Topodiagnosis of deafness: strategy for treatment of neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) causes bilateral hearing loss due to tumour growth in the cerebellopontine angle. We report the results of promontory t esting and transtympanic electrocochleography on subjects with deafness due to NF2 referred for an auditory brainstem implant. All 19 ears tested reve aled loss of cochlear microphonics. Nine ears (mainly without previous trea tment) revealed auditory perception during promontory stimulation, indicati ng cochlear deafness. One of these subjects has been successfully provided with a cochlear implant. The other 10 ears (mainly after previous surgery) revealed negative promontory stimulation, indicating additional retrocochle ar deafness. These findings indicate that neurofibromas initially cause a c ochlear dearness, so that a cochlear implant can be used if the auditory ne rve can be preserved. This option has to be considered in rehabilitating pa tients with bilateral tumours due to NF2.