Robot‐assisted cochlear implant surgery in a patient with partial ossification of the basal cochlear turn: A technical note

Abstract

Cochlear implantation (CI) has become the standard treatment for people with no functional hearing.1 Within recent years, minimally invasive procedures performed with a robot have been developed for neurotological surgeries.2, 3 The goal of robot-assisted CI surgery is to avoid extensive drilling of the mastoid bone, preserve residual hearing through more consistent insertion techniques and to enable implantation in complex anatomic cases, such as malformed middle and inner ears. To access the inner ear and cochlea, a tunnel bordered by the facial nerve and chorda tympani is drilled directly through the mastoid to the round window.3, 4 A safe trajectory is planned with an otological software based on image data of the temporal bone. In 2016, Caversaccio et al. performed the first robotic middle ear access for CI in a patient with a self-developed robotic system that was later commercialised as HEARO® system (CASCINATION AG, Bern, Switzerland and MED-EL GmbH, Innsbruck, Austria).5 Since then, a few patients have been successfully implanted with the robot.6 The first robotic inner ear access was subsequently performed in Belgium. In 2020, a European CE mark was obtained for the HEARO® robot for its use in patients above the age of 18 and it has thus become available in Austria. Here, we report on our departments experience with the HEARO® robotic system in a patient with a partially ossified basal cochlear turn. A 56-year-old male patient was recruited and consented to the robotic CI surgery on the left ear with the HEARO® system. Clinical routine work-up included audiological, medical and radiological examinations. The patient suffered from left-sided progressive sensorineural hearing loss with an unaided pure-tone average of 85 dB hearing level for octave frequencies ranging from 0.5 to 4 kilohertz and a word recognition score of 0% at 100 dB using the Freiburg monosyllable test. Complete deafness was present in his contralateral ear since an infection of the middle ear at the age of 5. Feasibility of HEARO® robotic procedure was evaluated based on the preoperative cone beam computed tomography (CBCT) dataset with OTOPLAN software (CASCINATION AG, Bern, Switzerland in collaboration with MED-EL GmbH,). Initially, image data were transferred to OTOPLAN through use of the Digital Imaging and Communications in Medicine (DICOM) file format. Imaging of the patient showed an ossification of the first 4 millimetres (mm) of the basal cochlear turn (Figure 1 left). Consequently, the milling depth was set to the end of the ossification (Figure 1 right). The surgery was performed under general anaesthesia on September, 17th 2021 at the department of Otorhinolaryngology, Head and Neck Surgery at a tertiary care hospital. The HEARO® carbon fibre head rest was used for positioning and immobilising the patient's head on the operating table. Needle electrodes were inserted into the perioral and periorbital muscles for controlled and free running facial neve monitoring. A C-shaped retro-auricular incision was performed. Four fiducial screws were placed onto the bone and served as landmarks for registration (Figure 2). The correct position of the fiducial screws had been estimated preoperatively on a 3D print of the patient's temporal bone. Upon the placement of the screws, an intraoperative CBCT image was acquired with 0.1 mm spatial resolution (xCAT XL, Xoran Ltd.,; Figure 3 left). Using OTOPLAN software, a safe trajectory was planned through the facial recess to the middle ear cavity. The safety margins of the planned trajectory to critical anatomical structures are shown in Table 1. The drilling depth was calculated to 33.4 mm, including the milling of 4 mm ossification within the basal cochlear turn. The planned trajectory would result in a cochleostomy with direct access to the scala tympani. While the planning procedure was performed, a tympanomeatal flap was created for later visualisation of the electrode insertion. The planned trajecto