The retrosigmoid approach is a workhorse of modern neurosurgery, providing access to tumors and vascular lesions in the cerebellopontine angle, a crowded region near the brainstem where acoustic neuromas, meningiomas and vascular compressions are commonly treated. Surgeons reach this area by drilling through the occipital bone behind the ear, creating a window over the posterior cranial fossa. But closing the resulting defect has long been an unsolved nuisance. Because the removed bone fragment is always smaller than the opening created by the trephine, and because surgeons frequently enlarge the craniotomy intraoperatively to improve visibility, gaps of up to seventeen millimeters can remain between the reinserted bone and the skull edge. These gaps are implicated in postoperative complications, including cerebrospinal fluid leaks, and often require additional closure with bone cement, a material whose mixing, handling and curing can add roughly fifteen minutes to the operation.

The Leipzig team, led by Svenja Jung and colleagues in the Department of Neurosurgery together with the Institute of Forensic Medicine and the Fraunhofer Institute for Machine Tools and Forming Technology, designed a two-part solution that pairs a surgical marking template with a matching patient-specific cranioplasty implant. The concept unfolds across four stages, only the last of which takes place in the operating room. Preoperatively, the template and implant are designed from segmented CT data and printed in advance. In surgery, the template is placed directly on the skull and its contours, an inner boundary that must not be undercut and an outer boundary that defines the maximum extent of the craniotomy, are traced onto the bone with a surgical marker. The surgeon then performs the D-shaped craniotomy, with a vertical cut along the mastoid, following these lines. Finally, the implant, which mirrors the template’s outer contour, is trimmed if necessary and fixed into place with plates and screws.

The geometry of the system is deliberately forgiving. Because the implant corresponds to the maximum allowable craniotomy rather than a fixed minimum, any opening smaller than the outer template contour can still be completely covered: an auxiliary guide, itself 3D printed, transfers the template’s inner contour onto the implant so that it can be accurately shortened at the operating table. Only a craniotomy exceeding the outer contour would defeat complete coverage, and the template’s markings are designed to discourage that outcome. Implant thickness was set at five to eight millimeters, matching comparable commercial implants and providing stability in a region where skull thickness varies from a few millimeters to as much as two centimeters.

Manufacturing the components required three distinct additive processes. The templates were produced by stereolithography, an inverted vat polymerization technique, using a biocompatible resin from Formlabs on a Formlabs 3BL printer, with build orientation chosen to keep support structures off the skull-contacting surface. The implants were fabricated by fused deposition modeling on an UltiMaker S7, oriented so that support structures and post-processing fell on the outer surface, preserving a smooth internal face for contact with the brain. The auxiliary trimming guide was printed in polyamide 12 by HP’s Multi Jet Fusion powder bed fusion process. Although the clinically established material polyetheretherketone, or PEEK, is the intended end point, the team used polylactic acid for the preclinical tests to control costs, noting that patient-specific PEEK implants currently run between six thousand and nine thousand euros per patient including the template.

Testing was conducted on a sophisticated 3D printed phantom replicating the posterior cranial fossa on both sides, complete with an integrated cerebellum for orientation and interchangeable skull modules that could be swapped between participants. The phantom itself combined four materials, three printing techniques and one casting process, and was mounted on a camera tripod for mobility. Nine senior and attending neurosurgeons from University Hospital Leipzig each performed bilateral craniotomies on the phantom, producing eighteen procedures in total, one of which could not be completed. After each craniotomy, the implant was trimmed, inserted and fixed, and the modules were scanned by CT at 0.625 millimeter slice thickness for gap analysis in the open-source software 3D Slicer, with nine standardized measurement points defined on each implant.

The results were striking. Across 154 recorded gap measurements, the new concept achieved a mean gap of 2.11 millimeters, roughly 3.5 millimeters smaller than the standard of care, with markedly lower variability. The worst-case gap shrank from 17.59 millimeters under the conventional approach to 9.87 millimeters with the template-implant system, and the best-case measurement fell from 0.72 to 0.07 millimeters. Timing data proved equally encouraging: positioning the template and performing the craniotomy took an average of five minutes and forty-five seconds, while trimming, placement and fixation of the implant added seven minutes and thirty-five seconds, for a total of thirteen minutes and twenty seconds. The researchers calculate that, after accounting for time that would be spent on craniotomy and closure regardless of method, the concept imposes only about five minutes of additional procedural effort, substantially less than bone cement reconstruction.

A comparison of printing accuracy reinforced the reliability of the workflow. Digitization of the printed templates, implants and phantom modules with a Keyence scanner and overlay against the original CAD models in GOM Inspect software revealed deviations consistently below one millimeter, attributable mainly to scan merging, support removal and minor resin residues rather than to systematic printing error. The surgical sets themselves were drawn from standard neurosurgical instrumentation, including a craniotomy set from Aesculag and a spiral bone drill from adeor medical, underscoring that the concept requires no exotic hardware beyond the printed components.

The study is candid about its limitations, which are considerable. The template functioned only as a marking guide, not a fixed cutting edge, leaving the final cut to each surgeon’s judgment, and several participants extended the craniotomy beyond what the implant could cover or inadvertently worked on the skull instead of the hand-held implant, creating unintended additional defects. Positioning relied on externally visible anatomical landmarks because no MRI data or neuronavigation were available for the reduced test models, whereas clinical practice would combine CT and MRI with neuronavigation to place the burr hole precisely over the sinus angle. The comparison dataset also came from 58 real patients with craniotomies of varying size and position, which naturally inflates the variability of the historical control group. A clinically meaningful assessment, the authors stress, will require validation on cadaveric specimens, which are planned next, followed by clinical studies addressing reproducibility, efficiency and safety.

Even so, the preclinical feasibility results represent a compelling proof of concept for bringing the template-based planning methods already routine in orthopedic, maxillofacial and vascular surgery, where guides are used to pre-cut stents, plan tumor resections and position screws, into an area of neurosurgery where they have been conspicuously absent. Smaller, occipitally located cranial defects have been covered with 3D printed cranioplasties before, but a guiding template for defining the surgical approach itself had not previously been reported. By defining the craniotomy preoperatively and manufacturing the implant to match its maximum extent, the Leipzig system converts an improvised closure problem into a planned, standardized procedure. If the upcoming cadaveric and clinical validations hold up, patients undergoing retrosigmoid surgery could benefit from tighter reconstruction, fewer gaps for cerebrospinal fluid to escape through, and more predictable outcomes, all delivered by technology that in many hospitals already sits one imaging study and one print job away.

The patient, a 21-year-old woman, presented with severe neurological symptoms including fever, headache, vomiting, and declining consciousness. Diagnostic magnetic resonance imaging (MRI) revealed six abscesses distributed across both frontal lobes, and the right temporal and occipital lobes, accompanied by marked cerebral edema and a midline shift, signaling imminent brain herniation. Given the critical multi-focal involvement, traditional open craniotomy would pose substantial risks and require multiple surgeries.

To address these challenges, Professor Jun Wang’s team employed a robot-assisted stereotactic navigation system. This technology integrates preoperative MRI with intraoperative computed tomography to generate a precise three-dimensional brain model. Surgeons planned four carefully calculated trajectories to access and drain all abscess cavities while avoiding eloquent brain regions, vital blood vessels, and ventricular structures. Notably, two trajectories leveraged a “one puncture, two injections” strategy, enabling drainage of two abscesses from a single cortical entry point—minimizing cortical injury and operative time.

Intraoperatively, each abscess was aspirated and irrigated with a gentamicin-saline solution to reduce infectious load locally. Concurrently, broad-spectrum antibiotics were administered and later tailored based on microbial cultures, which identified Streptococcus intermedius as the causative pathogen. The team also implemented a short, controlled dexamethasone regimen to alleviate cerebral edema without compromising the immune response, optimizing the patient’s recovery environment.

The clinical outcomes were remarkable. Fever resolved within 72 hours, neurological status rapidly improved, and follow-up MRI at one month showed complete resolution of abscesses and near-total absorption of abscess walls. Impressively, the patient regained full neurological function, maintaining a Karnofsky Performance Status of 100, with no recurrence observed at six- and twelve-month evaluations.

This case illustrates the transformative potential of robotic precision in neurosurgery for complex infectious cases. By enabling multi-target evacuation in a single minimally invasive procedure, this technology can dramatically reduce surgical trauma and expedite recovery times. While this report focuses on a single patient, it sets a precedent for future integration of robotics with multidisciplinary neurocritical care in treating multifocal intracranial infections.

Professor Wang emphasizes that this approach represents a paradigm shift, combining cutting-edge imaging, robotic navigation, and tailored pharmacologic management to tackle deeply seated brain abscesses effectively. Larger clinical studies are anticipated to validate the broad applicability of this strategy.

As robotic assistance and imaging modalities evolve, their integration promises to redefine emergency neurosurgical care, offering patients safer, faster, and more effective treatments for previously formidable brain infections.

Subject of Research: People
Article Title: Robot-guided stereotactic single‐stage evacuation of six intracranial abscesses: a rare case report with literature review
News Publication Date: 27-May-2026
References: DOI: 10.1186/s41016-026-00436-8
Image Credits: Professor Jun Wang from Department of Neurosurgery at the First Hospital of China Medical University, China

Keywords

Neuroscience, Clinical neuroscience, Neurology, Neurological disorders, Robotics

A pioneering study led by Dr. Youxiang Li at Beijing Tiantan Hospital, Capital Medical University, together with Dr. Wei Feng from Songyuan Jilin Oilfield Hospital, offers a robust analysis of treatment outcomes for BTAs in the modern era defined by flow diverter innovations. Published in the March 2026 issue of the Chinese Neurosurgical Journal, this important research fills a notable void in neurosurgical literature by systematically evaluating the efficacy and safety of minimally invasive endovascular treatments in a sizable cohort despite the aneurysms’ rarity.

The researchers performed a retrospective review spanning nearly five years, encompassing 2,759 patients who underwent interventions for cerebral aneurysms from 2018 through 2022. Within this large group, they identified 37 patients harboring basilar trunk artery aneurysms. This dataset was augmented by an exhaustive review of global clinical reports dating from 2013 to 2024 to contextualize their findings amidst evolving neurosurgical practices and device technologies.

Endovascular treatments for BTAs explored in this study ranged from traditional coil embolization techniques to advanced stent-assisted coiling and the increasingly popular flow diverter approach. Among these modalities, stent-assisted coiling predominated, employed in just over half the cases, serving as a versatile treatment for aneurysms unsuitable for simple coiling. Flow diverters—a technologically sophisticated implant that redirects blood flow away from the aneurysm sac to foster thrombosis and healing—were utilized in nearly 30% of patients. The latter was typically reserved for complex aneurysms characterized by large size or fusiform morphology, which remain innately difficult to treat.

The study’s imaging follow-up outcomes were striking. Approximately 72% of patients achieved complete aneurysm occlusion, signifying total isolation of the aneurysmal sac from cerebral circulation post-treatment. Another 19% demonstrated near-complete occlusion, painting an optimistic picture about the durability of modern endovascular approaches. These angiographic successes paralleled favorable clinical results, with almost 89% of patients experiencing minimal to no disability at follow-up. Such functional preservation is pivotal, given the brainstem’s indispensable role in autonomic and motor functions.

Despite these encouraging statistics, the study candidly acknowledges the inherent risks of treating BTAs, underscoring a procedure-related complication rate of around 11%. These adverse events encompassed both hemorrhagic and ischemic phenomena, reflecting the delicate balance between effective aneurysm exclusion and preservation of surrounding brain tissue. Tragically, two patients succumbed during the follow-up period, a somber reminder of the high-stakes nature of interventions in this complex vascular territory.

Intriguingly, aneurysm size emerged as an important, albeit statistically non-significant, factor correlating with outcomes. Larger BTAs tended to portend greater complication rates and less favorable recovery trajectories. This association underscores the necessity for meticulous preoperative planning and individualized therapeutic strategies tailored to the morphology and hemodynamic profile of each aneurysm, as emphasized by Dr. Li.

The evolution of endovascular technologies from traditional coiling to the deployment of flow diverters marks a transformative shift in neurosurgical practice. While coiling remains a foundational tool due to its simplicity and widespread experience, flow diverters represent a leap forward, particularly for anatomically challenging aneurysms that resist complete obliteration by simpler means. Their ability to reconstruct the parent artery and promote natural vessel healing offers a paradigm shift for managing complex cerebrovascular lesions.

The research’s retrospective design and single-center scope inherently limit the generalizability of its conclusions, a caveat duly noted by the authors. The rarity of BTAs constrains sample sizes, impeding large-scale prospective trials that could definitively establish treatment algorithms. Nonetheless, this study lays vital groundwork, highlighting key trends and initiating a framework for future multicenter collaborations and randomized investigations.

Beyond clinical intricacies, this body of work sheds light on the growing importance of minimally invasive methodologies in neurosurgery. Such approaches minimize surgical trauma, reduce perioperative morbidity, and facilitate swifter patient recoveries—an especially valuable advantage when operating near the brainstem’s critical neural networks.

Looking forward, the authors advocate for intensified research focused on optimizing management protocols for higher-risk individuals, particularly those presenting with large or giant BTAs. Innovations in device design, imaging modalities, and perioperative care hold promise for further improving both procedural safety and long-term neurological outcomes in this challenging patient population.

Ultimately, while BTAs continue to pose significant treatment challenges due to their rarity and anatomical complexity, this landmark study underscores that effective, durable management is attainable through tailored, cutting-edge endovascular techniques that harness the capabilities of modern neurointerventional technology.

Subject of Research: People
Article Title: Endovascular treatment for basilar trunk artery aneurysm in the flow diverter era: A consecutive series and review of literature
News Publication Date: 5-Mar-2026
References: DOI: 10.1186/s41016-025-00422-6
Image Credits: Dr. Wei Feng from Songyuan Jilin Oilfield Hospital, China, and Dr. Youxiang Li from Capital Medical University, China
Keywords: Neuroscience, Aneurysms, Surgery, Blood vessels, Neurosurgery, Radiology, Imaging, Biomedical engineering, Clinical studies