gms | German Medical Science

Objective: The auditory midbrain implant (AMI) is a newly designed auditory prosthesis for patients with neural deafness. It involves a penetrating electrode placed into the central nucleus of the inferior colliculus. In a cadaveric study, we have recently reported the surgical feasibility of accessing the cerebello-pontine angle (CPA) for tumor removal and the inferior colliculus (IC) for navigated electrode implantation by way of a lateral suboccipital craniotomy (LSC).

We now report on the first clinical experience performing concomitant tumor removal in the CPA and AMI implantation in three deaf patients with neurofibromatosis type 2 (NF2).

Methods: The current study for the implantation of the AMI (Cochlear, Ltd, Lane Cove, Australia) in humans was approved by an ethic committee and was conducted according to the study protocol. All 3 patients with the diagnosis of NF2 were deaf and had tumors in the CPA. Preoperative MRI and CT scans were performed in all three patients for surgery planning and for intraoperative navigation. The navigation system provided registration of individual surgical instruments using a trajectory guide (BrainLAB, Germany). All patients underwent a single-staged surgery in the semi-sitting position using a LSC. Following tumor removal via the retrosigmoid route, the IC was exposed via the infratentorial supracerebellar space. After implantation of the receiver-stimulator of the AMI in a bony bed superior-lateral to the LSC, the navigated placement of the penetrating electrode into the IC was conducted. Our experience with the surgical technique and feasibility, morbidity and neurological outcome in these first 3 cases is reported.

Results: Complete tumor removal was achieved in all 3 patients. The implantation of the AMI electrode succeeded in all patients within the region of the IC based on postoperative CT and CT/MRI fusion. In none of the patients did a bridging vein need to be sacrificed to access the IC. In none of the patients was there evidence of postoperative hemorrhage based on CCT. The neurological status after surgery was unchanged in all three patients and none of them suffered from postoperative CSF leak. There was no mortality.

Conclusions: These preliminary results demonstrate that tumor removal in the CPA and AMI device implantation can be safely performed in a single-staged procedure using a LSC. The insertion of a penetrating electrode can be achieved accurately with navigational guidance and does not result in neurological deficits stemming from irritations of the midbrain and/or adjacent structures.