Which waves are most likely affected by acoustic neuroma?

Acoustic neuroma, also known as vestibular schwannoma, is a benign tumor that typically affects the vestibulocochlear nerve (cranial nerve VIII), which has both vestibular and cochlear branches. The tumor often compresses this nerve, leading to disturbances in auditory functions and balance.

In the context of auditory brainstem responses (ABR), different waves correspond to the neural activity generated by the auditory pathway. Wave I is produced by the action potentials of the auditory nerve, Wave II comes from the distal portion of the auditory nerve, Waves III and IV are generated in the brainstem, and Wave V reflects activity at the level of the inferior colliculus.

As the acoustic neuroma progresses, it can hamper the conduction of signals along the entire auditory pathway due to its effects on the auditory nerve and the structures within the brainstem. This can lead to the potential loss or alteration of all waves in the ABR test, depending on the size and location of the tumor. The presence of the tumor might not only impact the early waves associated directly with the auditory nerve but also affect subsequent waves that arise from brainstem activity.

Therefore, all waves may be lost or severely impacted as the neuroma progresses, making this answer the