Hearing decrease after loss of cerebrospinal fluid. A new hydrops model?

In a prospective study of 12 patients undergoing operation for acoustic neuromas the hearing on the contralateral ear was tested before and systematically day by day after operation. In 11 cases a perceptive loss of at least 20 dB was found at one or more frequencies during the first 2 postoperative weeks. A maximal average threshold decrease of 16.5 dB was found in the treble (2.4, 8 kHz average), while a tendency of a more pronounced decrease of 19.6 dB was seen in the low frequencies (125, 250, 500 Hz average). After 3 months the hearing had normalized in all cases. The explanation for the transitional loss supports the present theory: The loss of cerebro-spinal fluid during operation diminishes the CSF pressure. This decrease is transmitted to the perilymph via the cochlear aqueduct producing a transitory perilymphatic hypotonia, which in turn hydromechanically results in a relative endolymphatic hypertension mimicking an endolymphatic hydrops thus representing a human hydrops model.