Miniaturized handheld confocal microscopy for neurosurgery: results in an experimental glioblastoma model

Intraoperative in vivo confocal endomicroscopy of the glioma margin: performance assessment of image interpretation by neurosurgeon users

Objectives

Confocal laser endomicroscopy (CLE) is an intraoperative real-time cellular resolution imaging technology that images brain tumor histoarchitecture. Previously, we demonstrated that CLE images may be interpreted by neuropathologists to determine the presence of tumor infiltration at glioma margins. In this study, we assessed neurosurgeons' ability to interpret CLE images from glioma margins and compared their assessments to those of neuropathologists.

Methods

In vivo CLE images acquired at the glioma margins that were previously reviewed by CLE-experienced neuropathologists were interpreted by four CLE-experienced neurosurgeons. A numerical scoring system from 0 to 5 and a dichotomous scoring system based on pathological features were used. Scores from assessments of hematoxylin and eosin (H&E)-stained sections and CLE images by neuropathologists from a previous study were used for comparison. Neurosurgeons' scores were compared to the H&E findings. The inter-rater agreement and diagnostic performance based on neurosurgeons' scores were calculated. The concordance between dichotomous and numerical scores was determined.

Results

In all, 4275 images from 56 glioma margin regions of interest (ROIs) were included in the analysis. With the numerical scoring system, the inter-rater agreement for neurosurgeons interpreting CLE images was moderate for all ROIs (mean agreement, 61%), which was significantly better than the inter-rater agreement for the neuropathologists (mean agreement, 48%) (p < 0.01). The inter-rater agreement for neurosurgeons using the dichotomous scoring system was 83%. The concordance between the numerical and dichotomous scoring systems was 93%. The overall sensitivity, specificity, positive predictive value, and negative predictive value were 78%, 32%, 62%, and 50%, respectively, using the numerical scoring system and 80%, 27%, 61%, and 48%, respectively, using the dichotomous scoring system. No statistically significant differences in diagnostic performance were found between the neurosurgeons and neuropathologists.

Conclusion

Neurosurgeons' performance in interpreting CLE images was comparable to that of neuropathologists. These results suggest that CLE could be used as an intraoperative guidance tool with neurosurgeons interpreting the images with or without assistance of the neuropathologists. The dichotomous scoring system is robust yet simple and may streamline rapid, simultaneous interpretation of CLE images during imaging.

Intraoperative confocal laser endomicroscopy: prospective in vivo feasibility study of a clinical-grade system for brain tumors

OBJECTIVE

The authors evaluated the feasibility of using the first clinical-grade confocal laser endomicroscopy (CLE) system using fluorescein sodium for intraoperative in vivo imaging of brain tumors.

METHODS

A CLE system cleared by the FDA was used in 30 prospectively enrolled patients with 31 brain tumors (13 gliomas, 5 meningiomas, 6 other primary tumors, 3 metastases, and 4 reactive brain tissue). A neuropathologist classified CLE images as interpretable or noninterpretable. Images were compared with corresponding frozen and permanent histology sections, with image correlation to biopsy location using neuronavigation. The specificities and sensitivities of CLE images and frozen sections were calculated using permanent histological sections as the standard for comparison. A recently developed surgical telepathology software platform was used in 11 cases to provide real-time intraoperative consultation with a neuropathologist.

RESULTS

Overall, 10,713 CLE images from 335 regions of interest were acquired. The mean duration of the use of the CLE system was 7 minutes (range 3-18 minutes). Interpretable CLE images were obtained in all cases. The first interpretable image was acquired within a mean of 6 (SD 10) images and within the first 5 (SD 13) seconds of imaging; 4896 images (46%) were interpretable. Interpretable image acquisition was positively correlated with study progression, number of cases per surgeon, cumulative length of CLE time, and CLE time per case (p ≤ 0.01). The diagnostic accuracy, sensitivity, and specificity of CLE compared with frozen sections were 94%, 94%, and 100%, respectively, and the diagnostic accuracy, sensitivity, and specificity of CLE compared with permanent histological sections were 92%, 90%, and 94%, respectively. No difference was observed between lesion types for the time to first interpretable image (p = 0.35). Deeply located lesions were associated with a higher percentage of interpretable images than superficial lesions (p = 0.02). The study met the primary end points, confirming the safety and feasibility and acquisition of noninvasive digital biopsies in all cases. The study met the secondary end points for the duration of CLE use necessary to obtain interpretable images. A neuropathologist could interpret the CLE images in 29 (97%) of 30 cases.

CONCLUSIONS

The clinical-grade CLE system allows in vivo, intraoperative, high-resolution cellular visualization of tissue microstructure and identification of lesional tissue patterns in real time, without the need for tissue preparation.

Development, Implementation and Application of Confocal Laser Endomicroscopy in Brain, Head and Neck Surgery—A Review

When we talk about visualization methods in surgery, it is important to mention that the diagnosis of tumors and how we define tumor borders intraoperatively in a correct way are two main things that would not be possible to achieve without this grand variety of visualization methods we have at our disposal nowadays. In addition, histopathology also plays a very important role, and its importance cannot be neglected either. Some biopsy specimens, e.g., frozen sections, are examined by a histopathologist and lead to tumor diagnosis and the definition of its borders. Furthermore, surgical resection is a very important point when it comes to prognosis and life survival. Confocal laser endomicroscopy (CLE) is an imaging technique that provides microscopic information on the tissue in real time. CLE of disorders, such as head, neck and brain tumors, has only recently been suggested to contribute to both immediate tumor characterization and detection. It can be used as an additional tool for surgical biopsies during biopsy or surgical procedures and for inspection of resection margins during surgery. In this review, we analyze the development, implementation, advantages and disadvantages as well as the future directions of this technique in neurosurgical and otorhinolaryngological disciplines.

Confocal laser imaging in neurosurgery: A comprehensive review of sodium fluorescein-based CONVIVO preclinical and clinical applications

Given the established direct correlation that exists among extent of resection and postoperative survival in brain tumors, obtaining complete resections is of primary importance. Apart from the various technological advancements that have been introduced in current clinical practice, histopathological study still remains the gold-standard for definitive diagnosis. Frozen section analysis still represents the most rapid and used intraoperative histopathological method that allows for an intraoperative differential diagnosis. Nevertheless, such technique owes some intrinsic limitations that limit its overall potential in obtaining real-time diagnosis during surgery. In this context, confocal laser technology has been suggested as a promising method to have near real-time intraoperative histological images in neurosurgery, thanks to the results of various studies performed in other non-neurosurgical fields. Still far to be routinely implemented in current neurosurgical practice, pertinent literature is growing quickly, and various reports have recently demonstrated the utility of this technology in both preclinical and clinical settings in identifying brain tumors, microvasculature, and tumor margins, when coupled to the intravenous administration of sodium fluorescein. Specifically in neurosurgery, among different available devices, the ZEISS CONVIVO system probably boasts the most recent and largest number of experimental studies assessing its usefulness, which has been confirmed for identifying brain tumors, offering a diagnosis and distinguishing between healthy and pathologic tissue, and studying brain vessels. The main objective of this systematic review is to present a state-of-the-art summary on sodium fluorescein-based preclinical and clinical applications of the ZEISS CONVIVO in neurosurgery.

Surgical Treatment of Glioblastoma: State-of-the-Art and Future Trends

Glioblastoma (GBM) is a highly aggressive disease and is associated with poor prognosis despite treatment advances in recent years. Surgical resection of tumor remains the main therapeutic option when approaching these patients, especially when combined with adjuvant radiochemotherapy. In the present study, we conducted a comprehensive literature review on the state-of-the-art and future trends of the surgical treatment of GBM, emphasizing topics that have been the object of recent study.

Introduction of In Vivo Confocal Laser Endomicroscopy and Real-Time Telepathology for Remote Intraoperative Neurosurgery-Pathology Consultation

BACKGROUND

Precise communication between neurosurgeons and pathologists is crucial for optimizing patient care, especially for intraoperative diagnoses. Confocal laser endomicroscopy (CLE) combined with a telepathology software platform (TSP) provides a novel venue for neurosurgeons and pathologists to review CLE images and converse intraoperatively in real-time.

OBJECTIVE

To describe the feasibility of integrating CLE and a TSP in the surgical workflow for real-time review of in vivo digital fluorescence tissue imaging in 3 patients with intracranial tumors.

METHODS

Although the neurosurgeon used the CLE probe to generate fluorescence images of histoarchitecture within the operative field that were displayed on monitors in the operating room, the pathologist simultaneously remotely viewed the CLE images. The neurosurgeon and pathologist discussed in real-time the histological structures of intraoperative imaging locations.

RESULTS

The neurosurgeon placed the CLE probe at various locations on and around the tumor, in the surgical resection bed, and on surrounding brain tissue with communication through the TSP. The neurosurgeon oriented the pathologist to the location of the CLE, and the pathologist and neurosurgeon discussed the CLE images in real-time. The TSP and CLE were integrated successfully and rapidly in the operating room in all 3 cases. No patient had perioperative complications.

CONCLUSION

Two novel digital neurosurgical cellular imaging technologies were combined with intraoperative neurosurgeon-pathologist communication to guide the identification of abnormal histoarchitectural tissue features in real-time. CLE with the TSP may allow rapid decision-making during tumor resection that may hold significant advantages over the frozen section process and surgical workflow in general.

Characterization of ex vivo and in vivo intraoperative neurosurgical confocal laser endomicroscopy imaging

Background

The new US Food and Drug Administration-cleared fluorescein sodium (FNa)-based confocal laser endomicroscopy (CLE) imaging system allows for intraoperative on-the-fly cellular level imaging. Two feasibility studies have been completed with intraoperative use of this CLE system in ex vivo and in vivo modalities. This study quantitatively compares the image quality and diagnostic performance of ex vivo and in vivo CLE imaging.

Methods

Images acquired from two prospective CLE clinical studies, one ex vivo and one in vivo, were analyzed quantitatively. Two image quality parameters – brightness and contrast – were measured using Fiji software and compared between ex vivo and in vivo images for imaging timing from FNa dose and in glioma, meningioma, and intracranial metastatic tumor cases. The diagnostic performance of the two studies was compared.

Results

Overall, the in vivo images have higher brightness and contrast than the ex vivo images (p < 0.001). A weak negative correlation exists between image quality and timing of imaging after FNa dose for the ex vivo images, but not the in vivo images. In vivo images have higher image quality than ex vivo images (p < 0.001) in glioma, meningioma, and intracranial metastatic tumor cases. In vivo imaging yielded higher sensitivity and negative predictive value than ex vivo imaging.

Conclusions

In our setting, in vivo CLE optical biopsy outperforms ex vivo CLE by producing higher quality images and less image deterioration, leading to better diagnostic performance. These results support the in vivo modality as the modality of choice for intraoperative CLE imaging.

Real-time intraoperative surgical telepathology using confocal laser endomicroscopy

OBJECTIVE

Communication between neurosurgeons and pathologists is mandatory for intraoperative decision-making and optimization of resection, especially for invasive masses. Handheld confocal laser endomicroscopy (CLE) technology provides in vivo intraoperative visualization of tissue histoarchitecture at cellular resolution. The authors evaluated the feasibility of using an innovative surgical telepathology software platform (TSP) to establish real-time, on-the-fly remote communication between the neurosurgeon using CLE and the pathologist.

METHODS

CLE and a TSP were integrated into the surgical workflow for 11 patients with brain masses (6 patients with gliomas, 3 with other primary tumors, 1 with metastasis, and 1 with reactive brain tissue). Neurosurgeons used CLE to generate video-flow images of the operative field that were displayed on monitors in the operating room. The pathologist simultaneously viewed video-flow CLE imaging using a digital tablet and communicated with the surgeon while physically located outside the operating room (1 pathologist was in another state, 4 were at home, and 6 were elsewhere in the hospital). Interpretations of the still CLE images and video-flow CLE imaging were compared with the findings on the corresponding frozen and permanent H&E histology sections.

RESULTS

Overall, 24 optical biopsies were acquired with mean ± SD 2 ± 1 optical biopsies per case. The mean duration of CLE system use was 1 ± 0.3 minutes/case and 0.25 ± 0.23 seconds/optical biopsy. The first image with identifiable histopathological features was acquired within 6 ± 0.1 seconds. Frozen sections were processed within 23 ± 2.8 minutes, which was significantly longer than CLE usage (p < 0.001). Video-flow CLE was used to correctly interpret tissue histoarchitecture in 96% of optical biopsies, which was substantially higher than the accuracy of using still CLE images (63%) (p = 0.005).

CONCLUSIONS

When CLE is employed in tandem with a TSP, neurosurgeons and pathologists can view and interpret CLE images remotely and in real time without the need to biopsy tissue. A TSP allowed neurosurgeons to receive real-time feedback on the optically interrogated tissue microstructure, thereby improving cross-functional communication and intraoperative decision-making and resulting in significant workflow advantages over the use of frozen section analysis.

Preliminary Report: Rapid Intraoperative Detection of Residual Glioma Cell in Resection Cavity Walls Using a Compact Fluorescence Microscope

Objective: The surgical eradication of malignant glioma cells is theoretically impossible. Therefore, reducing the number of remaining tumor cells around the brain–tumor interface (BTI) is crucial for achieving satisfactory clinical results. The usefulness of fluorescence–guided resection for the treatment of malignant glioma was recently reported, but the detection of infiltrating tumor cells in the BTI using a surgical microscope is not realistic. Therefore, we have developed an intraoperative rapid fluorescence cytology system, and exploratorily evaluated its clinical feasibility for the management of malignant glioma. Materials and methods: A total of 25 selected patients with malignant glioma (newly diagnosed: 17; recurrent: 8) underwent surgical resection under photodiagnosis using photosensitizer Talaporfin sodium and a semiconductor laser. Intraoperatively, a crush smear preparation was made from a tiny amount of tumor tissue, and the fluorescence emitted upon 620/660 nm excitation was evaluated rapidly using a compact fluorescence microscope in the operating theater. Results: Fluorescence intensities of tumor tissues measured using a surgical microscope correlated with the tumor cell densities of tissues evaluated by measuring the red fluorescence emitted from the cytoplasm of tumor cells using a fluorescence microscope. A “weak fluorescence” indicated a reduction in the tumor cell density, whereas “no fluorescence” did not indicate the complete eradication of the tumor cells, but indicated that few tumor cells were emitting fluorescence. Conclusion: The rapid intraoperative detection of fluorescence from glioma cells using a compact fluorescence microscope was probably useful to evaluate the presence of tumor cells in the resection cavity walls, and could provide surgical implications for the more complete resection of malignant gliomas.

Socio-Organizational Impact of Confocal Laser Endomicroscopy in Neurosurgery and Neuropathology: Results from a Process Analysis and Expert Survey

During brain tumor resection surgery, it is essential to determine the tumor borders as the extent of resection is important for post-operative patient survival. The current process of removing a tissue sample for frozen section analysis has several shortcomings that might be overcome by confocal laser endomicroscopy (CLE). CLE is a promising new technology enabling the digital in vivo visualization of tissue structures in near real-time. Research on the socio-organizational impact of introducing this new methodology to routine care in neurosurgery and neuropathology is scarce. We analyzed a potential clinical workflow employing CLE by comparing it to the current process. Additionally, a small expert survey was conducted to collect data on the opinion of clinical staff working with CLE. While CLE can contribute to a workload reduction for neuropathologists and enable a shorter process and a more efficient use of resources, the effort for neurosurgeons and surgery assistants might increase. Experts agree that CLE offers huge potential for better diagnosis and therapy but also see challenges, especially due to the current state of experimental use, including a risk for misinterpretations and the need for special training. Future studies will show whether CLE can become part of routine care.

Redosing of Fluorescein Sodium Improves Image Interpretation During Intraoperative Ex Vivo Confocal Laser Endomicroscopy of Brain Tumors

Background

Fluorescein sodium (FNa) is a fluorescence agent used with a wide-field operating microscope for intraoperative guidance and with confocal laser endomicroscopy (CLE) to evaluate brain tissue. Susceptibility of FNa to degradation over time may affect CLE image quality during prolonged surgeries. This study describes improved characteristics of CLE images after intraoperative redosing with FNa.

Methods

A retrospective analysis was performed using CLE images obtained ex vivo from samples obtained during tumor resections with FNa-based fluorescence guidance with a wide-field operating microscope. The comparison groups included CLE images acquired after FNa redosing (redose imaging group), images from the same patients acquired after the initial FNa dose (initial-dose imaging group), and images from patients in whom redosing was not used (single-dose imaging group). A detailed assessment of image quality and interpretation regarding different FNa dosage and timing of imaging after FNa administration was conducted for all comparison groups.

Results

The brightest and most contrasting images were observed in the redose group compared to the initial-dose and single-dose groups (P<0.001). The decay of FNa signal negatively correlated with brightness (rho = -0.52, P<0.001) and contrast (rho = -0.57, P<0.001). Different doses of FNa did not significantly affect the brightness (P=0.15) or contrast (P=0.09) in CLE images. As the mean timing of imaging increased, the percentage of accurately diagnosed images decreased (P=0.03).

Conclusions

The decay of the FNa signal is directly associated with image brightness and contrast. The qualitative interpretation scores of images were highest for the FNa redose imaging group. Redosing with FNa to improve the utility of CLE imaging should be considered a safe and beneficial strategy during prolonged surgeries.

Confocal Laser Microscopy in Neurosurgery: State of the Art of Actual Clinical Applications

Achievement of complete resections is of utmost importance in brain tumor surgery, due to the established correlation among extent of resection and postoperative survival. Various tools have recently been included in current clinical practice aiming to more complete resections, such as neuronavigation and fluorescent-aided techniques, histopathological analysis still remains the gold-standard for diagnosis, with frozen section as the most used, rapid and precise intraoperative histopathological method that permits an intraoperative differential diagnosis. Unfortunately, due to the various limitations linked to this technique, it is still unsatisfactorily for obtaining real-time intraoperative diagnosis. Confocal laser technology has been recently suggested as a promising method to obtain near real-time intraoperative histological data in neurosurgery, due to its established use in other non-neurosurgical fields. Still far to be widely implemented in current neurosurgical clinical practice, this technology was initially studied in preclinical experiences confirming its utility in identifying brain tumors, microvasculature and tumor margins. Hence, ex vivo and in vivo clinical studies evaluated the possibility with this technology of identifying and classifying brain neoplasms, discerning between normal and pathologic tissue, showing very promising results. This systematic review has the main objective of presenting a state-of-the-art summary on actual clinical applications of confocal laser imaging in neurosurgical practice.

Structural and Functional Imaging in Glioma Management

The goal of glioma surgery is maximal safe resection in order to provide optimal tumor control and survival benefit to the patient. There are multiple imaging modalities beyond traditional contrast-enhanced magnetic resonance imaging (MRI) that have been incorporated into the preoperative workup of patients presenting with gliomas. The aim of these imaging modalities is to identify cortical and subcortical areas of eloquence, and their relationship to the lesion. In this article, multiple modalities are described with an emphasis on the underlying technology, clinical utilization, advantages, and disadvantages of each. functional MRI and its role in identifying hemispheric dominance and areas of language and motor are discussed. The nuances of magnetoencephalography and transcranial magnetic stimulation in localization of eloquent cortex are examined, as well as the role of diffusion tensor imaging in defining normal white matter tracts in glioma surgery. Lastly, we highlight the role of stimulated Raman spectroscopy in intraoperative histopathological diagnosis of tissue to guide tumor resection. Tumors may shift the normal arrangement of functional anatomy in the brain; thus, utilization of multiple modalities may be helpful in operative planning and patient counseling for successful surgery.

Visualization of brain microvasculature and blood flow in vivo: Feasibility study using confocal laser endomicroscopy

OBJECTIVE

Qualitative and quantitative analyses of blood flow in normal and pathologic brain and spinal cord microvasculature were performed using confocal laser endomicroscopy (CLE).

METHODS

Blood flow in cortical, dural, and spinal cord microvasculature was assessed in vivo in swine. We assessed microvasculature under normal conditions and after vessel occlusion, brain injury due to cold or surgical trauma, and cardiac arrest. Tumor-associated microvasculature was assessed in vivo and ex vivo in 20 patients with gliomas.

RESULTS

We observed erythrocyte flow in vessels 5-500 µm in diameter. Thrombosis, flow arrest and redistribution, flow velocity changes, agglutination, and cells rolling were assessed in normal and injured brain tissue. Microvasculature in in vivo CLE images of gliomas was classified as normal in 68% and abnormal in 32% of vessels on the basis of morphological appearance. Dural lymphatic channels were discriminated from blood vessels. Microvasculature CLE imaging was possible for up to 30 minutes after a 1 mg/kg intravenous dose of fluorescein.

CONCLUSIONS

CLE imaging allows assessment of cerebral and tumor microvasculature and blood flow alterations with subcellular resolution intraoperative imaging demonstrating precise details of real-time cell movements. Research and clinical scenarios may benefit from this novel intraoperative in vivo microscopic fluorescence imaging modality.

Ex Vivo Fluorescein-Assisted Confocal Laser Endomicroscopy (CONVIVO® System) in Patients With Glioblastoma: Results From a Prospective Study

Background

Confocal laser endomicroscopy (CLE) allowing intraoperative near real-time high-resolution cellular visualization is a promising method in neurosurgery. We prospectively tested the accuracy of a new-designed miniatured CLE (CONVIVO® system) in giving an intraoperative first-diagnosis during glioblastoma removal.

Methods

Between January and May 2018, 15 patients with newly diagnosed glioblastoma underwent fluorescein-guided surgery. Two biopsies from both tumor central core and margins were harvested, dividing each sample into two specimens. Biopsies were firstly intraoperatively ex vivo analyzed by CLE, subsequently processed for frozen and permanent fixation, respectively. Then, a blind comparison was conducted between CLE and standard permanent section analyses, checking for CLE ability to provide diagnosis and categorize morphological patterns intraoperatively.

Results

Blindly comparing CONVIVO® and frozen sections images we obtained a high rate of concordance in both providing a correct diagnosis and categorizing patterns at tumor central core (80 and 93.3%, respectively) and at tumor margins (80% for both objectives). Comparing CONVIVO® and permanent sections, concordance resulted similar at central core (total/partial concordance in 80 and 86.7% for diagnosis and morphological categorization, respectively) and lower at tumor margins (66.6% for both categories). Time from fluorescein injection and time from biopsy sampling to CONVIVO® scanning was 134 ± 31 min (122–214 min) and 9.23 min (1–17min), respectively. Mean time needed for CONVIVO® images interpretation was 5.74 min (1–7 min).

Conclusions

The high rate of diagnostic/morphological consistency found between CONVIVO® and frozen section analyses suggests the possibility to use CLE as a complementary tool for intraoperative diagnosis of ex vivo tissue specimens during glioblastoma surgery.

Characteristics of Fluorescent Intraoperative Dyes Helpful in Gross Total Resection of High-Grade Gliomas-A Systematic Review

Background: A very important aspect in the treatment of high-grade glioma is gross total resection to reduce the risk of tumor recurrence. One of the methods to facilitate this task is intraoperative fluorescence navigation. The aim of the study was to compare the dyes used in this technique fluorescent intraoperative navigation in terms of the mechanism of action and influence on the treatment of patients. Methods: The review was carried out on the basis of articles found in PubMed, Google Scholar, and BMC search engines, as well as those identified by searched bibliographies and suggested by experts during the preparation of the article. The database analysis was performed for the following phrases: "glioma", "glioblastoma", "ALA", "5ALA", "5-ALA", "aminolevulinic acid", "levulinic acid", "fluorescein", "ICG", "indocyanine green", and "fluorescence navigation". Results: After analyzing 913 citations identified on the basis of the search criteria, we included 36 studies in the review. On the basis of the analyzed articles, we found that 5-aminolevulinic acid and fluorescein are highly effective in improving the percentage of gross total resection achieved in high-grade glioma surgery. At the same time, the limitations resulting from the use of these methods are marked-higher costs of the procedure and the need to have neurosurgical microscope in combination with a special light filter in the case of 5-aminolevulinic acid (5-ALA), and low specificity for neoplastic cells and the dependence on the degree of damage to the blood-brain barrier in the intensity of fluorescence in the case of fluorescein. The use of indocyanine green in the visualization of glioma cells is relatively unknown, but some researchers have suggested its utility and the benefits of using it simultaneously with other dyes. Conclusion: The use of intraoperative fluorescence navigation with the use of 5-aminolevulinic acid and fluorescein allows the range of high-grade glioma resection to be increased.

Intraoperative Confocal Laser Endomicroscopy Ex Vivo Examination of Tissue Microstructure During Fluorescence-Guided Brain Tumor Surgery

Background

Noninvasive intraoperative optical biopsy that provides real-time imaging of histoarchitectural (cell resolution) features of brain tumors, especially at the margin of invasive tumors, would be of great value. To assess clinical-grade confocal laser endomicroscopy (CLE) and to prepare for its use intraoperatively in vivo, we performed an assessment of CLE ex vivo imaging in brain lesions.

Methods

Tissue samples from patients who underwent intracranial surgeries with fluorescein sodium (FNa)–based wide-field fluorescence guidance were acquired for immediate intraoperative ex vivo optical biopsies with CLE. Hematoxylin-eosin–stained frozen section analysis of the same specimens served as the gold standard for blinded neuropathology comparison. FNa 2 to 5 mg/kg was administered upon induction of anesthesia, and FNa 5 mg/kg was injected for CLE contrast improvement. Histologic features were identified, and the diagnostic accuracy of CLE was assessed.

Results

Of 77 eligible patients, 47 patients with 122 biopsies were enrolled, including 32 patients with gliomas and 15 patients with other intracranial lesions. The positive predictive value of CLE optical biopsies was 97% for all specimens and 98% for gliomas. The specificity of CLE was 90% for all specimens and 94% for gliomas. The second FNa injection in seven patients, a mean of 2.6 h after the first injection, improved image quality and increased the percentage of accurately diagnosed images from 67% to 93%. Diagnostic CLE features of lesional glioma biopsies and normal brain were identified. Seventeen histologic features were identified.

Conclusions

Results demonstrated high specificity and positive predictive value of ex vivo intraoperative CLE optical biopsies and justify an in vivo intraoperative trial. This new portable, noninvasive intraoperative imaging technique provides diagnostic features to discriminate lesional tissue with high specificity and is feasible for incorporation into the fluorescence-guided surgery workflow, particularly for patients with invasive brain tumors.

Role of Resection in Glioblastoma Management

Whenever possible, maximal safe resection is the first intervention for management of glioblastoma. Resection offers tissue for diagnosis, decompression of the brain, cytoreduction, and has been associated with prolonged survival in numerous retrospective studies. In this review, we provide a critical overview of the literature associating glioblastoma resection with survival. We discuss techniques that enhance extent of resection, and the role of clinical and surgeon-variables. At last, we analyze the covariates and confounders that might influence the relationship between extent of resection and survival for glioblastoma, as these might ultimately also influence outcomes and other therapeutic interventions tested in trials.

Confocal Laser Endomicroscopy Assessment of Pituitary Tumor Microstructure: A Feasibility Study

This is the first study to assess confocal laser endomicroscopy (CLE) use within the transsphenoidal approach and show the feasibility of obtaining digital diagnostic biopsies of pituitary tumor tissue after intravenous fluorescein injection. We confirmed that the CLE probe reaches the tuberculum sellae through the transnasal transsphenoidal corridor in cadaveric heads. Next, we confirmed that CLE provides images with identifiable histological features of pituitary adenoma. Biopsies from nine patients who underwent pituitary adenoma surgery were imaged ex vivo at various times after fluorescein injection and were assessed by a blinded board-certified neuropathologist. With frozen sections used as the standard, pituitary adenoma was diagnosed as “definitively” for 13 and as “favoring” in 3 of 16 specimens. CLE digital biopsies were diagnostic for pituitary adenoma in 10 of 16 specimens. The reasons for nondiagnostic CLE images were biopsy acquisition <1 min or >10 min after fluorescein injection (n = 5) and blood artifacts (n = 1). In conclusion, fluorescein provided sufficient contrast for CLE at a dose of 2 mg/kg, optimally 1–10 min after injection. These results provide a basis for further in vivo studies using CLE in transsphenoidal surgery.

Compact and contactless reflectance confocal microscope for neurosurgery

Visual guidance at the cellular level during neurosurgical procedures is essential for complete tumour resection. We present a compact reflectance confocal microscope with a 20 mm working distance that provided <1.2 µm spatial resolution over a 600 µm × 600 µm field of view in the near-infrared region. A physical footprint of 200 mm × 550 mm was achieved using only standard off-the-shelf components. Theoretical performance of the optical design was first evaluated via commercial Zemax software. Then three specimens from rodents: fixed brain, frozen calvaria and live hippocampal slices, were used to experimentally assess system capability and robustness. Results show great potential for the proposed system to be translated into use as a next generation label-free and contactless neurosurgical microscope.

Investigation of confocal microscopy for differentiation of renal cell carcinoma versus benign tissue. Can an optical biopsy be performed?

Objective

Novel optical imaging modalities are under development with the goal of obtaining an “optical biopsy” to efficiently provide pathologic details. One such modality is confocal microscopy which allows in situ visualization of cells within a layer of tissue and imaging of cellular-level structures. The goal of this study is to validate the ability of confocal microscopy to quickly and accurately differentiate between normal renal tissue and cancer.

Methods

Specimens were obtained from patients who underwent robotic partial nephrectomy for renal mass. Samples of suspected normal and tumor tissue were extracted from the excised portion of the kidney and stained with acridine orange. The stained samples were imaged on a Nikon E600 C1 Confocal Microscope. The samples were then submitted for hematoxylin and eosin processing and read by an expert pathologist to provide a gold-standard diagnosis that can later be compared to the confocal images.

Results

This study included 11 patients, 17 tissue samples, and 118 confocal images. Of the 17 tissue samples, 10 had a gold-standard diagnosis of cancer and seven were benign. Of 118 confocal images, 66 had a gold-standard diagnosis of cancer and 52 were benign. Six confocal images were used as a training set to train eight observers. The observers were asked to rate the test images on a six point scale and the results were analyzed using a web based receiver operating characteristic curve calculator. The average accuracy, sensitivity, specificity, and area under the empirical receiver operating characteristic curve for this study were 91%, 98%, 81%, and 0.94 respectively.

Conclusion

This preliminary study suggest that confocal microscopy can be used to distinguish cancer from normal tissue with high sensitivity and specificity. The observers in this study were trained quickly and on only six images. We expect even higher performance as observers become more familiar with the confocal images.

Current Trends for Improving Safety of Stereotactic Brain Biopsies: Advanced Optical Methods for Vessel Avoidance and Tumor Detection

Stereotactic brain needle biopsies are indicated for deep-seated or multiple brain lesions and for patients with poor prognosis in whom the risks of resection outweigh the potential outcome benefits. The main goal of such procedures is not to improve the resection extent but to safely acquire viable tissue representative of the lesion for further comprehensive histological, immunohistochemical, and molecular analyses. Herein, we review advanced optical techniques for improvement of safety and efficacy of stereotactic needle biopsy procedures. These technologies are aimed at three main areas of improvement: (1) avoidance of vessel injury, (2) guidance for biopsy acquisition of the viable diagnostic tissue, and (3) methods for rapid intraoperative assessment of stereotactic biopsy specimens. The recent technological developments in stereotactic biopsy probe design include the incorporation of fluorescence imaging, spectroscopy, and label-free imaging techniques. The future advancements of stereotactic biopsy procedures in neuro-oncology include the incorporation of optical probes for real-time vessel detection along and around the biopsy needle trajectory and in vivo confirmation of the diagnostic tumor tissue prior to sample acquisition.

Molecular and Clinical Insights into the Invasive Capacity of Glioblastoma Cells

The invasive capacity of GBM is one of the key tumoral features associated with treatment resistance, recurrence, and poor overall survival. The molecular machinery underlying GBM invasiveness comprises an intricate network of signaling pathways and interactions with the extracellular matrix and host cells. Among them, PI3k/Akt, Wnt, Hedgehog, and NFkB play a crucial role in the cellular processes related to invasion. A better understanding of these pathways could potentially help in developing new therapeutic approaches with better outcomes. Nevertheless, despite significant advances made over the last decade on these molecular and cellular mechanisms, they have not been translated into the clinical practice. Moreover, targeting the infiltrative tumor and its significance regarding outcome is still a major clinical challenge. For instance, the pre- and intraoperative methods used to identify the infiltrative tumor are limited when trying to accurately define the tumor boundaries and the burden of tumor cells in the infiltrated parenchyma. Besides, the impact of treating the infiltrative tumor remains unclear. Here we aim to highlight the molecular and clinical hallmarks of invasion in GBM.

Progress in Confocal Laser Endomicroscopy for Neurosurgery and Technical Nuances for Brain Tumor Imaging With Fluorescein

Background: Previous studies showed that confocal laser endomicroscopy (CLE) images of brain tumors acquired by a first-generation (Gen1) CLE system using fluorescein sodium (FNa) contrast yielded a diagnostic accuracy similar to frozen surgical sections and histologic analysis. We investigated performance improvements of a second-generation (Gen2) CLE system designed specifically for neurosurgical use.

Methods: Rodent glioma models were used for in vivo and rapid ex vivo CLE imaging. FNa and 5-aminolevulinic acid were used as contrast agents. Gen1 and Gen2 CLE images were compared to distinguish cytoarchitectural features of tumor mass and margin and surrounding and normal brain regions. We assessed imaging parameters (gain, laser power, brightness, scanning speed, imaging depth, and Z-stack [3D image acquisition]) and evaluated optimal values for better neurosurgical imaging performance with Gen2.

Results: Efficacy of Gen1 and Gen2 was similar in identifying normal brain tissue, vasculature, and tumor cells in masses or at margins. Gen2 had smaller field of view, but higher image resolution, and sharper, clearer images. Other advantages of the Gen2 were auto-brightness correction, user interface, image metadata handling, and image transfer. CLE imaging with FNa allowed identification of nuclear and cytoplasmic contours in tumor cells. Injection of higher dosages of FNa (20 and 40 mg/kg vs. 0.1–8 mg/kg) resulted in better image clarity and structural identification. When used with 5-aminolevulinic acid, CLE was not able to detect individual glioma cells labeled with protoporphyrin IX, but overall fluorescence intensity was higher (p < 0.01) than in the normal hemisphere. Gen2 Z-stack imaging allowed a unique 3D image volume presentation through the focal depth.

Conclusion: Compared with Gen1, advantages of Gen2 CLE included a more responsive and intuitive user interface, collection of metadata with each image, automatic Z-stack imaging, sharper images, and a sterile sheath. Shortcomings of Gen2 were a slightly slower maximal imaging speed and smaller field of view. Optimal Gen2 imaging parameters to visualize brain tumor cytoarchitecture with FNa as a fluorescent contrast were defined to aid further neurosurgical clinical in vivo and rapid ex vivo use. Further validation of the Gen2 CLE for microscopic visualization and diagnosis of brain tumors is ongoing.

Utilization of intraoperative confocal laser endomicroscopy in brain tumor surgery

Precise identification of tumor margins is of the utmost importance in neuro-oncology. Confocal microscopy is capable of rapid imaging of fresh tissues at cellular resolution and has been miniaturized into handheld probe-based systems suitable for use in the operating room. We aimed to perform a literature review to provide an update on the current status of confocal laser endomicroscopy (CLE) technology for brain tumor surgery. Aside from benchtop confocal microscopes used in ex vivo fashion, there are four CLE systems that have been investigated for potential application in the workflow of brain tumor surgery. Preclinical studies on animal tumor models and clinical studies on human brain tumors have assessed in vivo and ex vivo imaging approaches, suggesting that confocal microscopy holds promise for rapid identification of the characteristic (diagnostic) histological features of tumor and normal brain tissues. However, there are few studies assessing diagnostic accuracy sufficient to provide a definitive determination of the clinical and economical value of CLE in brain tumor surgery. Intraoperative real-time, high-resolution tissue imaging has significant clinical potential in the field of neuro-oncology. CLE is an emerging imaging technology that shows promise for improving brain tumor surgery workflow in in vivo and ex vivo studies. Future clinical studies are necessary to demonstrate clinical and economic benefit of CLE.

Prospects for Theranostics in Neurosurgical Imaging: Empowering Confocal Laser Endomicroscopy Diagnostics via Deep Learning

Confocal laser endomicroscopy (CLE) is an advanced optical fluorescence imaging technology that has potential to increase intraoperative precision, extend resection, and tailor surgery for malignant invasive brain tumors because of its subcellular dimension resolution. Despite its promising diagnostic potential, interpreting the gray tone fluorescence images can be difficult for untrained users. CLE images can be distorted by motion artifacts, fluorescence signals out of detector dynamic range, or may be obscured by red blood cells, and thus interpreted as nondiagnostic (ND). However, just a single CLE image with a detectable pathognomonic histological tissue signature can suffice for intraoperative diagnosis. Dealing with the abundance of images from CLE is not unlike sifting through a myriad of genes, proteins, or other structural or metabolic markers to find something of commonality or uniqueness in cancer that might indicate a potential treatment scheme or target. In this review, we provide a detailed description of bioinformatical analysis methodology of CLE images that begins to assist the neurosurgeon and pathologist to rapidly connect on-the-fly intraoperative imaging, pathology, and surgical observation into a conclusionary system within the concept of theranostics. We present an overview and discuss deep learning models for automatic detection of the diagnostic CLE images and discuss various training regimes and ensemble modeling effect on power of deep learning predictive models. Two major approaches reviewed in this paper include the models that can automatically classify CLE images into diagnostic/ND, glioma/nonglioma, tumor/injury/normal categories, and models that can localize histological features on the CLE images using weakly supervised methods. We also briefly review advances in the deep learning approaches used for CLE image analysis in other organs. Significant advances in speed and precision of automated diagnostic frame selection would augment the diagnostic potential of CLE, improve operative workflow, and integration into brain tumor surgery. Such technology and bioinformatics analytics lend themselves to improved precision, personalization, and theranostics in brain tumor treatment.

Scanning Fiber Endoscope Improves Detection of 5-Aminolevulinic Acid-Induced Protoporphyrin IX Fluorescence at the Boundary of Infiltrative Glioma

OBJECTIVE

Fluorescence-guided surgery with protoporphyrin IX (PpIX) as a photodiagnostic marker is gaining acceptance for resection of malignant gliomas. Current wide-field imaging technologies do not have sufficient sensitivity to detect low PpIX concentrations. We evaluated a scanning fiber endoscope (SFE) for detection of PpIX fluorescence in gliomas and compared it to an operating microscope (OPMI) equipped with a fluorescence module and to a benchtop confocal laser scanning microscope (CLSM).

METHODS

5-Aminolevulinic acid-induced PpIX fluorescence was assessed in GL261-Luc2 cells in vitro and in vivo after implantation in mouse brains, at an invading glioma growth stage, simulating residual tumor. Intraoperative fluorescence of high and low PpIX concentrations in normal brain and tumor regions with SFE, OPMI, CLSM, and histopathology were compared.

RESULTS

SFE imaging of PpIX correlated to CLSM at the cellular level. PpIX accumulated in normal brain cells but significantly less than in glioma cells. SFE was more sensitive to accumulated PpIX in fluorescent brain areas than OPMI (P < 0.01) and dramatically increased imaging time (>6×) before tumor-to-background contrast was diminished because of photobleaching.

CONCLUSIONS

SFE provides new endoscopic capabilities to view PpIX-fluorescing tumor regions at cellular resolution. SFE may allow accurate imaging of 5-aminolevulinic acid labeling of gliomas and other tumor types when current detection techniques have failed to provide reliable visualization. SFE was significantly more sensitive than OPMI to low PpIX concentrations, which is relevant to identifying the leading edge or metastasizing cells of malignant glioma or to treating low-grade gliomas. This new application has the potential to benefit surgical outcomes.

Diagnostic Accuracy of a Confocal Laser Endomicroscope for In Vivo Differentiation Between Normal Injured And Tumor Tissue During Fluorescein-Guided Glioma Resection: Laboratory Investigation

OBJECTIVE

Glioma resection with fluorescein sodium (FNa) guidance has a potential drawback of nonspecific leakage of FNa from nontumor areas with a compromised blood-brain barrier. We investigated the diagnostic accuracy of in vivo confocal laser endomicroscopy (CLE) after FNa administration to differentiate normal brain, injured normal brain, and tumor tissue in an animal glioma model.

METHODS

GL261-Luc2 gliomas in C57BL/6 mice were used as a brain tumor model. CLE images of normal, injured normal, and tumor brain tissues were collected after intravenous FNa administration. Correlative sections stained with hematoxylin and eosin were taken at the same sites. A set of 40 CLE images was given to 1 neuropathologist and 3 neurosurgeons to assess diagnostic accuracy and rate image quality (1-10 scale). Additionally, we developed a deep convolution neural network (DCNN) model for automatic image classification.

RESULTS

The mean observer accuracy for correct diagnosis of glioma compared with either injured or uninjured brain using CLE images was 85%, and the DCNN model accuracy was 80%. For differentiation of tumor from nontumor tissue, the experts' mean accuracy, specificity, and sensitivity were 90%, 86%, and 96%, respectively, with high interobserver agreement overall (Cohen κ = 0.74). The percentage of correctly identified images was significantly higher for images with a quality rating >5 (104/116, 90%) than for images with a quality rating ≤5 (32/44, 73%) (P = 0.007).

CONCLUSIONS

With sufficient FNa present in tissues, CLE was an effective tool for intraoperative differentiation among normal, injured normal, and tumor brain tissue. Clinical studies are warranted to confirm these findings.

Confocal scanning microscopy provides rapid, detailed intraoperative histological assessment of brain neoplasms: Experience with 106 cases

OBJECTIVES

Frozen section histological analysis is currently the mainstay for intraprocedural tissue diagnosis during the resection of intracranial neoplasms and for evaluating tumor margins. However, frozen sections are time-consuming and often do not reveal the histological features needed for final diagnosis when compared with permanent sections. Confocal scanning microscopy (CSM) with certain stains may be a valuable technology that can add rapid and detailed histological assessment advantage for the neurosurgical operating room. This study describes potential advantages of CSM imaging of fresh human brain tumor tissues labeled with acriflavine (AF), acridine orange (AO), cresyl violet (CV), methylene blue (MB), and indocyanine green (ICG) within the neurosurgical operating room facility.

PATIENTS AND METHODS

Acute slices from orthotopic human intracranial neoplasms were incubated with AF/AO and CV solutions for 10 s and 1 min respectively. Staining was also attempted with MB and ICG. Samples were imaged using a bench-top CSM system. Histopathologic features of corresponding CSM and permanent hematoxylin and eosin images were reviewed for each case.

RESULTS

Of 106 cases, 30 were meningiomas, 19 gliomas, 13 pituitary adenomas, 9 metastases, 6 schwannomas, 4 ependymomas, and 25 other pathologies. CSM using rapid fluorophores (AF, AO, CV) revealed striking microvascular, cellular and subcellular structures that correlated with conventional histology. By rapidly staining and optically sectioning freshly resected tissue, images were generated for intraoperative consultations in less than one minute. With this technique, an entire resected tissue sample was imaged and digitally stored for tele-pathology and archiving.

CONCLUSION

CSM of fresh human brain tumor tissue provides clinically meaningful and rapid histopathological assessment much faster than frozen section. With appropriate stains, including specific cellular structure or antibody staining, CSM could improve the timeliness of intraoperative decision-making, and the neurosurgical-pathology workflow during resection of human brain tumors, ultimately improving patient care.

Intraoperative Probe-Based Confocal Laser Endomicroscopy in Surgery and Stereotactic Biopsy of Low-Grade and High-Grade Gliomas: A Feasibility Study in Humans

BACKGROUND

The management of gliomas is based on precise histologic diagnosis. The tumor tissue can be obtained during open surgery or via stereotactic biopsy. Intraoperative tissue imaging could substantially improve biopsy precision and, ultimately, the extent of resection.

OBJECTIVE

To show the feasibility of intraoperative in vivo probe-based confocal laser endomicroscopy (pCLE) in surgery and biopsy of gliomas.

METHODS

In our prospective observational study, 9 adult patients were enrolled between September 2014 and January 2015. Two contrast agents were used: 5-aminolevulinic acid (3 cases) or intravenous fluorescein (6 cases). Intraoperative imaging was performed with the Cellvizio system (Mauna Kea Technologies, Paris). A 0.85-mm probe was used for stereotactic procedures, with the biopsy needle modified to have a distal opening. During open brain surgery, a 2.36-mm probe was used. Each series corresponds to a separate histologic fragment.

RESULTS

The diagnoses of the lesions were glioblastoma (4 cases), low-grade glioma (2), grade III oligoastrocytoma (2), and lymphoma (1). Autofluorescence of neurons in cortex was observed. Cellvizio images enabled differentiation of healthy "normal" tissue from pathological tissue in open surgery and stereotactic biopsy using fluorescein. 5-Aminolevulinic acid confocal patterns were difficult to establish. No intraoperative complications related to pCLE or to use of either contrast agent were observed.

CONCLUSION

We report the initial feasibility and safety of intraoperative pCLE during primary brain tumor resection and stereotactic biopsy procedures. Pending further investigation, pCLE of brain tissue could be utilized for intraoperative surgical guidance, improvement in brain biopsy yield, and optimization of glioma resection via analysis of tumor margins.

ABBREVIATIONS

5-ALA, 5-aminolevulinic acidpCLE, probe-based confocal laser endomicroscopyPpIX, protoporphyrin IX.

Laser application in neurosurgery

BACKGROUND

Technological innovations based on light amplification created by stimulated emission of radiation (LASER) have been used extensively in the field of neurosurgery.

METHODS

We reviewed the medical literature to identify current laser-based technological applications for surgical, diagnostic, and therapeutic uses in neurosurgery.

RESULTS

Surgical applications of laser technology reported in the literature include percutaneous laser ablation of brain tissue, the use of surgical lasers in open and endoscopic cranial surgeries, laser-assisted microanastomosis, and photodynamic therapy for brain tumors. Laser systems are also used for intervertebral disk degeneration treatment, therapeutic applications of laser energy for transcranial laser therapy and nerve regeneration, and novel diagnostic laser-based technologies (e.g., laser scanning endomicroscopy and Raman spectroscopy) that are used for interrogation of pathological tissue.

CONCLUSION

Despite controversy over the use of lasers for treatment, the surgical application of lasers for minimally invasive procedures shows promising results and merits further investigation. Laser-based microscopy imaging devices have been developed and miniaturized to be used intraoperatively for rapid pathological diagnosis. The multitude of ways that lasers are used in neurosurgery and in related neuroclinical situations is a testament to the technological advancements and practicality of laser science.

Optical technologies for intraoperative neurosurgical guidance

Biomedical optics is a broadly interdisciplinary field at the interface of optical engineering, biophysics, computer science, medicine, biology, and chemistry, helping us understand light-tissue interactions to create applications with diagnostic and therapeutic value in medicine. Implementation of biomedical optics tools and principles has had a notable scientific and clinical resurgence in recent years in the neurosurgical community. This is in great part due to work in fluorescence-guided surgery of brain tumors leading to reports of significant improvement in maximizing the rates of gross-total resection. Multiple additional optical technologies have been implemented clinically, including diffuse reflectance spectroscopy and imaging, optical coherence tomography, Raman spectroscopy and imaging, and advanced quantitative methods, including quantitative fluorescence and lifetime imaging. Here we present a clinically relevant and technologically informed overview and discussion of some of the major clinical implementations of optical technologies as intraoperative guidance tools in neurosurgery.

Handheld confocal laser endomicroscopic imaging utilizing tumor-specific fluorescent labeling to identify experimental glioma cells in vivo

Background:

We have reported that handheld confocal laser endomicroscopy (CLE) can be used with various nonspecific fluorescent dyes to improve the microscopic identification of brain tumor and its boundaries. Here, we show that CLE can be used experimentally with tumor-specific fluorescent labeling to define glioma margins in vivo.

Methods:

Thirteen rats underwent craniectomy and in vivo imaging 21 days after implantation with green fluorescent protein (GFP)-labeled U251 (n = 7) cells or epidermal growth factor receptor (EGFR) overexpressing F98 cells (n = 6). Fluorescein isothiocyanate (FITC) conjugated EGFR fluorescent antibody (FITC-EGFR) was applied for contrast in F98 tumors. Confocal images of normal brain, obvious tumor, and peritumoral zones were collected using the CLE system. Bench-top confocal microscopy and hematoxylin and eosin-stained sections were correlated with CLE images.

Results:

GFP and FITC-EGFR fluorescence of glioma cells were detected by in vivo visible-wavelength fluorescence CLE. CLE of GFP-labeled tumors revealed bright individual satellite tumor cells within peritumoral tissue, a definitive tumor border, and subcellular structures. Imaging with FITC-EGFR labeling provided weaker contrast in F98-EGFR tumors but was able to delineate tumor cells. Imaging with both methods in various tumor regions correlated with standard confocal imaging and clinical histology.

Conclusions:

These data suggest that in vivo CLE of selectively tagged neoplasms could allow specific interactive identification of tumoral areas. Imaging of GFP and FITC-EGFR provides real-time histologic information precisely related to the site of microscopic imaging of tumor.

Intraoperative Fluorescence Imaging for Personalized Brain Tumor Resection: Current State and Future Directions

INTRODUCTION

Fluorescence-guided surgery is one of the rapidly emerging methods of surgical "theranostics." In this review, we summarize current fluorescence techniques used in neurosurgical practice for brain tumor patients as well as future applications of recent laboratory and translational studies.

METHODS

Review of the literature.

RESULTS

A wide spectrum of fluorophores that have been tested for brain surgery is reviewed. Beginning with a fluorescein sodium application in 1948 by Moore, fluorescence-guided brain tumor surgery is either routinely applied in some centers or is under active study in clinical trials. Besides the trinity of commonly used drugs (fluorescein sodium, 5-aminolevulinic acid, and indocyanine green), less studied fluorescent stains, such as tetracyclines, cancer-selective alkylphosphocholine analogs, cresyl violet, acridine orange, and acriflavine, can be used for rapid tumor detection and pathological tissue examination. Other emerging agents, such as activity-based probes and targeted molecular probes that can provide biomolecular specificity for surgical visualization and treatment, are reviewed. Furthermore, we review available engineering and optical solutions for fluorescent surgical visualization. Instruments for fluorescent-guided surgery are divided into wide-field imaging systems and hand-held probes. Recent advancements in quantitative fluorescence-guided surgery are discussed.

CONCLUSION

We are standing on the threshold of the era of marker-assisted tumor management. Innovations in the fields of surgical optics, computer image analysis, and molecular bioengineering are advancing fluorescence-guided tumor resection paradigms, leading to cell-level approaches to visualization and resection of brain tumors.

Prospective evaluation of the utility of intraoperative confocal laser endomicroscopy in patients with brain neoplasms using fluorescein sodium: experience with 74 cases

OBJECTIVE

This study evaluated the utility, specificity, and sensitivity of intraoperative confocal laser endomicroscopy (CLE) to provide diagnostic information during resection of human brain tumors.

METHODS

CLE imaging was used in the resection of intracranial neoplasms in 74 consecutive patients (31 male; mean age 47.5 years; sequential 10-month study period). Intraoperative in vivo and ex vivo CLE was performed after intravenous injection of fluorescein sodium (FNa). Tissue samples from CLE imaging–matched areas were acquired for comparison with routine histological analysis (frozen and permanent sections). CLE images were classified as diagnostic or nondiagnostic. The specificities and sensitivities of CLE and frozen sections for gliomas and meningiomas were calculated using permanent histological sections as the standard.

RESULTS

CLE images were obtained for each patient. The mean duration of intraoperative CLE system use was 15.7 minutes (range 3–73 minutes). A total of 20,734 CLE images were correlated with 267 biopsy specimens (mean number of images/biopsy location, in vivo 84, ex vivo 70). CLE images were diagnostic for 45.98% in vivo and 52.97% ex vivo specimens. After initiation of CLE, an average of 14 in vivo images and 7 ex vivo images were acquired before identification of a first diagnostic image. CLE specificity and sensitivity were, respectively, 94% and 91% for gliomas and 93% and 97% for meningiomas.

CONCLUSIONS

CLE with FNa provided intraoperative histological information during brain tumor removal. Specificities and sensitivities of CLE for gliomas and meningiomas were comparable to those for frozen sections. These data suggest that CLE could allow the interactive identification of tumor areas, substantially improving intraoperative decisions during the resection of brain tumors.

Trends in fluorescence image-guided surgery for gliomas

Mounting evidence suggests that a more extensive surgical resection is associated with an improved life expectancy for both low-grade and high-grade glioma patients. However, radiographically complete resections are not often achieved in many cases because of the lack of sensitivity and specificity of current neurosurgical guidance techniques at the margins of diffuse infiltrative gliomas. Intraoperative fluorescence imaging offers the potential to improve the extent of resection and to investigate the possible benefits of resecting beyond the radiographic margins. Here, we provide a review of wide-field and high-resolution fluorescence-imaging strategies that are being developed for neurosurgical guidance, with a focus on emerging imaging technologies and clinically viable contrast agents. The strengths and weaknesses of these approaches will be discussed, as well as issues that are being addressed to translate these technologies into the standard of care.

Fluorescent cancer-selective alkylphosphocholine analogs for intraoperative glioma detection

BACKGROUND

5-Aminolevulinic acid (5-ALA)-induced tumor fluorescence aids brain tumor resections but is not approved for routine use in the United States. We developed and describe testing of 2 novel fluorescent, cancer-selective alkylphosphocholine analogs, CLR1501 (green) and CLR1502 (near infrared), in a proof-of-principle study for fluorescence-guided glioma surgery.

OBJECTIVE

To demonstrate that CLR1501 and CLR1502 are cancer cell-selective fluorescence agents in glioblastoma models and to compare tumor-to-normal brain (T:N) fluorescence ratios with 5-ALA.

METHODS

CLR1501, CLR1502, and 5-ALA were administered to mice with magnetic resonance imaging-verified orthotopic U251 glioblastoma multiforme- and glioblastoma stem cell-derived xenografts. Harvested brains were imaged with confocal microscopy (CLR1501), the IVIS Spectrum imaging system (CLR1501, CLR1502, and 5-ALA), or the Fluobeam near-infrared fluorescence imaging system (CLR1502). Imaging and quantitative analysis of T:N fluorescence ratios were performed.

RESULTS

Excitation/emission peaks are 500/517 nm for CLR1501 and 760/778 nm for CLR1502. The observed T:N ratio for CLR1502 (9.28±1.08) was significantly higher (P<.01) than for CLR1501 (3.51±0.44 on confocal imaging; 7.23±1.63 on IVIS imaging) and 5-ALA (4.81±0.92). Near-infrared Fluobeam CLR1502 imaging in a mouse xenograft model demonstrated high- contrast tumor visualization compatible with surgical applications.

CONCLUSION

CLR1501 (green) and CLR1502 (near infrared) are novel tumor-selective fluorescent agents for discriminating tumor from normal brain. CLR1501 exhibits a tumor-to-brain fluorescence ratio similar to that of 5-ALA, whereas CLR1502 has a superior tumor-to-brain fluorescence ratio. This study demonstrates the potential use of CLR1501 and CLR1502 in fluorescence-guided tumor surgery.

Ex vivo confocal microscopy imaging to identify tumor tissue on freshly removed brain sample

Confocal microscopy is a technique able to realize "optic sections" of a tissue with increasing applications. We wondered if we could apply an ex vivo confocal microscope designed for dermatological purpose in a routine use for the most frequent brain tumors. The aim of this work was to identify tumor tissue and its histopathological hallmarks, and to assess grading criteria used in neuropathological practice without tissue loss on freshly removed brain tissue. Seven infiltrating gliomas, nine meningiomas and three metastases of carcinomas were included. We compared imaging results obtained with the confocal microscope to frozen sections, smears and tissue sections of formalin-fixed tissue. Our results show that ex vivo confocal microscopy imaging can be applied to brain tumors in order to quickly identify tumor tissue without tissue loss. It can differentiate tumors and can assess most of grading criteria. Confocal microscopy could represent a new tool to identify tumor tissue on freshly removed sample and could help in selecting areas for biobanking of tumor tissue.

Use of a conformational switching aptamer for rapid and specific ex vivo identification of central nervous system lymphoma in a xenograft model

Improved tools for providing specific intraoperative diagnoses could improve patient care. In neurosurgery, intraoperatively differentiating non-operative lesions such as CNS B-cell lymphoma from operative lesions can be challenging, often necessitating immunohistochemical (IHC) procedures which require up to 24-48 hours. Here, we evaluate the feasibility of generating rapid ex vivo specific labeling using a novel lymphoma-specific fluorescent switchable aptamer. Our B-cell lymphoma-specific switchable aptamer produced only low-level fluorescence in its unbound conformation and generated an 8-fold increase in fluorescence once bound to its target on CD20-positive lymphoma cells. The aptamer demonstrated strong binding to B-cell lymphoma cells within 15 minutes of incubation as observed by flow cytometry. We applied the switchable aptamer to ex vivo xenograft tissue harboring B-cell lymphoma and astrocytoma, and within one hour specific visual identification of lymphoma was routinely possible. In this proof-of-concept study in human cell culture and orthotopic xenografts, we conclude that a fluorescent switchable aptamer can provide rapid and specific labeling of B-cell lymphoma, and that developing aptamer-based labeling approaches could simplify tissue staining and drastically reduce time to histopathological diagnoses compared with IHC-based methods. We propose that switchable aptamers could enhance expeditious, accurate intraoperative decision-making.

Laser scanning confocal endomicroscopy in the neurosurgical operating room: a review and discussion of future applications

Laser scanning confocal endomicroscopy (LSCE) is an emerging technology for examining brain neoplasms in vivo. While great advances have been made in macroscopic fluorescence in recent years, the ability to perform confocal microscopy in vivo expands the potential of fluorescent tumor labeling, can improve intraoperative tissue diagnosis, and provides real-time guidance for tumor resection intraoperatively. In this review, the authors highlight the technical aspects of confocal endomicroscopy and fluorophores relevant to the neurosurgeon, provide a comprehensive summary of LSCE in animal and human neurosurgical studies to date, and discuss the future directions and potential for LSCE in neurosurgery.

Quantitative confocal phase imaging by synthetic optical holography

We demonstrate quantitative phase mapping in confocal optical microscopy by applying synthetic optical holography (SOH), a recently introduced method for technically simple and fast phase imaging in scanning optical microscopy. SOH is implemented in a confocal microscope by simply adding a linearly moving reference mirror to the microscope setup, which generates a synthetic reference wave analogous to the plane reference wave of wide-field off-axis holography. We demonstrate that SOH confocal microscopy allows for non-contact surface profiling with sub-nanometer depth resolution. As an application for biological imaging, we apply SOH confocal microscopy to map the surface profile of an onion cell, revealing nanoscale-height features on the cell surface.

Neurosurgical confocal endomicroscopy: A review of contrast agents, confocal systems, and future imaging modalities

Background:

The clinical application of fluorescent contrast agents (fluorescein, indocyanine green, and aminolevulinic acid) with intraoperative microscopy has led to advances in intraoperative brain tumor imaging. Their properties, mechanism of action, history of use, and safety are analyzed in this report along with a review of current laser scanning confocal endomicroscopy systems. Additional imaging modalities with potential neurosurgical utility are also analyzed.

Methods:

A comprehensive literature search was performed utilizing PubMed and key words: In vivo confocal microscopy, confocal endomicroscopy, fluorescence imaging, in vivo diagnostics/neoplasm, in vivo molecular imaging, and optical imaging. Articles were reviewed that discussed clinically available fluorophores in neurosurgery, confocal endomicroscopy instrumentation, confocal microscopy systems, and intraoperative cancer diagnostics.

Results:

Current clinically available fluorescent contrast agents have specific properties that provide microscopic delineation of tumors when imaged with laser scanning confocal endomicroscopes. Other imaging modalities such as coherent anti-Stokes Raman scattering (CARS) microscopy, confocal reflectance microscopy, fluorescent lifetime imaging (FLIM), two-photon microscopy, and second harmonic generation may also have potential in neurosurgical applications.

Conclusion:

In addition to guiding tumor resection, intraoperative fluorescence and microscopy have the potential to facilitate tumor identification and complement frozen section analysis during surgery by providing real-time histological assessment. Further research, including clinical trials, is necessary to test the efficacy of fluorescent contrast agents and optical imaging instrumentation in order to establish their role in neurosurgery.

Synthetic optical holography for rapid nanoimaging

Holography has paved the way for phase imaging in a variety of wide-field techniques, including electron, X-ray and optical microscopy. In scanning optical microscopy, however, the serial fashion of image acquisition seems to challenge a direct implementation of traditional holography. Here we introduce synthetic optical holography (SOH) for quantitative phase-resolved imaging in scanning optical microscopy. It uniquely combines fast phase imaging, technical simplicity and simultaneous operation at visible and infrared frequencies with a single reference arm. We demonstrate SOH with a scattering-type scanning near-field optical microscope (s-SNOM) where it enables reliable quantitative phase-resolved near-field imaging with unprecedented speed. We apply these capabilities to nanoscale, non-invasive and rapid screening of grain boundaries in CVD-grown graphene, by recording 65 kilopixel near-field images in 26 s and 2.3 megapixel images in 13 min. Beyond s-SNOM, the SOH concept could boost the implementation of holography in other scanning imaging applications such as confocal microscopy.

Potential application of a handheld confocal endomicroscope imaging system using a variety of fluorophores in experimental gliomas and normal brain

Object

The authors sought to assess the feasibility of a handheld visible-wavelength confocal endomicroscope imaging system (Optiscan 5.1, Optiscan Pty., Ltd.) using a variety of rapid-acting fluorophores to provide histological information on gliomas, tumor margins, and normal brain in animal models.

Methods

Mice (n = 25) implanted with GL261 cells were used to image fluorescein sodium (FNa), 5-aminolevulinic acid (5-ALA), acridine orange (AO), acriflavine (AF), and cresyl violet (CV). A U251 glioma xenograft model in rats (n = 5) was used to image sulforhodamine 101 (SR101). A swine (n = 3) model with AO was used to identify confocal features of normal brain. Images of normal brain, obvious tumor, and peritumoral zones were collected using the handheld confocal endomicroscope. Histological samples were acquired through biopsies from matched imaging areas. Samples were visualized with a benchtop confocal microscope. Histopathological features in corresponding confocal images and photomicrographs of H & E–stained tissues were reviewed.

Results

Fluorescence induced by FNa, 5-ALA, AO, AF, CV, and SR101 and detected with the confocal endomicroscope allowed interpretation of histological features. Confocal endomicroscopy revealed satellite tumor cells within peritumoral tissue, a definitive tumor border, and striking fluorescent cellular and subcellular structures. Fluorescence in various tumor regions correlated with standard histology and known tissue architecture. Characteristic features of different areas of normal brain were identified as well.

Conclusions

Confocal endomicroscopy provided rapid histological information precisely related to the site of microscopic imaging with imaging characteristics of cells related to the unique labeling features of the fluorophores. Although experimental with further clinical trial validation required, these data suggest that intraoperative confocal imaging can help to distinguish normal brain from tumor and tumor margin and may have application in improving intraoperative decisions during resection of brain tumors.

Confocal laser endomicroscopy in neurosurgery: a new technique with much potential

Technical innovations in brain tumour diagnostic and therapy have led to significant improvements of patient outcome and recurrence free interval. The use of technical devices such as surgical microscopes as well as neuronavigational systems have helped localising tumours as much as fluorescent agents, such as 5-aminolaevulinic acid, have helped visualizing pathologically altered tissue. Nonetheless, intraoperative instantaneous frozen sections and histological diagnosis remain the only method of gaining certainty of the nature of the resected tissue. This technique is time consuming and does not provide close-to-real-time information. In gastroenterology, confocal endoscopy closed the gap between tissue resection and histological examination, providing an almost real-time histological diagnosis. The potential of this technique using a confocal laser endoscope EndoMAG1 by Karl Storz Company was evaluated by our group on pig brains, tumour tissue cell cultures, and fresh human tumour specimen. Here, the authors report for the first time on the results of applying this new technique and provide first confocal endoscopic images of various brain and tumour structures. In all, the technique harbours a very promising potential to provide almost real-time intraoperative diagnosis, but further studies are needed to provide evidence for the technique's potential.

Emerging operative strategies in neurosurgical oncology

PURPOSE OF REVIEW

In recent years, the safety and efficacy of neurosurgical intervention has rapidly improved for brain tumor patients. Technological advances, combined with refined intraoperative techniques, now enable well tolerated surgical access to any region of the human brain. For patients with gliomas, these improvements have redefined the clinical possibilities, and here we review several emerging operative strategies that are essential for next-generation neurosurgical oncologists and major brain tumor centers.

RECENT FINDINGS

The value of glioma extent of resection remains controversial, but review of the modern literature reveals important opportunities for early neurosurgical intervention. Although microsurgical resection must be balanced by the risk of neurological compromise, improvements in intraoperative stimulation techniques now enable resection of highly eloquent tumors with minimal morbidity. Additionally, the emergence of fluorescence-guided surgery as a new operative paradigm provides a unique opportunity to resect tumors to the margins of microscopic infiltration.

SUMMARY

Neurosurgical intervention remains the first step in effective glioma management. With intraoperative mapping techniques, aggressive microsurgical resection can be safely pursued even when tumors occupy essential functional pathways. With the development of tumor-specific fluorophores, such as 5-aminolevulinic acid, real-time microscopic visualization of tumor infiltration can be surgically targeted prior to adjuvant therapy.