Blood-Labyrinthine Barrier Permeability Assessed Using Postcontrast Delayed 3D-FLAIR MRI Imaging in Vestibular Schwannoma

Background: The primary mechanism(s) driving hearing loss in untreated vestibular schwannoma (VS) remain controversial. Leading hypotheses include cochlear nerve or labyrinthine artery compression, cochlear nerve invasion, or compromise of fluid circulation in the fundus or cochlea. Delayed gadolinium enhanced three-dimensional fluid-attenuated inversion recovery (3D-FLAIR). MRI is a novel imaging technique that previously showed promise in evaluating the integrity of the blood-labyrinthine barrier (BLB). While delayed 3D-FLAIR imaging was previously used to investigate multiple pathologies of the inner ear, to date no current study has evaluated the technique in VS patients. This is the first study examining whether this imaging modality can provide valuable insight into the underlying pathophysiology driving audiovestibular injury in VS patients.

Methods: Patients under surveillance for small to medium-sized radiographically diagnosed VS were recruited. Consented patients received a standard dose of intravenous gadolinium and underwent MR imaging on a 3T MRI scanner, followed by repeat imaging 4 to 8 hours later. During each session, 3D-FLAIR imaging was performed generating precontrast, immediate (10 minute) postcontrast, and delayed (4–8 hours) images. Using image software, a region of interest (ROI) was drawn around the cochlea and vestibule in both the ipsilateral and contralateral ears through its greatest diameter on 3D-FLAIR axial slices. From the ROI, signal intensity ratios (SIRs) were generated comparing inner ear structures on the tumor-affected side versus the nonaffected side. The difference in SIR from immediate to delayed images was compared through Wilcoxon ranked sum testing. Simple linear regression was used to assess any relationship between SIRs and pure tone averages (PTAs) of the tumor-affected ear and the degree of hearing asymmetry across ears through PTAs and word recognition score difference ([Figs. 1] and [2]).

Results: Five males and three females with a mean tumor size of 7.5 mm were included. Nearly all delayed 3D-FLAIR imaging demonstrated asymmetric enhancement of inner ear structures only occasionally seen on the tumor-affected side of immediate postcontrast scans. Mean cochlear SIRs for delayed imaging were significantly greater than the SIRs on immediate scans (1.91 vs. 1.21; p < 0.05). The mean vestibular SIR for delayed imaging was also significantly greater than the SIRs on immediate scans (1.74 vs. 1.15; p < 0.05). While linear regression showed increasing differences in PTAs from tumor-affected ear to nonaffected ear with greater SIRs, there was only a significant association with SIRs at the vestibule (p < 0.05). No significant correlations were found between immediate postcontrast image SIRs or SIRs and tumor characteristics or audiometric data (p > 0.05).

Conclusion: This is the first study to utilize delayed gadolinium MRI to assess BLB permeability in patients under observation for VS. Our study demonstrates that BLB permeability appears enhanced in the presence of VS. More investigations into the significance of these findings, as well as their potential clinical relevance are warranted.

Fig. 1. PTA difference versus delayed cochlear SIR.

Fig. 2. PTA difference versus vestibular SIR.