Eric P. Wilkinson

Implementation, calibration and accuracy testing of an image-enhanced endoscopy system

This paper presents a new method for image-guided surgery called image-enhanced endoscopy. Registered real and virtual endoscopic images (perspective volume renderings generated from the same view as the endoscope camera using a preoperative image) are displayed simultaneously; when combined with the ability to vary tissue transparency in the virtual images, this provides surgeons with the ability to see beyond visible surfaces and, thus, provides additional exposure during surgery. A mount with four photoreflective spheres is rigidly attached to the endoscope and its position and orientation is tracked using an optical position sensor. Generation of virtual images that are accurately registered to the real endoscopic images requires calibration of the tracked endoscope. The calibration process determines intrinsic parameters (that represent the projection of three-dimensional points onto the two-dimensional endoscope camera imaging plane) and extrinsic parameters (that represent the transformation from the coordinate system of the tracker mount attached to the endoscope to the coordinate system of the endoscope camera), and determines radial lens distortion. The calibration routine is fast, automatic, accurate and reliable, and is insensitive to rotational orientation of the endoscope. The routine automatically detects, localizes, and identifies dots in a video image snapshot of the calibration target grid and determines the calibration parameters from the sets of known physical coordinates and localized image coordinates of the target grid dots. Using nonlinear lens-distortion correction, which can be performed at real-time rates (30 frames per second), the mean projection error is less than 0.5 mm at distances up to 25 mm from the endoscope tip, and less than 1.0 mm up to 45 mm. Experimental measurements and point-based registration error theory show that the tracking error is about 0.5-0.7 mm at the tip of the endoscope and less than 0.9 mm for all points in the field of view of the endoscope camera at a distance of up to 65 mm from the tip. It is probable that much of the projection error is due to endoscope tracking error rather than calibration error. Two examples of clinical applications are presented to illustrate the usefulness of image-enhanced endoscopy. This method is a useful addition to conventional image-guidance systems, which generally show only the position of the tip (and sometimes the orientation) of a surgical instrument or probe on reformatted image slices.

Small acoustic neuromas: surgical outcomes versus observation or radiation.

Objective: Evaluate factors affecting outcomes of small acoustic neuroma (AN) removal via a middle cranial fossa (MCF) approach, and compare results to published data on observation and radiation therapy. Study Design: Retrospective chart review. Setting: Academic tertiary referral center. Methods: 162 consecutive patients (ages 19-70) with unilateral AN (0.2-2.5 cm in largest dimension) removed through a MCF approach were reviewed focusing on preservation of hearing, facial nerve function and complications. One hundred thirteen patients had pre-operative word recognition scores (WRS) >70%. Results: Both tumor size and pre-operative WRS were related to post-operative WRS (p < 0.01). Overall, at least some hearing was preserved in 94 (60%) of the 156 patients who had hearing before surgery. If the WRS was also >70% (N = 113), 56 (50%) maintained WRS >70%. Importantly, WRS for 12 others improved to >70% after surgery. When the patients were stratified by tumor size, the patients with small tumors (2-10 mm) faired better than the overall group. At least some hearing was preserved in 65 (72%) of the 90 patients. If the WRS was also >70% (N = 66), 39 (59%) maintained WRS >70%. WRS for eight others improved to >70% after surgery. When the tumor was 1.1-1.4 cm (N = 34), the chance of preserving some hearing decreased to 42% (14/33). If the WRS was also >70% (N = 23), 9 (39%) maintained WRS >70%. WRS for three others improved to >70% after surgery. When the tumor reached 1.5-2.5 cm (N = 35), the hearing preservation rate was 43%. If the WRS was also >70% (N = 24), only eight (33%) maintained WRS of 70%, and one other improved to >70%. The addition of intra-operative whole eighth nerve near field monitoring improved results during small tumor (≤ 1.0 cm) removal preserving some hearing in 80% (32/40) and preserving >70% WRS in 76% (22/29) of those with >70% pre-operative WRS. Good facial nerve function (HB I-II) was achieved in 97% (86% HB I). When tumor size was ≤ 1.0 cm (N = 93), however, good facial nerve function was obtained in 100% (94% HB I). Complications included CSF leak: 9 (5.5%); seizure: 2 (1.2%); and recurrence: 1 (0.6%). Conclusion: Our results suggest that removal of unilateral AN through an MCF approach when the tumor is small and hearing is good provides the best opportunity for hearing preservation and normal facial nerve function. Observation historically results in tumor growth in young and middle-age patients with subsequent hearing loss. Radiation may prevent most tumors from growing, and more data are needed to determine long-term tumor control and hearing preservation rates.

Audiologic outcomes with the penetrating electrode auditory brainstem implant.

Objective: The penetrating electrode auditory brainstem implant (PABI) is an extension of auditory brainstem implant (ABI) technology originally developed for individuals deafened by neurofibromatosis type 2. Whereas the conventional ABI uses surface electrodes on the cochlear nuclei, the PABI uses 8 or 10 penetrating microelectrodes in conjunction with a separate array of 10 or 12 surface electrodes. The goals of the PABI were to use microstimulation to reduce threshold current levels, increase the range of pitch percepts, and improve electrode selectivity and speech recognition. Patients and Protocol: In a prospective clinical trial, 10 individuals, all with neurofibromatosis type 2, received a PABI after vestibular schwannoma removal via a translabyrinthine approach. All study participants met strict requirements for informed consent as part of a Food and Drug Administration clinical trial. Approximately 8 weeks after implantation, PABI devices were activated and tested at our tertiary clinical and research facility. Mean follow-up time was 33.8 months. Study Design: Using a single-subject design, we measured thresholds and dynamic ranges, electrode-specific pitch percepts, and speech perception performance at regular intervals. Results: Penetrating electrodes produced auditory thresholds at substantially lower charge levels than surface electrodes, a wide range of electrode-specific pitch sensations, and minimal cross-electrode interference and could be used in speech maps either alone or in combination with surface electrodes. However, less than 25% of penetrating electrodes resulted in auditory sensations, whereas more than 60% of surface electrodes were effective. Even after more than 3 years of experience, patients using penetrating electrodes did not achieve improved speech recognition compared with those using surface electrode ABIs. In patients with usable penetrating electrodes, City University of New York Sentence Test scores with sound and visual information were 61.6% in the PABI group and 64.7% in a surface ABI cohort (p = not significant). Conclusion: The PABI met the goals of lower threshold, increased pitch range, and high selectivity, but these properties did not result in improved speech recognition.

Evolution in the management of facial nerve schwannoma

To design a treatment algorithm based on experience with facial nerve schwannomas (FNS) over a 30‐year period.

Single vertical incision for Baha implant surgery: preliminary results.

Objectives: A single vertical skin incision with subcutaneous tissue removal is a cosmetic alternative for Baha implant placement. We aimed to determine the preliminary complication rate using a 4-cm vertical skin incision. Study Design: Retrospective review. Subjects and Methods: Vertical incision Baha implant placements from January 2006 to August 2007 were reviewed. Complications including skin irritation, skin overgrowth, and implant extrusion were tallied. A total of 71 patients underwent surgery, with a mean follow-up time of 7 months. Results: There were five minor complications (three cases of skin irritation, one wound infection requiring oral antibiotics, one postoperative hematoma) and seven major complications (one case of irritation requiring abutment removal, six cases of skin overgrowth or infection requiring flap revision), for a total complication rate of 16.9 percent. Conclusions: A single vertical incision for Baha implant placement has a complication rate similar to that of traditional dermatome use in this preliminary study. Patients with thick scalps or risk factors for hypertrophic scarring may require longer abutments.

Outcomes following Semicircular Canal Plugging.

Objectives To examine audiometric outcomes, symptom control rates, and complication rates following semicircular canal plugging for superior semicircular canal dehiscence syndrome. Study Design Retrospective chart review. Setting Private, neurotologic tertiary referral center. Subjects and Methods Patients undergoing semicircular canal plugging for superior semicircular canal dehiscence syndrome from January 1, 2007, to December 31, 2012. Pre- and postoperative audiometry, vestibular testing, operative findings, and clinical symptoms were assessed through chart review. Results A total of 24 ears underwent a canal plugging procedure during the study period for superior canal dehiscence syndrome. Pre- and postoperative air conduction pure-tone averages were 21.1 and 22.5 dB (P = .42, not significant [NS]). The average pre- and postoperative word recognition scores were 95.8% and 95.1% (P = .48, NS). Vestibular evoked myogenic potential data showed reduced thresholds in 7 patients with canal dehiscence. Complications were limited to a single, temporary facial weakness. Complete symptom improvement was noted in 35.7% of all patients, while at least partial symptom improvement was found in over 80% of patients. Conclusion Semicircular canal plugging procedures are associated with excellent hearing outcomes and may reduce preoperative symptoms in patients with superior semicircular canal dehiscence.

Hearing preservation with the middle cranial fossa approach for neurofibromatosis type 2.

Objectives To examine hearing preservation rates, facial nerve outcomes, and tumor recurrence rates in patients with neurofibromatosis Type 2 undergoing a primary middle cranial fossa approach for vestibular schwannoma removal. Study Design Retrospective chart review. Setting Private practice tertiary neurotology referral center. Patients All patients with neurofibromatosis Type 2 undergoing attempted hearing preservation via a middle cranial fossa approach for removal of vestibular schwannoma from January 1, 2000, to June 1, 2010. Intervention Primary middle cranial fossa approach for removal of vestibular schwannoma. Main Outcome Measures Preoperative, postoperative, and change in hearing thresholds, word recognition scores, and American Academy of Otolaryngology–Head and Neck Surgery hearing class, House-Brackmann facial nerve grade, and tumor recurrence. Results Class A or B hearing according to the American Academy of Otolaryngology–Head and Neck Surgery was maintained in 50% of cases, whereas 63.6% had Class A, B, or C hearing, with an average word recognition score of 93.8% at an average follow-up period of 32.5 months. Facial nerve outcomes were excellent; 75% of cases maintained House-Brackmann Grade 1, whereas 94.3% had Grade 1 or 2 at an average of 25 months after surgery. Tumor growth within the surgical field was observed radiographically in 59% of cases. Conclusion In patients with neurofibromatosis Type 2, proactive treatment of smaller tumors provides a chance to maintain serviceable hearing and obtain tumor control for extended periods. When examining hearing outcomes, it is important to use word recognition scores, in addition to American Academy of Otolaryngology–Head and Neck Surgery hearing class, to better assess functionality. Although facial nerve outcomes tend to be favorable, the growth of new tumors, including facial schwannomas, may occur within the surgical field. Continued surveillance with serial magnetic resonance scans after surgery is mandatory.

Correction of Progressive Hearing Loss in Superior Canal Dehiscence Syndrome

A 44‐year‐old woman presented with typical vestibular symptoms of superior semicircular canal dehiscence syndrome (SSCDS). In addition, the patient experienced a rapidly progressive mixed hearing loss in the affected ear prior to surgical intervention that was unresponsive to oral steroid administration. Following middle fossa craniotomy with repair of the dehiscence, the patients mixed hearing loss resolved to normal levels with no air‐bone gap. In this report, we discuss the possible etiology of this rapidly progressive hearing loss and its implications on the differential diagnosis of patients with new onset mixed hearing losses. We also contrast the index case of progressive mixed loss with the more frequent conductive hearing loss seen in SSCDS.

Case report: Cochlear implant magnet migration.

A 13‐month‐old cochlear implant recipient underwent routine device activation. Three months postoperatively, the patient sustained a fall with contact to the area of the implant without immediate complication. Ten months postoperatively, the position of the external coil appeared to have moved and the patient did not seem to be responding as well to sound. Audiological testing could not elicit normal device impedances. AP and lateral plain radiographs of the skull revealed migration of the internal magnet from its position within the internal coil to a position over the receiver/stimulator. This is the first known published case of cochlear implant magnet migration.

Side-to-end hypoglossal to facial anastomosis with transposition of the intratemporal facial nerve.

Objective To describe results in a large series of patients using a recent variation of hypoglossal-facial nerve anastomosis (HFA) in which the intratemporal facial nerve segment is used, obviating the need for a sensory nerve “jump graft.” Study Design Retrospective chart review. Setting Tertiary neurotologic referral center. Patients Nineteen patients (12 female/7 male subjects) with facial paralysis because of posterior fossa surgery for tumor (n = 15), Bell’s palsy (n = 1), facial neuroma (n = 1), hemangioma (n = 1), and trauma (n = 1) who underwent HFA from 1997 to 2011, with at least 1-year follow-up. Mean age at surgery is 47.4 years (range, 11.2–83 yr). Mean follow-up is 4.0 years. Intervention Side-to-end hypoglossal to facial anastomosis with transposition of the intratemporal facial nerve (swingdown HFA). Main Outcome Measure House-Brackmann (H-B) facial nerve grade. Results Seven patients (36.8%) achieved an H-B Grade III, 9 patients (47.4%) a grade IV, and 3 patients (15.8%) a grade V at last follow-up. No patients complained of dysphagia, dysarthria, or had evidence of oral incompetence. One patient complained of mild tongue weakness. Age at time of HFA (p ⩽ 0.049, III younger than V) and time from facial nerve injury to HFA (p ⩽ 0.02, III<IV and V) were significant factors for ultimate facial nerve outcome. All patients with an H-B III result had HFA within 6 months of injury. Other factors were not significant. Conclusion The HFA swingdown technique is a safe and effective method to restore facial nerve function in patients with facial paralysis and obviates the need for an interposition jump graft.