Correlation of intraoperative ultrasound tumor volumes and margins with preoperative computerized tomography scans. An intraoperative method to enhance tumor resection

Technical Aspects of Motor and Language Mapping in Glioma Patients

Gliomas are infiltrative primary brain tumors that often invade functional cortical and subcortical regions, and they mandate individualized brain mapping strategies to avoid postoperative neurological deficits. It is well known that maximal safe resection significantly improves survival, while postoperative deficits minimize the benefits associated with aggressive resections and diminish patients’ quality of life. Although non-invasive imaging tools serve as useful adjuncts, intraoperative stimulation mapping (ISM) is the gold standard for identifying functional cortical and subcortical regions and minimizing morbidity during these challenging resections. Current mapping methods rely on the use of low-frequency and high-frequency stimulation, delivered with monopolar or bipolar probes either directly to the cortical surface or to the subcortical white matter structures. Stimulation effects can be monitored through patient responses during awake mapping procedures and/or with motor-evoked and somatosensory-evoked potentials in patients who are asleep. Depending on the patient’s preoperative status and tumor location and size, neurosurgeons may choose to employ these mapping methods during awake or asleep craniotomies, both of which have their own benefits and challenges. Regardless of which method is used, the goal of intraoperative stimulation is to identify areas of non-functional tissue that can be safely removed to facilitate an approach trajectory to the equator, or center, of the tumor. Recent technological advances have improved ISM’s utility in identifying subcortical structures and minimized the seizure risk associated with cortical stimulation. In this review, we summarize the salient technical aspects of which neurosurgeons should be aware in order to implement intraoperative stimulation mapping effectively and safely during glioma surgery.

Simulation of surgery for supratentorial gliomas in virtual reality using a 3D volume rendering technique: a poor man's neuronavigation

OBJECTIVE

Different techniques of performing image-guided neurosurgery exist, namely, neuronavigation systems, intraoperative ultrasound, and intraoperative MRI, each with its limitations. Except for ultrasound, other methods are expensive. Three-dimensional virtual reconstruction and surgical simulation using 3D volume rendering (VR) is an economical and excellent technique for preoperative surgical planning and image-guided neurosurgery. In this article, the authors discuss several nuances of the 3D VR technique that have not yet been described.

METHODS

The authors included 6 patients with supratentorial gliomas who underwent surgery between January 2019 and March 2021. Preoperative clinical data, including patient demographics, preoperative planning details (done using the VR technique), and intraoperative details, including relevant photos and videos, were collected. RadiAnt software was used for generating virtual 3D images using the VR technique on a computer running Microsoft Windows.

RESULTS

The 3D VR technique assists in glioma surgery with a preoperative simulation of the skin incision and craniotomy, virtual cortical surface marking and navigation for deep-seated gliomas, preoperative visualization of morbid cortical surface and venous anatomy in surfacing gliomas, identifying the intervenous surgical corridor in both surfacing and deep-seated gliomas, and pre- and postoperative virtual 3D images highlighting the exact spatial geometric residual tumor location and extent of resection for low-grade gliomas (LGGs).

CONCLUSIONS

Image-guided neurosurgery with the 3D VR technique using RadiAnt software is an economical, easy-to-learn, and user-friendly method of simulating glioma surgery, especially in resource-constrained countries where expensive neuronavigation systems are not readily available. Apart from cortical sulci/gyri anatomy, FLAIR sequences are ideal for the 3D visualization of nonenhancing diffuse LGGs using the VR technique. In addition to cortical vessels (especially veins), contrast MRI sequences are perfect for the 3D visualization of contrast-enhancing high-grade gliomas.

Efficacy of intraoperative ultrasonography in neurosurgical tumor resection

OBJECTIVE Intraoperative ultrasonography (IOUS) is a widely accessible imaging modality that provides real-time surgical guidance with minimal identified risk or additional operative time. A recent study by the authors found a strong correlation between IOUS and postoperative MRI findings when evaluating the extent of tumor resection, suggesting that IOUS might have significant clinical implications. The objective of this study was to expand on results from the previous study in order to provide more evidence on the usage of IOUS in the determination of gross-total resection (GTR) in both adult and pediatric patients with brain tumors. METHODS This study consisted of a retrospective review of adult and pediatric neurosurgical patients who were treated at Albany Medical Center between August 2009 and March 2016 for a tumor of the brain. All patients were treated with IOUS and then underwent postoperative MRI (with and without contrast) within 1 week of surgery. RESULTS A total of 260 patients (55% of whom were males) met inclusion criteria for the study (age range 3 months to 84 years). IOUS results showed a strong association with postoperative MRI results (φ = 0.693, p < 0.001) and an 81% intended GTR rate. In cases in which GTR was pursued, 19% had false-negative results. IOUS was able to accurately identify residual tumor in 100% of subtotal resection cases where resection was stopped due to invasion of tumor into eloquent locations. Cases involving gliomas had a 75% intended GTR rate and a 25% false-negative rate. Cases involving metastatic tumors had an 87% intended GTR rate and a 13% false-negative rate. The sensitivity, specificity, negative predictive value, and positive predictive value are reported for IOUS in all included tumor pathologies, glioma cases, and metastatic tumor cases, respectively. CONCLUSIONS The use of IOUS may allow for a reliable imaging modality to achieve a more successful GTR of brain tumors in both adult and pediatric neurosurgical patients. When attempting GTR, the authors demonstrated an 81% GTR rate. The authors also report false-negative IOUS results in 19% of attempted GTR cases. The authors support the use of IOUS in both adult and pediatric CNS tumor surgery to improve surgical outcomes. However, further studies are warranted to address existing limitations with its use to further improve its efficacy and better define its role as an intraoperative imaging tool.

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.

Correlation between intraoperative ultrasound and postoperative MRI in pediatric tumor surgery

OBJECTIVE Malignant disease of the CNS is the primary etiology for deaths resulting from cancer in the pediatric population. It has been well documented that outcomes of pediatric neurosurgery rely on the extent of tumor resection. Therefore, techniques that improve surgical results have significant clinical implications. Intraoperative ultrasound (IOUS) offers real-time surgical guidance and a more accurate means for detecting residual tumor that is inconspicuous to the naked eye. The objective of this study was to evaluate the correlation of extent of resection between IOUS and postoperative MRI. The authors measured the correlation of extent of resection, negative predictive value, and sensitivity of IOUS and compared them with those of MRI. METHODS This study consisted of a retrospective review of the medical charts of all pediatric patients who underwent neurosurgical treatment of a tumor between August 2009 and July 2015 at Albany Medical Center. Included were patients who were aged ≤ 21 years, who underwent brain or spinal tumor resection, for whom IOUS was used during the tumor resection, and for whom postoperative MRI (with and without contrast) was performed within 1 week of surgery. RESULTS Sixty-two patients met inclusion criteria for the study (33 males, mean age 10.0 years). The IOUS results very significantly correlated with postoperative MRI results (φ = 0.726; p = 0.000000011; negative predictive value 86.3% [95% CI 73.7%-94.3%]). These results exemplify a 71% overall gross-total resection rate and 80% intended gross-total resection rate with the use of IOUS (i.e., excluding cases performed only for debulking purposes). CONCLUSIONS The use of IOUS may play an important role in achieving a greater extent of resection by providing real-time information on tumor volume and location in the setting of brain shift throughout the course of an operation. The authors support the use of IOUS in pediatric CNS tumor surgery to improve clinical outcomes at low cost with minimal additional operating-room time and no identified additional risk.

Resection of C6 gliomas in rats with the aid of the waterjet technique

OBJECTIVES

While clinically the safety and efficacy of waterjet resection of brain tumors have been shown, evidence that waterjet dissection improves tumor resection radicality in comparison with conventional techniques is still missing. In the present study, resection radicality and tumor-free long-term survival of both techniques were evaluated in a C6-glioma model.

MATERIAL AND METHODS

Fifty-thousand C6-glioma cells were stereotactically transplanted in the left frontal lobe of 100 male Sprague-Dawley rats. After MRI-scanning for evaluation of tumor extension, microsurgical tumor resection was performed with conventional techniques (n=50) or with the waterjet dissector at pressures of 6bar (n=50). Twenty-five animals of each group were sacrificed after surgery for histological analysis. For analysis of survival after tumor resection, twenty-five animals of each group were followed-up to analyze tumor-free survival using the Kaplan Meier method.

RESULTS

In the waterjet group, the resection cavity was free of C6-tumor cells in 10/25 (40%) rats showing a trend (p=0.3) towards better resection radicality compared to the rats that were treated conventionally (7/10; 28%). R1-resection with up to 250C6 cells/object slice was found in 14/25 (56%) rats after waterjet dissection compared to 6/25 (24%) rats treated conventionally showing significance (p<0.01). Probability of survival was 38% after 2 weeks and 20% after 6 months in the waterjet group compared to 30% and 16% respectively in the conventional group. Diffuse tumor cell spreading with possible influence on survival was shown in 47/50 rats.

CONCLUSION

In this experimental model, waterjet tumor resection did reveal significantly better resection radicality compared to the conventional technique. Although a direct transfer of these results to human glioma surgery is prohibited, the waterjet technique might contribute to the best possible resection radicality in human gliomas. Nevertheless, tumor cell spreading remains a major problem. Further studies have to address that the surgical results - in deed - improve the postoperative outcome.

Intraoperative stereotactic injection of Indigo Carmine dye to mark ill-defined tumor margins: a prospective phase I-II study

OBJECT

A critical goal in neurosurgical oncology is maximizing the extent of tumor resection while minimizing the risk to normal white matter tracts. Frameless stereotaxy and white matter mapping are indispensable tools in this effort, but deep tumor margins may not be accurately defined because of the "brain shift" at the end of the operation. The authors investigated the safety and efficacy of a technique for marking the deep margins of intraaxial tumors with stereotactic injection of Indigo Carmine dye.

METHODS

Investigational New Drug study approval for a prospective study in adult patients with gliomas was obtained from the FDA (Investigational New Drug no. 112680). At surgery, 1-3 stereotactic injections of 0.01 ml of Indigo Carmine dye were performed through the initial bur holes into the deep tumor margins before elevation of the bone flap. White light microscopic resection was conducted in standard fashion by using frameless stereotactic navigation until the injected margins were identified. The resection of the injected tumor margins and the extent of resection of the whole tumor volume were determined by using postoperative volumetric MRI.

RESULTS

In total 17 injections were performed in 10 enrolled patients (6 male, 4 female), whose mean age was 49 years. For all patients, the injection points were identified intraoperatively and tumor was resected at these points. The staining pattern was reproducible; it was a sphere of stained tissue approximately 5 mm in diameter. A halo of stained tissue and a backflow of dye through the needle tract were also noted, but these were clearly distinct from the staining pattern of the injection point, which was vividly colored and demarcated. Postoperative MR images verified the resection of all injection points. The mean extent of resection of the tumor as a whole was 97.1%. For 1 patient, a brain abscess developed on postoperative Day 16 and needed additional surgical treatment.

CONCLUSIONS

Stereotactic injection of Indigo Carmine dye can be used to demarcate multiple deep tumor margins, which can be readily identified intraoperatively by using standard white light microscopy. This technique may enhance the accuracy of frameless stereotactic navigation and increase the extent of resection of intraaxial tumors.

The benefits of navigated intraoperative ultrasonography during resection of fourth ventricular tumors in children

BACKGROUND

Safe and radical excision of pediatric fourth ventricular tumors is by far the best line of management. Pediatric fourth ventricular tumor surgery is a challenge for neurosurgeons. The aim of the study is to present the authors' experience and to evaluate the possible benefits of neuro-navigated intraoperative ultrasonography (NIOUS) during the surgery of fourth ventricular tumors in children.

METHODS

Nonrandomized clinical trial study was conducted on 60 children with fourth ventricular tumors who were treated at Children's Cancer Hospital-Egypt. Mean age was 5.2 (±2.6) years. Thirty cases were operated upon utilizing the conventional microneurosurgical techniques. Another 30 cases were operated upon utilizing the NIOUS technique.

RESULTS

Total tumor excision was achieved in 29 cases (96.7%) of NIOUS group versus 24 cases (80%) in the conventional group. Mean operative time NIOUS group was 150 min [standard deviation (SD) = 18.28) versus 140.6 min (SD = 18.6) in the conventional group (p value = 0.055). The mean operative blood loss was 67.5 ml (SD = 17) in NIOUS group versus 71 ml (SD = 15.4) in the conventional group. Postoperative cerebellar mutism occurred in one case (3.3%) of NIOUS group versus in six cases (20%) of the conventional group.

CONCLUSIONS

Integration of navigated intraoperative ultrasonography in surgery of pediatric fourth ventricular tumors is a useful technology. It safely monitors maximum stepwise tumor excision. It is associated with less operative morbidity without significantly added operative time. It is a real-time, cost-effective, easily applicable, and easily interpretable tool that could substitute the use of intraoperative MRI especially in pediatric neurosurgery.

Identification of venous sinus, tumor location, and pial supply during meningioma surgery by transdural indocyanine green videography

OBJECT

Indocyanine green (ICG) videography is commonly used in the neurosurgical field for minimally invasive neurosurgery. The aim of this study was to evaluate a new intraoperative imaging modality by performing transdural ICG videography during surgery for meningiomas.

METHODS

Between March 2011 and April 2012, 10 patients with meningiomas received intravenous injection of 12.5 mg ICG just prior to dural opening. The cases comprised 8 convexity meningiomas and 2 foramen magnum meningiomas. Efficacy of the transdural ICG videography was assessed in terms of the tumor volume, the circulation time from the first appearance of the vessel to the appearance of the venous sinus, the tendency to bleed, and the discrimination of the venous sinus.

RESULTS

The mean tumor volume was 71.6 ± 87.9 ml (the mean is expressed ± SD throughout). The cortical arteries, veins, and the venous sinus were identified by the ICG videography transdurally. The projection of the meningiomas was identified by a shadow (which the authors call the eclipse sign). Total eclipse signs were obtained in 8 cases and partial eclipse signs were obtained in 2 cases; tumor volume in the latter was more than 200 ml. In 5 of 10 cases the adjacent venous sinuses were exposed and were successfully visualized by ICG videography in 5.92 ± 1.05 seconds from the first appearance of the vessel. In 5 of 10 cases the total and the partial eclipse signs were diminished in 3.46 ± 1.31 seconds. The diminishment of the total and the partial eclipse sign was earlier than the visualization of the venous sinus (p = 0.011, t-test), revealing bleeding from the tumor that was observed until coagulation of the feeding arteries from the intracranial arteries.

CONCLUSIONS

Prior to opening of the dura mater, transdural ICG videography was used successfully to visualize the dural attachment of meningiomas and the venous sinus, resulting in safe and appropriate dural opening. The diminishment of the total and partial eclipse signs may represent significant feeding from the intracranial arteries and a tendency to bleed during resection.

Intraoperative confocal microscopy for brain tumors: a feasibility analysis in humans

BACKGROUND

The ability to diagnose brain tumors intraoperatively and identify tumor margins during resection could maximize resection and minimize morbidity. Advances in optical imaging enabled production of a handheld intraoperative confocal microscope.

OBJECTIVE

To present a feasibility analysis of the intraoperative confocal microscope for brain tumor resection.

METHODS

Thirty-three patients with brain tumor treated at Barrow Neurological Institute were examined. All patients received an intravenous bolus of sodium fluorescein before confocal imaging with the Optiscan FIVE 1 system probe. Optical biopsies were obtained within each tumor and along the tumor-brain interfaces. Corresponding pathologic specimens were then excised and processed. These data was compared by a neuropathologist to identify the concordance for tumor histology, grade, and margins.

RESULTS

Thirty-one of 33 lesions were tumors (93.9%) and 2 cases were identified as radiation necrosis (6.1%). Of the former, 25 (80.6%) were intra-axial and 6 (19.4%) were extra-axial. Intra-axial tumors were most commonly gliomas and metastases, while all extra-axial tumors were meningiomas. Among high-grade gliomas, vascular neoproliferation, as well as tumor margins, were identifiable using confocal imaging. Meningothelial and fibrous meningiomas were distinct on confocal microscopy--the latter featured spindle-shaped cells distinguishable from adjacent parenchyma. Other tumor histologies correlated well with standard neuropathology tissue preparations.

CONCLUSION

Intraoperative confocal microscopy is a practicable technology for the resection of human brain tumors. Preliminary analysis demonstrates reliability for a variety of lesions in identifying tumor cells and the tumor-brain interface. Further refinement of this technology depends upon the approval of tumor-specific fluorescent contrast agents for human use.

Preclinical molecular imaging of the translocator protein (TSPO) in a metastases model based on breast cancer xenografts propagated in the murine brain

Previous studies have demonstrated the feasibility of translocator protein (TSPO) imaging to visualize and quantify human breast adenocarcinoma (MDA-MB-231) cells in vivo using a TSPO-targeted near-infrared (NIR) probe (NIR-conPK11195). This study aimed to extend the use of the TSPO-targeted probe to a more biologically relevant and clinically important tumor microenvironment as well as to assess our ability to longitudinally detect the presence and progression of breast cancer cells in the brain. The in vivo biodistribution and accumulation of NIR-conPK11195 and free (unconjugated) NIR dye were quantitatively evaluated in intracranial MDA-MB-231-bearing mice and non-tumor-bearing control mice longitudinally once a week from two to five weeks post-inoculation. The in vivo time-activity curves illustrate distinct clearance profiles for NIR-conPK11195 and free NIR dye, resulting in preferential accumulation of the TSPO-targeted probe in the intracranial tumor bearing hemisphere (TBH) with significant tumor contrast over normal muscle tissue (p < 0.005 at five weeks; p < 0.01 at four weeks). In addition, the TSPO-labeled TBHs demonstrated significant contrast over the TBHs of mice injected with free NIR dye (p < 0.001 at four and five weeks) as well as over the TSPO-labeled non-tumor-bearing hemispheres (NTBHs) of control mice (p < 0.005 at four and five weeks). Overall, TSPO-targeted molecular imaging appears useful for visualizing and quantifying breast cancer xenografts propagated in the murine brain and may assist in preclinical detection, diagnosis and monitoring of metastatic disease as well as drug discovery. Furthermore, these results indicate it should be possible to perform TSPO-imaging of breast cancer cells in the brain using radiolabeled TSPO-targeted agents, particularly in light of the fact that [11C]-labeled TSPO probes such as [11C]-PK 11195 have been successfully used to image gliomas in the clinic.

Objective assessment of utility of intraoperative ultrasound in resection of central nervous system tumors: A cost-effective tool for intraoperative navigation in neurosurgery

Background:

Localization and delineation of extent of lesions is critical for safe maximal resection of brain and spinal cord tumors. Frame-based and frameless stereotaxy and intraoperative MRI are costly and not freely available especially in economically constrained nations. Intraoperative ultrasound has been around for a while but has been relegated to the background. Lack of objective evidence for its usefulness and the perceived “user unfriendliness” of US are probably responsible for this. We recount our experience with this “forgotten” tool and propose an objective assessment score of its utility in an attempt to revive this practice.

Materials and Methods:

Seventy seven intraoperative ultrasound (IOUS) studies were carried out in patients with brain and spinal cord tumors. Seven parameters were identified to measure the “utility” of the IOUS and a “utility score” was devised (minimum 0 and maximum 7). Individual parameter and overall scores were calculated for each case.

Results:

IOUS was found to be useful in many ways. The median overall score was 6 (mean score 5.65). There were no scores less than 4 with the majority demonstrating usefulness in 5 or more parameters (91%). The use of the IOUS significantly influenced the performance of the surgery in these cases without significantly prolonging surgery.

Conclusions:

The IOUS is a very useful tool in intraoperative localization and delineation of lesions and planning various stages of tumor resection. It is easy, convenient, reliable, widely available, and above all a cost-effective tool. It should be increasingly used by neurosurgeons in the developing world where costlier intraoperative localization and imaging is not available freely.

Intraoperative 3-dimensional ultrasound for resection control during brain tumour removal: preliminary results of a prospective randomized study

INTRODUCTION

The amount of resection is closely related to survival in brain tumours. To enhance resection, especially intraoperative magnetic resonance imaging (MRI) has been applied. The aim of this prospective, randomized study was to test if intraoperative 3-D ultrasound likewise can be used for resection control.

METHODS

16 patients, who underwent surgery for intraaxial tumours in non-eloquent brain areas, were initially included into this prospective study. In two patients, the small size of the craniotomy hindered intraoperative ultrasound imaging. In 14 patients, 3-D ultrasound images were obtained before and after opening of the dura, during tumour removal, prior to evaluation by a blinded investigator for identification of tumour remnants, and after dura closure. Seven patients were randomized to complete tumour removal according to the impression of the surgeon (group 1). Seven patients were randomized to incomplete tumour removal (tumour remnant <1cm) (group 2); in these patients, the neurosurgeon intentionally left a tumour remnant prior to evaluation by the blinded investigator. The tumour remnant was then removed. It was tested if 3-D ultrasound can correctly identify complete and incomplete tumour resection. All patients underwent early postoperative MRI.

RESULTS

In two patients (one each of the two groups) the image quality was too poor for a meaningful intraoperative evaluation. In the six patients randomized for incomplete tumour removal, 3-D ultrasound correctly identified tumour remnants in four patients (67%). In six patients randomized for complete tumour removal, 3-D ultrasound confirmed complete tumour resection in three patients. In addition, 3-D ultrasound identified correctly one tumour remnant in a patient randomized for complete tumour removal. Thus, the sensitivity for tumour remnant detection increased to 71% (five of seven patients) and that of confirmation of complete tumour removal was 60 % (three of five patients).

CONCLUSION

The number of investigated patients is still to low to allow definite conclusions. However, the study results suggest, that 3-D ultrasound is especially helpful for detection of overseen brain tumour tissue.

Role of intraoperative ultrasound in resection of pediatric brain tumors

PURPOSE

In neurosurgery, ultrasound is useful in determination of the tumor location, differentiation between solid tumors and cystic components, as well as definition of the shortest and safest access to the mass. This study aims to evaluate the role of the intraoperative ultrasound in resection of pediatric brain tumors.

METHODS

Intraoperative ultrasonography (conventional B-Mode) was performed in 25 pediatric patients with brain tumors pre-, during, and post-resection, in whom eight patients were supratentorial and 17 were infratentorial. Post-op Grayscale images of the brain tumors on conventional ultrasound were compared with the results of immediate postoperative magnetic resonance imaging.

RESULTS

The border of the tumor and post-resection residual tumor were more distinguishable from healthy brain on ultrasound during the operation. Improved definition of the tumor tissue from normal brain with ultrasound was demonstrated in all cases aiding in tumor resection.

CONCLUSION

Intraoperative ultrasound is suggested to be a useful imaging technique in defining the border between the tumor and healthy brain tissue pre-resection, in detecting residual tumor tissues after the resection of the mass, and in guiding to the shortest and safest access to the tumor during neurosurgery.

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

INTRODUCTION

Recent developments in optical science and image processing have miniaturized the components required for confocal microscopy. Clinical confocal imaging applications have emerged, including assessment of colonic mucosal dysplasia during colonoscopy. We present our initial experience with handheld, miniaturized confocal imaging in a murine brain tumor model.

METHODS

Twelve C57/BL6 mice were implanted intracranially with 10(5) GL261 glioblastoma cells. The brains of 6 anesthetized mice each at 14 and 21 days after implantation were exposed surgically, and the brain surface was imaged using a handheld confocal probe affixed to a stereotactic frame. The probe was moved systematically over regions of normal and tumor-containing tissue. Intravenous fluorescein and topical acriflavine contrast agents were used. Biopsies were obtained at each imaging site beneath the probe and assessed histologically. Mice were killed after imaging.

RESULTS

Handheld confocal imaging produced exquisite images, well-correlated with corresponding histologic sections, of cellular shape and tissue architecture in murine brain infiltrated by glial neoplasm. Reproducible patterns of cortical vasculature, as well as normal gray and white matter, were identified. Imaging effectively distinguished between tumor and nontumor tissue, including infiltrative tumor margins. Margins were easily identified by observers without prior neuropathology training after minimum experience with the technology.

CONCLUSION

Miniaturized handheld confocal imaging may assist neurosurgeons in detecting infiltrative brain tumor margins during surgery. It may help to avoid sampling error during biopsy of heterogeneous glial neoplasms, with the potential to supplement conventional intraoperative frozen section pathology. Clinical trials are warranted on the basis of these promising initial results.

Radio-guided neurosurgery (RGNS): early experience with its use in brain tumour surgery

DEFINITION

Radio Guided Neurosurgery(1) (RGNS) is a technique using systemic administration of radionuclide in which a gamma probe is used intra-operatively to identify isotope-rich brain tumour, and check for residual lesions after excision of visually identifiable lesion.

AIMS

To assess the usefulness of this technique in surface-localizing brain tumours, in real time, intra-operative identification of tumour from brain, and in assessing completeness of excision. Tumours in or near eloquent areas are of special interest.

SETTINGS AND DESIGN

Prospective, non-randomized and non-blinded.

METHODS AND MATERIAL

The study included 19 patients with intrinsic brain tumours operated between July 2005 & December 2006. A high degree of radioisotope uptake was confirmed on Single Positron Emission Computed Tomography (SPECT) with fusion of Computed Tomographic (CT) images (SPECT-CT) in all patients after IV injections of 99m Technetium Sestamibi (Tc). We use a Euro 4 Probe (Euro Medical Instruments, Paris) which detects gamma emissions. Intra-operatively, the probe was used to identify tumour from normal brain using a difference in activity of a factor of 2. The end point was complete tumour removal as determined by absence of significant residual activity.

RESULTS AND CONCLUSIONS

This inexpensive and highly portable system provides realtime, intra-operative identification of tumour and assessment of completeness of tumour excision. It can guide the location of craniotomy and identify visually indistinct tumor from normal brain, a situation where the surgeon may leave behind residual tumour to avoid serious deficits. The use of RGNS enhances the neurosurgeon's confidence with tumours in or near eloquent areas and provides reliable proof of the completeness of excision in real time.

Tumor targeting using liposomal antineoplastic drugs

During the last years, liposomes (microparticulate phospholipid vesicles) have been used with growing success as pharmaceutical carriers for antineoplastic drugs. Fields of application include lipid-based formulations to enhance the solubility of poorly soluble antitumor drugs, the use of pegylated liposomes for passive targeting of solid tumors as well as vector-conjugated liposomal carriers for active targeting of tumor tissue. Such formulation and drug targeting strategies enhance the effectiveness of anticancer chemotherapy and reduce at the same time the risk of toxic side-effects. The present article reviews the principles of different liposomal technologies and discusses current trends in this field of research.

Ultrasonic radio-frequency spectrum analysis differentiates normal and edematous brain tissue from meningioma intraoperatively

Intraoperative ultrasound imaging of the brain is used for tumor localization and resection control. The aim of the present study was to prove whether spectral analysis of radio-frequency (rf) signals is able to improve its diagnostic capabilities by adding quantitative acoustical parameters to pure visual analysis. Meningioma was chosen as a first model because of its distinct borders during surgery as well as in ultrasound imaging. Rf signals were captured intraoperatively. Spectral analysis of rf signals was performed off-line in areas of normal brain, edematous tissue, and meningioma within the bandwidth of the transducer. At 5.0 MHz, attenuation allowed significant differentiation for normal brain versus edema (P= .00002), normal brain versus meningioma (P= .000004), and edema versus meningioma (P= .002). The slope of attenuation reached significant levels among the three groups, too. Backscatter analysis consisted of determination of the power spectral density with a significant difference for edema versus meningioma at 5 MHz (P= .02). The same was true for a relative integrated backscatter coefficient (P= .01). Frequency-dependent backscatter coefficients were estimated using a standard phantom with edema showing the highest values followed by parenchyma and meningioma. Spectral analysis of rf signals has the potential of differentiating intracranial tissues as could be shown exemplarily with meningioma in this study. If this is also true for infiltrating tumors, the method might serve as a tool to better define tumor borders, thus improving the extent of resection.

Ultrasonic radio-frequency spectrum analysis of normal brain tissue

Acoustic tissue properties can be estimated using texture and/or spectral parameter analysis. Spectral analysis is based on the rf-signals whose frequency-content is commonly neglected in conventional B-mode imaging. Attenuation and backscatter values of normal brain tissue were analyzed. Unprocessed rf-data of 20 patients were sampled intraoperatively after craniotomy using a modified conventional ultrasonic device (Hitachi CS 9600) and analyzed off-line by a custom-made software routine. Before parameter estimation, influences of the diffraction pattern were compensated by means of a correction function obtained using a tissue-mimicking phantom. Attenuation of white matter showed a linear frequency dependence with a slope of 0.94 +/- 0.13 dB cm(-1) MHz(-1). The spectral slope was determined using 10 distinct frequencies between 2.5 and 5.75 MHz. Backscattering properties were analyzed by determining the power spectral density (PSD) and a relative backscatter coefficient (rel BSC) against the values derived from the tissue-mimicking phantom. PSD and rel BSC values were frequency-dependent, with highest PSD values at the probe's center frequency (-75.69 +/- 8.26 dB V(2) Hz(-1)). The corresponding rel BSC value at 5 MHz was determined as 15.39 +/- 8.26 dB. Finally, backscatter coefficients (BSC) of brain tissue were computed using the known BSC of the phantom. The data provided in this study are meant to serve as a base for intended future characterization of brain tissue that potentially allows intraoperative differentiation between normal and pathologic areas and therefore provides the surgeon with additional information for defining the extent of resection in brain more precisely.

Quantum dots are phagocytized by macrophages and colocalize with experimental gliomas

OBJECTIVE

The identification of neoplastic tissue within normal brain during biopsy and tumor resection remains a problem in the operative management of gliomas. A variety of nanoparticles are phagocytized by macrophages in vivo. This feature may allow optical nanoparticles, such as quantum dots, to colocalize with brain tumors and serve as an optical aid in the surgical resection or biopsy of brain tumors.

METHODS

Male Fisher rats (Charles River Labs, Wilmington, MA) were implanted intracranially with C6 gliosarcoma cell lines to establish tumors. Two weeks after the implantation of tumors, 705-nm emission Qdot ITK Amino(PEG) Quantum Dots (Quantum Dot Corp., Hayward, CA) were injected via the tail vein at doses of 3 to 17 nmol. The animals were sacrificed 24 hours after the injection of quantum dots and their tissues were examined.

RESULTS

Quantum dots are avidly phagocytized by macrophages and are taken up by the liver, spleen, and lymph nodes. A dose-response relationship was noted. At low doses, the majority of the quantum dots are sequestered in the liver, spleen, and lymph nodes. At higher doses, increasing quantities of quantum dots are noted within the experimental brain tumors. Macrophages and microglia colocalize with glioma cells, carrying the quantum dot and thereby optically outlining the tumor. Excitation with blue or ultraviolet wavelengths stimulates the quantum dots, which give off a deep red fluorescence detectable with charge-coupled device cameras, optical spectroscopy units, and in dark-field fluorescence microscopy.

CONCLUSION

Quantum dots are optical nanoparticles that, when delivered in nanomole doses, are phagocytized by the macrophages and microglia that infiltrate experimental gliomas. The optical signal may be detected, allowing for improved identification and visualization of tumors, potentially augmenting brain tumor biopsy and resection.

In vivo optical imaging using quantum dots for the management of brain tumors

The surgical management of brain tumors requires the precise localization of tumor tissues within normal brain parenchyma in order to achieve accurate diagnostic biopsy and complete surgical resection. Quantum dots are optical semiconductor nanocrystals that exhibit stable, bright fluorescence. The intravenous injection of quantum dots is accompanied by reticuloendothelial system and macrophage sequestration. Macrophages infiltrate brain tumors and phagocytize intravenously injected quantum dots, optically labeling the tumors. Macrophage-mediated delivery of quantum dots to brain tumors may represent a novel technique to label tumors preoperatively. Quantum dots within tumors may be detected with optical imaging and optical spectroscopy tools, providing the surgeon with real-time optical feedback during the resection and biopsy of brain tumors.

Intraoperative optical spectroscopy identifies infiltrating glioma margins with high sensitivity

OBJECTIVE

Adult gliomas have indistinct borders. As the ratio of neoplastic cells to normal cells becomes lower, the ability to detect these cells diminishes. We describe a device designed to augment intraoperative identification of both solid tumor and infiltrating tumor margins.

METHODS

A novel, intraoperative, optical spectroscopic tool, using both white light reflectance and 337-nm excitation fluorescence spectroscopy, is described. Discrimination algorithms have been developed to segregate neoplastic tissues from normal glial and neuronal elements. The spectroscopy device was used to measure 5 to 10 locations during glioma resection. Beneath the tool, a biopsy sample was obtained and the pathological results were reviewed in a blinded fashion. Samples were classified as solid tumor, infiltrating tumor, or normal gray or white matter. Comparisons were made between the optical spectra and the histopathological results of sampled areas in evaluating the sensitivity and specificity of the tool for tissue discrimination.

RESULTS

Spectral data were obtained from 24 patients with glioma and from 11 patients with temporal lobe epilepsy. A sensitivity of 80% and a specificity of 89% in discriminating solid tumor from normal tissues were obtained. In addition, infiltrating tumor margins were distinguished from normal tissues with a sensitivity of 94% and a specificity of 93%.

CONCLUSION

We have developed a handheld, optical spectroscopic device that may be used rapidly and in near real time with high sensitivity and reproducibility as an optical tissue discrimination tool in glioma surgery.

Bromophenol blue staining of tumors in a rat glioma model

OBJECTIVE

For patients with gliomas, decreasing the tumor burden with macroscopic surgical resection may affect quality of life, time to tumor progression, and survival. Injection of bromophenol blue (BPB) may enhance intraoperative visualization of an infiltrating tumor and its margins and improve the extent of resection. In this study, we investigated the uptake of BPB in experimental rat brain tumors.

METHODS

We first conducted a toxicity study with bolus intravenous injections of 5, 60, and 360 mg/kg doses of BPB in nontumor-bearing Fischer 344 rats. No adverse effects were observed in any of the animals during the 60 day observation period. We then injected 9L tumor cells intracerebrally into Fischer 344 rats and approximately 2 weeks later, administered a bolus intravenous injection of 5 to 360 mg/kg BPB. Fifteen minutes after BPB injection, we sacrificed the animals and removed their brains. In a subsequent study, we injected 180 mg/kg BPB and sacrificed animals at several time points to monitor tumor staining over time.

RESULTS

The stain was clearly visible and localized to the tumor for all BPB concentrations 60 mg/kg or greater, and in an additional experiment, we found that tumor staining persisted for at least 8 hours after BPB injection.

CONCLUSION

We conclude that BPB helped visualize experimental tumors at time points from a few minutes to several hours after injection. Because BPB also proved to be nontoxic to the animals at effective concentrations, we believe the compound may be potentially useful in helping neurosurgeons visualize brain tumors in humans.

Delineation of brain tumor margins using intraoperative sononavigation: implications for tumor resection

PURPOSE

Sonography has been employed for real-time intraoperative delineation of tumor boundaries during resection of brain tumors. However, the variably hyperechoic appearance of brain edema or gliosis surrounding the brain may interfere with accurate depiction of tumor margins. The goal of the present study was to use sononavigation, which provides coregistration between real-time sonograms and MRI scans, to assess the accuracy of sonographic determination of tumor margins.

METHODS

Sononavigation was performed on 12 brain tumors (7 metastatic brain tumors, 2 meningiomas, 1 anaplastic oligodendroglioma, 1 anaplastic pilocytic astrocytoma, and 1 anaplastic astrocytoma). Sonograms of tumor margins were categorized into 1 of 3 types: in type 1, the tumor margin was clearly visualized and corresponded to the margin of the enhanced lesion on MR scan in all areas; in type 2, the tumor margin was clearly seen in some areas but was obscure in others due to hyperechoic edema; and in type 3, the tumor margin was indistinguishable from surrounding tissues in all areas.

RESULTS

Three metastatic brain tumors and 1 meningioma were categorized as type 1. Three metastatic brain tumors, 1 meningioma, and 1 anaplastic oligodendroglioma were categorized as type 2. The anaplastic pilocytic astrocytoma, 1 metastatic brain tumor (which consisted mainly of necrotic tissue), and the anaplastic astrocytoma were categorized as type 3. These data assist in determining whether the sonographic appearance of tumor margins is accurate and whether to rely on information from either sonography (type 1) or the sononavigation system when resecting tumor types 1, 2, and 3.

CONCLUSIONS

Sononavigation can help categorize the sonographic tumor margins into 3 different patterns, and this categorization can assist in determining which imaging modalities are needed to better delineate the tumor margins for subsequent resection.

Ability of navigated 3D ultrasound to delineate gliomas and metastases--comparison of image interpretations with histopathology

BACKGROUND

The objective of the study was to test the ability of a 3D ultrasound (US) based intraoperative imaging and navigation system to delineate gliomas and metastases in a clinical setting. The 3D US data is displayed as reformatted 2D image slices. The quality of the displayed 3D data is affected both by the resolution of the acquired data and the reformatting process. In order to investigate whether or not 3D US could be used for reliable guidance in tumour surgery, a study was initiated to compare interpretations of imaged biopsy sites with histopathology. The system also enabled concomitant comparison of navigated preoperative MR with histopathology.

METHOD

Eighty-five biopsies were sampled between 2-7 mm from the tumour border visible in the ultrasound images. Biopsies were collected from 28 operations (7 low-grade astrocytomas, 8 anaplastic astrocytomas, 7 glioblastomas and 6 metastases). Corresponding cross-sections of preoperative MR T1, MR T2 and intraoperative US were concomitantly displayed, steered by the biopsy forceps equipped with a positioning sensor. The surgeons' interpretation of the images at the electronically indicated biopsy sites were compared with the histopathology of the samples.

FINDINGS

The ultrasound findings were in agreement with histopathology in 74% (n = 31) for low-grade astrocytomas, 83% (n = 18) for anaplastic astrocytomas, 77% (n = 26) for glioblastomas and 100% (n = 10) for metastases. Excluding irradiated patients, the results for glioblastomas improved to 80% concurrence (n = 20). As expected tumour cells were found in biopsies outside the US visible tumour border, especially in low-grade gliomas. Navigated 3D US have a significantly better agreement with histopathology than navigated MR T1 for low-grade astrocytomas.

CONCLUSION

Reformatted images from 3D US volumes give a good delineation of metastases and the solid part of gliomas before starting the resection. Navigated 3D US is at least as reliable as navigated 3D MR to delineate gliomas and metastases.

Accurate characterization of the main trunk of the anterior cerebral artery by means of intraoperative sononavigation with Doppler sonography: implications for brain tumor surgery

OBJECTIVE

Doppler sonography can be used for real-time intraoperative localization of arteries within or near brain tumors but is less useful for distinguishing between arteries with similar diameters, such as the main trunk and branches of the anterior cerebral artery (ACA). By contrast, sononavigation provides real-time information in alignment with magnetic resonance imaging scans and may be of use in characterizing the identity of individual arteries on Doppler sonographic images. The goal of this study was to determine whether sononavigation can distinguish the main trunk of the ACA from the branches of the ACA on Doppler sonographic images.

METHODS

Doppler sonography was used in 3 patients undergoing surgical resection of brain tumors involving the main trunk of the ACA. The location of the main trunk of the ACA was characterized by sononavigation.

RESULTS

With these data, tumor resection was performed with preservation of the main trunk of the ACA. Gross total resection was achieved in 1 case.

CONCLUSIONS

Intraoperative sononavigation with Doppler sonography accurately localized the main trunk of the ACA and enabled preservation of this structure during tumor resection. This method may be applicable to the characterization of other critical arteries and may allow tumor resection with decreased morbidity.

Ultrasound guidance in intracranial tumor resection: correlation with postoperative magnetic resonance findings

PURPOSE

To determine the inter-method agreement between intraoperative ultrasonography and postoperative contrast-enhanced magnetic resonance imaging (MRI) in detecting tumor residue.

MATERIAL AND METHODS

After resection was completed, the cavity borders of 32 tumors were examined with a 7 MHz intraoperative probe. Any echogenic region >5 mm in thickness extending from the surgical cavity into the brain substance was taken as the sonographic criterion for residual tumor. A continuous echogenic rim< 5 mm was considered normal. Results were correlated with gadolinium-enhanced MRI obtained within 48 h after surgery.

RESULTS

The kappa value for inter-method agreement was 0.72. There were four cases in whom MRI showed residue despite a negative sonography: extensive edema or Surgicel along the cavity borders (three cases with glioblastoma multiforme) and the cystic component in the vicinity of cerebrospinal fluid (a case with pituitary macroadenoma) may be the reason for the residue going undetected. In a case with glioblastoma multiforme, residual enhancement was < 5 mm in thickness.

CONCLUSION

Intraoperative ultrasound is an effective tool for maximizing the extent of intracranial tumor resection. Surgical use has to be minimized if intraoperative ultrasound is to be used as an adjunct to surgery. Tumors with preoperatively detected cystic components in the proximity of CSF-containing spaces have to be carefully evaluated with intraoperative ultrasound if residual cystic components are to be detected. A low-thickness echogenic rim should not be considered a reliable sign of the absence of residue.

Strain processing of intraoperative ultrasound images of brain tumours: initial results

The purpose of the study was to investigate a method for strain calculation and its ability to discriminate between brain tumour and normal brain. During surgery of a low-grade astrocytoma and a metastasis, we acquired ultrasound (US) radiofrequency (RF) data with a hand-held probe at the dura mater. Using cross-correlation and phase-sensitive processing, we quantified the tissue displacements between consecutive US images and, subsequently, the local strain. In the elastograms, the tumour lesions were associated with lower strain levels than those found in the surrounding normal tissue. For both investigated cases, the strain images showed good agreement with the B-mode images. However, the results also indicated that the tumour interpretation might be different in the two modalities. An important finding was that the tissue motion caused by arterial pulsation is sufficient for generating elastograms. Requiring no specialised equipment or changes to acquisition procedures, strain data can be obtained as easily as conventional US imaging.

Coregistration accuracy and detection of brain shift using intraoperative sononavigation during resection of hemispheric tumors

OBJECTIVE

Sononavigation, which combines real-time anatomic ultrasound data with neuronavigation techniques, is a potentially valuable adjunct during the surgical excision of brain tumors.

METHODS

In this study, we report our preliminary observations using this technology on 58 adult patients harboring hemispheric tumors. Data regarding coregistration accuracy was collected from various landmarks that typically do not shift as well as from tumor boundaries and the cortical surface. In a subset of patients, we evaluated the extent and direction of postresection brain displacement and its relationship with patient age, tumor histology, tumor volume, and use of mannitol.

RESULTS

For all structures excluding the cortex, average coregistration accuracy measurements between ultrasound and preoperatively acquired magnetic resonance imaging scans were within the range of 2 mm. The most accurate alignments were obtained with the choroid plexus and the falx, and the least reliable structure in terms of coregistration accuracy was the cortical surface.

CONCLUSION

Sononavigation provides real-time information during tumor removal in alignment with the preoperative magnetic resonance imaging scans, thus enabling the surgeon to detect intraoperative hemorrhage, cyst drainage, and tumor resection, and it allows for calculation of brain shift during the use of standard navigation techniques.

Intracarotid RMP-7 enhanced indocyanine green staining of tumors in a rat glioma model

OBJECTIVE

The extent of resection in patients with primary brain tumors may affect the quality of life, time to tumor progression, and survival. Currently, the extent of resection during surgery is guided by the visual appearance and consistency of tumor, frozen sections of the margins, intraoperative ultrasound, and frameless navigational systems and intraoperative imaging modalities. A new method that enhances the visualization of an infiltrating tumor and its margins may further aid in obtaining a more complete resection. A study was thus undertaken to assess the staining of brain tumors using Indocyanine green (ICG), a water-soluble emerald green tricarbocynanine dye concomitantly with RMP-7, a bradykinin analog, that selectively increases vascular permeability in brain tumors.

METHODS

A syngeneic ethyl-nitrosourea-induced F-344 rat cell line (36B-10) was stereotactically implanted into 25 rats, and allowed to mature for 15-18 days. Intracarotid administration of 0.75 ml of RMP-7 at a standard dose of 0.4 microg/ml over 15 min was then infused. Varying doses of ICG (range, 0-60 mg/kg) were then injected 15 min after the RMP-7 infusion ended. The animals were sacrificed 15 min after the ICG infusion was completed, and the brains examined macroscopically and microscopically for evidence of tumor staining.

RESULTS

This study demonstrated consistent staining of the tumor at only slightly lower ICG doses than previously described, however uptake at the tumor margins was evident at much lower doses. Thus the combination of ICG and RMP-7 administered preoperatively may provide visual enhancement of an infiltrating tumor and its margins to help facilitate a radical tumor removal.

Postoperative neuroimaging of high-grade gliomas: comparison of transcranial sonography, magnetic resonance imaging, and computed tomography

BACKGROUND

A precise and comprehensive knowledge of tumor burden and its extent and growth pattern in the pre- and postsurgical states is required to optimize tumor therapy and to determine treatment success and failure. This prospective study compares the diagnostic potential of computed tomography (CT), magnetic resonance imaging (MRI), and transcranial sonography (TCS) in the postoperative follow-up of brain tumors.

METHOD

Twenty-six patients with high-grade gliomas were included in the study. After tumor debulking, a total of 31 biopsy specimens were obtained from the resection margin in 21 patients and histological findings were compared with the findings of early postoperative TCS, CT, and MRI. Findings indicating residual tumor tissue were nonlinear contrast enhancement at the resection site revealed by CT or MRI or hyperechogenic lesions revealed by TCS. Follow-up examinations using all three imaging techniques were performed every 3 months. The end points of the follow-up were tumor recurrence as defined by CT and MRI, death, or severe clinical deterioration.

RESULTS

On the basis of the above criteria, TCS identified residual tumor more often than did CT or MRI. In the group of 19 patients with histologically proven tumor remnants, residual tumor tissue was identified by TCS in all patients, whereas MRI and CT failed to show contrast enhancement in three and eight patients, respectively. However, the results of the TCS were false positive for one patient because of hemorrhage into the resection site. The average time to identification of tumor regrowth was 27 weeks using TCS, 29 weeks using CT, and 33 weeks using MRI. Only the differences between TCS and MRI reached statistical significance. For one patient, multicentric tumor recurrence was not detected using TCS.

CONCLUSION

TCS may complement CT and MRI in the postoperative follow-up of patients with high-grade gliomas. Because none of these modalities alone is both sensitive and specific, an integrated analysis of imaging findings is recommended.

Intraoperative brain shift and deformation: a quantitative analysis of cortical displacement in 28 cases

OBJECTIVE

A quantitative analysis of intraoperative cortical shift and deformation was performed to gain a better understanding of the nature and extent of this problem and the resultant loss of spatial accuracy in surgical procedures coregistered to preoperative imaging studies.

METHODS

Three-dimensional feature tracking and two-dimensional image analysis of the cortical surface were used to quantify the observed motion. Data acquisition was facilitated by a ceiling-mounted robotic platform, which provided a number of precision tracking capabilities. The patient's head position and the size and orientation of the craniotomy were recorded at the start of surgery. Error analysis demonstrated that the surface displacement measuring methodology was accurate to 1 to 2 mm. Statistical tests were performed to examine correlations between the amount of displacement and the type of surgery, the nature of the cranial opening, the region of the brain involved, the duration of surgery, and the degree of invasiveness.

RESULTS

The results showed that a displacement of an average of 1 cm occurred, with the dominant directional component being associated with gravity. The mean displacement was determined to be independent of the size and orientation of the cranial opening.

CONCLUSION

These data suggest that loss of spatial registration with preoperative images is gravity-dominated and of sufficient extent that attention to errors resulting from misregistration during the course of surgery is warranted.

Use of intraoperative ultrasound for localizing tumors and determining the extent of resection: a comparative study with magnetic resonance imaging

A prospective study of 70 patients with intraparenchymal brain lesions (36 gliomas and 34 metastases) was performed to evaluate the efficacy of intraoperative ultrasound (IOUS) in localizing and defining the borders of tumors and in assessing the extent of their resection. Eighteen of the 36 glioma patients had no previous therapy. All of these 18 tumors were well localized by IOUS; margins were well defined in 15 and moderately defined in three. The extent of resection was well defined on IOUS in all 18 patients, as confirmed by measurements taken on postoperative magnetic resonance (MR) images (p = 0.90). The remaining 18 patients with gliomas had undergone previous surgery and/or radiation therapy; five had recurrent tumors and 13 had radiation-induced changes. The extent of resection of the recurrent tumors was well defined in all but one patient, as confirmed by postoperative MR imaging. The extent of resection was poorly defined in all 13 patients whose pathology showed radiation effects. All 34 metastatic lesions were well localized and had well-defined margins. In addition, IOUS accurately determined the extent of resection in all cases, the results were confirmed with postoperative MR imaging. In conclusion, IOUS is not only helpful in localizing and defining the margins of gliomas and metastatic brain lesions, it also accurately determines the extent of resection, as confirmed by postoperative MR imaging. This assessment does not apply, however when the lesion is due primarily to radiation effect.

Enhanced optical imaging of human gliomas and tumor margins

One of the potential variables affecting the overall survival and quality of life of patients with intracranial gliomas is the extent of tumor resection that results in the smallest volume of residual disease. A technique involving enhanced optical imaging of human gliomas has the potential to localize tumors, identify tumor remaining at the resection margins, and determine the grade of the tumor. In a preliminary study involving nine patients undergoing surgery for the removal of intrinsic brain tumors, enhanced optical imaging was performed using indocyanine green as an intravenous contrast-enhancement agent. Optical images were obtained before and after injection of the indocyanine green. The studies in the nine patients showed differences in the dynamic optical signals among normal brain, low-grade astrocytomas, and malignant astrocytomas. Optical imaging of the resection margins in malignant tumors showed differences between adjacent normal tissue and remaining tumor tissue. Enhanced optical imaging of human gliomas using a contrast-enhancing dye, indocyanine green, provides a potential means to differentiate between normal brain and tumor tissue at the cortical surface and the depths of the resection margins. Having the ability to obtain real-time information and feedback in the operating room may allow neurosurgeons to maximize the extent of tumor resection while sparing normal brain and increasing the diagnostic accuracy of intraoperative biopsies. Enhanced optical imaging potentially could facilitate the accuracy and safety of surgery when tumors are removed at sites even outside the central nervous system.

Correlation of intra-operative ultrasound with histopathologic findings after tumour resection in supratentorial gliomas. A method to improve gross total tumour resection

The aim of this study was to evaluate whether intra-operative ultrasound (= IOUS) is a suitable tool to detect residual tumour tissue after gross total resection in supratentorial gliomas. During a period of 18 months 45 patients with supratentorial gliomas (38 high-grade and 9 low-grade, according to the WHO-grading system [42]) were operated on. A series of 78 biopsies was taken from the resection cavity under continuous sonographic control at the end of surgery. Gross total tumour resection was intended in 34 patients (= 76%). The biopsy specimens were matched with the sonographic features at each biopsy site. The sonographic appearance of the resection margins were classified into 2 groups: (1) Irregular hyperechoic areas extending from the cavity into the iso-echogenic brain tissue and (2) a dense small (< or = 3 mm in diameter) rather regular hyperechoic rim surrounding the resection cavity. 47 out of 53 biopsies taken from hyperechoic areas (group I) (36 high-grade/11 low-grade) revealed solid tumour tissue (= 89%). 34 (= 72%) of these 47 areas were microscopically assessed as inconspicuous by the surgeon. 6 samples (4 high-grade/2 low-grade) contained tumour infiltration zone. 25 biopsies (23 high-grade/2 low-grade) taken from the hyperechoic rim [group 2] were diagnosed as follows: Normal brain tissue in 11, tumour infiltration zone in 8 and solid tumour tissue in 6 cases. Of 34 cases with "gross total removal" according to the surgeon's assessment 25 showed sonographic signs of residual tumour tissue, which was confirmed histologically as solid tumour tissue in 22 of these cases. It is concluded, that IOUS following resection of supratentorial gliomas can detect residual tumour tissue with high specificity and thus improve gross total resection. However, a thin hyperechoic rim surrounding the resection cavity (less than 3 mm in diameter) is a non-specific finding, which can mask thin residual tumour layers and therefore needs further evaluation of its nature.

Preoperative and postoperative follow-up in high-grade gliomas: comparison of transcranial color-coded real-time sonography and computed tomography findings

Twenty patients with high-grade gliomas were prospectively studied by pre- and postoperative transcranial color-coded real-time sonography (TCCS) and CT, to determine the sensitivity of TCCS in the identification of residual tumor and tumor regrowth. Each patient was subjected to preoperative and early postoperative CT (postoperative day 1) and TCCS examinations (postoperative days 6 to 8) and subsequent CT and TCCS follow-up examinations within a time interval of 6 weeks to 3 months. In eight patients, a total of 15 biopsy specimens were intraoperatively obtained from the wall of the resection cavity. Histological findings of intraoperative biopsy specimens showed that hyperechogenic areas adjacent to the resection cavity always contained residual tumor tissue. Early postoperative TCCS identified these hyperechogenic areas in 19 of 20 patients. In 12 patients, postoperative CT revealed contrast enhancement at the resection margin, indicating residual tumor. In these patients the extension of these hyperechogenic areas on TCCS exceeded the contrast-enhancing areas on CT by a mean of 58%. In eight patients, postoperative CT displayed no contrast enhancement along the border of resection. TCCS and histological findings indicated residual tumor in seven of these eight patients. The size of the hyperechogenic lesions identified by postoperative TCCS increased in time and follow-up examinations revealed that tumor regrowth arose from these hyperechogenic areas in all patients. In four patients, tumor regrowth was identified, on average 0.7 months earlier by TCCS than by CT. From these data we conclude that the sensitivity of TCCS in detection of residual tumor and tumor regrowth seems to be superior to CT. The value of TCCS requires further clarification by comparative studies including histology and MRI.

Reliability of transcranial colour-coded real-time sonography in assessment of brain tumours: correlation of ultrasound, computed tomography and biopsy findings

Transcranial colour-coded real-time sonography (TCCS) was carried out in 25 patients with brain tumours to determine whether this noninvasive method provides additional information about the extent of solid tumour, its differentiation from oedema, and its tissue components. All 25 patients had serial computed tomography (CT)-guided stereotactic biopsies. Comparison of ultrasound, CT and histological findings revealed that the vast majority of contrast enhancing areas on CT were hyperechogenic (32/33; 97%) and contained tumour tissue (29/32; 91%). Hyperechogenic areas always represented solid tumour (23/23 patients), even when CT showed low density non-enhancing lesions. In lesions hypoechogenic on TCCS and low density on CT, histology consistently revealed necrotic tumour (7/7). Biopsies obtained from parenchyma with normal echogenicity revealed tumour in only 3 of 16 specimens. Despite the high specificity of TCCS in the differentiation of tumour components, its sensitivity to tumour was inferior to that of CT (24/25; 96%). TCCS thus allows noninvasive preoperative identification of tumour tissue and its extent setting.

Enhanced optical imaging of rat gliomas and tumor margins

Current intraoperative methods used to maximize the extent of tumor removal are limited to intraoperative biopsies, ultrasound, and stereotactic volumetric resections. A new technique involving the optical imaging of an intravenously injected dye has the potential to localize tumors and their margins with a high degree of accuracy. In a rat glioma model, enhanced optical imaging was performed and indocyanine green was used as the contrast-enhancing agent. In all 22 animals, the peak optical change in the tumor was greater than in the ipsilateral brain around the tumor and the contralateral normal hemisphere. The clearance of the dye was significantly delayed to a greater extent in the tumor than in the brain around the tumor and the normal brain. After attempts were made at complete microscopic resection, enhanced optical imaging of the tumor margins and the histological samples demonstrated a specificity of 93% and a sensitivity of 89.5%. Enhanced optical imaging was capable of outlining the tumor even when the imaging was done through the cranium. The optical imaging of rat gliomas with a contrast-enhancing dye is able to differentiate between normal brain and tumor tissue both at the cortical surface and at the tumor margins. The application of these studies in an intraoperative clinical setting may allow for the more accurate determination of tumor margins and may increase the extent of tumor removal.

A comparison between preoperative magnetic resonance and intraoperative ultrasound tumor volumes and margins

A major obstacle in surgical neuro-oncology is differentiating the interface between tumor and normal brain. Twenty-two brain tumors were evaluated preoperatively with magnetic resonance imaging. Intraoperative ultrasonography was used to guide surgical resection of these tumors, and results were compared with surgical and pathologic findings. Ultrasound tumor volume estimates were larger than T1 gadolinium-enhanced and T1 non-gadolinium-enhanced volumes, but these differences did not reach statistical significance. Similarly T2 volumes were larger than the corresponding sonographic volumes, except for the subset of low-grade gliomas, and in that instance the difference was small, but again the differences were not statistically significant. Ultrasonography enhanced identification of infiltrating tumor cells beyond falsely underestimated tumor margins as defined by T1 images. Ultrasound images helped differentiate edema as seen on T2 images from solid tumor and normal brain. The information gained from ultrasound images can be used to enhance tumor resection and improve patient survival and quality of life.

Lasers in neurosurgery

Lasers have been used in neurosurgery for the past 25 years, undergoing modifications to suit the specific needs of this medical discipline. The present report reviews the current use of lasers in neurosurgical practice and examines the pros and cons of lasers in specific neurosurgical applications. In spite of their advantages, laser use is still not widespread in neurosurgery. One reason is the continued lack of complete control over real-time laser interactions with neural tissue. A greater acceptance and use of lasers by neurosurgeons will depend upon automated control over defined specific parameters for laser applications based upon the type of tissue, the desired effect on tissue, and application to the clinical situation without loss of precision and a lot of expense. This will require the integration of newer lasers, computers, robotics, stereotaxy, and concepts of minimally invasive surgery into the routine management of neurosurgical problems.

Low-grade gliomas associated with intractable epilepsy: seizure outcome utilizing electrocorticography during tumor resection

Adults and children with low-grade gliomas often present with medically refractory epilepsy. Currently, controversy exists regarding the need for intraoperative electrocorticography (ECoG) to identify and, separately, resect seizure foci versus tumor removal alone to yield maximum seizure control in this patient population. Forty-five patients with low-grade gliomas and intractable epilepsy were retrospectively analyzed with respect to preoperative seizure frequency and duration, number of antiepileptic drugs, intraoperative ECoG data (single versus multiple foci), histology of resected seizure foci, and postoperative control of seizures with or without antiepileptic drugs. Multiple versus single seizure foci were more likely to be associated with a longer preoperative duration of epilepsy. Of the 45 patients studied, 24 were no longer taking antiepileptic drugs and were seizure-free (mean follow-up interval 54 months). Seventeen patients, who all had complete control of their seizures, remained on antiepileptic drugs at lower doses (mean follow-up interval 44 months); seven of these patients were seizure-free postoperatively, yet the referring physician was reluctant to taper the antiepileptic drugs. Four patients continued to have seizures while receiving antiepileptic drugs, although at a reduced frequency and severity. In this series 41% of the adults versus 85% of the children were seizure-free while no longer receiving antiepileptic drugs, with mean postoperative follow-up periods of 50 and 56 months, respectively. This difference was statistically significant (p = 0.016). Therefore, based on this experience and in comparison with numerous retrospective studies involving similar patients, ECoG is advocated, especially in children and in any patient with a long-standing seizure disorder, to maximize seizure control while minimizing or abolishing the need for postoperative antiepileptic drugs.