13ABR overlap and the integrated test battery
ECochG and ABR are not competing tests. The AP of ECochG is the same physiological event as wave I of the ABR — generated by the same distal auditory nerve volley. ABR adds waves II–V, which sample progressively central generators. Used together, the two tests cover the entire peripheral auditory pathway from hair cell to upper brainstem.
FShared generators, different scales
The most important point in this module: the AP of the ECochG and wave I of the ABR are the same physiological event — the synchronous spike volley of the distal auditory nerve, generated at the cochlear base near the spiral ganglion.[2014] What differs is the recording geometry. ECochG places the recording electrode close to the generator (tiptrode, TM, or transtympanic), giving large amplitudes; ABR uses far-field scalp electrodes, giving small amplitudes but at the benefit of recording wave V (upper brainstem) and the intervening waves II–IV.
| Component | Generator | ECochG | ABR |
|---|---|---|---|
| CM | Outer hair cells (receptor potential) | Present, prominent | Filtered out |
| SP | Hair cell + dendritic DC component | Present, central diagnostic feature | Filtered out |
| AP / Wave I | Distal auditory nerve (spike volley at cochlear base) | Large, easy to identify | Smaller; sometimes obscured by noise at low intensities |
| Wave II | Proximal auditory nerve / cochlear nucleus entry | Not recordable (too far for the recording electrode) | Present |
| Wave III | Cochlear nucleus / superior olivary complex | Not recordable | Present |
| Wave V | Lateral lemniscus / inferior colliculus | Not recordable | Present, the most robust ABR component |
ECochG sees the cochlea and the most peripheral auditory nerve. ABR sees the auditory nerve and the brainstem up to the inferior colliculus. The two views overlap at the wave-I / AP generator, and the practical implication is that combining them gives the most complete electrophysiological picture of the peripheral auditory pathway available without imaging.[2023]
TWhat ECochG adds to ABR
In a routine clinical setting, ABR is the more widely used test — non-invasive, well-tolerated, available in most audiology clinics. ECochG is used when ABR alone is insufficient for the clinical question:
- Enhanced wave I identification. A clear wave I is required to compute the I–V interpeak interval, the principal retrocochlear marker on ABR. At low stimulus levels or in patients with hearing loss, scalp-recorded wave I is small and may be obscured. Tympanic or transtympanic ECochG dramatically enhances wave I amplitude (the recording electrode is much closer to the generator), allowing reliable I–V measurement when conventional ABR fails.[1989][2024]
- SP measurement.ABR's bandpass filtering removes the SP. ECochG preserves it, which is essential for any clinical question involving hydrops (Module 5), third window (Module 6), or synaptopathy (Module 11).
- CM authenticity testing. The polarity-reversal manoeuvre that confirms a biological CM in suspected ANSD (Module 7) requires ECochG. ABR filtering removes the CM entirely.
- Intraoperative monitoring during CI insertion. Module 12's Campbell 2022 RCT used intracochlear ECochG via the CI's own electrodes. ABR cannot be recorded from the CI in real time the same way.
- Surgical hearing-preservation monitoring during CPA surgery. The ASNM position statement recommends both ECochG-CAP and ABR during vestibular schwannoma resection — ECochG samples cochlear and distal nerve function while ABR adds brainstem-level information. Studies show preserved TM-ECochG with lost ABR can indicate deafferentation of an otherwise functional cochlea — a finding ECochG alone cannot distinguish, but the combined view can.[2024][2023]
TTest selection across scenarios
The integrated picture is clearer when applied to specific clinical scenarios. Across nine common presentations — sudden SNHL, suspected Ménière's, suspected superior canal dehiscence, suspected ANSD in a neonate, asymmetric SNHL with unilateral tinnitus, CI surgery with residual hearing preservation, vestibular schwannoma resection with hearing preservation, threshold estimation in a young child, and suspected hidden hearing loss — the recommended battery falls into a clear pattern. ECochG plays a primary role in intraoperative CI monitoring (Campbell 2022 RCT, ≥30% CM-drop intervention) and in neonatal ANSD diagnosis (Berlin polarity-reversal protocol). It plays an adjunctive role alongside MRI and audiometry in Ménière's, SCD, and asymmetric SNHL workup. It is not indicated for routine threshold estimation in children (ABR has largely replaced it) or for individual-level diagnosis of hidden hearing loss (no validated cutoff exists).
The defensible rule across scenarios: ABR triages, ECochG answers specific questions. Where two tests are listed as primary for the same scenario, the implication is that they are used together rather than either-or. Use the scenario picker below to explore the recommended battery for each of the nine common presentations.
The most defensible practical rule for non-specialist clinicians is: ABR is the screening tool, ECochG is the question-answering tool. ABR triages — is the auditory pathway working at all, where is the lesion approximately — and ECochG digs deeper into specific questions (hydrops? third window? CM authenticity? synaptopathy? real-time intraoperative monitoring?). Neither test alone is sufficient when the clinical question is specific; together they cover most of what non-imaging electrophysiology can offer.
TCase 13.1 — asymmetric SNHL, unreliable scalp wave I
What is the most appropriate next step?