Optic Nerve Sheath Dilation Is a Possible Marker of CSF Dyshomeostasis in Idiopathic Intracranial Hypertension.

Purpose: Idiopathic intracranial hypertension (IIH) is a complex neurological disease characterized by symptoms of raised intracranial pressure of unclear etiology. Although optic nerve sheath dilation is a common MR neuroimaging feature of IIH, how and why it occurs remains poorly understood. The purpose of the presented analysis was to investigate if optic nerve sheath dilation might be associated with neuroimaging correlates of cerebrospinal and interstitial fluid homeostasis.

Methods: IIH patients were retrospectively identified from 2016-2023 from our tertiary healthcare system. Brain MRIs were computationally segmented using FreeSurfer. Additionally, diffusion tensor imaging along the perivascular space (DTI-ALPS) was employed to assess cerebral glymphatic flow. The mean perioptic subarachnoid space (PSAS) to optic nerve sheath diameter (ONSD) ratio from both eyes was correlated with neuroimaging markers of CSF and interstitial fluid homeostasis (choroid plexus, ventricle, and gray and white matter volume) and glymphatic flow. All volumes of interest were normalized to total intracranial volume. Multiple linear regression was used to evaluate for associations between continuous variables accounting for covariates of patient age, sex, and body mass index.

Results: In total, 55 IIH patients (89% female; mean age: 30.3 years [SD: 7.6]) were included. Increasing PSAS/ONSD was found to be significantly associated with increasing normalized total choroid plexus volume (p = 0.001, R = 0.48) and total ventricle volume (P = 0.014, R = 0.39). Additionally, increasing PSAS/ONSD was associated with declining/worsening cerebral glymphatic clearance based on DTI-APLS (p = 0.043, R = 0.34). Additionally, there was a significant association between increasing PSAS/ONSD and increasing normalized total gray matter volume (p = 0.025, R = 0.36) and declining normalized total white matter volume (p = 0.012, R = 0.40).

Conclusion: These findings suggest that MR optic nerve sheath dilation in IIH might be associated with CSF dyshomeostasis with possible choroid plexus hyperplasia and impaired cerebral glymphatic flow based on DTI-ALPS. These findings encourage future research into the ocular glymphatic system in IIH patients.