Impact of endolymphatic mastoid shunt surgery on saccule and lateral semicircular canal function.

Endolymphatic mastoid shunt surgery (EMSS) is widely performed in patients with medically intractable Meniere's disease. Although many patients report an improvement of symptoms after surgery, the mechanisms which are responsible for the relief of complaints are not known. To date, only few studies exist which studied the influence of EMSS on vestibular function. The present study examines the effect of EMSS on saccule function by measuring vestibular evoked myogenic potentials and the effect on lateral semicircular canal function by sinusoidal harmonic acceleration (SHA) testing. No changes in vestibulo-collic reflexes were found after surgery compared to before surgery. SHA testing resulted in comparable phase lag and gain pre- and postoperatively. Although central compensation is clinically evident no effect in specific vestibular diagnostic testing is seen. Modulations of canal-otolith interaction might suggest a change of symptoms. The only method so far to evaluate the success of EMSS is the patient's subjective assessment.