Cerebrospinal fluid loss and threshold changes. 1. Hearing loss in the contralateral ear after operation for acoustic neuroma: an analysis of the incidence, time course, frequency range, size and pathophysiological considerations.

In a prospective study, 60 patients who underwent surgery for unilateral acoustic neuromas had the hearing on the contralateral ear tested before and several times after surgery. In 40 patients, a threshold increase was found during the following 9 days. The changes were greatest in the low frequencies immediately after surgery, but after 1 week the treble also became involved. After 3 months, the hearing was normalized. The elder patients more than 50 years of age were more often affected, whereas sex, tumor size, surgical approach or duration of surgery had no influence. The pathophysiological mechanisms are discussed and an intracochlear fluid dysfunction caused by the loss of cerebrospinal fluid is suggested.