a few reasons 
including that in one “astronaut case report, a normal opening 
pressure on lumbar puncture was documented after a mission in the 
presence of asymmetric disc edema” (Mader et al., 2016). 
Optic Canal
THEORY 2
Mader et al. says that in that same astronaut they found unilateral loss of spontaneous 
venous pulsations in the same eye during space flight that continued to be absent 21 
months post-flight (Mader et al., 2015). 
In a recent case of an astronaut with asymmetric optic disc swelling and globe flattening, 
Mader et al. suggested this unilateral nature of SANS may be due to asymmetric 
pressure changes within the perioptic subarachnoid space - this based on lumbar 
puncture opening pressures 7 and 365 days post-flight (Mader et al., 2017).
Subarachnoid 
Space
OUR THEORY
Explains Mader et al.’s theory, but digs deeper into why there 
may be differences between the R and L pressures in the 
perioptic subarachnoid space.
Subarachnoid 
Space
OUR THEORY
An asymmetry of venous drainage 
sinuses near the orbits may be a stronger 
contributing factor than asymmetric optic 
nerve diameter suggested by Bidot et 
al., 2015, and may be a major 
contributor to Mader et al.’s theory of 
asymmetric pressure changes within the 
perioptic subarachnoid space. 
References: Keller et al., 2009
REVIEW OF ORBITAL BLOOD DRAINAGE
Blood from the orbit first enters the: 
Cavernous Sinus
From there, it goes to the: Superior 
Petrosal Sinus
 Where it combines with the: Transverse 
Sinus
 Then goes to the: Sigmoid Sinus
 And drains into the: Internal Jugular Vein.
The Cavernous Sinus also drains into 
the: Inferior Petrosal Sinus 
 Which also drains into the: Internal 
Jugular Vein.
Unilateral Tendencies
References: Keller et al., 2009
Blood from the Cavernous Sinus goes to the: Superior Petrosal Sinus
 Where it combines with the: Transverse Sinus
 Then goes to the: Sigmoid Sinus
 And drains into the: Internal Jugular Vein.
TWO MRI STUDIES
There is a well established, large populational asymmetry in the 
transverse sinus.
Study 1: Ayanzen et al. 2000
 100 MRI cases, transverse sinus flow gaps were observed in as many as 31% 
of patients with normal MR imaging findings.
 More surprisingly, the transverse sinus was found to be right dominant 59% of 
the cases, left dominant in 25%, and codominant in 16%.
Study 2: Scotti et al. 1988
 105 MRI cases, twenty-one (20%) cases had aplasias of the left sinus and 41 
(39%) had hypoplasias of the left sinus. 
 33 (31%) were symmetric, 6 (6%) had hypoplasia of the right sinus, and 4 
(4%) had aplasias of the right sinus. 
Transverse 
Sinus
WHAT THIS MEANS
Approximately 60% of the population has a right dominant 
Transverse Sinus.
In this 60% of the population, the right venous sinuses are 
responsible for draining significantly more venous blood than the 
left venous sinuses.
Could the fluid shift that causes cranial venous pooling lead to too 
much venous volume and pressure in the dural sinuses on the right 
side?
 This could lead to increased strain on the right Superior Petrosal Vein 
 This would explain why the right eye is more affected than the left.
 It would also support Mader et al.’s idea that there may be “asymmetric 
pressure changes within the perioptic subarachnoid space” Transverse 
Sinus
A right side dominant Transverse Sinus means:
• Less Laminar flow
• More venous drainage requirement on the Sigmoid Sinuses 
• Increased Venous Pressure
Right Left
References: Mader et al., 2015, 2017
WHAT THIS MEANS
All of which is in addition to the 
already elevated venous 
pressures caused by microgravity 
mediated fluid shifts (which 
cause cranial venous pooling)
Elevated venous pressure due to the fluid shifts of 
microgravity could mean:
• Elevated strain on the venous network of the brain
• Decreases in total CSF drainage
Even more elevated right sided venous pressure due 
to right dominant Transverse Sinus could mean:
• Additional strain on the right sided orbital venous 
mechanisms
• Additional strain on right sided CSF drainage 
mechanisms
• Elevated right sided perioptic subarachnoid space 
pressures (as Mader et al. suggests)
Signs/Sx of SANS (predominant on right)
Right
Left
References: Mader et al., 2015, 2017
ALL TOGETHER RECOMMENDATIONS
• Review astronaut MRIs 
retrospectively/prospectively
• Compare venous sinus drainage 
patterns in astronauts affected by 
and not affected by SANS
• Analyze if there is a statistically 
significant contribution from 
transverse venous sinus dominance 
to the development of SANS
REFERENCES
Wall, M., & White, W. N. (1998). Asymmetric papilledema in idiopathic intracranial hypertension: Prospective interocular comparison of 
sensory visual function. Investigative Ophthalmology and Visual Science, 39(1), 134–142.
Mader, T. H., Gibson, C. R., Pass, A. F., Kramer, L. A., Lee, A. G., Fogarty, J., … Polk, J. D. (2011). Optic Disc Edema, Globe Flattening, 
Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight. Ophthalmology, 118(10), 2058–2069. 
Mader, T. H., Gibson, C. R., Hart, S. F., & Lee, A. G. (2016). Asymmetric Papilledema in Idiopathic Intracranial Hypertension. Journal of Neuro-
Ophthalmology, 36(1), 111–112. 
Mader, T. H., Gibson, C. R., Pass, A. F., Lee, A. G., Killer, H. E., Hansen, H.-C., … Pettit, D. R. (2013). Optic Disc Edema in an Astronaut After 
Repeat Long-Duration Space Flight. Journal of Neuro-Ophthalmology, 33(3), 249–255. 
Bidot, S., Bruce, B. B., Saindane, A. M., Newman, N. J., & Biousse, V. (2015). Asymmetric papilledema in idiopathic intracranial hypertension. 
Journal of Neuro-Ophthalmology : The Official Journal of the North American Neuro-Ophthalmology Society, 35(1), 31–6. 
Bidot, S., Saindane, A. M., Peragallo, J. H., Bruce, B. B., Newman, N. J., & Biousse, V. (2015). Brain Imaging in Idiopathic Intracranial 
Hypertension. Journal of Neuro-Ophthalmology, 35, 400–411. 
Ayanzen, R. H., Bird, C. R., Keller, P. J., McCully, F. J., Theobald, M. R., & Heiserman, J. E. (2000). Cerebral MR Venography: Normal Anatomy 
and Potential Diagnostic Pitfalls. American Journal of Neuroradiology, 21(1).
Scotti, G., Yu, C. Y., Dillon, W. P., Norman, D., … Wilson, C. B. (1988). MR imaging of cavernous sinus involvement by pituitary adenomas. AJR. 
American Journal of Roentgenology, 151(4), 799–806. 


Spaceflight Associated Neuro-ocular Syndrome A Mechanism for the Unilateral Tendencies

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