Sonolucent Cranial Implants: Cadaveric Study and Clinical Findings Supporting Diagnostic and Therapeutic Transcranioplasty Ultrasound

Review of Functional Cranioplasty and Implantable Neurotechnology

Cranioplasty for secondary reconstruction of cranial defects has historically focused on simply replacing the missing cranial bone to restore cerebral protection and fluid dynamics, but recent innovations have led to the development of customized cranial implants that address both bone and soft tissue deficits while avoiding postoperative complications such as temporal hollowing. In addition, customized cranial implants have incorporated implantable neurotechnology like ventriculostomy shunts, intracranial pressure monitoring devices, and medicine delivery systems within low-profile designs to convert previously "basic" implants into "smart" implants for added functionality. These "smart" implants aim to reduce complications and improve patient outcomes by leveraging the cranial space to house advanced technologies, providing benefits such as real-time biosensing, and treatment of chronic neurological conditions. This review outlines the progression of cranioplasty from basic bone replacement to functional implants with embedded neurotechnologies, highlighting the multidisciplinary approaches that enhance surgical outcomes and patient quality of life.

Bone Regrowth After Frontal Burr Hole Craniostomy: Natural History of 14-mm and 20-mm Burr Holes and Implications for Postoperative Trans-Burr Hole Ultrasound

BACKGROUND AND OBJECTIVE

Burr hole craniostomy is performed for ventriculoperitoneal shunt insertion and endoscopic third ventriculostomy in patients with cerebrospinal fluid disorders. These burr holes are increasingly being used as windows for postoperative ultrasound, an investigational alternative to computed tomography or MRI for follow-up imaging of ventricular caliber. However, bone regrowth reduces ultrasound visibility, and little is known about burr hole regrowth rates in adults. Our study evaluates burr hole regrowth patterns and implications for transcranial ultrasound imaging.

METHODS

We retrospectively analyzed 101 consecutive patients who had frontal burr hole craniostomy for new ventriculoperitoneal shunt insertion or endoscopic third ventriculostomy over a 3-year period. A mix of standard 14-mm burr holes and expanded 20-mm burr holes were used. Burr hole bone regrowth was assessed using serial follow-up computed tomography scans. Linear and logistic regression analyses examined if bone regrowth correlated with any clinical variables.

RESULTS

There was wide variability in rate and degree of burr hole regrowth. The average percentage closure was 25% at 6 months, with minimal additional closure over the following 18 months. The mean residual diameter for 14-mm and 20-mm burr holes stabilized around 9.4 mm and 15.4 mm, respectively. Bone regrowth was not associated with patient characteristics, including age, sex, skull thickness, or etiology of cerebrospinal fluid disorder. Rate of bone regrowth was similar between both cohorts.

CONCLUSION

Bone regrowth after burr hole craniostomy is common, even in elderly patients, occurring rapidly within the first 6 to 12 months and subsequently stabilizing. It is frequently severe enough to restrict ultrasound visualization. Regrowth could not be predicted with any investigated variables, so uniform techniques are needed to block regrowth to allow for longitudinal ultrasound imaging, such as full-thickness cylindrical burr hole implants.

Do Open Access Articles Have a Citation Advantage Over Toll Access Articles? A Comparative Analysis of Articles Published in the Journal of Craniofacial Surgery From 2019 to 2023 Based on Web of Science Data

OBJECTIVE

This study aimed to compare the citation rates of open access (OA), and toll access (TA) articles published in the Journal of Craniofacial Surgery between 2019 and 2023, and to examine whether OA articles received more citations.

METHODS

Using the Web of Science database, articles published in the Journal of Craniofacial Surgery between 2019 and 2023 were listed, excluding those with corrections or retractions. Articles were divided into 2 groups: OA and TA. The number of articles and citation counts for each group were analyzed by year. Citation rates were compared using the independent sample t test, with a p-value of <0.05 considered statistically significant.

RESULTS

A total of 4691 articles were analyzed, of which 7.14% were OA and 92.86% were TA. Published in 2021, 2020, and 2019, OA articles had statistically significantly higher citation counts than TA articles. OA articles were found to be funded at a higher rate than TA articles.

CONCLUSION

This study demonstrated that OA articles received more citations over time and were more likely to be funded. Although it is not definitively clear whether the citation advantage stems from the quality of the articles or their open-access status, the citation advantage of OA articles is striking.

Ultrasound-Guided Mechanical High-Intensity Focused Ultrasound (Histotripsy) Through an Acoustically Permeable Polyolefin-Based Cranioplasty Device

Histotripsy is a non-thermal focused ultrasound therapy in development for the non-invasive ablation of cancerous tumors. Intracranial histotripsy has been limited by significant pressure attenuation through the skull, requiring large, complex array transducers to overcome this effect.

OBJECTIVE

Recently, a biocompatible, polyolefin-based cranioplasty device was developed to allow ultrasound (US) transmission into the intracranial space with minimal distortion. In this study, we investigated the in vitro feasibility of applying US-guided histotripsy procedures across the prosthesis.

METHODS

Pressure waveforms and beam profiles were collected for single- and multi-element histotripsy transducers. Then, high-speed optical images of the bubble cloud with and without the prosthesis were collected in water and tissue-mimicking agarose gel phantoms. Finally, red blood cell (RBC) tissue phantom and excised brain tissue experiments were completed to test the ablative efficacy across the prosthesis.

RESULTS

Single element tests revealed increased pressure loss with increasing transducer frequency and increasing transducer-to-prosthesis angle. Array transducer measurements at 1 MHz showed average pressure losses of >50% across the prosthesis. Aberration correction recovered up to 18% of the pressure lost, and high-speed optical imaging in water, agarose gels, and RBC phantoms demonstrated that histotripsy bubble clouds could be generated across the prosthesis at pulse repetition frequencies of 50-500 Hz. Histologic analysis revealed a complete breakdown of brain tissue treated across the prosthesis. Conclusion & Significance: Overall, the results of this study demonstrate that the cranial prosthesis may be used as an acoustic window through which intracranial histotripsy can be applied under US guidance without the need for large transcranial array transducers.

Neuroplastic Surgery Principles of Computerized Surgical Planning in Complex Cranioplasty Reconstruction

This article explores the evolution and implementation of three-dimensional (3D) models and Computerized Surgical Planning (CSP) for complex cranioplasty reconstruction and the advances in neuroplastic surgery principles for improved surgical outcomes. Over recent years, CSP has revolutionized the field by employing detailed medical imaging to enhance the accuracy and efficacy of 3D models and for the creation of customized cranial implants (CCIs). The study discusses the advancements of solid alloplastic implants to the future of implants with sophisticated and integrated neurotechnology to treat or enhance patient outcomes. CSP can be used to identify and mitigate complications that can occur within cranioplasty reconstruction and to create CCIs to address the postoperative challenge of temporal hollowing. Despite the promising advancements, the article acknowledges the current limitations of CSP, including cost and technological accessibility, and proposes future directions for research and development. The findings suggest that with further improvements in imaging, biomaterials, and manufacturing techniques, CSP in neuroplastic surgery and other specialties will continue to significantly enhance the precision and personalized care of cranioplasty reconstruction.

Functional ultrasound imaging of human brain activity through an acoustically transparent cranial window

Visualization of human brain activity is crucial for understanding normal and aberrant brain function. Currently available neural activity recording methods are highly invasive, have low sensitivity, and cannot be conducted outside of an operating room. Functional ultrasound imaging (fUSI) is an emerging technique that offers sensitive, large-scale, high-resolution neural imaging; however, fUSI cannot be performed through the adult human skull. Here, we used a polymeric skull replacement material to create an acoustic window compatible with fUSI to monitor adult human brain activity in a single individual. Using an in vitro cerebrovascular phantom to mimic brain vasculature and an in vivo rodent cranial defect model, first, we evaluated the fUSI signal intensity and signal-to-noise ratio through polymethyl methacrylate (PMMA) cranial implants of different thicknesses or a titanium mesh implant. We found that rat brain neural activity could be recorded with high sensitivity through a PMMA implant using a dedicated fUSI pulse sequence. We then designed a custom ultrasound-transparent cranial window implant for an adult patient undergoing reconstructive skull surgery after traumatic brain injury. We showed that fUSI could record brain activity in an awake human outside of the operating room. In a video game "connect the dots" task, we demonstrated mapping and decoding of task-modulated cortical activity in this individual. In a guitar-strumming task, we mapped additional task-specific cortical responses. Our proof-of-principle study shows that fUSI can be used as a high-resolution (200 μm) functional imaging modality for measuring adult human brain activity through an acoustically transparent cranial window.

Sonolucent Cranial Implants: A Window into the Future of Management of Neurosurgical Patients? A Systematic Review and Cost Analysis

BACKGROUND

Computeed tomography (CT) is a cornerstone of the identification and management of acute changes in neurosurgery patients. In addition to the monetary expense of CT scans, further costs are incurred due to the time of patient transport and radiation exposure. Ultrasounds (USs)offer a safe, inexpensive, and bedside alternative to CT but obstacles remain due to decreased penetrance in the adult skull. Sonolucent Cranial Implants (SCIs) offer a window for USs to view intracranial architectures.

METHODS

The authors performed a PRISMA guidelines-based systematic review of the literature. Information was extracted from included articles in regards to illness pathology, US imaging feasibility, comparison to standard imaging, infections, and revisions. Costs were collected in regards to price of implant and follow-up imaging.

RESULTS

A total of 226 articles resulted, of which 5 were included in the study. Ninety non-duplicate patients who received SCIs were analyzed. The pathologies of included patients is as follows: 51 patients were after extracranial-intracranial bypass, 37 after ventriculoperitoneal shunt placement for hydrocephalus, 1 after tumor resection, and 1 after cranioplasty following decompressive hemicraniectomy. All studies noted feasibility of US and comparability to standard imaging following SCI placement. Follow-up imaging with trans-sonolucent cranial implant ultrasound was estimated to save up to $4,000 per patient depending on the procedure.

CONCLUSIONS

Initial studies suggest that US imaging through SCIs is a safe and efficacious alternative to CT imaging in neurosurgical patients. Cost analysis suggests that SCI and subsequent US can offer a cost savings compared with current treatment.

Patient Satisfaction and Radiologic Assessability After Treatment of Complex Skull Defects With a Custom-Made Cranioplasty From a Thin Titanium Sheet

OBJECTIVE

The cosmetically good coverage of skull defects is a challenge in neurosurgical clinics. In addition, the skull treated with implants and the underlying structures must remain radiologically assessable. In this examination, the postoperative courses of patients after implantation of CranioTop is described. Digital x-ray, computed tomography, and magnetic resonance images after implantation of CranioTop were evaluated with regard to their assessability.

MATERIALS AND METHODS

Between 2018 and 2020, 23 titanium cranioplasties (CranioTop) were implanted to 21 patients. The intraoperative handling, the accuracy of fit, the healing process, the cosmetic result and the physical condition of the patients were examined. In addition, digital x-rays, magnetic resonance imaging, and computed tomography scans of the cranium supplied with CranioTop were examined.

RESULTS

The evaluation showed good to very good results regarding patients' satisfaction. There were no severe complications; thirteen patients found the cosmetic result very good; 8 patients assessed the cosmetic result as good. Because of the low thickness and density of the CranioTop plastic there was only low formation of radial stripe artifacts (streaking) and susceptibility artifacts. The assessment of digital x-ray, computed tomography, and magnetic resonance imaging images is possible after implantation of CranioTop.

CONCLUSION

The patients treated with CranioTop showed a high level of satisfaction with regard to the cosmetic result and their physical condition. Furthermore, the cranium supplied with CranioTop remains well assessable in radiologic imaging with only slight limitations in magnetic resonance imaging.

Transcranioplasty Ultrasonography Through a Sonolucent Prosthesis: A Review of Feasibility, Safety, and Benefits

Data on the effectiveness of transcranioplasty ultrasonography through sonolucent cranioplasty (SC) are new and heterogeneous. We performed the first systematic literature review on SC. Ovid Embase, Ovid Medline, and Web of Science Core Collection were systematically searched and published full text articles detailing new use of SC for the purpose of neuroimaging were critically appraised and extracted. Of 16 eligible studies, 6 reported preclinical research and 12 reported clinical experiences encompassing 189 total patients with SC. The cohort age ranged from teens to 80s and was 60% (113/189) female. Sonolucent materials in clinical use are clear PMMA (polymethylmethacrylate), opaque PMMA, polyetheretherketone, and polyolefin. Overall indications included hydrocephalus (20%, 37/189), tumor (15%, 29/189), posterior fossa decompression (14%, 26/189), traumatic brain injury (11%, 20/189), bypass (27%, 52/189), intracerebral hemorrhage (4%, 7/189), ischemic stroke (3%, 5/189), aneurysm and subarachnoid hemorrhage (3%, 5/189), subdural hematoma (2%, 4/189), and vasculitis and other bone revisions (2%, 4/189). Complications described in the entire cohort included revision or delayed scalp healing (3%, 6/189), wound infection (3%, 5/189), epidural hematoma (2%, 3/189), cerebrospinal fluid leaks (1%, 2/189), new seizure (1%, 2/189), and oncologic relapse with subsequent prosthesis removal (<1%, 1/189). Most studies utilized linear or phased array ultrasound transducers at 3-12 MHz. Sources of artifact on sonographic imaging included prosthesis curvature, pneumocephalus, plating system, and dural sealant. Reported findings were mainly qualitative. We, therefore, suggest that future studies should collect quantitative measurement data during transcranioplasty ultrasonography to validate imaging techniques.

Sonolucent cranioplasty: Is therapeutic FUS the next frontier?

Focused ultrasound (FUS) has emerged as a promising area of research in neuro-oncology. Preclinical and clinical investigation has demonstrated the utility of FUS in therapeutic applications including blood brain barrier disruption for therapeutic delivery, and high intensity FUS for tumor ablation. However, FUS as it exists today is relatively invasive as implantable devices are necessary to achieve adequate intracranial penetration. Sonolucent implants, composed of materials permeable to acoustic waves, have been used for cranioplasty and intracranial imaging with ultrasound. Given the overlap in ultrasound parameters with those used for intracranial imaging, and the demonstrated efficacy of sonolucent cranial implants, we believe that therapeutic FUS through sonolucent implants represents a promising avenue of future research. The potential applications of FUS and sonolucent cranial implants may confer the demonstrated therapeutic benefits of existing FUS applications, without the drawbacks and complications of invasive implantable devices. Here we briefly summarize existing evidence regarding sonolucent implants and describe applications for therapeutic FUS.

Establishing proof of concept for sonolucent cranioplasty and point of care ultrasound imaging after posterior fossa decompression for Chiari malformation

BACKGROUND

Evaluation after posterior fossa decompression for Chiari malformation can require repeated imaging, particularly with persistent symptoms. Typically, CT or MRI is used. However, CT carries radiation risk and MRI is costly. Ultrasound is an inexpensive, radiation-free, point-of-care modality that has, thus far, been limited by intact skull and traditional cranioplasty materials. Ultrasound also allows for imaging in different head positions and body postures, which may lend insight into cause for persistent symptoms despite adequate decompression on traditional neutral static CT or MRI. We evaluate safety and feasibility of ultrasound as a post-operative imaging modality in patients reconstructed with sonolucent cranioplasty during posterior fossa decompression for Chiari malformation.

METHODS

Outcomes were analyzed for 26 consecutive patients treated with a Chiari-specific sonolucent cranioplasty. This included infection, need for revision, CSF leak, and pseudomeningocele. Ultrasound was performed point-of-care in the outpatient clinic by the neurosurgery team to assess feasibility.

RESULTS

In eight months mean follow up, there were no surgical site infections or revisions with this novel sonolucent cranioplasty. Posterior fossa anatomy was discernable via transcutaneous ultrasound obtained point-of-care in the clinic setting at follow up visits.

CONCLUSION

We demonstrate proof of concept for ultrasound as a post-operative imaging modality after posterior fossa decompression for Chiari malformation. With further investigation, ultrasound may prove to serve as an alternative to CT and MRI in this patient population, or as an adjunct to provide positional and dynamic information. Use of sonolucent cranioplasty is safe. This technique deserves further study.

Sonolucent Cranioplasty in Extracranial to Intracranial Bypass Surgery: Early Multicenter Experience of 44 Cases

BACKGROUND

The new sonolucent cranioplasty implant (clear polymethyl methacrylate, PMMA) adds functionality besides surgical reconstruction. One possible application uses the transcranioplasty ultrasound (TCUS) technique after PMMA cranioplasty to assess graft patency of extracranial-intracranial (EC-IC) bypass procedures.

OBJECTIVE

To report our early multicenter experience.

METHODS

This is a multicenter analysis of consecutive EC-IC bypass patients from 5 US centers (2019-2022) with closure postbypass using PMMA implant.

RESULTS

Forty-four patients (median age 53 years, 68.2% females) were included. The most common indication for bypass was Moyamoya disease/syndrome (77.3%), and superficial temporal artery to middle cerebral artery bypass was the most common procedure (79.5%). Pretreatment modified Rankin Scales of 0 and 1 to 2 were noted in 11.4% and 59.1% of patients, respectively. Intraoperative imaging for bypass patency involved a combination of modalities; Doppler was the most used modality (90.9%) followed by indocyanine green and catheter angiography (86.4% and 61.4%, respectively). Qualitative TCUS assessment of graft patency was feasible in all cases. Postoperative inpatient TCUS confirmation of bypass patency was recorded in 56.8% of the cases, and outpatient TCUS surveillance was recorded in 47.7%. There were no cases of bypass failure necessitating retreatment. Similarly, no implant-related complications were encountered in the cohort. Major complications requiring additional surgery occurred in 2 patients (4.6%) including epidural hematoma requiring evacuation (2.3%) and postoperative surgical site infection (2.3%) that was believed to be unrelated to the implant.

CONCLUSION

This multicenter study supports safety and feasibility of using sonolucent PMMA implant in EC-IC bypass surgery with the goal of monitoring bypass patency using TCUS.

First Experience With Postoperative Transcranial Ultrasound Through Sonolucent Burr Hole Covers in Adult Hydrocephalus Patients

BACKGROUND

Managing patients with hydrocephalus and cerebrospinal fluid (CSF) disorders requires repeated head imaging. In adults, it is typically computed tomography (CT) or less commonly magnetic resonance imaging (MRI). However, CT poses cumulative radiation risks and MRI is costly. Ultrasound is a radiation-free, relatively inexpensive, and optionally point-of-care alternative, but is prohibited by very limited windows through an intact skull.

OBJECTIVE

To describe our initial experience with transcutaneous transcranial ultrasound through sonolucent burr hole covers in postoperative hydrocephalus and CSF disorder patients.

METHODS

Using cohort study design, infection and revision rates were compared between patients who underwent sonolucent burr hole cover placement during new ventriculoperitoneal shunt placement and endoscopic third ventriculostomy over the 1-year study time period and controls from the period 1 year before. Postoperatively, trans-burr hole ultrasound was performed in the clinic, at bedside inpatient, and in the radiology suite to assess ventricular anatomy.

RESULTS

Thirty-seven patients with sonolucent burr hole cover were compared with 57 historical control patients. There was no statistically significant difference in infection rates between the sonolucent burr hole cover group (1/37, 2.7%) and the control group (0/57, P = .394). Revision rates were 13.5% vs 15.8% (P = 1.000), but no revisions were related to the burr hole or cranial hardware.

CONCLUSION

Trans-burr hole ultrasound is feasible for gross evaluation of ventricular caliber postoperatively in patients with sonolucent burr hole covers. There was no increase in infection rate or revision rate. This imaging technique may serve as an alternative to CT and MRI in the management of select patients with hydrocephalus and CSF disorders.

Discussion on: "Let's Smarten Up: Smart Devices and the Internet of Things, an Untapped Resource for Innovation in Craniofacial Surgery"

Prior to Dr. Paul Tessier's teachings in the 1960's, many neurosurgeons and craniofacial surgeons took shortcuts and employed alloplastic materials fraught with complication, and soon thereafter, both surgical specialties moved the pendulum towards the side of bone grafts being the gold standard for neurosurgical reconstruction and the art of cranioplasty. But now half a century later, neuroplastic surgery is moving the pendulum the other way. Without a doubt, the brain is a critical organ that needs some form of modulation as opposed to replacement. The intervention delivered can be in the form of electricity, light, medicine, etc. Regardless of the medium, it needs to be housed somewhere. And there is no better real estate than to be housed within a sterile alloplastic case with embedded smart technologies; in a way that prevents obvious, visual deformity. For example, it would be naïve to think that the future of embedded neurotechnologies will one day be housed safely and dependably within one's own bone flap. Hence, moving forward, time-tested alloplastic materials will become the new gold standard for cranioplasty reconstruction as the world starts to welcome a generation of smart cranial devices; some of which may house Bluetooth-connected, Wifi-enabled, MRI-compatible pumps to perform convection-enhanced delivery of time-tested medicines - thereby forever changing the way we approach chronic neurological disease and the forever-obstructing, blood-brain barrier. As this happens, I feel confident saying that both Tessier and Cushing are somewhere applauding and smiling on these efforts.

Neuroimaging through Sonolucent Cranioplasty: A Systematic Scoping Review Protocol

Cranioplasty is a neurosurgical procedure in which the skull bone is repaired after craniectomy. Recently, studies have suggested that sonolucent synthetic materials are safe and useful for cranioplasty. Sonolucent cranioplasty (SC) implants provide unprecedented opportunity in adult neurosurgery to monitor neuroanatomy, assess hemodynamics, view devices located within the implant, and conduct focused ultrasound treatments. Current research on SC includes proof-of-concept cadaveric studies, patient-related safety and feasibility studies, and case series demonstrating transcranioplasty ultrasonography (TCUS). The purpose of this protocol is to investigate the current literature on SC use and outcomes in TCUS. We will perform a systematic literature search following PRISMA-ScR guidelines. The search will be conducted using Ovid Embase, Ovid Medline, and Web of Science Core Collection databases. Titles, abstracts, and full texts will be screened. Joanna Briggs Institute critical appraisal tools will be utilized. Data extraction points will include subject characteristics, SC implant characteristics, ultrasound characteristics, and sonographic findings. These findings will provide a comprehensive review of the literature on sonolucent cranioplasty and directions for future research.

Ultrasonography for Serial Monitoring and Management of Cerebrospinal Fluid Dynamic Disorders After Decompressive Craniectomy

Decompressive craniectomy (DC) is widely used to treat intracranial hypertension following severe head injury. However, impairments of cerebrospinal fluid (CSF) hydrodynamics such as hydrocephalus and subdural effusion are common complications that occur after DC. Therefore, monitoring of intracranial pressure is a staple of neurocritical care post-DC. The aim of this study was to assess the usefulness of transcranial duplex sonography (TDS) for serial monitoring and management of CSF disorders after DC.

Cranioplasty Outcomes From 500 Consecutive Neuroplastic Surgery Patients

BACKGROUND

Cranioplasty is critical to cerebral protection and restoring intracranial physiology, yet this procedure is fraught with a high risk of complications. The field of neuroplastic surgery was created to improve skull and scalp reconstruction outcomes in adult neurosurgical patients, with the hypothesis that a multidisciplinary team approach could help decrease complications.

OBJECTIVE

To determine outcomes from a cohort of cranioplasty surgeries performed by a neuroplastic surgery team using a consistent surgical technique and approach.

METHODS

The authors reviewed 500 consecutive adult neuroplastic surgery cranioplasties that were performed between January 2012 and September 2020. Data were abstracted from a prospectively maintained database. Univariate analysis was performed to determine association between demographic, medical, and surgical factors and odds of revision surgery.

RESULTS

Patients were followed for an average of 24 months. Overall, there was a reoperation rate of 15.2% (n = 76), with the most frequent complications being infection (7.8%, n = 39), epidural hematoma (2.2%, n = 11), and wound dehiscence (1.8%, n = 9). New onset seizures occurred in 6 (1.2%) patients. Several variables were associated with increased odds of revision surgery, including lower body mass ratio, 2 or more cranial surgeries, presence of hydrocephalus shunts, scalp tissue defects, large-sized skull defect, and autologous bone flaps. Importantly, implants with embedded neurotechnology were not associated with increased odds of reoperation.

CONCLUSIONS

These results allow for comparison of multiple factors that impact risk of complications after cranioplasty and lay the foundation for development of a cranioplasty risk stratification scheme. Further research in neuroplastic surgery is warranted to examine how designated centers concentrating on adult neuro-cranial reconstruction and multidisciplinary collaboration may lead to improved cranioplasty outcomes and decreased risks of complications in neurosurgical patients.

Ultrasounds induce blood–brain barrier opening across a sonolucent polyolefin plate in an in vitro isolated brain preparation

The blood–brain barrier (BBB) represents a major obstacle to the delivery of drugs to the central nervous system. The combined use of low-intensity pulsed ultrasound waves and intravascular microbubbles (MB) represents a promising solution to this issue, allowing reversible disruption of the barrier. In this study, we evaluate the feasibility of BBB opening through a biocompatible, polyolefin-based plate in an in vitro whole brain model. Twelve in vitro guinea pig brains were employed; brains were insonated using a planar transducer with or without interposing the polyolefin plate during arterial infusion of MB. Circulating MBs were visualized with an ultrasonographic device with a linear probe. BBB permeabilization was assessed by quantifying at confocal microscopy the extravasation of FITC-albumin perfused after each treatment. US-treated brains displayed BBB permeabilization exclusively in the volume under the US beam; no significant differences were observed between brains insonated with or without the polyolefin plate. Control brains not perfused with MB did not show signs of FITC-albumin extravasation. Our preclinical study suggests that polyolefin cranial plate could be implanted as a skull replacement to maintain craniotomic windows and perform post-surgical repeated BBB opening with ultrasound guidance to deliver therapeutic agents to the central nervous system.

Cranial sonolucent prosthesis: a window of opportunity for neuro-oncology (and neuro-surgery)

INTRODUCTION

Ultrasound (US) is a versatile technology, able to provide a real-time and multiparametric intraoperative imaging, and a promising way to treat neuro-oncological patients outside the operating room. Anyhow, its potential is limited both in imaging and therapeutic purposes by the existence of the bone shielding. To enhance the spectrum of uses, our group has designed a dedicated US-translucent cranial prosthesis. Herein, we provide the proof of concept of a long-term US-based follow-up and a potential bedside therapeutic exploitation of US.

METHODS

The prosthesis was first implanted in a cadaveric specimen to record any issue related to the cranioplasty procedure. Hence, the device was implanted in a patient undergoing surgery for a multi-recurrent anaplastic oligodendroglioma. US multiparametric scans through the device were acquired at 3, 6, 9, and 30 months after the procedure.

RESULTS

The prosthesis could be modeled and implanted through ordinary instruments, with no concerns over safety and feasibility. Trans-prosthesis multiparametric US imaging was feasible, with image quality comparable to intraoperative US. Long-term follow-up in an outpatient setting was possible with no adverse events. Trans-prosthesis mechanical interaction with microbubbles was also feasible during follow-up.

CONCLUSIONS

This report provides the first proof of concept for a potential breakthrough in the management of neuro-oncological patients. Indeed, through the implantation of an artificial acoustic window, the road is set to employ US both for a more dynamic long-term follow-up, and for US-guided therapeutic applications.

A Clinical Study on Individualized Surgical Scheme of Hydrocephalus Complicated With Skull Defect

OBJECTIVE

This study intends to discuss the individualized selection of surgical scheme of hydrocephalus complicated with skull defect.

METHODS

A total of 141 patients with hydrocephalus complicated with skull defect in our hospital from January 2012 to December 2018 were the main subjects of this study. Among these 141 patients, 78 patients underwent shunt and skull repair surgery in our hospital. In the present study, according to the classification of bone window tension, and combined with factors that affect the operation, different surgical schemes were selected, namely, repair surgery in the first phase and shunt surgery in the second phase, or simultaneous surgery, or shunt surgery in the first phase and repair surgery in the second phase.

RESULTS

The results of the present study show that an individualized surgical scheme can allow for the operation of hydrocephalus complicated with skull defect, without increasing the risk of complications, such as shunt infection, epidural hematoma, etc.

CONCLUSIONS

The surgical scheme for hydrocephalus complicated with skull defect differs in clinic.

Feasibility of Customised Polymethyl Methacrylate Implants Fabricated Using 3D Printed Flexible Moulds for Correction of Facial Skeletal Deformities

INTRODUCTION

Use of patient specific Polymethyl methacrylate (PMMA) implants for the reconstruction of cranial defects has become a standard practice with excellent long-term results. However, for the reconstruction of midface and mandibular osseous defects other alloplastic materials are preferred but their use is limited due to high cost. This is a report of our experience with the use of low-cost patient specific PMMA implants fabricated using 3D printed moulds in the reconstruction of osseous defects involving different areas of the facial skeleton not limited to cranium.

METHODS

The 25 consecutive patients with craniofacial osseous defects who underwent reconstruction using customized PMMA implants were analyzed. All PMMA implants were fabricated intraoperatively with the use of 3D printed flexible moulds or templates.

RESULTS

A total of 34 implants were used in 25 consecutive patients. Out of 34 implants 25 were used for midface and mandibular osseous defects. Most common etiology was post-traumatic deformity (n = 19) followed by tumor (n = 3), craniofacial anomalies (n = 2) and post-craniotomy (n = 1). One patient out of 25 (n = 1) had postoperative implant exposure. The follow-up was ranged from 3 to 19 months with an average of 12 months. The aesthetic outcome was found to be good to excellent with mean visual analogue score of 4.08.

CONCLUSIONS

Polymethyl methacrylate implants fabricated intraoperatively using 3D printed moulds provide accurate and precise reconstruction at an exceptionally low cost. PMMA has an excellent moulding property with low infection rates. As shown in our study its application may be easily extended to all areas of the craniofacial skeleton.

Load-Bearing Capacity and Design Advantages of a Custom-Made, Thin Pure-Titanium Cranioplasty (CranioTop)

BACKGROUND

Adequate and stable coverage of cranial contour and continuity defects of any origin is a common challenge in neurosurgical clinics. This study presents the results of investigations concerning the mechanical load-bearing capacity and design advantages of custom-made implants made from a thin, pure-titanium sheet (CranioTop) (CLinstruments, Attendorn, Germany) for covering complex cranial defects.

METHODS

In 9 test series, the stability of three differently shaped and sized thin titanium sheet implants was tested using vertical, uniaxial compression with 3 different compression stamps, to investigate the behaviour of these implants in relation to punctiform as well as planar forces.

RESULTS

All 9 model implants showed elastic behavior in the synchronously recorded force/displacement diagrams at an impression of up to 2 mm. The forces at 2 mm deformation were between 170.1 and 702.7 Newton.

CONCLUSION

Cranioplasty using CranioTop is a stable procedure for covering skull defects, even those of large dimensions. An added advantage is the significant reduction in effort required to prepare the area of the bone margins compared to other current techniques of cranioplasty.

Translucent Customized Cranial Implants Made of Clear Polymethylmethacrylate: An Early Outcome Analysis of 55 Consecutive Cranioplasty Cases

BACKGROUND

Large skull reconstruction, with the use of customized cranial implants, restores cerebral protection, physiologic homeostasis, and one's preoperative appearance. Cranial implants may be composed of either bone or a myriad of alloplastic biomaterials. Recently, patient-specific cranial implants have been fabricated using clear polymethylmethacrylate (PMMA), a visually transparent and sonolucent variant of standard opaque PMMA. Given the new enhanced diagnostic and therapeutic applications of clear PMMA, we present here a study evaluating all outcomes and complications in a consecutive patient series.

METHODS

A single-surgeon, retrospective, 3-year study was conducted on all consecutive patients undergoing large cranioplasty with clear PMMA implants (2016-2019). Patients who received clear PMMA implants with embedded neurotechnologies were excluded due to confounding variables. All outcomes were analyzed in detail and compared with previous studies utilizing similar alloplastic implant materials.

RESULTS

Fifty-five patients underwent cranioplasty with customized clear PMMA implants. Twenty-one (38%) were performed using a single-stage cranioplasty method (ie, craniectomy and cranioplasty performed during the same operation utilizing a prefabricated, oversized design and labor-intense, manual modification), whereas the remaining 34 (62%) underwent a standard, 2-stage reconstruction (craniectomy with a delayed surgery for cranioplasty and minimal-to-no implant modification necessary). The mean cranial defect size was 101.8 cm. The mean follow-up time was 9 months (range, 1.5-39). Major complications requiring additional surgery occurred in 7 patients (13%) consisting of 2 (4%) cerebrospinal fluid leaks, 2 (4%) epidural hematomas, and 3 (4%) infections. In addition, 3 patients developed self-limiting or nonoperative complications including 2 (4%) with new onset seizures and 1 (2%) with delayed scalp healing.

CONCLUSIONS

This is the first reported consecutive case series of cranioplasty reconstruction using customized clear PMMA implants, demonstrating excellent results with regard to ease of use, safety, and complication rates well below published rates when compared with other alloplastic materials. Clear PMMA also provides additional benefits, such as visual transparency and sonolucency, which is material specific and unavailable with autologous bone. Although these early results are promising, further studies with multicenter investigations are well justified to evaluate long-term outcomes.

In vitro and in vivo characterization of a cranial window prosthesis for diagnostic and therapeutic cerebral ultrasound

OBJECTIVE

The authors evaluated the acoustic properties of an implantable, biocompatible, polyolefin-based cranial prosthesis as a medium to transmit ultrasound energy into the intracranial space with minimal distortion for imaging and therapeutic purposes.

METHODS

The authors performed in vitro and in vivo studies of ultrasound transmission through a cranial prosthesis. In the in vitro phase, they analyzed the transmission of ultrasound energy through the prosthesis in a water tank using various transducers with resonance frequencies corresponding to those of devices used for neurosurgical imaging and therapeutic purposes. Four distinct, single-element, focused transducers were tested at fundamental frequencies of 500 kHz, 1 MHz, 2.5 MHz, and 5 MHz. In addition, the authors tested ultrasound transmission through the prosthesis using a linear diagnostic probe (center frequency 5.3 MHz) with a calibrated needle hydrophone in free water. Each transducer was assessed across a range of input voltages that encompassed their full minimum to maximum range without waveform distortion. They also tested the effect of the prosthesis on beam pressure and geometry. In the in vivo phase, the authors performed ultrasound imaging through the prosthesis implanted in a swine model.

RESULTS

Acoustic power attenuation through the prosthesis was considerably lower than that reported to occur through the native cranial bone. Increasing the frequency of the transducer augmented the degree of acoustic power loss. The degradation/distortion of the ultrasound beams passing through the prosthesis was minimal in all 3 spatial planes (XY, XZ, and YZ) that were examined. The images acquired in vivo demonstrated no spatial distortion from the prosthesis, with spatial relationships that were superimposable to those acquired through the dura.

CONCLUSIONS

The results of the tests performed on the polyolefin-based cranial prosthesis indicated that this is a valid medium for delivering both focused and unfocused ultrasound and obtaining ultrasound images of the intracranial space. The prosthesis may serve for several diagnostic and therapeutic ultrasound-based applications, including bedside imaging of the brain and ultrasound-guided focused ultrasound cerebral procedures.

Dural Substitutes Differentially Interfere with Imaging Quality of Sonolucent Transcranioplasty Ultrasound Assessment in Benchtop Model

BACKGROUND

Sonolucent cranioplasty implants were recently introduced into clinical practice and tested for use with transcranioplasty ultrasound (TCUS). In situations where dural substitutes (DSs) are needed during closure, such as in extracranial-intracranial bypass, it is unclear if the DS influences the imaging quality of TCUS. The aim of this study was to assess the influence of DSs on imaging quality during TCUS assessment with sonolucent cranioplasty.

METHODS

A tofu vascular brain model was constructed with a ClearFit implant in between 2 layers of tofu. Injection of saline solution through a 6-F Envoy DA XB endovascular catheter (6-F Envoy DA XB) inserted into the deeper tofu layer mimicked an intracranial vessel. TCUS image quality, including Doppler, with 4 different DSs (DuraGen, Durepair, DuraMatrix-Onlay, DuraMatrix Suturable) placed under the cranioplasty was compared against a control by 2 examiners. A literature search of MEDLINE and EMBASE was conducted to find previous reports of acoustic properties of DSs.

RESULTS

TCUS assessment including Doppler was feasible with the model in longitudinal and axial planes, and the pulsatile particle injection was visualized in real time. DuraGen and Durepair showed Doppler quality and picture detail comparable to the control, while the DuraMatrix-Onlay and DuraMatrix Suturable were inferior to the control. The literature search yielded only 1 previous report on acoustic properties of DSs.

CONCLUSIONS

DSs interfere differentially with imaging quality during TCUS assessment. However, these results are based on a benchtop model and need to be further assessed in the clinical setting.

First-In-Human Experience With Integration of Wireless Intracranial Pressure Monitoring Device Within a Customized Cranial Implant

BACKGROUND

Decompressive craniectomy is a lifesaving treatment for intractable intracranial hypertension. For patients who survive, a second surgery for cranial reconstruction (cranioplasty) is required. The effect of cranioplasty on intracranial pressure (ICP) is unknown.

OBJECTIVE

To integrate the recently Food and Drug Administration-approved, fully implantable, noninvasive ICP sensor within a customized cranial implant (CCI) for postoperative monitoring in patients at high risk for intracranial hypertension.

METHODS

A 16-yr-old female presented for cranioplasty 4-mo after decompressive hemicraniectomy for craniocerebral gunshot wound. Given the persistent transcranial herniation with concomitant subdural hygroma, there was concern for intracranial hypertension following cranioplasty. Thus, cranial reconstruction was performed utilizing a CCI with an integrated wireless ICP sensor, and noninvasive postoperative monitoring was performed.

RESULTS

Intermittent ICP measurements were obtained twice daily using a wireless, handheld monitor. The ICP ranged from 2 to 10 mmHg in the supine position and from -5 to 4 mmHg in the sitting position. Interestingly, an average of 7 mmHg difference was consistently noted between the sitting and supine measurements.

CONCLUSION

This first-in-human experience demonstrates several notable findings, including (1) newfound safety and efficacy of integrating a wireless ICP sensor within a CCI for perioperative neuromonitoring; (2) proven restoration of normal ICP postcranioplasty despite severe preoperative transcranial herniation; and (3) proven restoration of postural ICP adaptations following cranioplasty. To the best of our knowledge, this is the first case demonstrating these intriguing findings with the potential to fundamentally alter the paradigm of cranial reconstruction.

Elective Sonolucent Cranioplasty for Real-Time Ultrasound Monitoring of Flow and Patency of an Extra- to Intracranial Bypass

Cross-sectional imaging studies or catheter angiogram are the imaging modalities of choice to evaluate bypass patency after extra- to intracranial (EC-IC) bypass surgery. Although providing accurate results, these imaging modalities are time-consuming and/or present radiation risk for the patient. Ultrasound imaging is a fast and widely available imaging modality, but is limited in this setting due to the non-sonolucent autologous bone flap covering the bypass after surgery. The recently FDA approved clear polymethyl methacrylate (PMMA) cranioplasty implant overcomes this limitation by its sonolucent characteristic, but has not yet been used in the setting of EC-IC bypass surgery. Here, the authors describe for the first time the feasibility of an elective sonolucent cranioplasty to monitor flow and patency of an EC-IC bypass in real time using ultrasound. This moyamoya patient underwent a direct superficial temporal artery to middle cerebral artery (STA-MCA) bypass, after which a PMMA implant was used to close the craniotomy defect, instead of reimplanting the autologous bone flap. Immediate postoperative bedside transcranioplasty ultrasound confirmed bypass patency and allowed for quantitative flow measurements as well as for exclusion of postoperative hemorrhage. Postoperative CTA and catheter angiogram confirmed patency of the bypass without complications. This report shows for the first time that this technique is feasible and permits bedside transcranioplasty ultrasound assessment of bypass flow in real time, confirmed with angiography. This technique may permit easy comparison of baseline findings with follow up assessments and facilitate less invasive monitoring of bypass patency.

Safety, Feasibility, and Patient-Rated Outcome of Sonolucent Cranioplasty in Extracranial-Intracranial Bypass Surgery to Allow for Transcranioplasty Ultrasound Assessment

Objective

We sought to analyze the safety and feasibility of elective sonolucent cranioplasty in the setting of extracranial-to-intracranial (EC-IC) bypass surgery to monitor bypass patency using ultrasound.

Methods

Patients who underwent direct EC-IC bypass surgery agreed to sonolucent cranioplasty at the time of surgery and received a sonolucent polymethyl methacrylate (PMMA) implant. Besides monitoring clinical outcome, all patients received transcranioplasty ultrasound (TCUS) on postoperative day 1 and at last follow-up. In addition, bypass patency was confirmed using catheter angiogram and fit of implant using computed tomography. Patient-rated outcome was assessed through phone questionnaire.

Results

EC-IC bypass surgery with PMMA cranioplasty was successful in all 7 patients with patent bypasses on postoperative angiogram. Direct TCUS was feasible in all patients, and bypass patency was monitored. There were no complications such as postoperative hemorrhagic/ischemic complications related to the bypass procedure in this patient population, as well as no complications related to the PMMA implant. Postoperative computed tomography showed favorable cosmetic results of the PMMA implant in both the pterional area for superficial temporal artery−middle cerebral artery bypasses and parietooccipital area for occipital artery−middle cerebral artery bypasses as confirmed by high-rated overall patient satisfaction with favorable cosmetic, pain, and sensory patient-rated outcomes.

Conclusions

In this study we were able to show that this novel technique is safe, allows for patency assessment of the EC-IC bypass using bedside TCUS technique, and is cosmetically satisfying for patients.

Risk of Complications in Primary Versus Revision-Type Cranioplasty

INTRODUCTION

Cranioplasty (CP) is a multifaceted procedure in a heterogenous patient population, with a high risk for complication. However, no previous large-scale studies have compared outcomes in primary (ie, first attempt) CP versus revision CP (ie, following previous attempts). The authors, therefore, analyzed long-term outcomes of 506 consecutive primary and revision CPs, performed by a single surgeon.

METHODS

All CPs performed between 2012 and 2019 were analyzed under IRB protocol approval. Surgeries were categorized as either primary (no previous CP; n = 279) or revision CP (at least one previous CP; n = 227). Complications were defined as either major or minor. Subgroup analyses investigated whether or not CP complication risk directly correlated with the number of previous neuro-cranial surgeries and/or CP attempts.

RESULTS

The primary CP group experienced a major complication rate of 9% (26/279). In comparison, the revision CP group demonstrated a major complication rate of 32% (73/227). For the revision CP group, the rate of major complications rose with each additional surgery, from 4% (1 prior surgery) to 17% (2 prior surgeries) to 39% (3-4 prior surgeries) to 47% (≥5 prior surgeries).

CONCLUSION

In a review of 506 consecutive cases, patients undergoing revision CP had a 3-fold increase in incidence of major complications, as compared to those undergoing primary CP. These results provide critical insight into overall CP risk stratification and may guide preoperative risk-benefit discussions. Furthermore, these findings may support a center-of-excellence care model, particularly for those patients with a history of previous neuro-cranial surgeries and/or CP attempts.

Transcranial Sonography versus CT for Postoperative Monitoring After Decompressive Craniectomy

BACKGROUND AND PURPOSE

Computed tomography (CT) is the actual gold standard diagnostic tool for monitoring patients after decompressive craniectomy. It is validated and provides a wide number of information. However, it takes time, expensive, and requires patient transportation. Transcranial sonography (TCS) could represent an alternative diagnostic tool in these patients. The aim of this study is to compare TCS versus CT scan after decompressive craniectomy in terms of diagnosing complications and costs evaluation.

METHODS

We prospectively enrolled 10 craniectomized patients who were monitored with sonography and CT. Ventricular measurements and possible complications were evaluated by two independent observers. The two methods were compared using Fisher's exact test and Spearman's Rho coefficient. A costs analysis was also conducted.

RESULTS

A good correlation coefficient (ρ) between CT and TCS was found for frontal horn dimensions (ρ .9929), median cella (ρ .9516), and third ventricle (ρ .8989). All results were statistically significant (P < .0001) and Bland-Altman plots showed no systemic biases. Fisher's exact test showed no statistically significant differences between TCS and CT for all the studied predefined complications. Cost analysis showed a 68% cost reduction in favor of TCS.

CONCLUSIONS

TCS could be a reliable alternative diagnostic tool for major complications in patients undergoing decompressive craniectomy. It could limit the number of CT scans per patient overcoming several limitations, such as costs, radiation exposure, and need to move the patient.