CONCLUSION: All definite Meniere's disease (MD) had endolymphatic hydrops (EH) 
at least in the cochlea or the vestibule. Symptoms of MD may appear after 
formation of EH. It is assumed that the probability of immediate progression to 
bilateral MD from unilateral MD is very low in patients without EH on the 
non-affected side.
OBJECTIVE: To evaluate the EH on both sides in patients with unilateral and 
bilateral MD, and to investigate factors with progression to bilateral MD 
including the degree of EH, hearing level, and the duration of MD.
PATIENTS AND METHODS: The study included 29 patients with unilateral definite MD 
and 12 patients with bilateral definite MD. The endolymphatic space size was 
visualized by using 3-Tesla magnetic resonance imaging.
RESULTS: All patients with unilateral and bilateral MD had significant or mild 
EH at least in the cochlea or the vestibule on the affected side. On the 
non-affected side, EH was not observed at all in eight patients, but 
asymptomatic EH was observed in the cochlea in 14 patients and in the vestibule 
in 16 patients. There was no relationship between the EH on the non-affected 
side and the duration of MD.