Evaluation of the Facial Recess and Cochlea on the Temporal Bone of Stillbirths regarding the Percutaneous Cochlear Implant.

Introduction The literature shows that there are anatomical changes on the temporal bone anatomy during the first four years of life in children. Therefore, we decided to evaluate the temporal bone anatomy regarding the cochlear implant surgery in stillbirths between 32 and 40 weeks of gestational age using computed tomography to simulate the trajectory of the drill to the scala timpani avoiding vital structures. Objectives To measure the distances of the simulated trajectory to the facial recess, cochlea, ossicular chain and tympanic membrane, while performing the minimally invasive cochlear implant technique, using the Improvise imaging software (Vanderbilt University, Nashville, TN, US). Methods An experimental study with 9 stillbirth specimens, with gestational ages ranging between 32 and 40 weeks, undergoing tomographic evaluation with individualization and reconstruction of the labyrinth, facial nerve, ossicular chain, tympanic membrane and cochlea followed by drill path definition to the scala tympani. Improvise was used for the computed tomography (CT) evaluation and for the reconstruction of the structures and trajectory of the drill. Results Range of the distance of the trajectory to the facial nerve: 0.58 to 1.71 mm. to the ossicular chain: 0.38 to 1.49 mm; to the tympanic membrane: 0.85 to 1.96 mm; total range of the distance of the trajectory: 5.92 to 12.65 mm. Conclusion The measurements of the relationship between the drill and the anatomical structures of the middle ear and the simulation of the trajectory showed that the middle ear cavity at 32 weeks was big enough for surgical procedures such as cochlear implants. Although cochlear implantation at birth is not an indication yet, this study shows that the technique may be an option in the future.

Percutaneous cochlear access using bone-mounted, customized drill guides: demonstration of concept in vitro.

HYPOTHESIS: Percutaneous cochlear access can be performed using bone-mounted drill guides that are custom made on the basis of preintervention computed tomographic scans. BACKGROUND: We have previously demonstrated the ability to use image guidance based on fiducial markers to obtain percutaneous cochlear access in vitro. A simpler approach that has far less room for application error is to constrict the path of the drill to pass in a predetermined trajectory using a drill guide. METHODS: Cadaveric temporal bone specimens (n = 8) were affixed with three bone-implanted fiducial markers. The temporal bone computed tomographic scans were obtained and used in planning a straight trajectory from the mastoid surface to the cochlea without violating the boundaries of the facial recess, namely, the chorda tympani, the incus buttress, and the facial nerve. These surgical plans were used to manufacture a customized drill guide by means of rapid prototyping (MicroTargeting Platform; FHC Inc.; Bowdoinham, ME, U.S.A.) that mounts onto anchor pins previously used to mount fiducial markers. The specimens then underwent traditional mastoidectomy with facial recess. The drill guide was mounted, and a 1-mm drill bit was passed through the guide across the mastoid and the facial recess. The course of the drill bit and its relationship to the boundaries of the facial recess were photographed and measured. RESULTS: Eight cadaveric specimens were subjected to the study protocol. In seven of eight specimens, the drill bit trajectory was accurate; it passed from the lateral cortex to the lateral wall of the cochlea without compromise of any critical structures. In one specimen, the access to the middle ear was achieved, but the incus was hit by the drill. The average shortest distance +/- standard deviation from the edge of the drill bit to the boundaries of the facial recess was 0.78 +/- 0.56 mm (chorda tympani), 2.00 +/- 1.06 mm (incus buttress), and 1.27 +/- 0.54 mm (facial nerve). CONCLUSION: Our study demonstrates the ability to obtain percutaneous cochlear access in vitro using customized drill guides manufactured on the basis of preintervention radiographic studies.

Cadaveric Testing of Robot-Assisted Access to the Internal Auditory Canal for Vestibular Schwannoma Removal.

HYPOTHESIS: An image-guided robotic system can safely perform the bulk removal of bone during the translabyrinthine approach to vestibular schwannoma (VS). BACKGROUND: The translabyrinthine approach to VS removal involves extensive manual milling in the temporal bone to gain access to the internal auditory canal (IAC) for tumor resection. This bone removal is time consuming and challenging due to the presence of vital anatomy (e.g., facial nerve) embedded within the temporal bone. A robotic system can use preoperative imaging and segmentations to guide a surgical drill to remove a prescribed volume of bone, thereby preserving the surgeon for the more delicate work of opening the IAC and resecting the tumor. METHODS: Fresh human cadaver heads were used in the experiments. For each trial, the desired bone resection volume was planned on a preoperative computed tomography (CT) image, the steps in the proposed clinical workflow were undertaken, and the robot was programmed to mill the specified volume. A postoperative CT scan was acquired for evaluation of the accuracy of the milled cavity and examination of vital anatomy. RESULTS: In all experimental trials, the facial nerve and chorda tympani were preserved. The root mean squared surface accuracy of the milled cavities ranged from 0.23 to 0.65 mm and the milling time ranged from 32.7 to 57.0 minute. CONCLUSION: This work shows feasibility of using a robot-assisted approach for VS removal surgery. Further testing and system improvements are necessary to enable clinical translation of this technology.

Resection planning for robotic acoustic neuroma surgery.

Acoustic neuroma surgery is a procedure in which a benign mass is removed from the internal auditory canal (IAC). Currently, this surgical procedure requires manual drilling of the temporal bone followed by exposure and removal of the acoustic neuroma. This procedure is physically and mentally taxing to the surgeon. Our group is working on the development of an acoustic neuroma surgery robot (ANSR) to perform the initial drilling procedure. Planning the ANSR's drilling region using preoperative CT requires expertise and takes about 35 min. We propose an approach for automatically producing a resection plan for the ANSR that would avoid damage to sensitive ear structures and require minimal editing by the surgeon. We first compute an atlas-based segmentation of the mastoid section of the temporal bone, refine it based on the position of anatomical landmarks, and apply a safety margin to the result to produce the automatic resection plan. In experiments with CTs from nine subjects, our automated process resulted in a resection plan that was verified to be safe in every case. Approximately 2 min were required in each case for the surgeon to verify and edit the plan to permit functional access to the IAC. We measured a mean Dice coefficient of 0.99 and surface error of 0.08 mm between the final and automatically proposed plans. These preliminary results indicate that our approach is a viable method for resection planning for the ANSR and drastically reduces the surgeon's planning effort.

Accuracy of linear drilling in temporal bone using drill press system for minimally invasive cochlear implantation.

PURPOSE: A minimally invasive approach for cochlear implantation involves drilling a narrow linear path through the temporal bone from the skull surface directly to the cochlea for insertion of the electrode array without the need for an invasive mastoidectomy. Potential drill positioning errors must be accounted for to predict the effectiveness and safety of the procedure. The drilling accuracy of a system used for this procedure was evaluated in bone surrogate material under a range of clinically relevant parameters. Additional experiments were performed to isolate the error at various points along the path to better understand why deflections occur. METHODS: An experimental setup to precisely position the drill press over a target was used. Custom bone surrogate test blocks were manufactured to resemble the mastoid region of the temporal bone. The drilling error was measured by creating divots in plastic sheets before and after drilling and using a microscope to localize the divots. RESULTS: The drilling error was within the tolerance needed to avoid vital structures and ensure accurate placement of the electrode; however, some parameter sets yielded errors that may impact the effectiveness of the procedure when combined with other error sources. The error increases when the lateral stage of the path terminates in an air cell and when the guide bushings are positioned further from the skull surface. At contact points due to air cells along the trajectory, higher errors were found for impact angles of [Formula: see text] and higher as well as longer cantilevered drill lengths. CONCLUSION: The results of these experiments can be used to define more accurate and safe drill trajectories for this minimally invasive surgical procedure.

Increasing Safety of a Robotic System for Inner Ear Surgery Using Probabilistic Error Modeling Near Vital Anatomy.

Safe and effective planning for robotic surgery that involves cutting or ablation of tissue must consider all potential sources of error when determining how close the tool may come to vital anatomy. A pre-operative plan that does not adequately consider potential deviations from ideal system behavior may lead to patient injury. Conversely, a plan that is overly conservative may result in ineffective or incomplete performance of the task. Thus, enforcing simple, uniform-thickness safety margins around vital anatomy is insufficient in the presence of spatially varying, anisotropic error. Prior work has used registration error to determine a variable-thickness safety margin around vital structures that must be approached during mastoidectomy but ultimately preserved. In this paper, these methods are extended to incorporate image distortion and physical robot errors, including kinematic errors and deflections of the robot. These additional sources of error are discussed and stochastic models for a bone-attached robot for otologic surgery are developed. An algorithm for generating appropriate safety margins based on a desired probability of preserving the underlying anatomical structure is presented. Simulations are performed on a CT scan of a cadaver head and safety margins are calculated around several critical structures for planning of a robotic mastoidectomy.

Minimally invasive, image-guided, facial-recess approach to the middle ear: demonstration of the concept of percutaneous cochlear access in vitro.

HYPOTHESIS: Image-guided surgery will permit accurate access to the middle ear via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. BACKGROUND: The widespread use of image-guided methods in otologic surgery has been limited by the need for a system that achieves the necessary level of accuracy with an easy-to-use, noninvasive fiducial marker system. We have developed and recently reported such a system (accuracy within the temporal bone = 0.76 +/- 0.23 mm; n = 234 measurements). With this system, image-guided otologic surgery is feasible. METHODS: Skulls (n = 2) were fitted with a dental bite-block affixed fiducial frame and scanned by computed tomography using standard temporal-bone algorithms. The frame was removed and replaced with an infrared emitter used to track the skull during dissection. Tracking was accomplished using an infrared tracker and commercially available software. Using this system in conjunction with a tracked otologic drill, the middle ear was approached via the facial recess using a single drill hole from the lateral aspect of the mastoid cortex. The path of the drill was verified by subsequently performing a traditional temporal bone dissection, preserving the tunnel of bone through which the drill pass had been made. RESULTS: An accurate approach to the middle ear via the facial recess was achieved without violating the canal of the facial nerve, the horizontal semicircular canal, or the external auditory canal. CONCLUSIONS: Image-guided otologic surgery provides access to the cochlea via the facial recess in a minimally invasive, percutaneous fashion. While the present study was confined to in vitro demonstration, these exciting results warrant in vivo testing, which may lead to clinically applicable access.

A Compact, Bone-Attached Robot for Mastoidectomy.

Otologic surgery often involves a mastoidectomy, which is the removal of a portion of the mastoid region of the temporal bone, to safely access the middle and inner ear. The surgery is challenging because many critical structures are embedded within the bone, making them difficult to see and requiring a high level of accuracy with the surgical dissection instrument, a high-speed drill. We propose to automate the mastoidectomy portion of the surgery using a compact, bone-attached robot. The system described in this paper is a milling robot with four degrees-of-freedom (DOF) that is fixed to the patient during surgery using a rigid positioning frame screwed into the surface of the bone. The target volume to be removed is manually identified by the surgeon pre-operatively in a computed tomography (CT) scan and converted to a milling path for the robot. The surgeon attaches the robot to the patient in the operating room and monitors the procedure. Several design considerations are discussed in the paper as well as the proposed surgical workflow. The mean targeting error of the system in free space was measured to be 0.5 mm or less at vital structures. Four mastoidectomies were then performed in cadaveric temporal bones, and the error at the edges of the target volume was measured by registering a postoperative computed tomography (CT) to the pre-operative CT. The mean error along the border of the milled cavity was 0.38 mm, and all critical anatomical structures were preserved.

Registration of medical images using an interpolated closest point transform: method and validation.

Image registration is an important procedure for medical diagnosis. Since the large inter-site retrospective validation study led by Fitzpatrick at Vanderbilt University, voxel-based methods and more specifically mutual information-based registration methods (see for instance [IEEE Trans. Med. Imag. 22 (8) (2003) 986] for a review on these methods) have been regarded as the method of choice for rigid-body intra-subject registration problems. In this study we propose a method that is based on the Iterative Closest Point algorithm and a pre-computed closest point map obtained with a slight modification of the fast marching method proposed by Sethian. Pre-computing the closest point map speeds up the process because at each iteration point correspondence can be established by table lookup. We also show that because the closest point map is defined on a regular grid it introduces a registration error and we propose an interpolation scheme that addresses this issue. The method has been tested both on synthetic and real images, and registration results have been assessed quantitatively using the data set provided by the Retrospective Registration Evaluation Project. For these volumes, MR and CT head surfaces were extracted automatically using a level-set technique. Results show that on these data sets this registration method leads to accuracy numbers that are comparable to those obtained with voxel-based methods.

Minimally invasive image-guided cochlear implantation surgery: first report of clinical implementation.

OBJECTIVES/HYPOTHESIS: Minimally invasive image-guided approach to cochlear implantation (CI) involves drilling a narrow, linear tunnel to the cochlea. Reported herein is the first clinical implementation of this approach. STUDY DESIGN: Prospective cohort study. METHODS: On preoperative computed tomography (CT), a safe linear trajectory through the facial recess targeting the scala tympani was planned. Intraoperatively, fiducial markers were bone-implanted, a second CT was acquired, and the trajectory was transferred from preoperative to intraoperative CT. A customized microstereotactic frame was rapidly designed and constructed to constrain a surgical drill along the desired trajectory. Following sterilization, the frame was employed to drill the tunnel to the middle ear. After lifting a tympanomeatal flap and performing a cochleostomy, the electrode array was threaded through the drilled tunnel and into the cochlea. RESULTS: Eight of nine patients were successfully implanted using the proposed approach with six insertions completely within the scala tympani. Traditional mastoidectomy was performed on one patient following difficulty threading the electrode array via the narrow tunnel. Other difficulties encountered included use of the backup implant when an electrode was dislodged during threading via the tunnel, tip fold-over, and facial nerve paresis (House-Brackmann II/VI at 12 months) secondary to heat during drilling. The average time of intervention was 182 ± 36 minutes. CONCLUSIONS: Minimally invasive image-guided CI is clinically achievable. Further clinical study is necessary to address technological difficulties during drilling and insertion, and to assess potential benefits including decreased time of intervention, standardization of surgical intervention, and decreased tissue dissection potentially leading to shorter recovery and earlier implant activation.

Minimally invasive image-guided access for drainage of petrous apex lesions: a case report.

OBJECTIVE: In this case report, we present a novel, minimally invasive image-guided approach to drainage of a petrous apex lesion. PATIENT(S): A 34-year-old man diagnosed with a petrous apex lesion consistent with cholesterol granuloma. The granuloma was large and caused mild compression of the brainstem with associated neurologic symptoms and seizure-like activity. INTERVENTIONS: Based on the anatomic location of the lesion, it was determined that the treatment plan would be to surgically drain the lesion via 2 linear paths-one after an infralabyrinthine approach and the other a subarcuate approach. Customized microstereotactic frames that mount on bone-implanted markers and constrain the drill along the desired path were used to accurately drill these desired paths and avoid damage to surrounding critical structures. After a simple mastoidectomy, the petrous apex was successfully reached without damage to vital adjacent structures by drilling the 2 linear channels using 2 custom microstereotactic frames. MAIN OUTCOME MEASURES: Viscous brown liquid and debris was recovered by irrigating through one of the channels and suctioning through the other. RESULTS: Drainage of the petrous apex was successfully performed via 2 linear channels without any complications. Custom microstereotactic frames were used to accurately drill those linear channels. Postoperative CT ensured no complications. Postoperative course of the patient was remarkable with normal hearing and normal facial nerve function. CONCLUSION: We presented a successful implementation of an image-guided approach to drain petrous apex.

Preliminary Testing of a Compact, Bone-Attached Robot for Otologic Surgery.

Otologic surgery often involves a mastoidectomy procedure, in which part of the temporal bone is milled away in order to visualize critical structures embedded in the bone and safely access the middle and inner ear. We propose to automate this portion of the surgery using a compact, bone-attached milling robot. A high level of accuracy is required to avoid damage to vital anatomy along the surgical path, most notably the facial nerve, making this procedure well-suited for robotic intervention. In this study, several of the design considerations are discussed and a robot design and prototype are presented. The prototype is a 4 degrees-of-freedom robot similar to a four-axis milling machine that mounts to the patient's skull. A positioning frame, containing fiducial markers and attachment points for the robot, is rigidly attached to the skull of the patient, and a CT scan is acquired. The target bone volume is manually segmented in the CT by the surgeon and automatically converted to a milling path and robot trajectory. The robot is then attached to the positioning frame and is used to drill the desired volume. The accuracy of the entire system (image processing, planning, robot) was evaluated at several critical locations within or near the target bone volume with a mean free space accuracy result of 0.50 mm or less at all points. A milling test in a phantom material was then performed to evaluate the surgical workflow. The resulting milled volume did not violate any critical structures.

Forces and trauma associated with minimally invasive image-guided cochlear implantation.

OBJECTIVE: Minimally invasive image-guided cochlear implantation (CI) utilizes a patient-customized microstereotactic frame to access the cochlea via a single drill-pass. We investigate the average force and trauma associated with the insertion of lateral wall CI electrodes using this technique. STUDY DESIGN: Assessment using cadaveric temporal bones. SETTING: Laboratory setup. SUBJECTS AND METHODS: Microstereotactic frames for 6 fresh cadaveric temporal bones were built using CT scans to determine an optimal drill path following which drilling was performed. CI electrodes were inserted using surgical forceps to manually advance the CI electrode array, via the drilled tunnel, into the cochlea. Forces were recorded using a 6-axis load sensor placed under the temporal bone during the insertion of lateral wall electrode arrays (2 each of Nucleus CI422, MED-EL standard, and modified MED-EL electrodes with stiffeners). Tissue histology was performed by microdissection of the otic capsule and apical photo documentation of electrode position and intracochlear tissue. RESULTS: After drilling, CT scanning demonstrated successful access to cochlea in all 6 bones. Average insertion forces ranged from 0.009 to 0.078 N. Peak forces were in the range of 0.056 to 0.469 N. Tissue histology showed complete scala tympani insertion in 5 specimens and scala vestibuli insertion in the remaining specimen with depth of insertion ranging from 360° to 600°. No intracochlear trauma was identified. CONCLUSION: The use of lateral wall electrodes with the minimally invasive image-guided CI approach was associated with insertion forces comparable to traditional CI surgery. Deep insertions were obtained without identifiable trauma.

Minimally invasive image-guided cochlear implantation for pediatric patients: clinical feasibility study.

OBJECTIVE: Minimally invasive image-guided cochlear implantation (CI) involves accessing the cochlea via a linear path from the lateral skull to the cochlea avoiding vital structures including the facial nerve. Herein, we describe and demonstrate the feasibility of the technique for pediatric patients. STUDY DESIGN: Prospective. SETTING: Children's Hospital. SUBJECTS AND METHODS: Thirteen pediatric patients (1.5 to 8 years) undergoing traditional CI participated in this Institutional Review Board-approved study. Three fiducial markers were bone-implanted surrounding the ear, and a CT scan was acquired. The CT scan was processed to identify the marker locations and critical structures of the temporal bone. A safe linear path was determined to target the cochlea avoiding damage to vital structures. A custom microstereotactic frame was fabricated that would mount on the fiducial markers and constrain a tool to the desired trajectory. After traditional mastoidectomy and prior to cochleostomy, the custom microstereotactic frame was mounted on the bone-implanted markers to confirm that the achieved trajectory was safe and accurately accessed the cochlea. RESULTS: For all the 13 patients, it was possible to determine a safe trajectory to the cochlea. Custom microstereotactic frames were validated successfully on 9 patients. Two of these patients had inner ear malformations, and this technique helped the surgeon confirm ideal location for cochleostomy. For patients with normal anatomy, the mean and standard deviation of the closest distance of the trajectory to facial nerve and chorda tympani were 1.1 ± 0.3 mm and 1.2 ± 0.5 mm, respectively. CONCLUSION: Minimally invasive image-guided CI is feasible for pediatric patients.

Clinical testing of an alternate method of inserting bone-implanted fiducial markers.

BACKGROUND: Deep brain stimulation (DBS) surgery utilizes image guidance via bone-implanted fiducial markers to achieve the desired submillimetric accuracy and to provide means for attaching microstereotactic frames. For maximal benefit, the markers must be inserted to the correct depth since over-insertion leads to stripping and under-insertion leads to instability. PURPOSE: The purpose of the study was to test clinically a depth-release drive system, the PosiSeat™, versus manual insertion (pilot hole followed by manual screwing until tactile determined correct seating) for implanting fiducial markers into the bone. METHODS: With institutional review board approval, the PosiSeat™ was used to implant markers in 15 DBS patients (57 fiducials). On post-insertion CT scans, the depth of the gap between the shoulder of the fiducial markers and the closest bone surface was measured. Similar depth measurements were performed on the CT scans of 64 DBS patients (250 fiducials), who underwent manual fiducial insertion. RESULTS: Median of shoulder-to-bone distance for PosiSeat™ and manual insertion group were 0.03 and 1.06 mm, respectively. Fifty percent of the fiducials had the shoulder-to-bone distances within 0.01-0.09 mm range for the PosiSeat group and 0.04-1.45 mm range for the manual insertion group. These differences were statistically significant. CONCLUSIONS: A depth-release drive system achieves more consistent placement of bone-implanted fiducial markers than manual insertion.

Evaluation of the Facial Recess and Cochlea on the Temporal Bone of Stillbirths regarding the Percutaneous Cochlear Implant

Abstract Introduction The literature shows that there are anatomical changes on the temporal bone anatomy during the first four years of life in children. Therefore, we decided to evaluate the temporal bone anatomy regarding the cochlear implant surgery in stillbirths between 32 and 40 weeks of gestational age using computed tomography to simulate the trajectory of the drill to the scala timpani avoiding vital structures. Objectives To measure the distances of the simulated trajectory to the facial recess, cochlea, ossicular chain and tympanic membrane, while performing the minimally invasive cochlear implant technique, using the Improvise imaging software (Vanderbilt University, Nashville, TN, US). Methods An experimental study with 9 stillbirth specimens, with gestational ages ranging between 32 and 40 weeks, undergoing tomographic evaluation with individualization and reconstruction of the labyrinth, facial nerve, ossicular chain, tympanic membrane and cochlea followed by drill path definition to the scala tympani. Improvise was used for the computed tomography (CT) evaluation and for the reconstruction of the structures and trajectory of the drill. Results Range of the distance of the trajectory to the facial nerve: 0.58 to 1.71mm. to the ossicular chain: 0.38 to 1.49 mm; to the tympanic membrane: 0.85 to 1.96 mm; total range of the distance of the trajectory: 5.92 to 12.65 mm. Conclusion The measurements of the relationship between the drill and the anatomical structures of the middle ear and the simulation of the trajectory showed that the middle ear cavity at 32 weeks was big enough for surgical procedures such as cochlear implants. Although cochlear implantation at birth is not an indication yet, this study shows that the technique may be an option in the future.

Implantation of the completely ossified cochlea: an image-guided approach.

OBJECTIVES: To report a novel modification of the cochlear drill-out procedure that uses customized microstereotactic frames as drill guides. PATIENT(S): A 34-year-old man with an 18-year history of profound bilateral hearing loss and completely ossified cochleae that underwent a previous unsuccessful conventional cochlear drill-out procedure in the contralateral ear. INTERVENTIONS: Image-guided cochlear implantation using customized microstereotactic frames to drill linear basal and apical cochlear tunnels. MAIN OUTCOME MEASURES: Transfacial recess cochlear drill-out procedure with full electrode insertion. RESULTS: Two linear paths were drilled using customized microstereotactic frames targeting the proximal and distal basal turn followed by a full split array insertion. Postoperative imaging confirmed 2 cochlear tunnels straddling the modiolus with adequate clearance of the facial nerve and internal carotid artery. The patient received auditory benefit with device use and did not experience any surgical complication. CONCLUSION: Successful cochlear implantation in the setting of total scalar obliteration poses a significant challenge. Image guidance technology may assist in navigating the ossified cochlea facilitating safe and precise cochlear tunnel drilling.

Validation of minimally invasive, image-guided cochlear implantation using Advanced Bionics, Cochlear, and Medel electrodes in a cadaver model.

PURPOSE: Validation of a novel minimally invasive, image-guided approach to implant electrodes from three FDA-approved manufacturers-Medel, Cochlear, and Advanced Bionics-in the cochlea via a linear tunnel from the lateral cranium through the facial recess to the cochlea. METHODS: Custom microstereotactic frames that mount on bone-implanted fiducial markers and constrain the drill along the desired path were utilized on seven cadaver specimens. A linear tunnel was drilled from the lateral skull to the cochlea followed by a marginal, round window cochleostomy and insertion of the electrode array into the cochlea through the drilled tunnel. Post-insertion CT scan and histological analysis were used to analyze the results. RESULTS: All specimens ([Formula: see text]) were successfully implanted without visible injury to the facial nerve. The Medel electrodes ([Formula: see text]) had minimal intracochlear trauma with 8, 8, and 10 (out of 12) electrodes intracochlear. The Cochlear lateral wall electrodes (straight research arrays) ([Formula: see text]) had minimal trauma with 20 and 21 of 22 electrodes intracochlear. The Advanced Bionics electrodes ([Formula: see text]) were inserted using their insertion tool; one had minimal insertion trauma and 14 of 16 electrodes intracochlear, while the other had violation of the basilar membrane just deep to the cochleostomy following which it remained in scala vestibuli with 13 of 16 electrodes intracochlear. CONCLUSIONS: Minimally invasive, image-guided cochlear implantation is possible using electrodes from the three FDA-approved manufacturers. Lateral wall electrodes were associated with less intracochlear trauma suggesting that they may be better suited for this surgical technique.

Evaluation of portable CT scanners for otologic image-guided surgery.

PURPOSE: Portable CT scanners are beneficial for diagnosis in the intensive care unit, emergency room, and operating room. Portable fixed-base versus translating-base CT systems were evaluated for otologic image-guided surgical (IGS) applications based on geometric accuracy and utility for percutaneous cochlear implantation. METHODS: Five cadaveric skulls were fitted with fiducial markers and scanned using both a translating-base, 8-slice CT scanner (CereTom(®)) and a fixed-base, flat-panel, volume CT (fpVCT) scanner (Xoran xCAT(®)). Images were analyzed for: (a) subjective quality (i.e., noise), (b) consistency of attenuation measurements (Hounsfield units) across similar tissue, and (c) geometric accuracy of fiducial marker positions. The utility of these scanners in clinical IGS cases was tested. RESULTS: Five cadaveric specimens were scanned using each of the scanners. The translating-base, 8-slice CT scanner had spatially consistent Hounsfield units, and the image quality was subjectively good. However, because of movement variations during scanning, the geometric accuracy of fiducial marker positions was low. The fixed-base, fpVCT system had high spatial resolution, but the images were noisy and had spatially inconsistent attenuation measurements, while the geometric representation of the fiducial markers was highly accurate. CONCLUSION: Two types of portable CT scanners were evaluated for otologic IGS. The translating-base, 8-slice CT scanner provided better image quality than a fixed-base, fpVCT scanner. However, the inherent error in three-dimensional spatial relationships by the translating-based system makes it suboptimal for otologic IGS use.

Variability of the temporal bone surface's topography: implications for otologic surgery.

Otologic surgery is performed for a variety of reasons including treatment of recurrent ear infections, alleviation of dizziness, and restoration of hearing loss. A typical ear surgery consists of a tympanomastoidectomy in which both the middle ear is explored via a tympanic membrane flap and the bone behind the ear is removed via mastoidectomy to treat disease and/or provide additional access. The mastoid dissection is performed using a high-speed drill to excavate bone based on a pre-operative CT scan. Intraoperatively, the surface of the mastoid component of the temporal bone provides visual feedback allowing the surgeon to guide their dissection. Dissection begins in "safe areas" which, based on surface topography, are believed to be correlated with greatest distance from surface to vital anatomy thus decreasing the chance of injury to the brain, large blood vessels (e.g. the internal jugular vein and internal carotid artery), the inner ear, and the facial nerve. "Safe areas" have been identified based on surgical experience with no identifiable studies showing correlation of the surface with subsurface anatomy. The purpose of our study was to investigate whether such a correlation exists. Through a three-step registration process, we defined a correspondence between each of twenty five clinically-applicable temporal bone CT scans of patients and an atlas and explored displacement and angular differences of surface topography and depth of critical structures from the surface of the skull. The results of this study reflect current knowledge of osteogenesis and anatomy. Based on two features (distance and angular difference), two regions (suprahelical and posterior) of the temporal bone show the least variability between surface and subsurface anatomy.