Milestone Research on Meniere’s Disease by Visualizing Endolymphatic Hydrops Using Gadolinium-Enhanced Inner Ear MRI and the Challenges in Clinical Applications

This review discusses the history of detecting Endolymphatic Hydrops (EH) and collecting evidence to diagnose Meniere's Disease (MD) using Gadoliniumenhanced Inner Ear MRI (Gd-IEMRI) and the challenges in clinical applications. EH was visualized in vivo using Gd-IEMRI in an animal model by Zou et al. in 2000 at the Karoliniska Institutet. The perilymphatic and endolymphatic spaces were observed separately in humans using Gd-IEMRI with a 1.5 T machine after transtympanic injection of Gadolinium Chelate (GdC) in 2005 at the University of Tampere. EH in patients with MD was clearly demonstrated by Nakashima et al. with a 3.0 T machine with a 3-Dimensional Fluid-Attenuated Inversion Recovery (3D-FLAIR) sequence in 2007 at Nagoya University. The oval window was shown to be the major pathway for GdC to enter the inner ear after transtympanic injection. Long-term hearing function assessment after intratympanic application of GdC showed no evidence of ototoxicity in patients. The image quality correlated with various coils in addition to the magnetic strength of MRI. Naganawa et al. developed the following sequences to improve sensitivity: 3-Dimensional Fluid-Attenuated Inversion Recovery (3D-FLAIR), Heavily T(2)-weighted (hT(2)W)-3D-FLAIR, subtracting a positive endolymph image from a positive perilymph image that was called HYDROPS (i.e., HYbriD of Reversed image Of Positive endolymph signal and native image of positive perilymph Signal), and the HYDROPS2-Mi2 method (i.e., HYbriD of Reversed image Of MR cisternography and a positive Perilymph Signal by heavily T2-weighted 3DFLAIR-Multiplied by T2). Computer-aided segmentation of endo- and perilymph spaces reduces the observer-dependence of hydrops quantification and allows for volumetric quantification.