Labyrinthine Signal Intensity on Non-contrast-enhanced 3D-real Inversion Recovery MR Imaging: Correlation with the Endolymphatic Volume Measured on Contrast-enhanced HYDROPS-Mi2.

Abstract

Purpose: To investigate the relationship between the signal intensity (SI) of the entire labyrinthine fluid on non-contrast-enhanced 3D real inversion recovery (3D-real IR) imaging and the endolymphatic volume measured on contrast-enhanced HYDROPS-Mi2 (HYbriD of Reversed image Of Positive endolymph signal and native image of positive perilymph Signal image Multiplied with hT2w MR cisternography) imaging.

Methods: This retrospective study included 37 patients (74 ears) with suspected endolymphatic hydrops (EH). The volume ratio of the endolymphatic space (%EL_vol) was measured on contrast-enhanced HYDROPS-Mi2 images, and the normalized volume-averaged signal intensity (nSI_vol) of the entire labyrinthine fluid was measured on non-contrast-enhanced 3D-real IR images. Statistical analyses included comparisons of nSI_vol between the cochlea and vestibule, side-to-side differences in EH-negative ears, paired comparisons of nSI_vol between larger- and smaller-%EL_vol sides, correlations between %EL_vol and nSI_vol, and receiver operating characteristic (ROC) curve analysis of nSI_vol for discriminating severe from mild/no EH. The presence of EH was defined based on the clinical diagnosis using Nakashima grading.

Results: The vestibular %EL_vol was significantly higher and the vestibular nSI_vol significantly lower than that in the cochlea (both P < 0.001). In EH-negative ears, no significant side-to-side difference in nSI_vol was observed. In both cochleae and vestibules, nSI_vol was significantly lower on the larger-%EL_vol side than on the smaller-%EL_vol side (cochlea: P = 0.002; vestibule: P = 0.007). Significant negative correlations between %EL_vol and nSI_vol were observed in both the cochlea (Spearman's rank correlation coefficient [R_s] = -0.598, P < 0.001) and vestibule (R_s = -0.417, P < 0.001). The area under the ROC curve was 0.827 in the cochlea, and 0.698 in the vestibule.

Conclusion: The SI of the entire labyrinthine fluid measured on non-contrast-enhanced 3D-real IR imaging showed a significant negative correlation with the endolymphatic volume measured on contrast-enhanced HYDROPS-Mi2. These findings suggest that the SI of labyrinthine fluid, as measured on non-contrast-enhanced 3D-real IR images, may serve as an indirect indicator for estimating the degree of EH.