Auditory Brainstem Response (ABR)
The Auditory Brainstem Response (ABR), also known as Brainstem Auditory Evoked Potential (BAEP), is an objective, non-invasive electrophysiological test used to evaluate the functional integrity of the auditory pathway from the cochlea to the brainstem.
Anatomical Generators
The ABR consists of a series of waveforms (I–V) occurring within the first 10 milliseconds after an auditory stimulus:
| Wave | Primary Anatomical Generator |
|---|---|
| Wave I | Distal portion of the Cochlear Nerve (CN VIII). |
| Wave II | Proximal portion of the Cochlear Nerve. |
| Wave III | Cochlear Nucleus. |
| Wave IV | Superior Olivary Complex. |
| Wave V | Lateral Lemniscus / Inferior Colliculus. |
Clinical Applications
- Universal Newborn Hearing Screening: Essential for early detection of hearing loss in infants.
- Retrocochlear Pathology: Useful in evaluating conditions like acoustic neuroma (vestibular schwannoma), where a delay in the inter-peak latency (e.g., I-V latency) is often observed.
- Neurological Assessment: Used in unconscious patients or intraoperative monitoring to ensure brainstem integrity.
High-Yield Exam Pearl:
- Wave V is the most robust and consistent wave; it is typically used for threshold estimation.
- Latency Prolongation: If Wave I is present but subsequent waves are delayed or absent, it points to a pathology located along the brainstem auditory pathway, rather than the cochlea itself.