Vestibular Schwannoma Surgery Hearing Outcomes Review

A systematic review of 34 studies involving 1,297 patients confirms that intraoperative auditory monitoring is essential for preserving hearing during vestibular schwannoma surgery. The review, led by Adéla Bubeníková and colleagues from Charles University, distinguishes between the diagnostic accuracy of monitoring thresholds and their interventional effectiveness, providing clearer guidance for surgeons.

**Two Main Technologies: Far-Field and Near-Field Monitoring**

The research focuses on two distinct monitoring approaches. Far-field techniques, like Auditory Brainstem Responses (ABR) or Brainstem Auditory Evoked Potentials (BAEP), record electrical signals from electrodes on the scalp. These are widely used and provide a stable, continuous overview of the auditory pathway’s health. Near-field techniques, such as Cochlear Nerve Action Potentials (CNAP), use electrodes placed directly on or near the nerve or cochlear nucleus during surgery. This provides a more immediate and precise signal but requires more technical expertise.

The review team separated studies that evaluated how well a specific monitoring threshold predicted postoperative hearing (diagnostic accuracy) from those that compared outcomes in monitored versus unmonitored surgeries (interventional effectiveness).

**What Works: Specific Thresholds Predict Outcomes**

For the commonly used ABR/BAEP, the review identified concrete thresholds that correlate with hearing outcomes. One key finding was that an interaural wave V latency difference of less than 1.12 milliseconds predicted early “serviceable” hearing (Grades I-II or AAO-HNS A-B) with a sensitivity of 86.3% and specificity of 77.8%. This means it correctly identified good hearing outcomes in most cases, while also correctly flagging poor outcomes in a majority.

A simpler “any deterioration” rule acted as a highly sensitive alarm—it caught 100% of early hearing losses, though it was less specific (33%). For surgeons wanting a more definitive “rule-in” criterion, a standardized amplitude measure (post-resection STIAS–Am-V ≥ 0.05 µV) showed strong performance, with 79% sensitivity and 92% specificity.

For near-field CNAP monitoring, a drop in amplitude greater than 80% was a balanced predictor, with 89% sensitivity and 67% specificity for early hearing loss. Complete disappearance of the signal was more specific (92%) but less sensitive (53%). In a small series, the mere presence of the N1 wave at the end of surgery ruled out immediate deafness.

**Does Monitoring Actually Improve Results?**

Only seven studies directly compared surgical outcomes with and without monitoring. The results were “directionally favorable but imprecise.” One cohort showed a relative risk (RR) of 1.28 for preserving serviceable hearing with monitoring, and another showed an RR of 2.50. While these numbers suggest monitoring helps—potentially doubling the chance of success—the confidence intervals were wide (0.54–3.04 and 0.83–7.49). This indicates a positive trend, but more robust, randomized studies are needed for conclusive proof of effectiveness.

The review also noted preliminary evidence that chirp-optimized ABR might outperform standard click-ABR, and that direct CNAP offers more decisive information than transtympanic Electrocochleography (ECochG).

**Practical Implications for Patients and Surgeons**

The findings support the routine use of intraoperative auditory monitoring in vestibular schwannoma surgery aimed at hearing preservation. ABR serves as a reliable, widely available early-warning system. Where technically feasible, near-field CNAP or Dorsal Cochlear Nucleus Action Potentials (DNAP) provide faster and more specific feedback, allowing surgeons to adjust their technique in real-time.

However, the evidence has limitations. Studies were nonrandomized, used heterogeneous thresholds, and often reported incomplete data. This highlights a need for standardized “threshold-to-action” protocols. Surgeons need agreed-upon rules: if the ABR latency difference exceeds 1.12 ms, or if the CNAP amplitude drops by 80%, what specific surgical intervention should follow? Multicenter studies using these standardized protocols are the next necessary step.

For patients facing vestibular schwannoma surgery, this review reinforces that asking about intraoperative auditory monitoring is reasonable. It is a established tool that provides objective data to guide the surgeon’s delicate work around the auditory nerve. The research connects to broader themes in hearing disorder management, such as the importance of precise diagnostic tools and the advancing role of technology in treatment, seen in areas like robot-assisted inner ear surgery. Understanding the brain’s complex role in hearing also contextualizes why monitoring these neural pathways is so critical.

The review by Bubeníková et al. consolidates the evidence and points the way forward. Intraoperative auditory monitoring is not just a diagnostic check; it is an active surgical guide. Refining and standardizing how its signals are used will likely improve hearing preservation rates for many patients.

**Source:** Bubeníková A, Fík Z, Koucký V, et al. Intraoperative auditory monitoring in vestibular schwannoma surgery: Diagnostic accuracy and interventional effectiveness – a systematic review. *Neurosurg Rev*. 2026;49(1):380. doi:[10.1007/s1014302604293y](https://doi.org/10.1007/s10143-026-04293-y). PMID: [42036522](https://pubmed.ncbi.nlm.nih.gov/42036522/).