Delineation of three-dimensional tumor margins based on normalized absolute difference mapping via volumetric optical coherence tomography

The extent of surgical resection is an important prognostic factor in the treatment of patients with glioblastoma. Optical coherence tomography (OCT) imaging is one of the adjunctive methods available to achieve the maximal surgical resection. In this study, the tumor margins were visualized with the OCT image obtained from a murine glioma model. A commercialized human glioblastoma cell line (U-87) was employed to develop the orthotopic murine glioma model. A swept-source OCT (SS-OCT) system of 1300 nm was used for three-dimensional imaging. Based on the OCT intensity signal, which was obtained via accumulation of each A-scan data, an en-face optical attenuation coefficient (OAC) map was drawn. Due to the limited working distance of the focused beam, OAC values decrease with depth, and using the OAC difference in the superficial area was chosen to outline the tumor boundary, presenting a challenge in analyzing the tumor margin along the depth direction. To overcome this and enable three-dimensional tumor margin detection, we converted the en-face OAC map into an en-face difference map with x- and y-directions and computed the normalized absolute difference (NAD) at each depth to construct a volumetric NAD map, which was compared with the corresponding H&E-stained image. The proposed method successfully revealed the tumor margin along the peripheral boundaries as well as the margin depth. We believe this method can serve as a useful adjunct in glioma surgery, with further studies necessary for real-world practical applications.

Clinical utility of intraoperative arterial spin labeling for resection control in brain tumor surgery at 3 T

Resection control in brain tumor surgery can be achieved in real time with intraoperative MRI (iMRI). Arterial spin labeling (ASL), a technique that measures cerebral blood flow (CBF) non-invasively without the use of intravenous contrast agents, can be performed intraoperatively, providing morpho-physiological information. This study aimed to evaluate the feasibility, image quality and potential to depict residual tumor of a pseudo-continuous ASL (PCASL) sequence at 3 T. Seventeen patients with brain tumors, primary (16) or metastatic (1), undergoing resection surgery with iMRI monitoring, were prospectively recruited (nine men, age 56 ± 16.6 years). A PCASL sequence with long labeling duration (3000 ms) and postlabeling delay (2000 ms) was added to the conventional protocol, which consisted of pre- and postcontrast 3D T₁ -weighted (T1w) images, optional 3D-FLAIR, and diffusion. Three observers independently assessed the image quality (four-point scale) of PCASL-derived CBF maps. In those with diagnostic quality (Scores 2-4) they evaluated the presence of residual tumor using the conventional sequences first, and the CBF maps afterwards (three-point scale). Inter-observer agreement for image quality and the presence of residual tumor was assessed using Fleiss kappa statistics. The intraoperative CBF ratio of the surgical margins (i.e., perilesional CBF values normalized to contralateral gray matter CBF) was compared with preoperative CBF ratio within the tumor (Wilcoxon's test). Diagnostic ASL image quality was observed in 94.1% of patients (interobserver Fleiss κ = 0.76). PCASL showed additional foci suggestive of high-grade residual component in three patients, and a hyperperfused area extending outside the enhancing component in one patient. Interobserver agreement was almost perfect in the evaluation of residual tumor with the conventional sequences (Fleiss κ = 0.92) and substantial for PCASL (Fleiss κ = 0.80). No significant differences were found between pre and intraoperative CBF ratios (p = 0.578) in patients with residual tumor (n = 7). iMRI-PCASL perfusion is feasible at 3 T and is useful for the intraoperative assessment of residual tumor, providing in some cases additional information to the conventional sequences.

Combining Pre-operative Diffusion Tensor Images and Intraoperative Magnetic Resonance Images in the Navigation Is Useful for Detecting White Matter Tracts During Glioma Surgery

Purpose

We developed a navigation system that superimposes the fractional anisotropy (FA) color map of pre-operative diffusion tensor imaging (DTI) and intraoperative magnetic resonance imaging (MRI). The current study aimed to investigate the usefulness of this system for neurophysiological monitoring and examination under awake craniotomy during tumor removal.

Method

A total of 10 glioma patients (4 patients with right-side tumors; 5 men and 5 women; average age, 34 years) were evaluated. Among them, the tumor was localized to the frontal lobe, insular cortex, and parietal lobe in 8, 1, and 1 patient, respectively. There were 3 patients who underwent surgery on general anesthesia, while 7 patients underwent awake craniotomy. The index of DTI anisotropy taken pre-operatively (magnetic field: 3 tesla, 6 motion probing gradient directions) was analyzed as a color map (FA color map) and concurrently co-registered in the intraoperative MRI within the navigation. In addition to localization of the bipolar coagulator and the cortical stimulator for brain mapping on intraoperative MRI, the pre-operative FA color map was also concurrently integrated and displayed on the navigation monitor. This white matter nerve functional information was confirmed directly by using neurological examination and referring to the electrophysiological monitoring.

Results

Intraoperative MRI, integrated pre-operative FA color map, and microscopic surgical view were displayed on one screen in all 10 patients, and white matter fibers including the pyramidal tract were displayed as a reference in blue. Regarding motor function, motor-evoked potential was monitored as appropriate in all cases, and removal was possible while directly confirming motor symptoms under awake craniotomy. Furthermore, the white matter fibers including the superior longitudinal fasciculus were displayed in green. Importantly, it was useful not only to localize the resection site, but to identify language-related, eye movement-related, and motor fibers at the electrical stimulation site. All motor and/or language white matter tracts were identified and visualized with the co-registration and then with an acceptable post-operative neurological outcome.

Conclusion

Co-registering an intraoperative MR images and a pre-operative FA color map is a practical and useful method to predict the localization of critical white matter nerve functions intraoperatively in glioma surgery.

[Intraoperative magnetic resonance imaging in surgery of brain gliomas]

Intraoperative magnetic resonance imaging (iMRI) is used in surgery of supratentorial gliomas to assess resection quality, as well as in neoplasm biopsy to control the needle position. Scanners coupled with operating table ensure fast intraoperative imaging, but they require the use of non-magnetic surgical tools. Surgery outside the scanner 5G line allows working with conventional instruments, but patient transportation takes time. Portable iMRI systems do not interfere with surgical workflow but these scanners have poor resolution. Positioning of MRI scanners in adjacent rooms allows imaging simultaneously for several surgeries. Low-field MRI scanners are effective for control of contrast-enhanced glioma resection quality. However, these scanners are less useful in demarcation of residual low-grade tumors. High-field MRI scanners have no similar disadvantage. These scanners ensure fast detection of residual gliomas of all types and functional imaging. Artifacts during iMRI are usually a result of iatrogenic traumatic brain injury and contrast agent leakage. Ways of their prevention are discussed in the review.

Image-Guided Brain Surgery

In neurosurgery, the extent of resection plays a critical role, especially in the management of malignant gliomas. These tumors are characterized through a diffuse infiltration into the surrounding brain parenchyma. Delineation between tumor and normal brain parenchyma can therefore often be challenging. During the recent years, several techniques, aiming at better intraoperative tumor visualization, have been developed and implemented in the field of brain tumor surgery. In this chapter, we discuss current strategies for intraoperative imaging in brain tumor surgery, comprising conventional techniques such as neuronavigation, techniques using fluorescence-guided surgery, and further highly precise developments such as targeted fluorescence spectroscopy or Raman spectroscopy.

Initial Experience Using Intraoperative Magnetic Resonance Imaging During a Trans-Sulcal Tubular Retractor Approach for the Resection of Deep-Seated Brain Tumors: A Case Series

BACKGROUND

Treatment of deep-seated subcortical intrinsic brain tumors remains challenging and may be improved with trans-sulcal tubular brain retraction techniques coupled with intraoperative magnetic resonance imaging (iMRI).

OBJECTIVE

To conduct a preliminary assessment of feasibility and efficacy of iMRI in tubular retractor-guided resections of intrinsic brain tumors.

METHODS

Assessment of this technique and impact upon outcomes were assessed in a preliminary series of brain tumor patients from 2 centers.

RESULTS

Ten patients underwent resection with a tubular retractor system and iMRI. Mean age was 53.2 ± 9.0 yr (range: 37-61 yr, 80% male). Lesions included 6 gliomas (3 glioblastomas, 1 recurrent anaplastic astrocytoma, and 2 low-grade gliomas) and 4 brain metastases (1 renal cell, 1 breast, 1 lung, and 1 melanoma). Mean maximal tumor diameter was 2.9 ± 0.95 cm (range 1.2-4.3 cm). The iMRI demonstrated subtotal resection (STR) in 6 of 10 cases (60%); additional resection was performed in 5 of 6 cases (83%), reducing STR rate to 2 of 10 cases (20%), with both having tumor encroaching on eloquent structures. Seven patients (70%) were stable or improved neurologically immediately postoperatively. Three patients (30%) had new postoperative neurological deficits, 2 of which were transient. Average hospital length of stay was 3.4 ± 2.0 d (range: 1-7 d).

CONCLUSION

Combining iMRI with tubular brain retraction techniques is feasible and may improve the extent of resection of deep-seated intrinsic brain tumors that are incompletely visualized with the smaller surgical exposure of tubular retractors.

The role of diffusion tractography in refining glial tumor resection

Primary brain tumors are notoriously hard to resect surgically. Due to their infiltrative nature, finding the optimal resection boundary without damaging healthy tissue can be challenging. One potential tool to help make this decision is diffusion-weighted magnetic resonance imaging (dMRI) tractography. dMRI exploits the diffusion of water molecule along axons to generate a 3D modelization of the white matter bundles in the brain. This feature is particularly useful to visualize how a tumor affects its surrounding white matter and plan a surgical path. This paper reviews the different ways in which dMRI can be used to improve brain tumor resection, its benefits and also its limitations. We expose surgical tools that can be paired with dMRI to improve its impact on surgical outcome, such as loading the 3D tractography in the neuronavigation system and direct electrical stimulation to validate the position of the white matter bundles of interest. We also review articles validating dMRI findings using other anatomical investigation techniques, such as postmortem dissections, manganese-enhanced MRI, electrophysiological stimulations, and phantom studies with known ground truth. We will be discussing the areas of the brain where dMRI performs well and where the future challenges are. We will conclude this review with suggestions and take home messages for neurosurgeons, tractographers, and vendors for advancing the field and on how to benefit from tractography's use in clinical practice.

Maximizing safe resections: the roles of 5-aminolevulinic acid and intraoperative MR imaging in glioma surgery-review of the literature

Malignant glioma surgery involves the challenge of preserving the neurological status of patients harboring these lesions while pursuing a maximal tumor resection, which is correlated with overall and progression-free survival. Presently, several tools exist for assisting neurosurgeons in visualizing malignant tissue. Fluorescence-guided surgery (FGS) with 5-aminolevulinic acid (5-ALA) has increasingly been used during the last decade for identifying malignant glioma. Intraoperative magnetic resonance imaging (iMRI), first introduced in the mid-1990s, is being evaluated as a further tool to maximize the extent of resection. We aimed to evaluate the literature and discuss synergies and differences between FGS with 5-ALA and iMRI. We conducted and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. After excluding non-relevant articles, 16 articles were evaluated and included in the qualitative analysis, comprising 2 (n = 2) reviews of the literatures, 1 (n = 1) book chapter, and 13 (n = 13) clinical articles. ALA-induced fluorescence goes beyond the borders of gadolinium contrast enhancement. Several studies stress the synergy between both tools, enabling increase in extent of resection. We point out advantages of combining both methods. iMRI, however, is not widely available, is expensive, and is not recommended as sole resection control tool in high-grade glioma. For these centers, FGS together with mapping and monitoring techniques, neuronavigation and, when needed, intraoperative ultrasound provides an excellent setting for achieving state-of-the-art gross total resection of high-grade gliomas.

Defining Glioblastoma Resectability Through the Wisdom of the Crowd: A Proof-of-Principle Study

BACKGROUND

Extent of resection (EOR) correlates with glioblastoma outcomes. Resectability and EOR depend on anatomical, clinical, and surgeon factors. Resectability likely influences outcome in and of itself, but an accurate measurement of resectability remains elusive. An understanding of resectability and the factors that influence it may provide a means to control a confounder in clinical trials and provide reference for decision making.

OBJECTIVE

To provide proof of concept of the use of the collective wisdom of experienced brain tumor surgeons in assessing glioblastoma resectability.

METHODS

We surveyed 13 academic tumor neurosurgeons nationwide to assess the resectability of newly diagnosed glioblastoma. Participants reviewed 20 cases, including digital imaging and communications in medicine-formatted pre- and postoperative magnetic resonance images and clinical vignettes. The selected cases involved a variety of anatomical locations and a range of EOR. Participants were asked about surgical goal, eg, gross total resection, subtotal resection (STR), or biopsy, and rationale for their decision. We calculated a "resectability index" for each lesion by pooling responses from all 13 surgeons.

RESULTS

Neurosurgeons' individual surgical goals varied significantly ( P = .015), but the resectability index calculated from the surgeons' pooled responses was strongly correlated with the percentage of contrast-enhancing residual tumor ( R = 0.817, P < .001). The collective STR goal predicted intraoperative decision of intentional STR documented on operative notes ( P < .01) and nonresectable residual ( P < .01), but not resectable residual.

CONCLUSION

In this pilot study, we demonstrate the feasibility of measuring the resectability of glioblastoma through crowdsourcing. This tool could be used to quantify resectability, a potential confounder in neuro-oncology clinical trials.

Survival in glioblastoma: a review on the impact of treatment modalities

Glioblastoma (GBM) is the most common and lethal tumor of the central nervous system. The natural history of treated GBM remains very poor with 5-year survival rates of 5 %. Survival has not significantly improved over the last decades. Currently, the best that can be offered is a modest 14-month overall median survival in patients undergoing maximum safe resection plus adjuvant chemoradiotherapy. Prognostic factors involved in survival include age, performance status, grade, specific markers (MGMT methylation, mutation of IDH1, IDH2 or TERT, 1p19q codeletion, overexpression of EGFR, etc.) and, likely, the extent of resection. Certain adjuncts to surgery, especially cortical mapping and 5-ALA fluorescence, favor higher rates of gross total resection with apparent positive impact on survival. Recurrent tumors can be offered re-intervention, participation in clinical trials, anti-angiogenic agent or local electric field therapy, without an evident impact on survival. Molecular-targeted therapies, immunotherapy and gene therapy are promising tools currently under research.

Low-grade Glioma Surgery in Intraoperative Magnetic Resonance Imaging

BACKGROUND:

The ideal treatment strategy for low-grade gliomas (LGGs) is a controversial topic. Additionally, only smaller single-center series dealing with the concept of intraoperative magnetic resonance imaging (iMRI) have been published.

OBJECTIVE:

To investigate determinants for patient outcome and progression-free-survival (PFS) after iMRI-guided surgery for LGGs in a multicenter retrospective study initiated by the German Study Group for Intraoperative Magnetic Resonance Imaging.

METHODS:

A retrospective consecutive assessment of patients treated for LGGs (World Health Organization grade II) with iMRI-guided resection at 6 neurosurgical centers was performed. Eloquent location, extent of resection, first-line adjuvant treatment, neurophysiological monitoring, awake brain surgery, intraoperative ultrasound, and field-strength of iMRI were analyzed, as well as progression-free survival (PFS), new permanent neurological deficits, and complications. Multivariate binary logistic and Cox regression models were calculated to evaluate determinants of PFS, gross total resection (GTR), and adjuvant treatment.

RESULTS:

A total of 288 patients met the inclusion criteria. On multivariate analysis, GTR significantly increased PFS (hazard ratio, 0.44; P &lt; .01), whereas “failed” GTR did not differ significantly from intended subtotal-resection. Combined radiochemotherapy as adjuvant therapy was a negative prognostic factor (hazard ratio: 2.84, P &lt; .01). Field strength of iMRI was not associated with PFS. In the binary logistic regression model, use of high-field iMRI (odds ratio: 0.51, P &lt; .01) was positively and eloquent location (odds ratio: 1.99, P &lt; .01) was negatively associated with GTR. GTR was not associated with increased rates of new permanent neurological deficits.

CONCLUSION:

GTR was an independent positive prognostic factor for PFS in LGG surgery. Patients with accidentally left tumor remnants showed a similar prognosis compared with patients harboring only partially resectable tumors. Use of high-field iMRI was significantly associated with GTR. However, the field strength of iMRI did not affect PFS.

Intraoperative Magnetic Resonance Imaging in Intracranial Glioma Resection: A Single-Center, Retrospective Blinded Volumetric Study

BACKGROUND

Intraoperative magnetic resonance imaging (IoMRI) was devised to overcome brain shifts during craniotomies. Yet, the acceptance of IoMRI is limited.

OBJECTIVE

To evaluate impact of IoMRI on intracranial glioma resection outcome including overall patient survival.

METHODS

A retrospective review of records was performed on a cohort of 164 consecutive patients who underwent resection surgery for newly diagnosed intracranial gliomas either with or without IoMRI technology performed by 2 neurosurgeons in our center. Patient follow-up was at least 5 years. Extent of resection (EOR) was calculated using pre- and postoperative contrast-enhanced and T2-weighted MR-images. Adjusted analysis was performed to compare gross total resection (GTR), EOR, permanent surgery-associated neurologic deficit, and overall survival between the 2 groups.

RESULTS

Overall median EOR was 92.1%, and 97.45% with IoMRI use and 89.9% without IoMRI, with crude (unadjusted) P < 0.005. GTR was achieved in 49.3% of IoMRI cases, versus in only 21.4% of no-IoMRI cases, P < 0.001. GTR achieved was more with the use of IoMRI among gliomas located in both eloquent and noneloquent brain areas, P = 0.017 and <0.001, respectively. Permanent surgery-associated neurologic deficit was not (statistically) more significant with no-IoMRI, P = 0.284 (13.8% vs. 6.7%). In addition, the IoMRI group had better 5-year overall survival, P < 0.001.

CONCLUSION

This study shows that the use of IoMRI was associated with greater rates of EOR and GTR, and better overall 5-year survival in both eloquent brain areas located and non-eloquent brain areas located gliomas, with no increased risk of neurologic complication.

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.

Neurosurgical oncology: advances in operative technologies and adjuncts

Modern glioma surgery has evolved around the central tenet of safely maximizing resection. Recent surgical adjuncts have focused on increasing the maximum extent of resection while minimizing risk to functional brain. Technologies such as cortical and subcortical stimulation mapping, intraoperative magnetic resonance imaging, functional neuronavigation, navigable intraoperative ultrasound, neuroendoscopy, and fluorescence-guided resection have been developed to augment the identification of tumor while preserving brain anatomy and function. However, whether these technologies offer additional long-term benefits to glioma patients remains to be determined. Here we review advances over the past decade in operative technologies that have offered the most promising benefits for glioblastoma patients.

Using intraoperative dynamic contrast-enhanced T1-weighted MRI to identify residual tumor in glioblastoma surgery

OBJECT

The goal of surgery in high-grade gliomas is to maximize the resection of contrast-enhancing tumor without causing additional neurological deficits. Intraoperative MRI improves surgical results. However, when using contrast material intraoperatively, it may be difficult to differentiate between surgically induced enhancement and residual tumor. The purpose of this study was to assess the usefulness of intraoperative dynamic contrast-enhanced T1-weighted MRI to guide this differential diagnosis and test it against tissue histopathology.

METHODS

Preoperative and intraoperative dynamic contrast-enhanced MRI was performed in 21 patients with histopathologically confirmed WHO Grade IV gliomas using intraoperative 3-T MRI. Standardized regions of interest (ROIs) were placed manually at 2 separate contrast-enhancing areas at the resection border for each patient. Time-intensity curves (TICs) were generated for each ROI. All ROIs were biopsied and the TIC types were compared with histopathological results. Pharmacokinetic modeling was performed in the last 10 patients to confirm nonparametric TIC analysis findings.

RESULTS

Of the 42 manually selected ROIs in 21 patients, 25 (59.5%) contained solid tumor tissue and 17 (40.5%) retained the brain parenchymal architecture but contained infiltrating tumor cells. Time-intensity curves generated from residual contrast-enhancing tumor and their preoperative counterparts were comparable and showed a quick and persistently increasing slope ("climbing type"). All 17 TICs obtained from regions that did not contain solid tumor tissue were undulating and low in amplitude, compared with those obtained from residual tumors ("low-amplitude type"). Pharmacokinetic findings using the transfer constant, extravascular extracellular volume fraction, rate constant, and initial area under the curve parameters were significantly different for the tumor mass, nontumoral regions, and surgically induced contrast-enhancing areas.

CONCLUSIONS

Intraoperative dynamic contrast-enhanced MRI provides quick, reproducible, high-quality, and simply interpreted dynamic MR images in the intraoperative setting and can aid in differentiating surgically induced enhancement from residual tumor.

Factors associated with a higher rate of distant failure after primary treatment for glioblastoma

Our purpose was to analyze the pattern of failure in glioblastoma (GBM) patients at first recurrence after radiotherapy and temozolomide and its relationship with different factors. From 77 consecutive GBM patients treated at our institution with fluorescence guided surgery and standard radiochemotherapy, 58 first recurrences were identified and included in a retrospective review. Clinical data including age, Karnofsky performance score, preoperative tumor volume and location, extend of resection, MGMT promoter methylation status, time to progression (PFS), overall survival (OS) and adjuvant therapies were reviewed for every patient. Recurrent tumor location respect the original lesion was the end point of the study. The recurrence pattern was local only in 65.5% of patients and non-local in 34.5%. The univariate and multivariate analysis showed that greater preoperative tumor volume in T1 gadolinium enhanced sequences, was the only variable with statistical signification (p < 0.001) for increased rate of non-local recurrences, although patients with MGMT methylation and complete resection of enhancing tumor presented non-local recurrences more frequently. PFS was longer in patients with non-local recurrences (13.8 vs. 6.4 months; p = 0.019, log-rank). However, OS was not significantly different in both groups (24.0 non-local vs. 19.3 local; p = 0.9). Rate of non-local recurrences in our series of patients treated with fluorescence guided surgery and standard radiochemotherapy was higher than previously published in GBM, especially in patients with longer PFS. Greater preoperative enhancing tumor volume was associated with increased rate of non-local recurrences.

High field strength magnetic resonance imaging in paediatric brain tumour surgery--its role in prevention of early repeat resections

PURPOSE

The purpose of this study is to compare the surgical and imaging outcome in children who underwent brain tumour surgery with intention of complete tumour resection, prior to and following the start of intra-operative MRI (ioMRI) service.

METHODS

ioMRI service for brain tumour resection commenced in October 2009. A cohort of patients operated between June 2007 and September 2009 with a pre-surgical intention of complete tumour resection were selected (Group A). A similar number of consecutive cases were selected from a prospective database of patients undergoing ioMRI (Group B). The demographics, imaging, pathology and surgical outcome of both groups were compared.

RESULTS

Thirty-six of 47 cases from Group A met the inclusion criterion and 36 cases were selected from Group B; 7 of the 36 cases in Group A had unequivocal evidence of residual tumour on the post-operative scan; 5 (14%) of them underwent repeat resection within 6 months post-surgery. In Group B, ioMRI revealed unequivocal evidence of residual tumour in 11 of the 36 cases following initial resection. In 10 of these 11 cases, repeat resections were performed during the same surgical episode and none of these 11 cases required repeat surgery in the following 6 months. Early repeat resection rate was significantly different between both groups (p = 0.003).

CONCLUSION

Following the advent of ioMRI at our institution, the need for repeat resection within 6 months has been prevented in cases where ioMRI revealed unequivocal evidence of residual tumour.

Usefulness of intraoperative computed tomography for the evacuation of lobar hemorrhage

There is a lot of debate on the treatment method for spontaneous intracerebral hemorrhage (ICH). Intraoperative computed tomography (iCT) provides excellent images of cerebrovascular lesions. In this paper, we describe the surgical procedure and the efficacy of iCT during lobar hemorrhage evacuations and subsequent patient outcomes. Fifty-eight patients with lobar hemorrhage were treated using iCT. We performed preoperative cerebral angiography and/or three-dimensional (3D) CT angiography to detect abnormal vessels and identify the spatial relationships between the cerebrovascular structures and the hematoma. After administration of local anesthesia, an enlarged burr-hole was created just above the hematoma. Microsurgical evacuation of the hematoma was performed, and an iCT image was obtained to assess real-time 3D information on residual hematoma or unexpected rebleeding. Mean hematoma volume, evacuation rate, and duration of the surgery were 42 mL, 93 %, and 89 min respectively. Postoperative rebleeding occurred in 1 case. The median Glasgow Coma Scale score upon admission was 12. At discharge, most patients (60 %) had good functional outcomes defined by modified Rankin Scale scores of 0-3. Postoperative neurological findings and consciousness levels showed early improvement. Safe, accurate, and effective evacuation of lobar hemorrhage was possible with iCT as an image-guided intraoperative navigation tool.

Use of preoperative 3D CT/MR fusion images and intraoperative CT to detect lesions that spread onto the brain surface

OBJECTIVE

Preoperative 3D CT/MR fusion images were prepared for preoperative evaluations and intraoperative assistance for the following lesions: arteriovenous -malformations (AVMs), meningiomas, and metastatic tumors that spread onto the brain surface.

METHOD

We prepared 3D CT/MR fusion images for 4 AVMs, 13 meningiomas, and 7 metastatic tumors, and demonstrate representative cases. Data acquired from 16-slice multidetector CT and 1.5-T MRI were used. The volume rendering technique was used. During operations, mobile 16-slice multidetector CT was used to update information.

RESULTS

Even after opening the dura mater, the relationship between a brain surface lesion and the surrounding structures on the preoperative 3D fusion images corresponded to the patient's operation field. Updated information via intraoperative CT was useful because operation fields might change owing to the brain shift. These images made extirpations of lesions easier and less invasive.

CONCLUSION

Not only the preoperative 3D information, but also intraoperative CT information are beneficial for smooth and safe operations.

Endoscopic removal of an intraventricular primitive neuroectodermal tumor: retrieval of a free-floating fragment using a urological basket retriever

The endoscopic resection of intraventricular tumors represents a unique challenge to the neurological surgeon. These neoplasms are invested deep within the brain parenchyma and are situated among neurologically vital structures. Additionally, the cerebrospinal fluid system presents a dynamic pathway for resected tumors to be mobilized and entrapped in other regions of the brain. In 2011, the authors treated a 3-year-old girl with a third ventricular mass identified on stereotactic brain biopsy as a WHO Grade IV CNS primitive neuroectodermal tumor. After successful neoadjuvant chemotherapy, endoscopic resection was performed. Despite successful resection of the tumor, the operation was complicated by mobilization of the resected tumor and entrapment in the atrial horn of the lateral ventricle. Using a urological stone basket retriever, the authors were able to retrieve the intact tumor without additional complications. The flexibility afforded by the nitinol urological stone basket was useful in the endoscopic removal of a free-floating intraventricular tumor. This device may prove to be useful for other practitioners performing these complicated intraventricular resections.

Application of low-field intraoperative magnetic resonance imaging in transsphenoidal surgery for pituitary adenomas: technical points to improve the visibility of the tumor resection margin

BACKGROUND

Intraoperative magnetic resonance imaging (iMRI) is proven to be advantageous in transsphenoidal surgery (TSS) for pituitary adenomas. We evaluated the efficacy of low-field iMRI. Also, we described several techniques to enhance the visibility of the tumor resection margin.

METHODS

Two hundred twenty-nine patients who underwent TSS using low-field iMRI were analyzed. iMRI was acquired in cases where the tumor removal was thought to meet the surgical goal after the tumor resection cavity had been packed with contrast-soaked cotton pledgets to improve the visibility of the tumor resection margin. Suspicious remnants were localized and explored using updated iMRI-based semi-real-time navigation. A merging technique was adopted for very small tumors. The final outcome was evaluated using postoperative 3-T diagnostic magnetic resonance imaging (MRI).

RESULTS

Among 198 patients in whom total resection was attempted, total resection seemed to have been achieved in 184 patients based on iMRI findings. However, immediate postoperative MRI revealed remnant tumors in 4 out of 184 patients (false-negative rate, 2.2 %). The other 31 patients underwent intended subtotal resection of the tumors. Overall, in 47 patients (20.5 %), the use of iMRI led to further resection. Those patients benefited from the use of iMRI to achieve the planned extent of tumor resection.

CONCLUSIONS

iMRI maximizes the extent of resection and minimizes the possibility of unexpected tumor remnants in TSS for pituitary adenomas. It is essential to reduce imaging artifacts and enhance the visibility of the tumor resection margin during the use of low-field iMRI.

The role of intraoperative magnetic resonance imaging in complex meningioma surgery

Intraoperative magnetic resonance imaging (iMRI) has gained importance in the treatment of gliomas and sellar tumors. In intracranial meningiomas, the extent of surgical tumor removal is one of the most important factors in the prevention of tumor recurrence and patient survival. Complex meningiomas located at the skull base or near eloquent brain regions show higher recurrence rates, morbidity and mortality. The aim of this study was to evaluate whether iMRI contributes to more extensive surgical resection in these tumors. Patients undergoing complex meningioma resection using iMRI from January 2007 to January 2011 were included in this study. The indication for iMRI-guided tumor resection included patients presenting with meningiomas located in the skull base or compressing eloquent brain areas in whom a radical resection was considered to be difficult. Intraoperative 0.15-T MRI scan (PoleStar; Medtronic Navigation, Louisville, CO, USA) was performed before and after maximal possible resection using standard microsurgical and neuronavigation techniques. All patients underwent fluorescence-guided resection. The following data were analyzed: tumor localization, histological grade, Simpson resection grade, duration of the procedure, iMRI scan time, iMRI findings, resection extent based on postresection iMRI, hospitalization time, surgical complications and outcome, and MRI follow-up 2-27months postoperation. Twenty-seven consecutive patients undergoing complex meningioma resection using iMRI were included. In this series, only one patient (3.4%) underwent resection of tumor remnant after iMRI, although without improvement of the Simpson resection grade. Temporary neurologic deficits were found in 8 patients (27.6%) postoperatively, whereas 11 patients (37.9%) had permanent postoperative neurologic deficits. In one case (3.4%), fatal postoperative bleeding occurred which was not detected by iMRI. Our results show that iMRI has no influence on intraoperative strategy in terms of resection grade or detection of early postoperative complications. The benefits of iMRI in complex meningioma surgery are therefore doubtful; however, it may still prove to be effective in certain subsets of complex meningiomas.

Intraoperative magnetic resonance spectroscopy for identification of residual tumor during low-grade glioma surgery: clinical article

OBJECT

The authors had previously shown that 3-T intraoperative MRI (ioMRI) detects residual tumor tissue during low-grade glioma and that it helps to increase the extent of resection. In a proportion of their cases, however, the ioMRI disclosed T2-hyperintense areas at the tumor resection border after the initial resection attempt and prompted a differential diagnosis between residual tumor and nontumoral changes. To guide this differential diagnosis the authors used intraoperative long-TE single-voxel proton MR spectroscopy (ioMRS) and tested the correlation of these findings with findings from pathological examination of resected tissue.

METHODS

Patients who were undergoing surgery for hemispheric or insular WHO Grade II gliomas and were found to have T2 changes around the resection cavity at the initial ioMRI were prospectively examined with ioMRS and biopsies were taken from corresponding localizations. In 14 consecutive patients, the ioMRS diagnosis in 20 voxels of interest was tested against the histopathological diagnosis. Intraoperative diffusion-weighted imaging (ioDWI) was also performed, as a part of the routine imaging, to rule out surgically induced changes, which could also appear as T2 hyperintensity.

RESULTS

Presence of tumor was documented in 14 (70%) of the 20 T2-hyperintense areas by histopathological examination. The sensitivity of ioMRS for identifying residual tumor was 85.7%, the specificity was 100%, the positive predictive value was 100%, and the negative predictive value was 75%. The specificity of ioDWI for surgically induced changes was high (100%), but the sensitivity was only 60%.

CONCLUSIONS

This is the first clinical series to indicate that ioMRS can be used to differentiate residual tumor from nontumoral changes around the resection cavity, with high sensitivity and specificity.

[First intraoperative magnetic resonance imaging in a Spanish hospital of the public healthcare system: initial experience, feasibility and difficulties in our environment]

OBJECTIVE

Intraoperative MRI is considered the gold standard among all intraoperative imaging technologies currently available. Its main indication is in the intraoperative detection of residual disease during tumour resections. We present our initial experience with the first intraoperative low-field MRI in a Spanish hospital of the public healthcare system. We evaluate its usefulness and accuracy to detect residual tumours and compare its intraoperative results with images obtained postoperatively using conventional high-field devices.

MATERIAL AND METHODS

We retrospectively reviewed the first 21 patients operated on the aid of this technology. Maximal safe resection was the surgical goal in all cases. Surgeries were performed using conventional instrumentation and the required assistance in each case.

RESULTS

The mean number of intraoperative studies was 2.3 per procedure (range: 2 to 4). Intraoperative studies proved that the surgical goal had been achieved in 15 patients (71.4%), and detected residual tumour in 6 cases (28.5%). After comparing the last intraoperative image and the postoperative study, 2 cases (9.5%) were considered as "false negatives".

CONCLUSIONS

Intraoperative MRI is a safe, reliable and useful tool for guided resection of brain tumours. Low-field devices provide images of sufficient quality at a lower cost; therefore their universalisation seems feasible.

The role of intraoperative magnetic resonance imaging in glioma surgery

For patients with gliomas, the goal of surgery is to maximize the extent of tumor resection while avoiding injury to functional tissue. The hope is to improve patients' survival and maintain the highest quality of life as possible. However, because of the infiltrative nature of gliomas these two goals often oppose each other so a compromise must be met. Many tools have been developed to help with this challenge of glioma surgery. Over the past two decades, intraoperative-magnetic resonance imaging (iMRI) has emerged as an increasingly important modality to enhance surgical safety while providing the surgeon with updated information to guide their resection. Here the authors review the studies that demonstrate a positive correlation between extent of resection (EOR) and overall survival (OS), although the data is clearer in patients with low-grade gliomas (LGG) and still somewhat controversial in those with higher-grade tumors. We will then review some of the studies that support the role of iMRI and how it has impacted glioma surgery by increasing the EOR. The value of iMRI usage in regards to overall patient outcome can be extrapolated through its effect on EOR. Overall, available data support the safe use of iMRI and as an effective adjunct in glioma surgery.

Fluorescence Lifetime Spectroscopy and Imaging in Neurosurgery

Clinical outcome of patients diagnosed with primary brain tumor has been correlated with the extent of surgical resection. In treating this disease, the neurosurgeon must balance between an aggressive, radical resection and minimizing the loss of healthy, functionally significant brain tissue. Numerous intra-operative methodologies and technological approaches have been explored as a means to improve the accuracy of surgical resection. This paper presents an overview of current conventional techniques and new emerging technologies with potential to impact the area of image-guided surgery of brain tumors. Emphasis is placed on techniques based on endogenous fluorescence lifetime contrast and their potential for intraoperative diagnosis of brain tumors.

Intraoperative image guidance in neurosurgery: development, current indications, and future trends

Introduction. As minimally invasive surgery becomes the standard of care in neurosurgery, it is imperative that surgeons become skilled in the use of image-guided techniques. The development of image-guided neurosurgery represents a substantial improvement in the microsurgical treatment of tumors, vascular malformations, and other intracranial lesions. Objective. There have been numerous advances in neurosurgery which have aided the neurosurgeon to achieve accurate removal of pathological tissue with minimal disruption of surrounding healthy neuronal matter including the development of microsurgical, endoscopic, and endovascular techniques. Neuronavigation systems and intraoperative imaging should improve success in cranial neurosurgery. Additional functional imaging modalities such as PET, SPECT, DTI (for fiber tracking), and fMRI can now be used in order to reduce neurological deficits resulting from surgery; however the positive long-term effect remains questionable for many indications. Method. PubMed database search using the search term "image guided neurosurgery." More than 1400 articles were published during the last 25 years. The abstracts were scanned for prospective comparative trials. Results and Conclusion. 14 comparative trials are published. To date significant data amount show advantages in intraoperative accuracy influencing the perioperative morbidity and long-term outcome only for cerebral glioma surgery.

Optimizing the extent of resection in eloquently located gliomas by combining intraoperative MRI guidance with intraoperative neurophysiological monitoring

Several methods have been introduced to improve the extent of resection in glioma surgery. Yet, radical tumor resections must not be attempted at the cost of neurological deterioration. We sought to assess whether the use of an intraoperative MRI (iMRI) in combination with multimodal neurophysiological monitoring is suitable to increase the extent of resection without endangering neurological function in patients with eloquently located gliomas. Fifty-four patients were included in this study. In 21 patients (38.9 %), iMRI led to additional tumor resection. A radiologically complete resection was achieved in 31 patients (57.4 %), while in 12 of these, iMRI had depicted residual tumor tissue before resection was continued. The mean extent of resection was 92.1 % according to volumetric analyses. Postoperatively, 13 patients (24.1 %) showed new or worsening of pre-existing sensory motor deficits. They were severe in 4 patients (7.4 %). There was no correlation between the occurrence of either any new (P = 0.77) or severe (P = 1.0) sensory motor deficit and continued resection after intraoperative image acquisition. Likewise, tumor location, histology, and tumor recurrence did not influence complication rate on uni- and multivariate analysis. We conclude that the combination of iMRI guidance with multimodal neurophysiological monitoring allows for extended resections in glioma surgery without inducing higher rates of neurological deficits, even in patients with eloquently located tumors.

Prospective study on the efficacy of low-field intraoperative magnetic resonance imaging in neurosurgical operations

BACKGROUND AND PURPOSE

The application of intraoperative magnetic resonance imaging (iMRI) is related to a series of challenges of both a technical and an organizational nature. We present our experience in the application of low-field iMRI in everyday neurosurgical practice.

MATERIAL AND METHODS

A group of 58 patients operated on using low-field iMRI was subject to prospective controlled observation. The significance of differences in the range of preparation time, duration and direct operation results between the iMRI group and controls was analysed. The influence of epidemiological and demographic factors and technical aspects related to iMRI application on direct outcome of the surgery was assessed.

RESULTS

Twenty-eight tumour resections using craniotomy, 17 transsphenoidal resections of pituitary adenomas and 13 stereotactic procedures were conducted in the group of 24 men and 34 women operated on using iMRI. The control group was not significantly different in terms of epidemiological and demographic factors. The preparation and operation times were significantly longer in the iMRI group (p < 0.001 and p = 0.002, respectively). Longer duration of the surgery was not related to an increased frequency of complications. A higher percentage of postoperative improvement in neurological status (31% vs. 14%, p = 0.045), lower complication percentage (10% vs. 28%, p = 0.03) and a similar time of hospitalization (13 ± 7 vs. 12 ± 4 days, p = 0.33) were noted in the iMRI group.

CONCLUSIONS

The application of low-field iMRI prolongs the duration of neurosurgical procedures but does not negatively influence their safety. It is associated with above-average functional results and a lower percentage of total complications.

Intraoperative MRI guidance and extent of resection in glioma surgery: a randomised, controlled trial

BACKGROUND

Intraoperative MRI is increasingly used in neurosurgery, although there is little evidence for its use. We aimed to assess efficacy of intraoperative MRI guidance on extent of resection in patients with glioma.

METHODS

In our prospective, randomised, parallel-group trial, we enrolled adults (≥18 years) with contrast enhancing gliomas amenable to radiologically complete resection who presented to Goethe University (Frankfurt, Germany). We randomly assigned patients (1:1) with computer-generated blocks of four and a sealed-envelope design to undergo intraoperative MRI-guided surgery or conventional microsurgery (control group). Surgeons and patients were unmasked to treatment group allocation, but an independent neuroradiologist was masked during analysis of all preoperative and postoperative imaging data. The primary endpoint was rate of complete resections as established by early postoperative high-field MRI (1·5 T or 3·0 T). Analysis was done per protocol. This study is registered with ClinicalTrials.gov, number NCT01394692.

FINDINGS

We enrolled 58 patients between Oct 1, 2007, and July 1, 2010. 24 (83%) of 29 patients randomly allocated to the intraoperative MRI group and 25 (86%) of 29 controls were eligible for analysis (four patients in each group had metastasis and one patient in the intraoperative MRI group withdrew consent after randomisation). More patients in the intraoperative MRI group had complete tumour resection (23 [96%] of 24 patients) than did in the control group (17 [68%] of 25, p=0·023). Postoperative rates of new neurological deficits did not differ between patients in the intraoperative MRI group (three [13%] of 24) and controls (two [8%] of 25, p=1·0). No patient for whom use of intraoperative MRI led to continued resection of residual tumour had neurological deterioration. One patient in the control group died before 6 months.

INTERPRETATION

Our study provides evidence for the use of intraoperative MRI guidance in glioma surgery: such imaging helps surgeons provide the optimum extent of resection.

FUNDING

None.

Clinical and economic outcomes of low-field intraoperative MRI-guided tumor resection neurosurgery

PURPOSE

To compare low-field (0.15 T) intraoperative magnetic resonance imaging (iMRI)-guided tumor resection with both conventional magnetic resonance imaging (cMRI)-guided tumor resection and high-field (1.5 T) iMRI-guided resection from the clinical and economic point of view.

MATERIALS AND METHODS

We retrospectively compared 65 iMRI patients with 65 cMRI patients in terms of hospital length of stay, repeat resection rate, repeat resection interval, complication rate, cost to the patient, cost to the hospital, and cost effectiveness. In addition, we compared our low-field results with previously published high-field results.

RESULTS

The complication rate was lower for iMRI vs. cMRI in patients presenting for their initial tumor resection (45 vs. 57 complications, P = 0.048). The iMRI repeat resection interval was longer for this cohort (20.1 vs. 6.7 months, P = 0.020). iMRI was more cost-effective than cMRI for patients who had repeat resections ($10,690/RFY vs. $76,874/RFY, P < 0.001). We found no other clinical or economic differences between iMRI- and cMRI-guided tumor resection surgeries. Overall, we did not find the advantages to low-field iMRI that have been reported for high-field iMRI.

CONCLUSION

There is no adequate justification for the widespread installation of low-field iMRI in its current development state.

Intraoperative MRI-guided resection of glioblastoma multiforme: a systematic review

We did a systematic review to address the added value of intraoperative MRI (iMRI)-guided resection of glioblastoma multiforme compared with conventional neuronavigation-guided resection, with respect to extent of tumour resection (EOTR), quality of life, and survival. 12 non-randomised cohort studies matched all selection criteria and were used for qualitative synthesis. Most of the studies included descriptive statistics of patient populations of mixed pathology, and iMRI systems of varying field strengths between 0·15 and 1·5 Tesla. Most studies provided information on EOTR, but did not always mention how iMRI affected the surgical strategy. Only a few studies included information on quality of life or survival for subpopulations with glioblastoma multiforme or high-grade glioma. Several limitations and sources of bias were apparent, which affected the conclusions drawn and might have led to overestimation of the added value of iMRI-guided surgery for resection of glioblastoma multiforme. Based on the available literature, there is, at best, level 2 evidence that iMRI-guided surgery is more effective than conventional neuronavigation-guided surgery in increasing EOTR, enhancing quality of life, or prolonging survival after resection of glioblastoma multiforme.

Intraoperative confocal microscopy in the visualization of 5-aminolevulinic acid fluorescence in low-grade gliomas

OBJECT

Greater extent of resection (EOR) for patients with low-grade glioma (LGG) corresponds with improved clinical outcome, yet remains a central challenge to the neurosurgical oncologist. Although 5-aminolevulinic acid (5-ALA)-induced tumor fluorescence is a strategy that can improve EOR in gliomas, only glioblastomas routinely fluoresce following 5-ALA administration. Intraoperative confocal microscopy adapts conventional confocal technology to a handheld probe that provides real-time fluorescent imaging at up to 1000× magnification. The authors report a combined approach in which intraoperative confocal microscopy is used to visualize 5-ALA tumor fluorescence in LGGs during the course of microsurgical resection.

METHODS

Following 5-ALA administration, patients with newly diagnosed LGG underwent microsurgical resection. Intraoperative confocal microscopy was conducted at the following points: 1) initial encounter with the tumor; 2) the midpoint of tumor resection; and 3) the presumed brain-tumor interface. Histopathological analysis of these sites correlated tumor infiltration with intraoperative cellular tumor fluorescence.

RESULTS

Ten consecutive patients with WHO Grades I and II gliomas underwent microsurgical resection with 5-ALA and intraoperative confocal microscopy. Macroscopic tumor fluorescence was not evident in any patient. However, in each case, intraoperative confocal microscopy identified tumor fluorescence at a cellular level, a finding that corresponded to tumor infiltration on matched histological analyses.

CONCLUSIONS

Intraoperative confocal microscopy can visualize cellular 5-ALA-induced tumor fluorescence within LGGs and at the brain-tumor interface. To assess the clinical value of 5-ALA for high-grade gliomas in conjunction with neuronavigation, and for LGGs in combination with intraoperative confocal microscopy and neuronavigation, a Phase IIIa randomized placebo-controlled trial (BALANCE) is underway at the authors' institution.

Special surgical considerations for functional brain mapping

The development of functional mapping techniques gives neurosurgeons many options for preoperative planning. Integrating functional and anatomic data can inform patient selection and surgical planning and makes functional mapping more accessible than when only invasive studies were available. However, the applications of functional mapping to neurosurgical patients are still evolving. Functional imaging remains complex and requires an understanding of the underlying physiologic and imaging characteristics. Neurosurgeons must be accustomed to interpreting highly processed data. Successful implementation of functional image-guided procedures requires efficient interactions between neurosurgeon, neurologist, radiologist, neuropsychologist, and others, but promises to enhance the care of patients.

Lows and highs: 15 years of development in intraoperative magnetic resonance imaging

Intraoperative magnetic resonance imaging (ioMRI) during neurosurgical procedures was first implemented in 1995. In the following decade ioMRI and image guided surgery has evolved from an experimental stage into a safe and routinely clinically applied technique. The development of ioMRI has led to a variety of differently designed systems which can be basically classified in one- or two-room concepts and low- and high-field installations. Nowadays ioMRI allows neurosurgeons not only to increase the extent of tumor resection and to preserve eloquent areas or white matter tracts but it also provides physiological and biological data of the brain and tumor tissue. This article tries to give a comprehensive review of the milestones in the development of ioMRI and neuronavigation over the last 15 years and describes the personal experience in intraoperative low and high-field MRI.

Impact of a low-field intraoperative MRI on the surgical results for high-grade gliomas

In this study the authors retrospectively evaluated the results of the operated intracranial high grade gliomas using low field intraoperative MRI system Polestar N 20+Stealth Station (Medtronic, Co, USA) at German Hospital, Istanbul. Between November 2006 and October 2008, 11 patients underwent microsurgical tumor resection with the use of intraoperative MRI for WHO Grade III and IV gliomas. There were six males and five females, mean age was 53 (range 30-73), and mean follow-up duration was 19 months (range 4-31). Ten total, one subtotal resection was achieved, whereas intraoperative MRI assessment demonstrated five residual tumors. Histopathological examination revealed that eight tumors were glioblastomas and three were anaplastic oligodendroglioma, anaplastic oligoastrocytoma and anaplastic ependymoma respectively. No complications directly related to the intraoperative scanning were observed and there was no mortality, but one patient with an insular tumor developed hemiparesis after the operation. Mean hospital stay was 4.8 day. Ten patients received additional radiotherapy and chemotherapy, one patient refused further therapy. Mean survival was 18.8 months for the entire group and 15.6 months for glioblastoma patients. In this small series of patients with high grade gliomas we found that the use of intraoperative MRI helps complete tumor removal and hence improves survival.