Blood Labyrinth Barrier Waste Clearance as Assessed by GBCAs on MRI: A Scoping Review.

Objective: The discovery of the glymphatic system in the brain and eye has raised the hypothesis of a similar system in the inner ear. Dysfunctional lymph fluid dynamics may contribute to inner ear conditions such as Meniere's Disease (MD) and endolymphatic hydrops (EH). This scoping review evaluates inner ear waste clearance mechanisms by tracking gadolinium-based contrast agent (GBCA) signal over time using magnetic resonance imaging. Data Sources: PubMed, Embase, Cochrane, Web of Science, and Scopus. Review Methods: A systematic search identified studies reporting inner ear GBCA signal > 4 h after intravenous (IV) administration. Data on study design, cohort characteristics, and time points were extracted. Results: Fifteen studies (three animal; 12 human) met inclusion criteria. Three studies had a goal of studying clearance. Animal studies demonstrated a decrease in GBCA signal following a 4-h peak. Of the human studies, three analyzed healthy controls, four studied EH without MD, three focused on MD, and two focused on neurological disorders but provided insight into inner ear enhancement. In healthy and MD ears, the internal auditory canal was enhanced before other inner ear structures. In EH, a reduced superior petrosal sinus area was noted, and delayed excretion rates were observed in MD patients 24 h post-IV administration. A positive association between endolymph and perilymph signal was identified in EH patients after 24 h. Conclusions: Most studies were not designed to assess clearance mechanisms. Future in vivo and histopathological studies are needed to clarify the potential presence of glymphatic system involvement in the inner ear.