Magnetic Steering of Robotically Inserted Lateral-wall Cochlear-implant Electrode Arrays Reduces Forces on the Basilar Membrane In Vitro.

HYPOTHESIS: Undesirable forces applied to the basilar membrane during surgical insertion of lateral-wall cochlear-implant electrode arrays (EAs) can be reduced via robotic insertion with magnetic steering of the EA tip. BACKGROUND: Robotic insertion of magnetically steered lateral-wall EAs has been shown to reduce insertion forces in vitro and in cadavers. No previous study of robot-assisted insertion has considered force on the basilar membrane. METHODS: Insertions were executed in an open-channel scala-tympani phantom. A force plate, representing the basilar membrane, covered the channel to measure forces in the direction of the basilar membrane. An electromagnetic source generated a magnetic field to steer investigational EAs with permanent magnets at their tips, while a robot performed the insertion. RESULTS: When magnetic steering was sufficient to pull the tip of the EA off of the lateral wall of the channel, it resulted in at least a 62% reduction of force on the phantom basilar membrane at insertion depths beyond 14.4 mm (p < 0.05), and these beneficial effects were maintained beyond approximately the same depth, even with 10 degrees of error in the estimation of the modiolar axis of the cochlea. When magnetic steering was not sufficient to pull the EA tip off of the lateral wall, a significant difference from the no-magnetic-steering case was not found. CONCLUSIONS: This in vitro study suggests that magnetic steering of robotically inserted lateral-wall cochlear-implant EAs, given sufficient steering magnitude, can reduce forces on the basilar membrane in the first basilar turn compared with robotic insertion without magnetic steering.

Optimizing the Magnetic Dipole-Field Source for Magnetically Guided Cochlear-Implant Electrode-Array Insertions.

Magnetic guidance of cochlear-implant electrode arrays during insertion has been demonstrated in vitro to reduce insertion forces, which is believed to be correlated to a reduction in trauma. In those prior studies, the magnetic dipole-field source (MDS) was configured to travel on a path that would be coincident with the cochlea's modiolar axis, which was an unnecessary constraint that was useful to demonstrate feasibility. In this paper, we determine the optimal configuration (size and location) of a spherical-permanent-magnet MDS needed to accomplish guided insertions with a 100 mT field strength required at the cochlea, and we provide a methodology to perform such an optimization more generally. Based on computed-tomography scans of 30 human subjects, the MDS should be lateral-to and slightly anterior-to the cochlea with an approximate radius (mean and standard deviation across subjects) of 64 mm and 4.5 mm, respectively. We compare these results to the modiolar configuration and find that the volume of the MDS can be reduced by a factor of five with a 43% reduction in its radius by moving it to the optimal location. We conservatively estimate that the magnetic forces generated by the optimal configuration are two orders of magnitude below the threshold needed to puncture the basilar membrane. Although subject-specific optimal configurations are computed in this paper, a one-size-fits-all version with a radius of approximately 75 mm is more robust to registration error and likely more practical. Finally, we explain how to translate the results obtained to an electromagnetic MDS.

An In-Vitro Insertion-Force Study of Magnetically Guided Lateral-Wall Cochlear-Implant Electrode Arrays.

HYPOTHESIS: Insertion forces can be reduced by magnetically guiding the tip of lateral-wall cochlear-implant electrode arrays during insertion via both cochleostomy and the round window. BACKGROUND: Steerable electrode arrays have the potential to minimize intracochlear trauma by reducing the severity of contact between the electrode-array tip and the cochlear wall. However, steerable electrode arrays typically have increased stiffness associated with the steering mechanism. In addition, steerable electrode arrays are typically designed to curve in the direction of the basal turn, which is not ideal for round-window insertions, as the cochlear hook's curvature is in the opposite direction. Lateral-wall electrode arrays can be modified to include magnets at their tips, augmenting their superior flexibility with a steering mechanism. By applying magnetic torque to the tip, an electrode array can be navigated through the cochlear hook and the basal turn. METHODS: Automated insertions of candidate electrode arrays are conducted into a scala-tympani phantom with either a cochleostomy or round-window opening. The phantom is mounted on a multi-degree-of-freedom force sensor. An external magnet applies the necessary magnetic bending torque to the magnetic tip of a modified clinical electrode array, coordinated with the insertion, with the goal of directing the tip down the lumen. Steering of the electrode array is verified through a camera. RESULTS: Statistical t-test results indicate that magnetic guidance does reduce insertion forces by as much as 50% with certain electrode-array models. Direct tip contact with the medial wall through the cochlear hook and the lateral wall of the basal turn is completely eliminated. The magnetic field required to accomplish these insertions varied from 77 to 225 mT based on the volume of the magnet at the tip of the electrode array. Alteration of the tip to accommodate a tiny magnet is minimal and does not change the insertion characteristic of the electrode array unless the tip shape is altered. CONCLUSION: Magnetic guidance can eliminate direct tip contact with the medial walls through the cochlear hook and the lateral walls of the basal turn. Insertion-force reduction will vary based on the electrode-array model, but is statistically significant for all models tested. Successful steering of lateral-wall electrode arrays is accomplished while maintaining its superior flexibility.

Multicenter US Clinical Trial With an Electric-Acoustic Stimulation (EAS) System in Adults: Final Outcomes.

OBJECTIVE: To demonstrate the safety and effectiveness of the MED-EL Electric-Acoustic Stimulation (EAS) System, for adults with residual low-frequency hearing and severe-to-profound hearing loss in the mid to high frequencies. STUDY DESIGN: Prospective, repeated measures. SETTING: Multicenter, hospital. PATIENTS: Seventy-three subjects implanted with PULSAR or SONATA cochlear implants with FLEX electrode arrays. INTERVENTION: Subjects were fit postoperatively with an audio processor, combining electric stimulation and acoustic amplification. MAIN OUTCOME MEASURES: Unaided thresholds were measured preoperatively and at 3, 6, and 12 months postactivation. Speech perception was assessed at these intervals using City University of New York sentences in noise and consonant-nucleus-consonant words in quiet. Subjective benefit was assessed at these intervals via the Abbreviated Profile of Hearing Aid Benefit and Hearing Device Satisfaction Scale questionnaires. RESULTS: Sixty-seven of 73 subjects (92%) completed outcome measures for all study intervals. Of those 67 subjects, 79% experienced less than a 30 dB HL low-frequency pure-tone average (250-1000 Hz) shift, and 97% were able to use the acoustic unit at 12 months postactivation. In the EAS condition, 94% of subjects performed similarly to or better than their preoperative performance on City University of New York sentences in noise at 12 months postactivation, with 85% demonstrating improvement. Ninety-seven percent of subjects performed similarly or better on consonant-nucleus-consonant words in quiet, with 84% demonstrating improvement. CONCLUSION: The MED-EL EAS System is a safe and effective treatment option for adults with normal hearing to moderate sensorineural hearing loss in the low frequencies and severe-to-profound sensorineural hearing loss in the high frequencies who do not benefit from traditional amplification.

Facial nerve outcomes after middle fossa decompression for Bell's palsy.

OBJECTIVE: Evaluate the long-term outcomes of facial nerve decompression via the middle fossa approach for Bell's palsy patients with poor prognosis based on clinical and electrodiagnostic testing. STUDY DESIGN: Retrospective case series. SETTING: Tertiary-care, academic medical center. PATIENTS: Fourteen patients underwent surgical decompression for Bell's palsy within 14 days of symptom onset from 2000 to 2012. Surgical criteria included greater than 90% degeneration on ENoG testing and no voluntary EMG potentials. INTERVENTION: Middle cranial fossa (MCF) bony decompression of the facial nerve, including the meatal foramen, labyrinthine segment, and geniculate ganglion. MAIN OUTCOME MEASURES: Long-term facial function, hearing results, and surgical complications. RESULTS: After MCF decompression, 10 patients (71.4%) regained normal or near-normal facial function (House-Brackmann [HB] I or II) within 1 year after surgery, and 5 of those patients (35.7%) improved to HB I. The remaining 4 patients (28.6%) improved to HB III. Patients older than 60 years (n = 3) had an HB III outcome and did significantly worse than the younger-than-60-years group (p = 0.002). The difference in preoperative and postoperative pure tone average and word recognition score was 2.1 dB and 0.9%, respectively. There were no major complications. Minor, transient complications occurred in 22.2% of patients. CONCLUSION: In patients with severe Bell's palsy at risk for a poor facial nerve outcome, MCF decompression of the facial nerve within 14 days of symptom onset provides good facial nerve outcomes with minimal morbidity.

Pitch adaptation patterns in bimodal cochlear implant users: over time and after experience.

OBJECTIVES: Pitch plasticity has been observed in Hybrid cochlear implant (CI) users. Does pitch plasticity also occur in bimodal CI users with traditional long-electrode CIs, and is pitch adaptation pattern associated with electrode discrimination or speech recognition performance? The goals of this study were to characterize pitch adaptation patterns in long-electrode CI users, to correlate these patterns with electrode discrimination and speech perception outcomes, and to analyze which subject factors are associated with the different patterns. DESIGN: Electric-to-acoustic pitch matches were obtained in 19 subjects over time from CI activation to at least 12 months after activation, and in a separate group of 18 subjects in a single visit after at least 24 months of CI experience. Audiometric thresholds, electrode discrimination performance, and speech perception scores were also measured. RESULTS: Subjects measured over time had pitch adaptation patterns that fit one of the following categories: (1) "Pitch-adapting," that is, the mismatch between perceived electrode pitch and the corresponding frequency-to-electrode allocations decreased; (2) "Pitch-dropping," that is, the pitches of multiple electrodes dropped and converged to a similar low-pitch; and (3) "Pitch-unchanging," that is, the electrode pitches did not change. Subjects measured after CI experience had a parallel set of adaptation patterns: (1) "Matched-pitch," that is, the electrode pitch was matched to the frequency allocation; (2) "Low-pitch," that is, the pitches of multiple electrodes were all around the lowest frequency allocation; and (3) "Nonmatched-pitch," that is, the pitch patterns were compressed relative to the frequency allocations and did not fit either the matched-pitch or low-pitch categories. Unlike Hybrid CI users which were mostly in the pitch-adapting or matched-pitch category, the majority of bimodal CI users were in the latter two categories, pitch-dropping/low-pitch or pitch-unchanging/nonmatched-pitch. Subjects with pitch-adapting or matched-pitch patterns tended to have better low-frequency thresholds than subjects in the latter categories. Changes in electrode discrimination over time were not associated with changes in pitch differences between electrodes. Reductions in speech perception scores over time showed a weak but nonsignificant association with dropping-pitch patterns. CONCLUSIONS: Bimodal CI users with more residual hearing may have somewhat greater similarity to Hybrid CI users and be more likely to adapt pitch perception to reduce mismatch with the frequencies allocated to the electrodes and the acoustic hearing. In contrast, bimodal CI users with less residual hearing exhibit either no adaptation, or surprisingly, a third pattern in which the pitches of the basal electrodes drop to match the frequency range allocated to the most apical electrode. The lack of association of electrode discrimination changes with pitch changes suggests that electrode discrimination does not depend on perceived pitch differences between electrodes, but rather on some other characteristics such as timbre. In contrast, speech perception may depend more on pitch perception and the ability to distinguish pitch between electrodes, especially since during multielectrode stimulation, cues such as timbre may be less useful for discrimination.

Minimal access cochlear implant fixation: temporalis pocket with a plate.

OBJECTIVE: Minimal access approaches for cochlear implants have recently gained popularity, offering a smaller incision and minimal hair shave. The current generation of thinner internal receiver stimulators is adaptable for these approaches. However, conventional bony fixation of the internal receiver stimulator is difficult through this limited exposure, and some minimal access techniques rely on soft tissue fixation only. Inadequate fixation can result in device migration, extrusion, and electrode migration. We compare wound complications and electrode migration for a group undergoing conventional exposure and device fixation using a bone well and sutures with a group undergoing minimal access with plate fixation. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Adults and children undergoing primary cochlear implant surgery using either technique. INTERVENTION(S): Therapeutic. MAIN OUTCOME MEASURE(S): Wound complications including device exposure or extrusion, electrode migration, wound breakdown, abscess, or cellulitis. RESULTS: There were 193 implants in the conventional group and 103 in the minimal access with plate group. The conventional group experienced an overall complication rate of 3.6%, and the minimal access with plate group experienced an overall complication rate of 2%. Major complications occurred in 1% of patients in either group. There were no incidents of device migration, extrusion, or electrode migration in either group. CONCLUSION: Cochlear implant surgery using the minimal access with plate fixation results in a similar wound complication rate as the conventional approach.

Preoperative embolization of the inferior petrosal sinus in surgery for glomus jugulare tumors.

OBJECTIVE: To compare the outcomes of surgery for glomus tumors involving the jugular foramen with and without preoperative venous embolization of the inferior petrosal sinus (IPS). STUDY DESIGN: Retrospective chart review. SETTING: Tertiary referral center. PATIENTS: Twenty-four patients with paragangliomas involving the jugular foramen treated between 1995 and 2008. INTERVENTION: All patients underwent surgical resection after receiving preoperative angioembolization with or without venous embolization of the IPS. MAIN OUTCOME MEASURES: Total operative duration, estimated blood loss, intensive care unit and total hospital days, and novel postoperative lower cranial nerve deficits were recorded, and appropriate statistical analysis was conducted. RESULTS: Twenty-four patients met inclusion criteria. Fourteen of these patients underwent preoperative embolization of the IPS in addition to angioembolization. The group that did not undergo embolization of the IPS was used as the control group (n = 10). These groups were compared with regard to the above outcome measures. Blood loss and new lower cranial nerve deficits were reduced in the venous embolization group, although neither measure reached statistical significance. Tumor size correlated with increased intraoperative hypotensive events and longer total hospital stay, and these correlations were statistically significant. CONCLUSION: Preoperative embolization of the IPS is possible in many patients undergoing surgery of the jugular foramen. The addition of venous embolization to the traditional arterial embolization of glomus jugulare tumors adds little additional time or expense to the procedure and facilitates control of bleeding once the jugular bulb has been opened.

Apparent cochlear nerve aplasia: to implant or not to implant?

OBJECTIVE: To describe the imaging findings and clinical outcomes of children with apparent cochlear nerve aplasia undergoing cochlear implantation. STUDY DESIGN: Retrospective case review. SETTING: Tertiary care center. PATIENTS: Three patients with imaging findings consistent with absent cochlear nerve canal on diagnostic imaging and questionable audiometric responses on testing who underwent promontory stimulation and subsequent cochlear implantation. INTERVENTION(S): Magnetic resonance imaging and computed tomography, audiologic assessment, and cochlear implantation. MAIN OUTCOME MEASURE(S): Audiologic performance after cochlear implantation. RESULTS: Three patients were identified to have hearing loss on newborn hearing screening and underwent auditory brainstem response testing revealing absent brainstem responses. ASSR testing was inconclusive when performed. Imaging in all cases identified 1 ear with a small internal auditory canal with 2 nerves present, one of which seems to enter the vestibule in each case and the other is assumed to be the functioning facial nerve. There was a bony plate present over the entrance to the cochlea in 2 of the 3 patients. Over time, 2 of the families reported responses to auditory stimuli with amplification. Promontory stimulation testing showed reproducible responses to electrical stimuli in the ears in question. After cochlear implantation, all 3 patients have shown responses to auditory stimuli. CONCLUSION: The absence of a visible cochlear nerve or cochlear nerve canal on radiologic imaging does not preclude auditory innervation of the cochlea. Cochlear implantation can be a viable option for patients with apparent cochlear nerve aplasia who have undergone appropriate testing. Electronically evoked auditory brainstem response is critical in the evaluation of this patient group.

Robotic surgery of the infratemporal fossa utilizing novel suprahyoid port.

OBJECTIVES/HYPOTHESIS: To develop a minimally invasive technique for robotic access to the infratemporal fossa and describe use of a novel suprahyoid port placement. STUDY DESIGN: A cadaveric study to assess feasibility of robotic dissection of the infratemporal fossa using a novel, midline suprahyoid port placement. METHODS: Six complete and two partial dissections of the infratemporal fossa were carried out on one fixed and three fresh cadaveric heads using the da Vinci surgical robot (Intuitive Surgical, Inc., Sunnyvale, CA). The suprahyoid port site was utilized to place one robotic arm into the vallecula. The second arm and 30 degrees camera were placed transorally, and dissections were performed through the lateral pharyngeal wall and into the infratemporal fossa with identification and preservation of the lingual nerve, inferior alveolar nerve, internal and external carotid arteries, jugular vein, and cranial nerves IX-XII. Surgical clips were placed at the extent of dissection, and computed tomography (CT) imaging was obtained after dissections. RESULTS: The transoral and midline suprahyoid port sites provide excellent access to the infratemporal fossa. The midline port site has excellent utility for accessing wide areas of the skull base bilaterally. CT imaging shows surgical clips placed successfully at the skull base foramina of major neurovascular structures. CONCLUSIONS: Robotic surgery offers several advantages over traditional endoscopic surgery with the addition of tremor-free, two-handed technique and microscopic three-dimensional visualization. A midline suprahyoid port placement provides minimally invasive access for excellent exposure of the infratemporal fossa bilaterally.

Acetaminophen ototoxicity after acetaminophen/hydrocodone abuse: evidence from two parallel in vitro mouse models.

OBJECTIVE: Acetaminophen/hydrocodone, a commonly used analgesic preparation, has been linked to rapidly progressing sensorineural hearing loss in human patients. The cellular and molecular mechanisms underlying the ototoxic effects of this drug combination are currently unknown, but are usually associated with high doses of hydrocodone. This study was aimed at identifying the specific agent responsible for hearing loss from toxic killing of cochlear sensory cells. STUDY DESIGN: Dose-response study. SETTING: University laboratory and private research facility. SUBJECTS AND METHODS: Math1 green fluorescent protein neonatal mouse cochlear cultures as well as a mouse auditory cell line (HEI-OC1) were exposed in vitro to different concentrations of acetaminophen, hydromorphone (the active metabolite of hydrocodone), and the micronutrient L-carnitine, either alone or combined. Using fluorescent and light microscopy, we quantified the sensory hair cells from a 600-microm basal segment before and after treatment. Acetaminophen/hydrocodone-induced apoptosis of HEI-OC1 was evaluated by caspase 3-activation studies. Statistically significant cell survival was determined with Student t test and analysis of variance. RESULTS: Cell death was associated mainly with exposure to acetaminophen, was slightly potentiated when combined with hydromorphone, and was partially prevented by L-carnitine. Exposure to hydrocodone or hydromorphone alone failed to kill either cochlear hair cells or HEI-OC1 cells. CONCLUSION: Our findings point to acetaminophen, rather than hydrocodone, as the primary cytotoxic agent. Hydrocodone, however, may work synergistically with acetaminophen, increasing the damage to auditory cells. These findings are an important first step toward understanding the mechanism of acetaminophen/hydrocodone ototoxicity and may lead to future treatment strategies for hearing loss from ototoxic medications.

Is there a correlation between vascular loops in the cerebellopontine angle and unexplained unilateral hearing loss?

OBJECTIVE: This study was a retrospective analysis of patients who had received magnetic resonance imaging scans of the internal auditory canal (IAC) to evaluate unexplained asymmetric hearing loss. The study aimed to correlate structural features of vascular loops formed by the anterior inferior cerebellar artery (AICA) within the cerebellopontine angle and IAC with asymmetric hearing loss. STUDY DESIGN: High-resolution thin-section T2 fast spin echo magnetic resonance imaging scans of 58 patients with asymmetric sensorineural hearing loss were obtained; the structure of the AICA was graded on both sides using 2 scoring systems. The grading senior head and neck radiologist was blinded to the clinical history. The first scoring system used was the Chavda classification, which is based on the anatomic location of the AICA loop. This system identified 92 loops within the cerebellopontine angle; 22 loops extending less than halfway into the IAC and 2 loops extending more than halfway into the IAC. A second classification system was used simultaneously to describe the extent of contact between the AICA loop and the vestibulocochlear nerve. The second system identified 24 loops that were not in contact with the nerve, 60 in which the loop was running adjacent to the nerve but not displacing it; 12 loops were identified that were displacing the vestibulocochlear nerve, and 24 loops were identified running between the facial and the vestibulocochlear nerve. Four loops were classified as both displacing the vestibulocochlear nerve and running between the facial and vestibulocochlear nerves. Tinnitus was present in addition to hearing loss. In 48 of the 58 patients, the statistical analysis was repeated for these patients. RESULTS: No statistically significant association was found between loops classified by the Chavda system and hearing loss. No statistically significant association was present between loops that made no contact with the nerve, ran adjacent to the nerve, or displaced the nerve. A statistically significant association was found between loops that ran between the facial and vestibulocochlear nerve and hearing loss, with a p value of 0.0162. The subset who had tinnitus in addition to hearing loss had similar results, with the only significant association being found between loops running between the facial nerve and the vestibulocochlear nerve, and a p value of 0.0433 was obtained. CONCLUSION: A correlation between vascular loops and hearing loss did not exist in the majority of the patients in this study. The subset of patients that had a vessel between the facial and vestibular cochlear nerves deserve further investigation.

Automatic identification and 3D rendering of temporal bone anatomy.

HYPOTHESIS: Using automated methods, vital anatomy of the middle ear can be identified in computed tomographic (CT) scans and used to create 3-dimensional (3D) renderings. BACKGROUND: Although difficult to master, clinicians compile 2D data from CT scans to envision 3D anatomy. Computer programs exist that can render 3D surfaces but are limited in that ear structures, for example, the facial nerve, can only be visualized after time-intensive manual identification for each scan. Here, we present results from novel computer algorithms that automatically identify temporal bone anatomy (external auditory canal, ossicles, labyrinth, facial nerve, and chorda tympani). METHODS: An atlas of the labyrinth, ossicles, and auditory canal was created by manually identifying the structures in a "normal" temporal bone CT scan. Using well-accepted techniques, these structures were automatically identified in (n = 14) unknown CT images by deforming the atlas to match the unknown volumes. Another automatic localization algorithm was implemented to identify the position of the facial nerve and chorda tympani. Results were compared with manual identification by measuring false-positive and false-negative error. RESULTS: The labyrinth, ossicles, and auditory canal were identified with mean errors less than 0.5 mm. The mean errors in facial nerve and chorda tympani identification were less than 0.3 mm. CONCLUSION: Automated identification of temporal bone anatomy is achievable. The presented combination of techniques was successful in accurately identifying temporal bone anatomy. These results were obtained in less than 10 minutes per patient scan using standard computing equipment.

Imaging characteristics of metastatic lesions to the cerebellopontine angle.

OBJECTIVE: To describe characteristic features of metastatic lesion to the cerebellopontine angle (CPA) and internal auditory canal (IAC). STUDY DESIGN: Retrospective review. SETTING: Tertiary care medical center. PATIENTS: Patients with metastatic lesions to the CPA. INTERVENTION: Diagnostic. MAIN OUTCOME MEASUREMENTS: Clinical presentation and imaging characteristics on magnetic resonance imaging and computed tomography. RESULTS: A total of 25 cases were reviewed. The average patient age was 56 years, and almost all patients presented with palsy of the cranial VII and VIII nerves. There were 14 cases of metastases to the CPA, 16 cases to the IAC, 5 cases to the CPA and IAC, and 7 cases to the dura. There were several identifiable patterns of metastases to the CPA/IAC, including the flocculus (5), pia/arachnoid (12), dura (7), and choroid plexus (3). T1 magnetic resonance imaging was most commonly isointense to hypointense to brain, with enhancement on T1 imaging with contrast. Lesions tend to be eccentric to the IAC. T2 and fluid-attenuated inversion-recovery (FLAIR) imaging shows adjacent cerebellar and brainstem vasogenic edema. Characteristics that differentiate metastatic lesions from benign lesions of the CPA include vasogenic edema on T2 and FLAIR imaging and multiple central nervous system lesions and lesions that are eccentric to the IAC. CONCLUSION: Recognizing characteristic patterns of spread to the CPA and IAC can aid the clinician in the diagnosis of metastatic lesions to this area. Clinical history of rapidly progressive cranial nerve deficits, particularly facial paralysis in a patient with a history of malignancy, increases the level of suspicion. Imaging characteristics of metastatic lesions to the CPA include adjacent vasogenic edema observed on T2-weighted imaging and FLAIR, eccentric location to the IAC, and multiple lesions observed on head and neck imaging.

Computed tomographic imaging of stapes implants.

HYPOTHESIS: Computed tomographic (CT) imaging of stapes prostheses is inaccurate. BACKGROUND: Clinical situations arise in which it would be helpful to determine the depth of penetration of a stapes prosthesis into the vestibule. The accuracy of CT imaging for this purpose has not been defined. This study was aimed to determine the accuracy of CT imaging to predict the depth of intrusion of stapes prostheses into the vestibule. METHODS: The measurement of stapes prostheses by CT scan was compared with physical measurements in 8 cadaveric temporal bones. RESULTS: The depth of intrusion into the vestibule of the piston was underestimated in specimens with the fluoroplastic piston by a mean of 0.5 mm when compared with the measurements obtained in the temporal bones. The depth of penetration of the stainless steel implant was overestimated by 0.5 mm when compared with that in the temporal bone. CONCLUSION: The type of implant must be taken into consideration when estimating the depth of penetration into the vestibule using CT scanning because the imaging characteristics of the implanted materials differ. The position of fluoroplastic pistons cannot be accurately measured in the vestibule. Metallic implants are well visualized, and measurements exceeding 2.2 mm increase the suspicion of otolithic impingement. Special reconstructions along the length of the piston may be more accurate in estimating the position of stapes implants.

Automatic segmentation of the facial nerve and chorda tympani in CT images using spatially dependent feature values.

In cochlear implant surgery, an electrode array is permanently implanted in the cochlea to stimulate the auditory nerve and allow deaf people to hear. A minimally invasive surgical technique has recently been proposed-percutaneous cochlear access-in which a single hole is drilled from the skull surface to the cochlea. For the method to be feasible, a safe and effective drilling trajectory must be determined using a preoperative CT. Segmentation of the structures of the ear would improve trajectory planning safety and efficiency and enable the possibility of automated planning. Two important structures of the ear, the facial nerve and the chorda tympani, are difficult to segment with traditional methods because of their size (diameters as small as 1.0 and 0.3 mm, respectively), the lack of contrast with adjacent structures, and large interpatient variations. A multipart, model-based segmentation algorithm is presented in this article that accomplishes automatic segmentation of the facial nerve and chorda tympani. Segmentation results are presented for ten test ears and are compared to manually segmented surfaces. The results show that the maximum error in structure wall localization is approximately 2 voxels for the facial nerve and the chorda, demonstrating that the method the authors propose is robust and accurate.

Congenital cholesteatoma of the mastoid temporal bone.

OBJECTIVE: Congenital mastoid cholesteatomas are rare lesions of the temporal bone. The clinical presentation of these lesions is variable, making them difficult to identify preoperatively. We evaluated our series of mastoid congenital cholesteatomas (CCs) in an effort to better define the clinical presentation, imaging characteristics, and surgical challenges specific to this lesion. STUDY DESIGN: Retrospective chart and radiologic study review. METHODS: The medical records of patients with the diagnosis of mastoid CC on radiologic imaging over a 15-year period were reviewed. All had surgical and pathologic confirmation. Eight patients underwent preoperative computed tomography (CT). Six also underwent magnetic resonance (MR) scanning. Demographic information, clinical presentation, imaging results, and operative findings were recorded. RESULTS: Nine patients with the diagnosis of mastoid CC satisfying the inclusion criteria were found. Clinical findings were variable, with the most common presentation being an incidental finding. Imaging findings were more uniform. All CT scans demonstrated an expansile, well-circumscribed mass centered within the mastoid portion of the temporal bone. All MR scans showed a well-circumscribed mass with high intensity on T2-weighted images with precontrasted T1 sequences showing the lesion to be isointense or slightly hyperintense to cerebrospinal fluid (CSF). Operative findings included lateral mastoid cortex erosion, sigmoid sinus exposure, ossicular destruction, facial nerve exposure, and associated postauricular abscess. Management of these lesions is reviewed. CONCLUSION: Congenital mastoid cholesteatomas have a variable and nonspecific clinical presentation. Surgical challenges arise from the indolent nature of this clinical entity, which belies the extent of otologic involvement. Imaging with CT and magnetic resonance imaging are diagnostic, defines the extent of these lesions, and facilitates preoperative surgical planning.

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.

Magnetic resonance appearance of the inner ear after hearing-preservation surgery.

OBJECTIVE: To determine whether the appearance of the inner ear on T2-weighted follow-up magnetic resonance imaging correlates with hearing status after hearing-preservation surgery for vestibular schwannoma. STUDY DESIGN: Retrospective chart review. SETTING: Tertiary referral medical center. PATIENTS: The study includes patients undergoing hearing-preservation surgery for vestibular schwannoma from 1998 to 2003. INTERVENTION: Diagnostic evaluation with magnetic resonance imaging and audiometric evaluation. MAIN OUTCOME MEASURES: Hearing results as reported in charts was correlated with appearance of membranous labyrinth on T2-weighted magnetic resonance images obtained at least 1 year after surgery. RESULTS: Twenty-nine patients were identified, 16 of whom satisfied the inclusion criteria. All 16 of the patients underwent middle fossa removal of vestibular schwannoma. Serviceable hearing according to American Academy of Otolaryngology-Head and Neck Surgery criteria was preserved in eight patients (50%). Of the eight patients without serviceable hearing, six had the cochlear nerve sacrificed at the time of surgery. All patients with serviceable hearing had normal appearing cochleovestibular signal on T2-weighted images, whereas six of eight patients (75%) with no hearing or poor hearing had abnormal low signal in the inner ear, suggesting inner ear ossification. The positive predictive value of a normal labyrinth for preserved hearing was 90%, whereas the negative predictive value of an abnormal labyrinth for no hearing was 100%. All but one patient who had the cochlear nerve sacrificed showed abnormal morphology of the labyrinth on T2-weighted magnetic resonance imaging. CONCLUSION: We describe the T2-weighted magnetic resonance findings after hearing-preservation surgery for acoustic tumor removal. Loss of inner ear signal on T2-weighted images correlates with loss of hearing postoperatively, whereas preserved inner ear signal correlates with hearing preservation after middle fossa surgery for vestibular schwannoma removal.

Revision lateral skull base surgery.

OBJECTIVE: To describe functional and reconstructive results after revision lateral skull base surgery with comparison of benign and malignant lesions. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: All patients undergoing revision surgery for benign and malignant lateral skull base tumors. INTERVENTIONS: Surgical resection of recurrent lateral skull base tumors and reconstruction of resulting defects. MAIN OUTCOME MEASURES: Cranial nerve function postoperative complications. RESULTS: Forty operations for recurrent lateral skull base tumors occurred between January 1, 1987, and December 31, 2003, with follow-up of at least 1 year. Thirty-three operations were for benign lesions, 27 of which were glomus tumors. Seven operations were for malignant tumors. Fifty-eight percent of patients had preoperative cranial nerve deficits (66% of benign tumors and 14% of malignancies). The most common preoperative deficit occurred in the Xth cranial nerve. Postoperative cranial nerve deficits were seen in 95% of patients and multiple nerve deficits were seen in 75%. The most common postoperative deficits were observed in the IXth and Xth cranial nerves. Thirty-one patients had one previous procedure, six had two previous procedures, and three had three previous procedures. Abdominal fat and temporoparietal fascia were the most common reconstruction materials. There was one case of meningitis, two cerebrospinal fluid leaks, and one pseudomeningocele. There was one recurrent adenoid cystic tumor resulting in death and two partially resected glomus tumors. Subsequent procedures are discussed. CONCLUSION: Postoperative cranial deficits are more common after revision skull base surgery than after primary surgery. Complete resection without recurrence can be expected for revision skull base surgery. Modern reconstruction techniques reduce major postoperative complications and morbidity from cranial nerve deficits.