Modalities – ABR

ABR or ABRS – Brainstem Auditory Evoked Potentials

BRs are responses of the auditory system to auditory (sound) stimuli used to measure hearing acuity, auditory nerve function, and brain function. ABRs also provide information about brainstem integrity. The brainstem is an extension of the spinal cord containing information about motor and sensory function, blood pressure, and breathing.

When recording ABRs, the stimuli used to evoke the sensory response is a clicking sound delivered to the ear using a small tube surrounded by foam. The sensory evoked responses are very small, so collecting dozens of responses and averaging them is crucial. The averaged responses are displayed as a waveform that has peaks and troughs that correspond to various locations throughout the hearing pathway and the brainstem. If a delay or reduction in the response occurs, this information is used to help locate and define any problem in the auditory canal or midbrain.

ABRs are commonly used in posterior fossa surgical approaches and in some microvascular decompressions. ABRs are also useful in certain aneurysm surgeries and arteriovenous malformations.

ABRs can be very effective and offer many benefits including:

• Not significantly altered by anesthetic agent
• Does not increase operative time or subject patients to additional risk
• Allows for rapid sampling of the VIIIth nerve and brainstem function
• Changes in ABRs are frequently noted and adjustment of the surgical approach typically results in improvement of the response, resulting in improved function postoperatively