Background and objectives <p>The onset of hearing loss due to vestibular schwannomas (VS) is inevitable but does not correlate with the size of the tumor. In patients with Neurofibromatosis Type 2 (NF2) and VS, we previously found an association between pre-contrast fluid-attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) signal in the labyrinth and hearing loss. Here, we asked whether FLAIR hyper-intensity could serve as a predictive biomarker for hearing loss in NF2 patients with VS.</p> Methods <p>A prospective longitudinal study (NCT00598351) of NF2 enrolled 168 subjects between 2008 and 2013. This study included 34 patients with small VS (total volume ≤ 500mm³). Middle fossa decompression surgery (<i>n</i> = 4 patients) was provided via a standard-of-care trial (NCT00060541).</p> Results <p>From 34 eligible subjects (mean age 26.8y) with NF2 and small VS, 53 ears met inclusion criteria. Abnormal hearing was recorded in 18 ears at study entry; all 18 ears had FLAIR hyper-intensity. Of the 35 ears with normal hearing, 16 had FLAIR hyper-intensity at study entry, 6 (37.5%) of which developed new hearing loss (median time to hearing loss of 4.45 years). Conversion to FLAIR hyper-intensity occurred in 11 ears, 3 of which proceeded to hearing loss. No hearing loss developed in the eight ears that remained FLAIR negative. FLAIR conversion has high sensitivity (1·00, 95% CI 0·39–1) and negative predictive value (1·00, 95% CI 0·63–1) for new-onset hearing loss. In 4 patients undergoing middle fossa decompression surgery, we found that surgery stabilized hearing but did not reverse FLAIR hyperintensity.</p> Conclusions <p>Our findings suggest that intralabyrinthine FLAIR hyper-intensity is a sensitive, non-invasive biomarker for hearing loss related to VS. Hearing decline followed FLAIR hyper-intensity by approximately 4 years but was absent in ears with normal FLAIR signal.</p> Trial registration <p>Registry: ClinicalTrials.gov, TRN: NCT00060541, Registration date: 4 June 2003.</p>