Objective: The utilization of fluorescein-guided biopsies and resection has been recently discussed as a suitable strategy to improve and expedite operative techniques for the resection of central nervous system (CNS) tumors. However, little is known about the optical properties of sodium fluorescein (NaFl) in human tumor tissue and their potential impact on ex vivo analyses involving fluorescence-based methods.Methods: Tumor tissue was obtained from a study cohort of an observational study on the utilization of fluorescein-guided biopsy and resection (n=5). The optical properties of fluorescein-stained tissue were compared to the optical features of the dye in vitro and in control samples consisting of tumor tissue of high-grade glioma patients (n=3) without intravenous (i.v.) application of NaFl. The dye-exposed tumor tissues were used for optical measurements to confirm the detectability of NaFl emission ex vivo. The tissue samples were fixed in 4%PFA, immersed in 30% sucrose, embedded in Tissue-Tek OCT compound, and cut to 10 μm cryosections. Spatially resolved emission spectra from tumor samples were recorded on representative slides with a Confocal Laser Scanning Microscope FV1000 (Olympus GmbH, Hamburg, Germany) upon excitation with λ_exc = 488 nm.Results: Optical measurements of fluorescein in 0.9% sodium chloride (NaCl) under in vitro conditions showed an absorption maximum of λ_{max abs} = 479 nm as detected with spectrophotometer Specord 200 and an emission peak at λ_{max em} = 538 nm recorded with the emCCD detection system of a custom-made microscope-based single particle setup using a 500 nm long-pass filter. Further measurements revealed pH- and concentration-dependent emission spectra of NaFl. Under ex vivo conditions, confocal laser scanning microscopy of fluorescein tumor samples revealed a slight bathochromic shift and a broadening of the emission band.Conclusion: Tumor uptake of NaFl leads to changes in the optical properties – a bathochromic shift and broadening of the emission band – possibly caused by the dye’s high pH sensitivity and concentration-dependent reabsorption acting as an inner filter of the dye’s emission, particularly in the short wavelength region of the emission spectrum where absorption and fluorescence overlap. Understanding the ex vivo optical properties of fluorescein is crucial for testing and validating its further applicability as an optical probe for intravital microscopy, immunofluorescence localization studies, and flow cytometry analysis.

The utilization of fluorescein-guided biopsies has recently been discussed to improve and expedite operative techniques in the detection of tumor-positive tissue, as well as to avoid making sampling errors. In this study, we aimed to report our experience with fluorescein-guided biopsies and elucidate distribution patterns in different histopathological diagnoses in order to develop strategies to increase the efficiency and accuracy of this technique. We report on 45 fluorescence-guided stereotactic biopsies in 44 patients (15 female, 29 male) at our institution from March 2016 to March 2021, including 25 frame-based stereotactic biopsies and 20 frameless image-guided biopsies using VarioGuide^®. A total number of 347 biopsy samples with a median of 8 samples (range: 4–18) per patient were evaluated for intraoperative fluorescein uptake and correlated to definitive histopathology. The median age at surgery was 63 years (range: 18–87). Of the acquired specimens, 63% were fluorescein positive. Final histopathology included glioblastoma (n = 16), B-cell non-Hodgkin lymphoma (n = 10), astrocytoma, IDH-mutant WHO grade III (n = 6), astrocytoma, IDH-mutant WHO grade II (n = 1), oligodendroglioma, IDH-mutant and 1p/19q-codeleted WHO grade II (n = 2), reactive CNS tissue/inflammation (n = 4), post-transplantation lymphoproliferative disorder (PTLD; n = 2), ependymoma (n = 1), infection (toxoplasmosis; n = 1), multiple sclerosis (n = 1), and metastasis (n = 1). The sensitivity for high-grade gliomas was 85%, and the specificity was 70%. For contrast-enhancing lesions, the specificity of fluorescein was 84%. The number needed to sample for contrast-enhancing lesions was three, and the overall number needed to sample for final histopathological diagnosis was five. Interestingly, in the astrocytoma, IDH-mutant WHO grade III group, 22/46 (48%) demonstrated fluorescein uptake despite no evidence for gadolinium uptake, and 73% of these were tumor-positive. In our patient series, fluorescein-guided stereotactic biopsy increases the likelihood of definitive neuropathological diagnosis, and the number needed to sample can be reduced by 50% in contrast-enhancing lesions.

OBJECTIVE: Robotics in neurosurgery is becoming increasingly prevalent. The integration of intraoperative imaging for patient registration into workflows of newer robotic systems enhances precision and has further driven their widespread adoption. In this study, the authors report on a lightweight, table-mounted robotic system integrating robotic cone-beam CT (CB-CT) for automated patient registration in cranial biopsies and stereotactic electroencephalography (sEEG). METHODS: This prospective cohort study included patients who underwent stereotactic biopsy or sEEG with the Cirq system from January 2023 to August 2024. For patient-to-image registration, an external registration matrix was secured near the patient’s head before conducting CB-CT with robotic Artis Pheno. CT was then fused with preoperative planning MRI and used as the navigation dataset. Demographic and clinical data were evaluated, and entry and target errors, as well as vector deviation of sEEG electrodes, were assessed and compared with those of patients who underwent biopsies and sEEG with the frameless VarioGuide system. RESULTS: In 26 Cirq-assisted surgical procedures, robotic CB-CT was used for image registration in 20 cases. Of these, 15 were biopsies (mean ± SD 7 ± 1 specimens) and 5 were sEEG with 31 depth electrodes, compared to 29 VarioGuide biopsies and 3 VarioGuide sEEG cases with 25 electrodes. The mean age was 56 ± 19 years, with a male/female ratio of 1.9:1. Lesion size averaged 19 ± 17 cm ³ on T1-weighted imaging and 61 ± 53 cm ³ on T2-weighted imaging for Cirq and 14 ± 14 cm ³ and 68 ± 47 cm ³ for VarioGuide. The mean surgical times were 117 ± 34 minutes for biopsy and 269 ± 54 minutes for sEEG in the Cirq group, with skin-to-skin times of 40 ± 23 minutes for biopsy and 208 ± 74 minutes for sEEG; in comparison, surgical times of 78 ± 21 minutes for biopsy and 218 ± 33 minutes for sEEG were reported with VarioGuide, with skin-to-skin times of 34 ± 13 and 158 ± 27 minutes. No complications occurred. The mean dosage area product was 983 ± 351 µGym ² for biopsies and 1772 ± 968 µGym ² for sEEG. Cirq-assisted sEEG electrodes had mean entry and target errors of 1.4 ± 1.2 mm and 2.6 ± 1.6 mm, compared to 5.3 ± 3.3 mm and 6.5 ± 2.8 mm with VarioGuide. Mean vector deviation was 1.6 ± 0.9 mm with Cirq versus 4.9 ± 2.9 mm with VarioGuide. CONCLUSIONS: The integration of a lightweight, table-mounted robotic alignment tool with intraoperative CB-CT for automated patient-to-image registration enables high precision and a seamless workflow. This combination is safe, has a manageable learning curve, and holds potential to replace traditional frame-based and frameless procedures. Its efficiency and accuracy are likely to contribute to the increasing adoption of robotics in neurosurgery.

The endovascular filament perforation model to mimic subarachnoid hemorrhage (SAH) is a commonly used model - however, the technique can cause a high mortality rate as well as an uncontrollable volume of SAH and other intracranial complications such as stroke or intracranial hemorrhage. In this protocol, a standardized SAH mouse model is presented, induced by endovascular filament perforation, combined with magnetic resonance imaging (MRI) 24 h after operation to ensure the correct bleeding site and exclude other relevant intracranial pathologies. Briefly, C57BL/6J mice are anesthetized with an intraperitoneal ketamine/xylazine (70 mg/16 mg/kg body weight) injection and placed in a supine position. After midline neck incision, the common carotid artery (CCA) and carotid bifurcation are exposed, and a 5-0 non-absorbable monofilament polypropylene suture is inserted in a retrograde fashion into the external carotid artery (ECA) and advanced into the common carotid artery. Then, the filament is invaginated into the internal carotid artery (ICA) and pushed forward to perforate the anterior cerebral artery (ACA). After recovery from surgery, mice undergo a 7.0 T MRI 24 h later. The volume of bleeding can be quantified and graded via postoperative MRI, enabling a robust experimental SAH group with the option to perform further subgroup analyses based on blood quantity.

The utilization of epidural electrodes in the preoperative evaluation of intractable epilepsy is a valuable but underrepresented tool. In recent years, we have adapted the use of cylindrical epidural 1-contact electrodes (1-CE) instead of Peg electrodes. 1-CEs are more versatile since their explantation is a possible bedside procedure. Here we report our experience with 1-CEs as well as associated technical nuances. This retrospective analysis included 56 patients with intractable epilepsy who underwent epidural electrode placement for presurgical evaluation at the Department of Neurosurgery at the Charité University Hospital from September 2011 to July 2021. The median age at surgery was 36.3 years (range: 18–87), with 30 (53.6%) female and 26 (46.4%) male patients. Overall, 507 electrodes were implanted: 93 Fo electrodes, 33 depth electrodes, and 381 epidural electrodes, with a mean total surgical time of 100.5 ± 38 min and 11.8 ± 5 min per electrode. There was a total number of 24 complications in 21 patients (8 Fo electrode dislocations, 6 CSF leaks, 6 epidural electrode dislocations or malfunction, 3 wound infections, and 2 hemorrhages); 11 of these required revision surgery. The relative electrode complication rates were 3/222 (1.4%) in Peg electrodes and 3/159 (1.9%) in 1-CE. In summary, epidural recording via 1-CE is technically feasible, harbours an acceptable complication rate, and adequately replaces Peg electrodes.