Nikolas H. Blevins

Visuohaptic simulation of bone surgery for training and evaluation

Visual and haptic simulation of bone surgery can support and extend current surgical training techniques. The authors present a system for simulating surgeries involving bone manipulation, such as temporal bone surgery and mandibular surgery, and discuss the automatic computation of surgical performance metrics. Experimental results confirm the systems construct validity

Providing metrics and performance feedback in a surgical simulator.

One of the most important advantages of computer simulators for surgical training is the opportunity they afford for independent learning. However, if the simulator does not provide useful instructional feedback to the user, this advantage is significantly blunted by the need for an instructor to supervise and tutor the trainee while using the simulator. Thus, the incorporation of relevant, intuitive metrics is essential to the development of efficient simulators. Equally as important is the presentation of such metrics to the user in such a way so as to provide constructive feedback that facilitates independent learning and improvement. This paper presents a number of novel metrics for the automated evaluation of surgical technique. The general approach was to take criteria that are intuitive to surgeons and develop ways to quantify them in a simulator. Although many of the concepts behind these metrics have wide application throughout surgery, they have been implemented specifically in the context of a simulation of mastoidectomy. First, the visuohaptic simulator itself is described, followed by the details of a wide variety of metrics designed to assess the users performance. We present mechanisms for presenting visualizations and other feedback based on these metrics during a virtual procedure. We further describe a novel performance evaluation console that displays metric-based information during an automated debriefing session. Finally, the results of several user studies are reported, providing some preliminary validation of the simulator, the metrics, and the feedback mechanisms. Several machine learning algorithms, including Hidden Markov Models and a Naïve Bayes Classifier, are applied to our simulator data to automatically differentiate users’ expertise levels.

A Collaborative Virtual Environment for the Simulation of Temporal Bone Surgery

We describe a framework for training-oriented simulation of temporal bone surgery. Bone dissection is simulated visually and haptically, using a hybrid data representation that allows smooth surfaces to be maintained for graphic rendering while volumetric data is used for haptic feedback. Novel sources of feedback are incorporated into the simulation platform, including synthetic drill sounds based on experimental data and simulated monitoring of virtual nerve bundles. Realistic behavior is modeled for a variety of surgical drill burrs, rendering the environment suitable for training low-level drilling skills. The system allows two users to independently observe and manipulate a common model, and allows one user to experience the forces generated by the other’s contact with the bone surface. This permits an instructor to remotely observe a trainee and provide real-time feedback and demonstration.

Virtual reality simulation in neurosurgery: technologies and evolution.

Neurosurgeons are faced with the challenge of learning, planning, and performing increasingly complex surgical procedures in which there is little room for error. With improvements in computational power and advances in visual and haptic display technologies, virtual surgical environments can now offer potential benefits for surgical training, planning, and rehearsal in a safe, simulated setting. This article introduces the various classes of surgical simulators and their respective purposes through a brief survey of representative simulation systems in the context of neurosurgery. Many technical challenges currently limit the application of virtual surgical environments. Although we cannot yet expect a digital patient to be indistinguishable from reality, new developments in computational methods and related technology bring us closer every day. We recognize that the design and implementation of an immersive virtual reality surgical simulator require expert knowledge from many disciplines. This article highlights a selection of recent developments in research areas related to virtual reality simulation, including anatomic modeling, computer graphics and visualization, haptics, and physics simulation, and discusses their implication for the simulation of neurosurgery.

Cochlear implantation in patients with neurofibromatosis type 2 and bilateral vestibular schwannoma.

Objective: To investigate the results of cochlear implantation in patients with neurofibromatosis Type 2 (NF2) and bilateral vestibular schwannoma. Study Design: Retrospective case review. Setting: Three academic tertiary referral centers. Patients: Seven patients with NF2 and bilateral vestibular schwannoma who lost hearing in at least one ear after treatment of their tumor (surgery or radiation therapy). Intervention: Cochlear implantation after treatment of their vestibular schwannoma. Main Outcome Measure: Postimplantation audiometric scores (pure-tone average thresholds, consonant-nucleus-consonant (CNC) words/phonemes, Central Institute for the Deaf (CID) sentences, Hearing in Noise Test (HINT) quiet/noise, and Monosyllable, Trochee, Spondee (MTS) recognition/category tests), patient satisfaction, and device use patterns. Results: The average age at implantation was 40 years (range, 16-57 yr). Follow-up ranged from 6 to 88 months after implantation. Three patients were implanted with residual useful hearing in the contralateral ear, whereas four patients had no hearing in the contralateral ear. Hearing loss was due to surgical excision of tumor (n = 5) or gamma-knife radiotherapy (n = 2). Postactivation pure-tone average thresholds in the implanted ear ranged from 30 to 55 dB (average, 32.5 dB), although speech reception testing varied considerably among subjects. Despite this variability, all patients continue to use the device on a daily basis. Conclusion: In selected cases of deafness in patients with NF2 where there has been anatomic preservation of the auditory nerve after acoustic neuroma resection or radiation therapy, cochlear implantation may offer some improvement in communication skills, including the possibility of open-set speech communication in some patients. These results compare favorably to the auditory brainstem implant offering an alternative for hearing rehabilitation in patients with NF2.

CT Angiography as a Screening Tool for Dural Arteriovenous Fistula in Patients with Pulsatile Tinnitus: Feasibility and Test Characteristics

BACKGROUND AND PURPOSE: The diagnosis of intracranial DAVF with noninvasive cross-sectional imaging such as CTA is challenging. We sought to determine the sensitivity and specificity of CTA compared with cerebral angiography for DAVF in patients presenting with PT. MATERIALS AND METHODS: Following approval of the institutional review board, we reviewed all patients who underwent CTA for PT from 2004 to 2009 and collected clinical and imaging data. Seven patients with PT and proved DAVF and 7 age- and sex-matched control patients with PT but no DAVF composed the study group. CTA images were blindly interpreted by 2 experienced neuroradiologists for the presence of 5 variables: asymmetric arterial feeding vessels, “shaggy” appearance of a dural venous sinus, transcalvarial venous channels, asymmetric venous collaterals, and abnormal size and number of cortical veins. Asymmetric attenuation of jugular veins was additionally assessed. RESULTS: The presence of arterial feeders showed good test characteristics for screening, with a sensitivity of 86% (95% CI, 42–99) and a specificity of 100% (95% CI, 52–100). A shaggy sinus or tentorium was highly specific: sensitivity of 42% (95% CI, 11–79) and specificity of 100% (95% CI, 56–100). The presence of transcalvarial venous channels demonstrated a poor sensitivity of 29% (95% CI, 5–70) but a high specificity 86% (95% CI, 42–99). CT attenuation of the jugular veins showed statistically significant asymmetry in the DAVF group versus the control group (P < .05). CONCLUSIONS: CTA can be used to screen for DAVF in patients with PT. The presence of asymmetrically visible and enlarged arterial feeding vessels has a high sensitivity and specificity for the diagnosis of DAVF.

Tympanic Membrane Collagen Fibers: A Key to High‐Frequency Sound Conduction

Objective: To investigate the significance of tympanic membrane collagen fiber layers in high frequency sound transmission.

Hearing Preservation Surgery for Cochlear Implantation: A Meta-Analysis

Objective To examine the results of hearing preservation in cochlear implantation surgery to identify surgical technical factors, electrode array design factors, and steroid usage, which predicts greater low-frequency hearing preservation. Data sources A thorough search of Medline and Pubmed of English studies from January 1, 1995, to January 1, 2013, was performed using the key words “electric and acoustic hearing” or “hybrid cochlear implant” or “EAS cochlear implant” or “partial deafness cochlear implant” or “bimodal hearing cochlear implant” or “hearing preservation cochlear implant.” Study selection The meta-analysis was conducted according to the PRISMA statement. Only articles in English were included. Studies were included if hearing preservation was the primary end point. A final number of 24 studies met the inclusion criteria. Data extraction Patient populations were analyzed as intention to treat. Data were extracted from raw audiograms where possible. Data were excluded if not all explanatory variables were present or if variable values were ambiguous. Data synthesis The weighted least-squares regression method was used to determine the predictive power of each explanatory variable across all studies. Conclusion In this meta-analysis, the following are associated with better hearing preservation: cochleostomy over the round window approach, posterior tympanotomy over the suprameatal approach, a slow electrode array insertion technique over insertion of less than 30 seconds, a soft tissue cochleostomy seal over a fibrin glue only seal and the use of postoperative systemic steroids. Longer electrode arrays, topical steroid use, and lubricant use for electrode array insertion did not give an advantage.

Evaluating the utility of non–echo‐planar diffusion‐weighted imaging in the preoperative evaluation of cholesteatoma: A meta‐analysis

To describe the accuracy of non–echo‐planar diffusion‐weighted magnetic resonance imaging (DW MRI) in identifying middle ear cholesteatoma.

Exposure of the Lateral Extremity of the Internal Auditory Canal through the Retrosigmoid Approach: A Radioanatomic Study

The recent trend toward earlier diagnosis of acoustic neuroma has substantially increased the number of candidates suitable for surgery with an attempt at hearing preservation. Although the retrosigmoid approach affords the possibility of saving hearing in selected cases, it is associated with a somewhat greater morbidity that other approaches, in terms of persistent headache, cerebrospinal fluid leakage, and cerebellar dysfunction. For this reason, it is best used selectively, when the probability of success in hearing conservation is high. Only a portion of the internal auditory canal can be exposed through the retrosigmoid approach without violating the inner ear, a maneuver that greatly reduces the chance of preserving residual hearing. Substantial variability exists between individuals as to just how far laterally the internal auditory canal may be opened without compromising labyrinthine integrity. To assess the magnitude of this variability, measurements were obtained from 60 high-resolution temporal bone computed tomography scans with a schema intended to model the surgical angle of view used during the retrosigmoid procedure. Intraoperative measurements in a series of cases established that the actual surgical point of view is situated along a line that passes approximately 1.5 cm behind the sigmoid sinus. In this typical surgical position, these data predict that an average of 3.0 mm (32% of the internal auditory canal length) must be left unexposed to avoid labyrinthine injury, with a range between 1.1 mm and 5.3 mm (9% to 58% of the internal auditory canal). Each additional 1-cm retraction on the cerebellum beyond that customarily used affords approximately 1 mm (10% of the internal auditory canal) further exposure of the canal. When considering the retrosigmoid approach to an acoustic neuroma, the clinician is urged to evaluate each patient individually to estimate the amount of internal auditory canal accessible without the removal of a portion of the inner ear. This can be ascertained from an axially oriented, gadolinium-enhanced magnetic resonance imaging scan in the internal auditory canal plane by drawing a line that originates 1.5 cm behind the posterior margin of the sigmoid sinus and passes tangential to the most medial extent of the labyrinth. If this line intersects the posterior margin of the internal auditory canal at least 2 mm lateral to the deepest point of tumor penetration, then adequate exposure with preservation of the labyrinth is likely an achievable goal.