Percutaneous Cochlear Implantation Research Articles

Automatic Pre- to Intra-Operative CT Registration for Image-Guided Cochlear Implant Surgery

Percutaneous cochlear implantation (PCI) is a minimally-invasive image-guided cochlear implant approach, where access to the cochlea is achieved by drilling a linear channel from the skull surface to the cochlea. The PCI approach requires pre- and intra-operative planning. Computation of a safe linear drilling trajectory is performed in a preoperative CT. This trajectory is mapped to intraoperative space using the transformation matrix that registers the pre- and intra-operative CTs. However, the difference in orientation between the pre- and intra-operative CTs is too extreme to be recovered by standard, gradient descent-based registration methods. Thus far, the registration has been initialized manually by an expert. In this paper, we present a method that aligns the scans completely automatically. We compared the performance of the automatic approach to the registration approach when an expert does the manual initialization on 11 pairs of scans. There is a maximum difference of 0.18 mm between the entry and target points of the trajectory mapped with expert initialization and the automatic registration method. This suggests that the automatic registration method is accurate enough to be used in a PCI surgery.

A Manually Operated, Advance Off-Stylet Insertion Tool for Minimally Invasive Cochlear Implantation Surgery

The current technique for cochlear implantation (CI) surgery requires a mastoidectomy to gain access to the cochlea for electrode array insertion. It has been shown that microstereotactic frames can enable an image-guided, minimally invasive approach to CI surgery called percutaneous cochlear implantation (PCI) that uses a single drill hole for electrode array insertion, avoiding a more invasive mastoidectomy. Current clinical methods for electrode array insertion are not compatible with PCI surgery because they require a mastoidectomy to access the cochlea; thus, we have developed a manually operated electrode array insertion tool that can be deployed through a PCI drill hole. The tool can be adjusted using a preoperative CT scan for accurate execution of the advance off-stylet (AOS) insertion technique and requires less skill to operate than is currently required to implant electrode arrays. We performed three cadaver insertion experiments using the AOS technique and determined that all insertions were successful using CT and microdissection.

Automatic segmentation of the facial nerve and chorda tympani in pediatric CT scans

Cochlear implant surgery is used to implant an electrode array in the cochlea to treat hearing loss. The authors recently introduced a minimally invasive image-guided technique termed percutaneous cochlear implantation. This approach achieves access to the cochlea by drilling a single linear channel from the outer skull into the cochlea via the facial recess, a region bounded by the facial nerve and chorda tympani. To exploit existing methods for computing automatically safe drilling trajectories, the facial nerve and chorda tympani need to be segmented. The goal of this work is to automatically segment the facial nerve and chorda tympani in pediatric CT scans. The authors have proposed an automatic technique to achieve the segmentation task in adult patients that relies on statistical models of the structures. These models contain intensity and shape information along the central axes of both structures. In this work, the authors attempted to use the same method to segment the structures in pediatric scans. However, the authors learned that substantial differences exist between the anatomy of children and that of adults, which led to poor segmentation results when an adult model is used to segment a pediatric volume. Therefore, the authors built a new model for pediatric cases and used it to segment pediatric scans. Once this new model was built, the authors employed the same segmentation method used for adults with algorithm parameters that were optimized for pediatric anatomy. A validation experiment was conducted on 10 CT scans in which manually segmented structures were compared to automatically segmented structures. The mean, standard deviation, median, and maximum segmentation errors were 0.23, 0.17, 0.18, and 1.27 mm, respectively. The results indicate that accurate segmentation of the facial nerve and chorda tympani in pediatric scans is achievable, thus suggesting that safe drilling trajectories can also be computed automatically.

Cadaveric Percutaneous CI with AB, Cochlear, and Medel Electrodes

Objective: 1) Describe advances made in percutaneous cochlear implantation (PCI) that involves a minimally invasive approach to the cochlea via a single, image-guided drill pass from the lateral cranium through the facial recess. 2) Demonstrate implementation of PCI in cadavers using Advanced Bionics (AB), Cochlear, and Medel electrodes. Method: PCI was performed on 7 cadaveric temporal bones with 2 AB, 2 Cochlear, and 3 Medel electrodes. This included preoperative CT scanning and PCI trajectory planning, placement of bone-implanted fiducial markers, intraoperative CT, CT registration, creation and attachment of customized microstereotactic frame, drilling from cortex to cochlea, and CI insertion. Results: PCI was successfully performed on all 7 specimens using the AB insertion tool for AB electrodes and via manually threading and endaural advancement for Cochlear and Medel electrodes. Postoperative electrode position was assessed by CT scanning and histopathology. CT correctly predicted 6 of the 7 electrodes to be in scala tympani and 1 in scala vestibuli. Histopathology revealed minimal insertion trauma with preservation of the osseous spiral lamina and basilar membrane and complete scala tympani insertion in 6 of 7 specimens. One specimen, due to violation of the basilar membrane at the round window cochleostomy, had complete scala vestibuli insertion. Conclusion: This is the first description of complete PCI using AB, Cochlear, and Medel electrodes. Using various insertion techniques, atraumatic electrode insertion was achieved in the majority of specimens, similar to results clinically reported for traditional CI surgery. Building on this, we anticipate clinical implementation of PCI in the near future.

Design of a Bone-Attached Parallel Robot for Percutaneous Cochlear Implantation

Access to the cochlea requires drilling in close proximity to bone-embedded nerves, blood vessels, and other structures, the violation of which can result in complications for the patient. It has recently been shown that microstereotactic frames can enable an image-guided percutaneous approach, removing reliance on human experience and hand-eye coordination, and reducing trauma. However, constructing current microstereotactic frames disrupts the clinical workflow, requiring multiday intrasurgical manufacturing delays, or an on-call machine shop in or near the hospital. In this paper, we describe a new kind of microsterotactic frame that obviates these delay and infrastructure issues by being repositionable. Inspired by the prior success of bone-attached parallel robots in knee and spinal procedures, we present an automated image-guided microstereotactic frame. Experiments demonstrate a mean accuracy at the cochlea of 0.20 ± 0.07 mm in phantom testing with trajectories taken from a human clinical dataset. We also describe a cadaver experiment evaluating the entire image-guided surgery pipeline, where we achieved an accuracy of 0.38 mm at the cochlea.

A Manual Insertion Mechanism for Percutaneous Cochlear Implantation

Percutaneous cochlear implantation (PCI) is a recently developed minimally invasive technique that utilizes image guidance and a custom-made microstereotactic frame to guide a drill directly to the cochlea. It enables cochlear access through a single drill port, reducing invasiveness in comparison to mastoidectomy. With the reduction in invasiveness, PCI enables a corresponding reduction in visualization and space in which to work at the cochlear entry point. This precludes standard cochlear implant deployment techniques and necessitates a new insertion tool that can deploy a cochlear implant into the cochlea while working down a deep, narrow channel. In this paper, we describe a manual insertion tool that we have developed for this purpose. The tool is capable of inserting an electrode array into the cochlea using the advance off-stylet technique, using simple manual controls on its handle.

Percutaneous cochlear implant drilling via customized frames: An in vitro study

Objective Percutaneous cochlear implantation (PCI) surgery uses patient-specific customized microstereotactic frames to achieve a single drill-pass from the lateral skull to the cochlea, avoiding vital anatomy. We demonstrate the use of a specific microstereotactic frame, called a “microtable,” to perform PCI surgery on cadaveric temporal bone specimens. Study Design Feasibility study using cadaveric temporal bones. Subjects and Methods PCI drilling was performed on six cadaveric temporal bone specimens. The main steps involved were 1) placing three bone-implanted markers surrounding the ear, 2) obtaining a CT scan, 3) planning a safe surgical path to the cochlea avoiding vital anatomy, 4) constructing a microstereotactic frame to constrain the drill to the planned path, and 5) affixing the frame to the markers and using it to drill to the cochlea. The specimens were CT scanned after drilling to show the achieved path. Deviation of the drilled path from the desired path was computed, and the closest distance of the mid-axis of the drilled path from critical structures was measured. Results In all six specimens, we drilled successfully to the cochlea, preserving the facial nerve and ossicles. In four of six specimens, the chorda tympani was preserved, and in two of six specimens, it was sacrificed. The mean ± standard deviation error at the target was found to be 0.31 ± 0.10 mm. The closest distances of the mid-axis of the drilled path to structures were 1.28 ± 0.17 mm to the facial nerve, 1.31 ± 0.36 mm to the chorda tympani, and 1.59 ± 0.43 mm to the ossicles. Conclusion In a cadaveric model, PCI drilling is safe and effective.