Microvascular Compression of the Vestibulocochlear Nerve

Microvascular contacts or compressions (MVC) of the vestibulocochlear nerve can result in tinnitus, both non-pulsatile and pulsatile tinnitus. For non-pulsatile tinnitus, the contact is most often located at the central nervous system segment, between the meatus and brainstem. For pulsatile tinnitus and typewriter tinnitus, the contact is at the intrameatal peripheral nervous system segment. The tinnitus is most commonly unilateral, presenting as intermittent paroxysms. Typically, in time more frequent bouts of tinnitus occur, which progressively last longer and longer. If a bilateral vascular compressions exist, the tinnitus alternates between left and right side. Associated symptoms are related to MVC of nearby nerves and include overt or cryptogenic hemifacial spasms, geniculate neuralgia, optokinetically induced short bouts of disabling positional vertigo, as well as hearing loss at the tinnitus frequency. The diagnosis is made based on a typical history and confirmed by magnetic resonance imaging (MRI) anatomically, and auditory brainstem responses (ABR) functionally. MRI with constructive interference in steady state can visualize MVC of the auditory nerve and correlates with intraoperative findings. ABR correlates with disease progress and clinical symptoms. Tinnitus is causally related to a decrease in amplitude of peak II in the ipsilaterally elicited ABR. Furthermore, tinnitus frequency-specific hearing loss is causally related to prolongation of the ipsilateral interpeak latency I-III. Compensatory prolongation of interpeak latency III-V occurs contralaterally and is a sign of slowed signal transmission in the brainstem. Microvascular decompression should be performed before irreversible nerve damage is induced, before 4–5 years of tinnitus onset. Surgical outcomes are better if patients present with both tinnitus and vertigo. In patients with tinnitus only, 28% are cured and 45% improved, whereas in patients with both tinnitus and vertigo, 62% are cured and 23% improved.