First principles simulations of microscopic mechanisms responsible for the drastic reduction of electrical deactivation defects in Se hyperdoped silicon.

By first principles simulations we systematically investigate Se hyperdoped silicon by computing, for different types of Se complexes, the formation energy as a function of dopant concentration. We identify the microscopic mechanisms responsible for the dramatic reduction of electrical deactivation defects as the dopant concentration approaches the critical value, xc, at which the insulator-to-metal transition occurs. We discuss the electrical properties of Se point defects and Se complexes, shedding light on the formation and the nature of the impurity band in the bandgap and how the presence of different types of complexes may increase the broadening of the impurity band and affects the insulator-to-metal transition. We identify the best doping range in which the properties of the impurity band can be engineered according to the needs of the electronic industry. Simulations of the structural properties of the complexes complete the work. Our findings are relevant for intermediate impurity band applications.

Complications of Halo Placement.

BACKGROUND: The halo vest is widely used throughout the world to manage craniovertebral and cervical instabilities. It can be used for postoperative immobilization or as an alternative to surgical fixation. METHOD: In this paper we present some cases of severe complications from our own practice and review the literature on halo complications. RESULTS: Like any therapeutic manoeuvre, halo placement may be followed by various complications. In the meantime, modern techniques of fixation offer safe and immediate stabilization. CONCLUSION: The halo vest remains a formidable method for cervical immobilization. However, it should not be used a priori instead of surgery.

European consensus conference on unruptured brain AVMs treatment (Supported by EANS, ESMINT, EGKS, and SINCH).

In December of 2016, a Consensus Conference on unruptured AVM treatment, involving 24 members of the three European societies dealing with the treatment of cerebral AVMs (EANS, ESMINT, and EGKS) was held in Milan, Italy. The panel made the following statements and general recommendations: (1) Brain arteriovenous malformation (AVM) is a complex disease associated with potentially severe natural history; (2) The results of a randomized trial (ARUBA) cannot be applied equally for all unruptured brain arteriovenous malformation (uBAVM) and for all treatment modalities; (3) Considering the multiple treatment modalities available, patients with uBAVMs should be evaluated by an interdisciplinary neurovascular team consisting of neurosurgeons, neurointerventionalists, radiosurgeons, and neurologists experienced in the diagnosis and treatment of brain AVM; (4) Balancing the risk of hemorrhage and the associated restrictions of everyday activities related to untreated unruptured AVMs against the risk of treatment, there are sufficient indications to treat unruptured AVMs grade 1 and 2 (Spetzler-Martin); (5) There may be indications for treating patients with higher grades, based on a case-to-case consensus decision of the experienced team; (6) If treatment is indicated, the primary strategy should be defined by the multidisciplinary team prior to the beginning of the treatment and should aim at complete eradication of the uBAVM; (7) After having considered the pros and cons of a randomized trial vs. a registry, the panel proposed a prospective European Multidisciplinary Registry.

Craniovertebral fusion in an infant using struts of banked adult bone.

PURPOSE: The aim of this paper is to discuss the problems of craniocervical instability and craniocervical fusion in infancy. Despite the relative frequency of carniovertebral joint malformations, actual instability is quite rare in infancy. METHODS: An infant 8 months of age presented with tetraparesis and sleep apnea due to a complex malformation of her craniovertebral joint. An initial attempt at conservative treatment using a rigid neck collar failed, so the patient was surgically managed by the onlay placement of two autologous rib grafts. The rigid collar was maintained for 5 months. RESULTS: Both rib grafts progressively reabsorbed within a few months, while the clinical deficits recurred. Reoperation consisted of occipitocervical interposition of two robust struts of banked cadaveric adult fibula. This time, the skull appeared mature enough to allow immobilization by the halo system. Adequate occipitocervical fusion was eventually achieved, and the patient fully recovered. CONCLUSIONS: To the best of our knowledge, there is no other reported case of an infant undergoing craniovertebral fusion using cadaveric adult bone. When screw placement is not considered advisable to manage small infants, appropriate stability may be obtained using struts of robust cadaveric bone. A meticulous carpentry technique with graft interposition under compression and adequate postoperative immobilization remains mandatory.

Traumatic injuries to the craniovertebral junction: a review of rare events.

The craniovertebral junction is a specific region of the spine with unique anatomical and biomechanical properties that yields a wide variety of injury patterns. Junctional traumatic fractures and/or dislocations are widely reported in clinical practice, but we could identify only a subgroup of upper cervical spine traumatic injuries with very few cases reported in the literature, and for this reason may be considered rare. In some of these cases, the absence of spinal biomechanical instability, in association with moderate clinical symptoms (neck stiffness and pain) and the difficulty in fracture identification through standard cervical radiographs, leads to a high percentage of missed injuries. In other cases, traumatic events have been commonly described only in autopsy series due to the high degree of spinal biomechanical instability. Herein, we have summarized all the relevant literature concerning this issue and also included our cases, with the aim of emphasizing prompt diagnosis and correct management. We provide a guide for correctly identifying "rare" craniovertebral junction traumatic injuries.

Donor wave functions delocalization in silicon nanowires: the peculiar [011] orientation.

The localization of the donor electron wave function can be of key importance in various silicon applications, since for example it determines the interactions between neighboring donors. Interestingly, the physical confinement of the electrons in quasi-one-dimensional nanostructures, like silicon nanowires, noticeably affects this property. Using fully ab initio calculations, we show that the delocalization of the donor electron wave function along the axis of a nanowire is much greater in [011] oriented nanowires for phosphorus and selenium donors. We also demonstrate that its value can be controlled by applying a compressive or tensile uniaxial strain. Finally, we discuss the implications of these features from both an experimental and a theoretical point of view.

Single fracture in the atlas vertebral arch: analysis of an unusual event.

STUDY DESIGN: Retrospective study. OBJECTIVE: The aim of this study is to show that a single traumatic fracture of the atlas is unusual but not rare and requires specific management strategies, which can be highlighted by the study of the junctional ligaments and membranes. SUMMARY OF BACKGROUND DATA: A single traumatic fracture of the atlas arch is considered a rare event and has been analyzed in few case reports. Ligaments and membranes play a primary role in providing stability to the craniovertebral junction area. METHODS: Here, we report 10 cases of a single traumatic fracture of the atlas arch: 4 cases were part of our series of spine injuries and were studied by magnetic resonance imaging during the acute phase to assess the junctional ligaments. The remaining 6 cases were obtained from the Literature. RESULTS: Indirect signs of a traumatic ligamentous injury were found only in 1 patient. However, in all cases, these fractures were considered biomechanically stable and all patients were discharged with a rigid collar. During the follow-up, all patients reported an improvement in their neck pain and tenderness, with radiologic signs of bone healing. CONCLUSIONS: A single fracture of the atlas arch is an unusual traumatic event that results from slow-force impact. Medical experience in treating this specific fracture subtype is nowadays poor because of the paucity of the literature; thus, this unusual condition may either be underestimated or even overstudied and overtreated. Nowadays, it seems reasonable to assume that the management should be conservative in all cases and that magnetic resonance imaging often plays only a marginal role.

Integrated spine trauma team protocol: Combined neurosurgical and orthopedic experience for the management of traumatic spinal injuries.

Objectives: During the last decades, spine surgery has grown exponentially. In spite of that, it remains a surgical specialty without a well-defined own certification. It is usually carried out, separately, by neurosurgeons and orthopedic surgeons, even if there is an overlapping of competence and skills. Materials and Methods: In our hospital, from January 2019, a systematic protocol called integrated spine trauma team protocol (ISTTP) was implemented to improve the management of traumatic spinal injuries in a multidisciplinary way. It is characterized by a specific algorithm from diagnosis to postoperative care. According to the new protocol, orthopedic spinal surgeons and neurosurgeons work together as an integrated spine trauma team. The authors analyzed, retrospectively, the results obtained by comparing patients treated before and after the application of the ISTTP. Results: The new protocol allowed a statistically significant reduction in waiting time before surgery and complication rate. Moreover, early discharge of patients was recorded. To the best of our knowledge, this is the first study that described a specific algorithm for a standardized multidisciplinary management of the spinal trauma with combined orthopedic and neurosurgeon expertise. Conclusion: Our preliminary results suggest that the application of our ISTTP leads to better results for treating traumatic spinal injury (TSI).

The anterior stand-alone approach (ASAA) during the acute phase of spondylodiscitis: results in 40 consecutively treated patients.

PURPOSE: Spondylodiscitis mainly affects the anterior part of the spine. In this paper, we retrospectively analyze our experience with the anterior stand-alone approach (ASAA) in the treatment of spinal infections. METHODS: Forty consecutive patients with severe spondylodiscitis underwent the ASAA during the acute infective phase. Treatment consisted of disease debridement, vertebral body reconstruction using titanium expandable prostheses and anterior fixation. RESULTS: There was neither mortality nor major morbidity. Successful arthrodesis was achieved in 39 out of 40 patients who remained disease free throughout the follow-up period. Six months after treatment, one patient experienced pseudarthrosis and required supplemented posterior spinal fixation for vertebral instability. However, adequate arthrodesis was eventually obtained even in this patient. CONCLUSIONS: ASAA with spine reconstruction using synthetic materials during the acute infection phase was safe and effective. The infections were rapidly defeated, the patients were allowed to stand up early after the procedure and the length of hospital stay was significantly reduced.

Spinal dural arteriovenous fistulas: outcome and prognostic factors.

The aim of this study is to review the clinical outcome of patients treated for spinal dural arteriovenous malformations and investigate the presence of pretreatment indicators of outcome after short- and midterm follow-up. The authors retrospectively reviewed the records of 65 consecutive patients treated either surgically or endovascularly in 3 neurosurgery departments between 1989 and 2009. After treatment, 80% of patients reported improvement of at least 1 symptom. Motor symptoms improved more than sensory disorders, pain, or sphincter impairment. Spinal dural arteriovenous fistulas at the thoracic level, and in particular at the lower level, responded better than those in other spinal areas. Spinal dural arteriovenous fistula is a rare pathology with a malignant course that should be treated aggressively. This study appears to confirm that neurological status before treatment, anatomical location of the fistula, and symptoms at presentation are all factors that can predict outcome. Early diagnosis of spinal dural arteriovenous malformations in the lower thoracic area in patients with an Aminoff scale score < 3 was associated with the most favorable outcome.

Confinement effects and hyperfine structure in se doped silicon nanowires.

We report a density functional study of the electronic properties and hyperfine structure of substitutional selenium in silicon nanowires using plane-wave pseudopotential techniques. We simulated hydrogen passivated [001] oriented nanowires with a diameter up to 2 nm, analyzing the effect of quantum confinement on the defect formation energy and on the hyperfine parameters as a function of the diameter and of the defect position. We show that substitutional Se in silicon has favorable configurations for positions near the surface with possible formation of chalcogen-hydrogen complexes. We also show that hyperfine interactions increase at small diameters, as long as the nanowire is large enough to prevent surface distortion which modifies the symmetry of the donor wave function. Moreover, surface effects lead to strong differences in the hyperfine parameters depending on the Se location inside the nanowire, allowing the identification of an impurity site on the basis of electron paramagnetic resonance spectra.

A minimally invasive approach for giant middle cerebral artery thrombosed aneurysms treatment.

BACKGROUND: Management of complex thrombosed aneurysms of the middle cerebral artery (MCA) is challenging. Lesions not amenable to endovascular techniques or direct clipping might require a bypass procedure with subsequent aneurysm occlusion. Various bypass techniques followed by surgical or endovascular closure of the aneurysm are available, but an unpredictable extension of the thrombus to the parent vessel and/or to perforator vessels can occur. We presented a multidisciplinary technique with the aim to reduce invasiveness and complications. METHODS: We present two patients, harboring a thrombosed giant MCA bifurcation aneurysm, who were treated with a minimally invasive three-steps multimodality procedure. In both cases, through a limited exposure of the sylvian fissure, a side-to-side anastomosis between the two M2 branches was performed, followed in the immediate postop by an endovascular occlusion of the frontal M2 branch, with the aim of transforming a bifurcation aneurysm in a sidewall aneurysm, that was then treated a few days later by flow diverter deployment. RESULTS: Both patients had excellent outcomes and were discharged after 7 days without neurological deficits. CONCLUSIONS: Treatment of complex thrombosed MCA aneurysms is challenging. Side-to-side M2 anastomosis with the aim of transforming a bifurcation aneurysm in a sidewall aneurysm, suitable to be treated few days later by flow diverter deployment, offers a minimally invasive multimodal approach with the possibility of reducing serious complications.

Theoretical investigations of oxygen vacancy effects in nickel-doped zirconia from ab initio XANES spectroscopy at the oxygen K-edge.

In this study, we present theoretical X-ray absorption near-edge structure (XANES) spectra at the K-edge of oxygen in zirconia containing Ni dopant atoms and O vacancies at varying concentrations. Specifically, our model system consist of a supercell composed of a zirconia (ZrO2) matrix containing two nickel dopants (2Ni), which substitute two Zr atoms at a finite separation. We found the 2Ni atoms to be most stable in a ferromagnetic configuration in the absence of oxygen vacancies. In this system, each Ni atom is surrounded by two shells of O with tetrahedral geometry, in a similar way as in bulk cubic zirconia. The oxygen K-edge XANES spectrum of this configuration shows a pre-edge peak, which is attributable to dipole transitions from O 1s to O 2p states that are hybridized with unoccupied Ni 3d states. The intensity of this pre-edge peak, however, reduces upon the introduction of a single vacancy in the 2Ni-doped zirconia matrix. The corresponding ground state remains ferromagnetic, while one of the nickel atoms adopts a trigonal bipyramidal geometry, and the other one remains in a tetrahedral geometry. Furthermore, the introduction of two vacancies in the 2Ni-doped zirconia results in the two Ni atoms having distorted octahedral and trigonal bipyramidal geometries and being coupled antiferromagnetically in the ground state. Additionally, the oxygen K-edge XANES spectrum shows a further decrease in the intensity of the pre-edge peak, compared to the case of a single vacancy. Thus, the changes in the intensity of the pre-edge peak evidence a major structural change in the local environment around nickel atoms and, by extension, in the zirconia matrix. This change is due to the structural disorder induced by the 2Ni dopants and the O vacancies. Furthermore, the analysis of the XANES signatures shows that the oxidation state of nickel atoms changes with the introduction of oxygen vacancies. Our study therefore shows a possibility to control the oxidation state and magnetic order in a typical diluted magnetic oxide. Such a finding may be crucial for spintronics-related applications.

Giant occipital meningocele in an 8-year-old child with Dandy-Walker malformation.

INTRODUCTION: The possibility of an association between Dandy-Walker malformation and occipital meningocele is well-known. However, just an overall number of about 40 cases have been previously reported. Giant occipital meningocele has been described only in three newborns. Incidence, pathology, clinical presentation, and proper management of this association are still poorly defined. REPORT OF THE CASE: An 8-year-old boy with Dandy-Walker malformation and giant (25 cm in diameter) occipital meningocele is presented. This boy was born without any apparent occipital mass and harbored no other significant malformations including hydrocephalus. On admission, he was neurologically intact and the giant occipital mass presented partially calcified cyst walls. Treatment consisted of the excision of the occipital malformation, cranioplasty, and cysto-peritoneal shunt. Outcome was excellent. CONCLUSIONS: To the best of our knowledge, among the few reported patients with Dandy-Walker malformation associated to occipital meningocele, this is the oldest one and the one with the largest occipital meningocele; he is unique with calcified walls of the occipital meningocele and the only one who survived the repair of the giant malformation. In Dandy-Walker malformation, occipital meningocele may develop and grow regardless of hydrocephalus. Giant size may be reached and the cyst may become calcified. Surgical repair may warrant favorable outcome.

Cerebellopontine Angle Surgery Assisted by Continuous Mapping of the Facial Nerve Via the Ultrasonic Aspirator.

BACKGROUND: Cerebellopontine angle (CPA) surgery carries the risk of lesioning the facial nerve. The goal of preserving the integrity of the facial nerve is usually pursued with intermittent electrical stimulation using a handheld probe that is alternated with the resection. We report our experience with continuous electrical stimulation delivered via the ultrasonic aspirator (UA) used for the resection of a series of vestibular schwannomas. METHODS: A total of 17 patients with vestibular schwannomas, operated on between 2010 and 2018, were included in this study. A constant-current stimulator was coupled to the UA used for the resection, delivering square-wave pulses throughout the resection. The muscle responses from upper and lower face muscles triggered by the electrical stimulation were displayed continuously on multichannel neurophysiologic equipment. The careful titration of the electrical stimulation delivered through the UA while tapering the current intensity with the progression of the resection was used as the main strategy. RESULTS: All operations were performed successfully, and facial nerve conduction was maintained in all patients except one, in whom a permanent lesion of the facial nerve followed a miscommunication to the neurosurgeon. CONCLUSION: The coupling of the electrical stimulation to the UA provided the neurosurgeon with an efficient and cost-effective tool and allowed a safe resection. Positive responses were obtained from the facial muscles with low current intensity (lowest intensity: 0.1 mA). The availability of a resection tool paired with a stimulator allowed the surgeon to improve the surgical workflow because fewer interruptions were necessary to stimulate the facial nerve via a handheld probe.

Anterior approach to thoracic and lumbar spine lesions: results in 145 consecutive cases.

OBJECT: The authors report on a series of 145 consecutive patients with different types of spine lesions surgically treated via an anterior approach (AA) at the thoracic and lumbar levels during the past 10 years. Indications, techniques, and surgical results are described. METHODS: This series included 92 patients with fractures, 30 with neoplasms, 13 with thoracic disc hernias, and 10 with spinal infections. Based on the lesion to be addressed, the AA was used for lesion excision, corpectomy, vertebral body reconstruction with cages, realignment, and/or plating or screwing. The approach was extracavitary in 55 patients and intracavitary in 90. In 126 patients (86.8%), neural decompression and spine stabilization were achieved via a stand-alone AA (SA-AA), whereas 19 patients (13.1%) were treated using a 2-stage anteroposterior approach. This circumferential approach was reserved for select cases of severe traumatic dislocation, particular types of tumors, or specific anatomical locations. The authors developed a simple neuronavigation-based method of identifying the severely injured patients who were eligible for the SA-AA by evaluating the angle of lateral dislocation. RESULTS: There were no deaths and no instances of major surgery-related morbidity. Minor morbidity was almost always transitory and was reported in 13 patients (8.9%). Neurological improvement was reported in 20% of injured patients with a preoperative incomplete lesion. Postoperatively, all patients were able to stand or at least sit without load pain. During the follow-up (mean +/- standard deviation 3.8 +/- 2.4 years), there were no cases of failure, fracture, dislocation, or bending of the anterior instrumentation, and the rate of pseudarthrosis was 0%. CONCLUSION: The anterior route provides direct access to most spine diseases and allows optimal neural decompression and the possibility of adequate realignment and strong reconstruction/fixation. Stability of the vertebral column is achieved, resolution of clinical pain is rapid and almost complete, and the rate of surgical complications is very low. The authors assert that the SA-AA offers so many advantages and has such good results that the 2-stage anteroposterior approach can be reserved for a minority of select cases and that the time for using the posterior approach alone is over.

Torcular Meningioma with Multi-Venous Sinus Invasion: Compensatory Drainage Veins and Surgical Strategy.

BACKGROUND: Torcular meningiomas involving major dural venous sinuses are rare entities and a great challenge for neurosurgeons. The deep knowledge of the patency of occlusion of the sinuses, the extent of the occlusion and potentially new developing of extra and intracranial collateral venous drainage as compensatory venous channels, are at the base of a correct operative strategy. CASE DESCRIPTION: A 45-year-old woman presented with persistent headache. Magnetic resonance imaging of the brain and digital subtraction angiography demonstrated a huge torcular meningioma with complete multi-venous sinus occlusion and a wide venous network for brain and tumor drainage. In these rare cases, we have hypothesized the presence of venous drainage shared by the brain and the tumor, which could generate undesirable venous occlusion during operative resection. This could be a cause of the well-known surgical complications, such as brain swelling and hemorrhagic infarction. CONCLUSIONS: We report our experience with a huge torcular meningioma with multi-venous sinus invasion and a literature review, with a special emphasis on compensatory drainage veins and surgical strategy.

Contemporary tools in arteriovenous malformations surgery.

Arteriovenous malformations (AVMs) are rare entities and therefore considered the main challenge for a neurosurgeon. Since the publication of the ARUBA study, one of the most popular debate regards the actual surgical indication for unruptured AVMs. Our group recently published a multicenter review of more than 500 cases underlying the important role of surgery. Over the last few decades, the expanding technologies used in the treatment of AVMs have shown an ongoing improvement overcoming some of the existing difficulties and shortcomings. In this paper, we reviewed the present literature to illustrate the main contemporary tools that, in our opinion, are crucial to obtain the best surgical and clinical outcome. Indocyanin green is nowadays considered a gold standard to identify arterial feeders, draining veins, and to detect any eventual residual. The use of non-stick, bipolar, 2-mm blade microclips, and thulium laser allows to obtain a better bleeding control and nidus removal. The development of the intraoperative ultrasound with neuronavigation, angiosonography, and color-Doppler improves the accuracy of AVM resection. Moreover, improvements have been developed with the use of intraoperative micro-Dopplers combined with flow measurements, which consent to verify the gradual reduction of flow through draining veins. The possibility to perform functional preoperative studies and intraoperative monitoring can be considered as an essential point in the decision making in eloquent or near-eloquent AVMs. Furthermore, the hybrid operating room represents the best expression of an excellent neurovascular team where the use of the intraoperative angiography allows neurosurgeons and neurointerventional radiologists to work at the same time in a combined approach to achieve the best surgical removal.

Unruptured Versus Ruptured AVMs: Outcome Analysis from a Multicentric Consecutive Series of 545 Surgically Treated Cases.

BACKGROUND: Recent literature strongly challenged indications to perform preventive surgery in unruptured arteriovenous malformation (AVM) claiming that invasive AVM treatment is associated with a significant risk of complications and thus conservative management may be a preferable alternative in many patients. On the other hand, the recent improvement of surgical instrumentation and treatment strategies (both surgical and interventional) yielded better outcomes than those achieved only a decade ago. Therefore, even among specialists, a wide variety of opinions, concerning the treatment of unruptured AVM, can be found. METHODS: This multicenter retrospective study analyzes a consecutive series of 545 surgically treated AVMs in 10 different hospitals in Italy. RESULTS: Patients with AVMs treated after hemorrhage had an unfavorable (modified Rankin Scale score >1) outcome in more than one third (37.69%) of the cases. Conversely, with proper indications, unruptured AVMs treated preventively have a good outcome in 93.8% of cases, increasing to 95.7%, with no death, if only Spetzler-Martin grades 1-3 are considered (P < 0.05). Outcomes on discharge significantly (P < 0.05) improve at 6 months with the disappearance of many of the initial neurologic deficits that turn out to be transient. CONCLUSIONS: In unruptured low-risk AVMs (Spetzler-Martin grades 1-3), over time, the risk of surgery-associated neurologic deficits becomes lower than that linked to spontaneous hemorrhage, with a crossover point at 6.5 years. Because the average bleeding age is less than 45 years, preventive surgery can be advocated to safeguard the patient and overcome the risks associated with the natural history of AVMs.

Use of Laser in Arteriovenous Malformation Surgery.

BACKGROUND: Arteriovenous malformation surgery is particularly demanding owing to the need to control bleeding of small, deep white matter vessels during and after removal of the nidus; this is probably one of the most critical moments of arteriovenous malformation surgery. The aim of this article is to describe a useful technique based on the use of tweezers to temporarily stop the blood flow followed by coagulation with the thulium laser. METHODS: Surgery was performed in 20 patients with unruptured cerebral arteriovenous malformations. In each case, the superficial feeder vessels were easily coagulated with nonstick bipolar tips. The finer and deeper feeder vessels were coagulated with use of tweezers and thulium laser. RESULTS: All patients were treated successfully. Optimal intraoperative hemostasis was achieved. CONCLUSIONS: Results were good with no postoperative complications. Our results could encourage a more standardized use of the described technique.