1291. Case report: Follow-up brain stiffness measurement in a patient with an episode of low-pressure hydrocephalus.

Authors: William C. Olivero, MD, FAANS; Arundhati Biswas, MD; Tracey Wszalek; Brad Sutton; Curtis Johnson (Sarasota, FL)

Introduction: Low-pressure hydrocephalus (LPH) is a rare condition where CSF drainage at a negative pressure is required to return ventricular size back to baseline. We previously presented a case of LPH that exhibited significantly reduced brain stiffness measured with magnetic resonance elastography (MRE) several weeks after recovery. Here we present a follow-up on the same patient two years later. Methods: This female patient had a ventriculoperitoneal shunt for acqueductal stenosis in 2014, was admitted for shunt malfunction in 2015 at age 19 where she developed LPH that required evd drainage to -3 cm of H2O. She had an MRE exam three weeks after recovery. She was readmitted in 2017 at age 21 with a history of headache, nausea, and photophobia; her CT scan demonstrated severe ventriculomegaly. Patient completed MRI with MRE several weeks following shunt revision surgery. Results: Post-operative MRE scan revealed average brain stiffness of 2.67 kPa – low for her age but near normal brain stiffness of approximately 3 kPa (11% lower). This is in contrast to her brain stiffness of 1.62 kPa at the time of the LPH event, which was 46% below the approximate normal brain stiffness. Her MRI scans at both time points were very similar and showed no residual ventriculomegaly. Conclusion: Why a patient would develop an episode of LPH is unclear. It is also unclear whether the conditions in the brain that lead to LPH persist or eventually return to a more normal state. One hypothesis of LPH causation is that the brain somehow develops a very low stiffness. We presented the first evidence to support this hypothesis, and we now present evidence that this low stiffness appears to recover with time. Mechanisms that might cause such temporary softening and recovery include severe neuroinflammation and are the subject of future research.