Table 3.
Modality-level summary focused on near-field and adjunct neuromonitoring constructs, presented within a rule-in framework for early hearing outcomes. “Threshold (direction)” specifies the positivity or deterioration rule; “Index outcome(s)” prioritizes early serviceable hearing (GR I–II / AAO-HNS A–B) where available, noting when studies reported broader endpoints (e.g., A–C) or later windows (e.g., 6-month intelligibility). “Evidence & key figures” lists representative study-level accuracy or quantitative correlations (e.g., Li 2023 for CNAP decrements/disappearance; Hochet 2023 for early CNAP presence; Morawski 2007 for TT-ECochG–PTA correlation), while “Notes” provide implementation caveats (require sustained changes, confirm persistence, consider surgical stage and artifacts). ABR/BAEP deterioration rules are included for clinical context but were not used as rule-in endpoints in the primary preservation analysis. Abbreviations: ABR/BAEP, auditory brainstem response/brainstem auditory evoked potentials; CNAP/DCAP, (direct) cochlear nerve compound action potential; DNAP, dorsal nucleus/central near-field action potential (as reported); ECochG, electrocochleography; IAC, internal auditory canal; PTA, pure-tone average; WRS, word-recognition score; GR, Gardner–Robertson; AAO-HNS, American Academy of Otolaryngology–Head and Neck Surgery
| Modality | Threshold (direction) | Index outcome(s) evaluated | Evidence & key figures | Notes |
|---|---|---|---|---|
| CNAP (near-field nerve) | N1 (± P1) amplitude ↓ ≥ 80% (sustained) or disappearance | Early hearing decline (significant postoperative loss) | Li 2023: CNAP ↓ > 80% → Se 0.889, Sp 0.667, LR + 2.67, LR − 0.17; CNAP disappearance → Se 0.529, Sp 0.923, LR + 6.87, LR − 0.51 (2-week outcome). | Near-field offers higher SNR and faster updates than ABR. Treat large, sustained decrements/loss as strong rule-in for decline; confirm persistence to avoid transient artifacts. Secure electrode placement is essential. |
| CNAP (near-field nerve) | CNAP present early (during exposure/initial dissection) | Speech-intelligible hearing at 6 months (AAO-HNS A–C) | Hochet 2023: derived from group counts — Se 0.80, Sp 0.59 for predicting A–C when early CNAP present; endpoint is not strictly early serviceability. | Timing/endpoint sensitive. Useful as an early preservation signal; complements closure-time criteria. For strict early A–B serviceability, published 2 × 2 denominators are rarely available. |
| TT-ECochG (peripheral adjunct) | AP/SP amplitude ↓; AP latency ↑ (stage-linked, sustained) | Early change vs. postoperative audiometry; AAO-HNS/GR shifts | Morawski 2007: intraoperative TT-ECochG change with early PTA shift. Han 2010; Attias 2008: combined ABR+ECochG improves interpretability of deteriorations during IAC/meatal work. | High temporal resolution; robust adjunct to confirm ABR/CNAP trends, especially during drilling/coagulation. Interpret with surgical stage; minimize artifact. |
| DNAP (near-field central) | Amplitude ↓/loss; latency shift (sustained) | Feasibility/real-time detection during prolonged CPA work | Predominantly feasibility/case-level literature; formal accuracy estimates pending. Provides near-real-time nerve status when far-field SNR is poor or delayed. | Consider as a second-scale update channel when ABR/CNAP degrade. Evidence base is early; standardization and 2 × 2 reporting are needed. |
| ABR/BAEP (context: decline rules) | Sustained wave‑V loss; latency ↑ ≥ ~1 ms; amplitude ↓ ≥ ~50% | Early/long-term decline (worse AAO‑HNS/GR; PTA/WRS loss) | Loss is typically highly specific but variably sensitive across case-mixes. James 2005 (CPA subgroup): limited discrimination for permanent loss under mixed pathology/conditions. | Practical intraoperative ‘red‑stop’ signals when sustained and repeatable; interpret in context. This review emphasizes preservation-oriented rule-in; decline-rules are included for clinical completeness. |