Aaron E. Bond

GAN GROWTH ON SI(111) SUBSTRATE USING OXIDIZED ALAS AS AN INTERMEDIATE LAYER

We have demonstrated that GaN can be grown epitaxially by atmospheric pressure metalorganic chemical vapor deposition on an aluminum oxide compound layer utilized as an intermediate layer between GaN and a Si(111). X-ray diffraction measurement indicates that single-crystal hexagonal GaN with its basal plane parallel to the Si(111) plane is grown. Using a scanning electron microscope, the macroscopic evolution of GaN grown on the AlOx/Si(111) substrate is found to be similar to that of GaN grown on a sapphire(0001) substrate. Cathodoluminescence (CL) spectrum shows a unique emission that consists of several peaks with the intensity comparable to that of the near-band-edge emission. Unique characteristics in CL spectrum are discussed in terms of a possible oxygen contamination of GaN grown on the AlOx/Si(111) substrate.

Retrospective analysis of a concurrent series of microscopic versus endoscopic transsphenoidal surgeries for Knosp Grades 0–2 nonfunctioning pituitary macroadenomas at a single institution

OBJECT The object of this study was to compare surgical outcomes and complications in a contemporaneous series of patients undergoing either microscopic or endoscopic transsphenoidal surgery for nonfunctioning pituitary macroadenomas without imaging evidence of cavernous sinus invasion. METHODS This is a retrospective analysis of a prospectively collected database from a single institution. Data were collected from patients whose surgery had occurred in the period from June 2010 to January 2013. Patients who underwent microscopic or endoscopic surgery for Knosp Grade 0, 1, or 2 nonfunctioning pituitary macroadenomas were included in the study. Patients who had clinically secreting or Knosp Grade 3 or 4 tumors and patients who were undergoing revision surgery were excluded from analysis. Eligible patient records were analyzed for outcomes and complications. Statistical analyses were performed on tumor volume, intraoperative factors, postoperative complications, and degree of resection on 1-year postoperative MRI. The results were used to compare the outcomes after microscopic and endoscopic approaches. RESULTS Forty-three patients underwent microscopic transsphenoidal surgery, and 56 underwent endoscopic transsphenoidal surgery. There were no statistical differences in the intraoperative extent of resection or endocrinological complications. There were significantly more intraoperative CSF leaks in the endoscopic group (58% vs 16%); however, there was no difference in the incidence of postoperative CSF rhinorrhea (12% microscopic vs 7% endoscopic). Length of hospitalization was significantly shorter in patients undergoing an endoscopic approach (3.0 days vs 2.4 days). Two-month follow-up imaging was available in 95% of patients, and 75% of patients had 1-year follow-up imaging. At 2 months postprocedure, there was no evidence of residual tumor in 79% (31 of 39) and 85% (47 of 55) of patients in the microscopic and endoscopic groups, respectively. At 1 year postprocedure, 83% (25 of 30) of patients in the microscopic group had no evidence of residual tumor and 82% (36 of 44) of those in the endoscopic group had no evidence of residual tumor. CONCLUSIONS The microscopic and endoscopic techniques provide similar outcomes in the surgical treatment of Knosp Grades 0-2 nonfunctioning pituitary macroadenomas.

Incidence Trends in the Anatomic Location of Primary Malignant Brain Tumors in the United States: 1992–2006

BACKGROUND This study sought to determine incidence trends of the anatomical origin of primary malignant brain tumors. METHODS Incidence data for histologically confirmed brain tumors were obtained from the Los Angeles County Cancer Surveillance Program (LAC), the California Cancer Registry (CCR), and the National Cancer Institutes Surveillance, Epidemiology, and End Results (SEER) program for 1992 to 2006. Age-adjusted incidence rates (AAIR) and annual percent changes (APC) were calculated by histologic subtypes and anatomic subsites. Statistical analyses were performed using the SEER*Stat analytic software and SAS statistical software. RESULTS Increased AAIRs of frontal (APC +2.4% to +3.0%, P ≤ 0.001) and temporal (APC +1.3% to +2.3%, P ≤ 0.027) lobe glioblastoma multiforme (GBM) tumors were observed across all registries, accompanied by decreased AAIRs in overlapping region GBMs (-2.0% to -2.8% APC, P ≤ 0.015). The AAIRs of GBMs in the parietal and occipital lobes remained stable. The AAIR of cerebellar GBMs increased according to CCR (APC +11.9%, P < 0.001). The AAIR of all gliomas, which includes all anatomical subsites, decreased (-0.5% to -0.8% APC, P ≤ 0.034). Low-grade and anaplastic astrocytomas demonstrated decreased AAIRs in the majority of brain regions. CONCLUSIONS Data from 3 major cancer registries demonstrate increased incidences of GBMs in the frontal lobe, temporal lobe, and cerebellum, despite decreased incidences in other brain regions. Although this may represent an effect of diagnostic bias, the incidence of both large and small tumors increased in these regions. The cause of these observed trends is unknown.

Operative strategies for minimizing hearing loss and other major complications associated with microvascular decompression for trigeminal neuralgia.

OBJECTIVE To retrospectively assess the surgical outcomes and complication rates following microvascular decompression (MVD) for trigeminal neuralgia, using a targeted, restricted retrosigmoid approach. METHODS During the period 1994-2009, a total of 119 patients underwent MVD for trigeminal neuralgia. A retrospective review was conducted in order to assess pain outcomes following surgery and at most recent follow-up. The intraoperative findings, Barrow Neurologic Institute (BNI) pain scores, medication usage, brainstem auditory evoked potential records, and complication rates (including postoperative hearing status) were reviewed and subsequently analyzed. RESULTS Of the 119 patients who underwent MVD, 61 (51%) were male and 58 (49%) were female. The mean age was 60 years (range 22-86 years). Operative findings included 94 patients (79%) with arterial compression, 16 patients (13%) with isolated venous compression, 1 patient (1%) with a small arteriovenous malformation, and 8 patients (7%) with no obvious source of compression. No perioperative deaths or major complications, including hearing loss, occurred in any patients. Minor complications occurred in 9 patients (8%), including a transient trochlear nerve palsy in 1 patient, transient nystagmus in 1 patient, cerebrospinal fluid leak requiring revision in 1 patient, wound infections requiring revision in 3 patients, and wound infections requiring antibiotics alone in 3 patients. Follow-up data were available for 109 patients, of whom 88 (81%) had excellent outcomes (BNI Score I-II). Ninety-eight patients (90%) had good outcomes (BNI scores I-IIIb), 7 patients (6%) had persistent pain that was not controlled with medications (BNI Score IV), and 4 patients (4%) experienced no relief following surgery (BNI Score V). CONCLUSION The use of a small craniectomy (<20 mm) in conjunction with a restricted retrosigmoid approach, inferolateral cerebellar retraction, and maintenance of the vestibular nerve arachnoid may minimize complications and optimize surgical outcomes associated with microvascular decompression for trigeminal neuralgia.

Concurrent Alzheimer’s pathology in patients with clinical normal pressure hydrocephalus: correlation of high-volume lumbar puncture results, cortical brain biopsies, and outcomes

OBJECTIVE Normal pressure hydrocephalus (NPH) remains most often a clinical diagnosis and has been widely considered responsive to the placement of a cerebrospinal fluid (CSF) shunt. The high incidence of patients with Alzheimers disease (AD) with NPH symptoms leads to poorer outcomes than would be expected in patients with NPH alone. This article reviews a series of patients operated on for presumed NPH in whom preoperative high-volume lumbar puncture (HVLP) and intraoperative cortical brain biopsies were performed. The data derived from these procedures were then used to understand the incidence of AD in patients presenting with NPH symptoms and to analyze the efficacy of HVLP in patients with NPH and patients with concurrent AD (NPH+AD). A review of the outcomes of shunt surgery is provided. METHODS The cases of all patients who underwent placement of a CSF shunt for NPH from 1998 to 2013 at the University of Virginia by the senior author were retrospectively reviewed. Patients who underwent HVLP and patients who underwent cortical brain biopsies were stratified based on the biopsy results into an NPH-only group and an NPH+AD group. The HVLP results and outcomes were then compared in these 2 groups. RESULTS From 1998 to 2013, 142 patients underwent shunt operations because of a preoperative clinical diagnosis of NPH. Of the patients with a shunt who had a diagnosis of NPH, 105 (74%) received HVLPs. Of 142 shunt-treated patients with NPH, 27 (19%) were determined to have concomitant Alzheimers pathology based on histopathological findings at the time of shunting. Patients who underwent repeat biopsies had an initial positive outcome. After they clinically deteriorated, they underwent repeat biopsies during shunt interrogation, and 13% of the repeat biopsies demonstrated Alzheimers pathology. Improvements in gait and cognition did not reach significance between the NPH and NPH+AD groups. In total, 105 patients underwent HVLP before shunt placement. In the NPH cohort, 44.6% of patients experienced improvement in symptoms with HVLP and went on to experience resolution or improvement. In the NPH+AD cohort, this proportion was lower (18.2%), and the majority of patients who experienced symptomatic relief with HVLP actually went on to experience either no change or worsening of symptoms (p = 0.0136). CONCLUSIONS A high prevalence of AD histopathological findings (19%) occurred in patients treated with shunts for NPH based on cortical brain biopsies performed during placement of CSF shunts. HVLP results alone were not predictive of clinical outcome. However, cortical brain biopsy results and the presence of Alzheimers pathology had a strong correlation with success after CSF shunting. Thirteen percent of patients who initially had a normal cortical brain biopsy result had evidence of AD pathology on repeat biopsy, demonstrating the progressive nature of the disease.

Ultrasound-determined diameter measurements are more accurate than axial computed tomography after endovascular aortic aneurysm repair

OBJECTIVE This study evaluated the correlation of ultrasound (US)-derived aortic aneurysm diameter measurements with centerline, three-dimensional (3-D) reconstruction computed tomography (CT) measurements after endovascular aortic aneurysm repair (EVAR). METHODS Concurrent CT and US examinations from 82 patients undergoing post-EVAR surveillance were reviewed. The aortic aneurysm diameter was defined as the major axis on the centerline images of 3-D CT reconstruction. This was compared with US-derived minor and major axis measurements, as well as with the minor axis measurement on the conventional axial CT images. Correlation was evaluated with linear regression analyses. Agreement between different imaging modalities and measurements was assessed with Bland-Altman plots. RESULTS The correlation coefficients from linear regression analyses were 0.92 between CT centerline major and US minor measurements, 0.94 between CT centerline major and US major measurements, and 0.93 between CT minor and centerline major measurements. Bland-Altman plots showed a mean difference of 0.11 mm between US major and CT centerline measurements compared with 5.38 mm between US minor and CT centerline measurements, and 4.25 mm between axial CT minor and centerline measurements. This suggested that, compared with axial CT and US minor axis measurements, US major axis measurements were in better agreement with CT centerline measurements. Variability between major and minor US and CT centerline diameter measurements was high (standard deviation of difference, 4.27-4.84 mm). However, high variability was also observed between axial CT measurements and centerline CT measurements (standard deviation of difference, 4.36 mm). CONCLUSIONS The major axis aneurysm diameter measurement obtained by US imaging for surveillance after EVAR correlates well and is in better agreement with centerline 3-D CT reconstruction diameters than axial CT.

132 A Randomized, Sham-Controlled Trial of Transcranial Magnetic Resonance-Guided Focused Ultrasound Thalamotomy Trial for the Treatment of Tremor-Dominant, Idiopathic Parkinson Disease.

INTRODUCTION Traditional stereotactic radiofrequency thalamotomy has been used with success in medication-refractory tremor-dominant Parkinson disease (PD). Recently, transcranial magnetic resonance-guided focused ultrasound (MRgFUS) has been used to successfully perform thalamotomy for essential tremor. We designed a double-blinded, randomized controlled trial to investigate the effectiveness of MRgFUS thalamotomy in tremor-dominant PD. METHODS Patients with medication-refractory, tremor-dominant PD were enrolled in the 2-center study and randomly assigned 1:2 to receive either a sham procedure or treatment. After the 3-month blinded phase, the sham group was offered treatment. Outcome was measured with blinded Clinical Rating Scale for Tremor (CRST) and Unified Parkinsons Disease Rating Scale (UPDRS) ratings. The primary outcome compared improvement in hand tremor between the treatment and sham procedure at 3 months. Secondary outcomes were measured with UPDRS and hand tremor at 12 months. Safety was assessed with MRI, adverse events, and comprehensive neurocognitive assessment. RESULTS Twenty-seven patients were enrolled and 6 were randomly assigned to a sham procedure. For the primary outcome assessment, there was a mean 50% improvement in hand tremor from MRgFUS thalamotomy at 3 months compared with a 22% improvement from the sham procedures (P = .088). The 1-year tremor scores for all 19 patients treated with 1-year follow-up data (blinded and unblinded) showed a reduction in tremor scores of 40.6% (P = .0154) and a mean reduction in medicated UPDRS motor scores of 3.7 (32%, P = .033). Sham patients had a notable placebo effect with a mean 21.5% improvement in tremor scores at 3 months. Twenty-seven patients completed the primary analysis, 19 patients completed the 12-month assessment, 3 patients opted for deep brain stimulation, 3 were lost to follow-up, 1 patient opted for no treatment, and 1 is pending a 12-month evaluation. CONCLUSION Transcranial MRgFUS demonstrates a trend toward improvement in hand tremor, and a clinically significant reduction in mean UPDRS. A significant placebo response was noted in the randomized trial.cause of intractable epilepsy in children. Seizure freedom following resection of FCD is determined by complete resection of the dysplastic cortical tissue.However, difficulty with intraoperative identification of the FCD lesion may limit the ability to achieve the surgical objective of complete extirpation of these lesions. The use of intraoperative magnetic resonance imaging (iMRI) may aid in real-time detection of these lesions and improve seizure control outcomes compared with traditional resective surgery.

Monolithically integrated surface and substrate emitting vertical cavity lasers for smart pixels

The authors present a way to monolithically integrate surface—and substrate—emitting vertical cavity surface emitting lasers (VCSELs) on a single substrate for use in smart pixel applications. Spatially selective oxidation is used to adjust the reflectivity of distributed Bragg reflectors to fabricate surface and substrate emitting VCSELs with threshold currents of 65–70 μA, far field FWHMs of 9°–16°, and slope efficiencies of 16%–18%. Threshold currents and far field angles for various aperture dimensions are measured and discussed.

Changes in cerebrospinal fluid flow assessed using intraoperative MRI during posterior fossa decompression for Chiari malformation

OBJECT The authors completed a prospective, institutional review board-approved study using intraoperative MRI (iMRI) in patients undergoing posterior fossa decompression (PFD) for Chiari I malformation. The purpose of the study was to examine the utility of iMRI in determining when an adequate decompression had been performed. METHODS Patients with symptomatic Chiari I malformations with imaging findings of obstruction of the CSF space at the foramen magnum, with or without syringomyelia, were considered candidates for surgery. All patients underwent complete T1, T2, and cine MRI studies in the supine position preoperatively as a baseline. After the patient was placed prone with the neck flexed in position for surgery, iMRI was performed. The patient then underwent a bone decompression of the foramen magnum and arch of C-1, and the MRI was repeated. If obstruction was still present, then in a stepwise fashion the patient underwent dural splitting, duraplasty, and coagulation of the tonsils, with an iMRI study performed after each step guiding the decision to proceed further. RESULTS Eighteen patients underwent PFD for Chiari I malformations between November 2011 and February 2013; 15 prone preincision iMRIs were performed. Fourteen of these patients (93%) demonstrated significant improvement of CSF flow through the foramen magnum dorsal to the tonsils with positioning only. This improvement was so notable that changes in CSF flow as a result of the bone decompression were difficult to discern. CONCLUSIONS The authors observed significant CSF flow changes when simply positioning the patient for surgery. These results put into question intraoperative flow assessments that suggest adequate decompression by PFD, whether by iMRI or intraoperative ultrasound. The use of intraoperative imaging during PFD for Chiari I malformation, whether by ultrasound or iMRI, is limited by CSF flow dynamics across the foramen magnum that change significantly when the patient is positioned for surgery.

The influence of stents on the performance of an ultrasonic navigation system for endovascular procedures

OBJECTIVE Image-guided surgery provides a mechanism to accurately and quickly assess the location of surgical tools relative to a preoperative image. Traditional image-guided surgery relies on infrared or radiofrequency triangulation to determine an instrument location relative to a preoperative image and has been primarily used in head and neck procedures. Advances in ultrasonic tracking devices, designed for tracking catheters within vessels, may provide an opportunity for image-guided endovascular procedures. This study evaluates the positional accuracy of an ultrasonic navigation system for tracking an endovascular catheter when different stents and graft materials have been deployed in an in vitro system. METHODS Stent and graft materials commonly used in endovascular procedures were used for this study in combination with a custom three-head ultrasonic transducer navigation system. The stents evaluated were composed of Dacron/nitinol, polytetrafluoroethylene (PTFE)/nitinol, and bare nitinol. They were deployed into excised porcine tissue cannulized with a rotary drill, and a catheter with a custom microtransducer probe was inserted. The distance from each ultrasonic tracking module to a probe mounted on an endovascular catheter was measured using time of flight techniques, and the catheter position in three-dimensions was calculated using triangulation. RESULTS The measured position was compared to the actual catheter position determined by a precision translation stage. The PTFE/nitinol, bare nitinol, and Dacron/nitinol stent materials were evaluated and resulted in a maximum error of 1.7, 3.0, and 3.6 mm and an SD of 0.7, 1.2, and 1.4 mm, respectively. A reduction in signal intensity of up to 6x was observed during passage of the endovascular probe through the stent materials, but no reduction in the accuracy of the ultrasonic navigation system was evident. CONCLUSION The use of an ultrasonic-based navigation system is feasible in endovascular procedures, even in the presence of common stent materials. It may have promise as a navigational tool for endovascular procedures.