The aim of this study was to prospectively assess the effect of mTBI on optic nerve sheath (ONS) dilation post transient increase in ICP.

Our cross-sectional study demonstrated that those with a history of mild traumatic brain injury (mTBI) at least one year following their injury have significant ONS dilation after Valsalva as measured by ultrasound compared to those without a history of mTBI. This showed that ONS dilation after Valsalva could be a potential non-invasive method of identifying individuals with a history of mTBI but needed prospective confirmation.

Mixed martial arts competitors that did not have ONS dilation of more than 0.5 mm on Valsalva, a value set based on cross-sectional study results, were enrolled in this prospective observational cohort study. Baseline pre and post-Valsalva optic nerve sheath diameter (ONSD) measurements were obtained for screening purposes. Additional ONSD measurements were collected after 1, 6, and 12 months of enrollment. Participants were monitored for suspected mTBI via self-report and monthly calls. Within two weeks following a physician-confirmed mTBI, the participant was scanned.

Twenty-one participants were enrolled and 16 (76.2%) were followed up with for one year. Three participants experienced a mTBI. Scans conducted within two weeks of the mTBI showed no significant ONS dilation post-Valsalva, which was most likely due to an elevated pre-Valsalva value compared to the participant’s baseline and one-year pre-Valsalva ONSD. At the one-year testing, individuals in the mTBI group had a significantly larger post than pre-Valsalva ONSD and a significant ONS dilation post-Valsalva (n=3, mean=1.01mm) when compared those who did not experience a mTBI (n=13, mean= -0.12mm; p=0.0032).

This study confirms the cross-sectional study results that following a mTBI, the ONS dilates significantly following Valsalva. Further exploration is needed into exactly when this dilation is seen during a patient’s recovery and why it seems delayed.