Backgrounds: This study aimed to clarify the prognosis of asymptomatic endolymphatic hydrops (EH) in healthy volunteers via five-year follow-ups with inner ear magnetic resonance imaging (MRI).

Methods: Inner ear MRI was performed on 115 participants recruited as controls in a previous study on Meniere’s disease. The endolymphatic space was visualized using Naganawa’s method of contrast-enhanced MRI with intravenous gadolinium injection and evaluated using Nakashima’s method of 2D imaging analysis.

Results: Cochlear or vestibular EH was present in 7.0% of participants (n = 8), with all cases being unilateral (laterality), moderate (severity), and asymptomatic (onset). Only cochlear-localized EH, only vestibular-localized EH, and both EH were present in 1.7% (n = 2) (C group), 4.3% (n = 5) (V group), and 0.9% (n = 1) (CV group) of participants, respectively. Conducting inner ear MRI after five years showed that EH had almost disappeared in two participants in the C and V groups (4/8, 50.0%). EH was still present in three participants in the V group and one in the CV group (4/8, 50.0%). One participant in the V group and another in the CV group presented with residual inner ear EH and developed typical symptomatic Meniere’s disease (2/8, 25.0%).

Conclusions: Approximately 7% of healthy participants showed asymptomatic EH. Therefore, EH is not the definitive marker for making a diagnosis as Meniere’s disease or the suitable predictor for development of Meniere’s disease. Among these participants, 25% maintained EH and subsequently developed typical Meniere’s disease within the next five years. Schellong-positive participants maintained persistent EH in the inner ear, and participants with higher scores on the self-rating depression scale developed Meniere’s symptoms after five years.