The effect of the endolymphatic subarachnoid shunt operation on vestibular function.

Preoperative vestibular function was studied in 56 patients undergoing the endolymphatic subarachnoid shunt procedure for Ménière's disease by electronystagmographic recording of bithermal air caloric stimulation. Fifty-two percent had normal vestibular function while 48% had a reduced vestibular response on the affected side using 20% difference as being significant. Best results of surgery with relief of vertigo were found in the group of patients with normal preoperative vestibular function (82%) while the group with reduced vestibular response preoperatively showed 63% with a good result. Postoperatively, 81% had a reduced vestibular response in the operated-on ear with 62% obtaining relief of vertigo. In patients with normal vestibular function postoperatively excellent relief of vertigo was obtained. Of patients with normal vestibular function preoperatively, 69% developed a reduced vestibular response postoperatively with only 55% having relief of vertigo. The results of surgery could be predicted more accurately using the results of vestibular function tests than audiometric data. It appears that for best results the endolymphatic subarachnoid shunt procedure should be performed early in the course of Ménière's disease when hearing is fluctuating and vestibular function is normal.