Retrosigmoid approach for auditory brainstem implant

The present paper reports our experience with the surgical retrosigmoid-tra nsmastoid (RS-TM) technique for implanting auditory brainstem implants (ABI s). From April 1997 to August 1998, four patients with neurofibromatosis type 2 (NF2) were operated on for vestibular schwannoma removal with ABI implanta tion. The subjects (three men and one women) ranged in age from 22 to 31 ye ars. Tumour size ranged from 12 to 30 mm. A classical RS-TM approach was performed. After tumour excision, identifica tion of landmarks (VIIth, VIIIth and IXth cranial nerves, choroid plexus) t o the foramen of Luschka was carefully carried out. The choroid plexus was partially removed and the tela choroidea divided and deflected. The floor o f the lateral recess of the fourth ventricle and the convolution of the dor sal cochlear nucleus became visible, The electrode array was then inserted into the lateral recess and placed in the correct position with the help of electrically-evoked auditory brain stem responses. Auditory sensations were induced in all patients with various numbers of el ectrodes. Different pitch sensations could be identified with different ele ctrode stimulation. Details of the results are presented. In our series, the RS-TM approach rep resents the elective route for ABI insertion.