Labyrinthine signal intensity of the patients with internal auditory canal mass on pre-enhanced and 4-hour delayed-enhanced 3D-FLAIR MRI

Abstract

Purpose Recently 4-hour delayed-enhanced three-dimensional fluid-attenuated inversion recovery magnetic resonance imaging (3D-FLAIR MRI) has been used in pathophysiologic analysis of the inner ear in many auditory diseases. It has been reported that 4-hour delayed-enhanced 3D-FLAIR MRI is also useful for showing not only perilymphatic space but also inner ear enhancement. There was no study about detailed analysis of labyrinthine signal intensity and hearing loss correlated with internal auditory canal (IAC) mass in 4-hour delayed-enhanced 3D-FLAIR MR finding of the IAC mass. The purpose of this study is to evaluate the correlation between labyrinthine signal intensity and intracanalicular tumor size or degree of hearing loss in patients with unilateral IAC mass on pre-enhanced, and 4-hour delayed-enhanced 3D-FLAIR MRI. Materials and Methods Total 22 patients with unilateral mass in IAC, who underwent 3D-FLAIR MRI with pre-enhanced, and 4-hour delayed enhancement after intravenous gadolinium injection, from November 2012 to October 2017, were retrospectively analyzed.. The tumor size, IAC widening, visibility scores of the inner ear structure were assessed. The visibility scores of pre-enhanced and 4-hour delayed enhanced 3D-FLAIR images were measured by 2 neuroradiologists blinded to the clinical presentation. The scores of cochlea, vestibule, and semicircular canal are determined 0 or 1 point by comparing the signal intensity between affected and unaffected ear: if the cochlear signal intensity of affected ear is higher than unaffected side, it scores 1 point. The visibility score is the sum of each inner ear compartment score, with range of 0 to 3. Then, medical record including pure tone audiometry (PTA) within 2 weeks was analyzed. The Mann-Whitney test, student T test, and Fisher exact test were used to compare various variables between the patients who showed high signal intensity and those who did not on pre-enhanced and 4-hour delayed-enhanced 3D-FLAIR MRI. The Jonckheere-Terpstra test was used to assess the tendency of intracanalicular longitudinal and transverse tumor length and PTA results according to the visibility score groups on pre-enhanced and 4-hour delayed-enhanced images. Results Labyrinthine FLAIRhyperintensity was seen in 17 of 22 patients with IAC mass. The intracanalicular longitudinal and transverse tumor length were significant factor (P= 0.04, P=0.019, T test) affecting labyrinthine hyperintensity. In the higher pre-enhanced 3D-FLAIR visibility score group, the intracanalicular longitudinal and transverse tumor length tended to be increased, which showed statistically significance (P<0.001, P= 0.008, Jonckheere-Terpstra test). Prominent four hours delayed enhancement of inner ear structures was seen in 20 of 22 patients with IAC mass. In the higher 4-hour delayed-enhanced 3D-FLAIR MRI visibility score group, the PTA and intracanalicular longitudinal tumor size tended to be increased, which showed statistically significance (P= 0.03, P=0.038, Jonckheere-Terpstra test). Conclusion Labyrinthine hyperintensity and delayed enhancement were seen in more than two thirds of the patients with IAC mass. The intracanalicular longitudinal and transverse tumor length was significantly longer in the patients with inner ear high signal intensity on pre-enhanced 3D-FLAIR MRI, and they were correlated with visibility score on pre-enhanced 3D-FLAIR MRI. The intracanalicular longitudinal tumor length and initial PTA threshold were significantly correlated with visibility score on 4-hour delayed-enhanced 3D-FLAIR MRI. The intracanalicular longitudinal tumor length and visibility score on pre-enhanced and 4-hour delayed-enhanced 3D-FLAIR images may be helpful in assessing labyrinthine FLAIR hyperintensity and predicting degree of hearing loss in patients with IAC mass. And large number study will be required to clarify association between hearing loss and 4-hour delayed-enhanced visibility score, and prognostic value of 4-hour delayed-enhanced visibility score.