Case: Vestibular nerve section with incomplete loss

Timothy C. Hain, MD • Page last modified: March 10, 2021

Vestibular nerve sections are delicate procedures and there is generally a desire to spare hearing, leaving the cochlear nerve intact.  Because some vestibular fibers are intermingled with the cochlear nerve, this means that some VNS may be incomplete. An incomplete VNS is a potential reason for continued vertigo.

Here is an example of a person with Meniere's disease, having persistent vertigo spells after a left sided VNS, and an ENG that clearly shows retained vestibular function.

The audiogram below shows abnormal hearing on both sides, with the left operated side far worse.   Because hearing is impaired on both sides, this person could be having vertigo from either side.



The ENG showed a nystagmus that reversed between warm and cold. Because the responses were low, our audiologist did ice water, which clearly shows a strong response that reverses with prone.  This proves that there is retained vestibular function on the left, and again that vertigo could be coming from either side.


Diagnostic thoughts:

Since this case was originally written up, technology has advanced.

The ice-caloric test remains an excellent test for detecting residual horizontal canal function, but as the ear contains 5 sensors, and this tests one of the 5, a lot can be missed.

The oVEMP and cVEMP tests are good tests for detecting residual otolith function.

The 3D VHIT, in our opinion, has potential but is not good enough to be especially helpful here. It does have the potential though to detect wrongly vectored VOR (see following). Hopefully this will eventually emerge.

Several of these tests are hard to do -- the 3D VHIT, and oVEMP, but we offer them in our dizzy practice in Chicago, and they are also available in certain large medical institutions.

Theory and decision making regarding failed VNS:

So here we have an incomplete VNS. Lets think here about what might be making the person dizzy.

One possibility is that the person might be dizzy from another cause than the disorder for which the VNS was recommended -- examples being

If these are a reasonable possibility, the first step should be medical management of these conditions.

If we accept that the dizziness is still coming from the ear on the side of the VNS, there are 3 ways to imagine that information flow might be distorted. Two of them should be helped by PT.

  1. One way to be dizzy is from an incomplete set of information coming from the nerve where top is sectioned, and bottom is present. This is a 3D matrix problem. In theory, PT should help with this.
  2. A second way is for the nerve to be miswired (we call this "aberrant regeneration". ) Again, PT should help.
  3. A third way to be dizzy is from a damaged vestibular nerve that is irritable. PT shouldn't help here.

In our view, for this situation, the first step should a vigorous attempt at PT (the gaze-stabilization part especially). After this, low dose gentamicin is worth considering, as it might help for mechanisms 1-2. If both PT and low dose gentamicin fails, all that is left is a "redo".