[Reversible hearing loss in the contralateral ear after surgery of acoustic neurinoma].

In a prospective study of 12 patients undergoing operation for acoustic neuromas, the hearing on the contralateral ear was tested before and systematically after operation. In 11 cases a perceptive loss of at least 20 dB was found at one or more frequencies during the first two postoperative weeks. The maximal average threshold decrease was 16.5 dB in the treble and 19.6 in the low frequencies. After three months the hearing had normalized in all cases. The loss of cerebrospinal fluid during operation diminishes the CSF pressure, which is then transmitted to the perilymph via the cochlear aqueduct, producing a transitory perilymphatic hypotonia and a relative endolymphatic hypertension mimicking an endolymphatic hydrops.