Intracranial navigation by using low-field intraoperative magnetic resonance imaging: preliminary experience

Comparison meta-analysis of intraoperative MRI-guided needle biopsy versus conventional stereotactic needle biopsies

Background

MRI-guided needle biopsy (INB) is an emerging alternative to conventional frame-based or frameless stereotactic needle biopsy (SNB). Studies of INB have been limited to select case series, and comparative studies between INB and SNB remain a missing gap in the literature. We performed a meta-analysis to compare INB and SNB literature in terms of diagnostic yield, surgical morbidity and mortality, tumor size, and procedural time.

Methods

We identified 36 separate cohorts in 26 studies of SNB (including both frameless and frame-based biopsies, 3374 patients) and 27 studies of INB (977 patients). Meta-regression and meta-analysis by proportions were performed.

Results

Relative to publications that studied SNB, publications studying INB more likely involved brain tumors located in the eloquent cerebrum (79.4% versus 62.6%, P = 0.004) or are smaller in maximal diameter (2.7 cm in INB group versus 3.6 cm in the SNB group, P = .032). Despite these differences, the pooled estimate of diagnostic yield for INB was higher than SNB (95.4% versus 92.3%, P = .026). The pooled estimate of surgical morbidity was higher in the SNB group (12.0%) relative to the INB group (6.1%) (P = .004). Mortality after the procedure was comparable between INB and SNB (1.7% versus 2.3%, P = .288). Procedural time was statistically comparable at 90.3 min (INB) and 103.7 min (SNB), respectively (P = .526).

Conclusions

Our meta-analysis indicates that, relative to SNB, INB is more often performed for the challenging, smaller-sized brain tumors located in the eloquent cerebrum. INB is associated with lower surgical morbidity and improved diagnostic yield.

iMRI During Transsphenoidal Surgery

A variety of intraoperative MRI (iMRI) systems are in use during transsphenoidal surgery (TSS). The variations in iMRI systems include field strengths, magnet configurations, and room configurations. Most studies report that the primary utility of iMRI during TSS lies in detecting resectable tumor residuals following maximal resection with conventional technique. Stereotaxis, neuronavigation, and complication avoidance/detection are enhanced by iMRI use during TSS. The use of iMRI during TSS can lead to increased extent of resection for large tumors. Improved remission rates from hormone-secreting tumors have also been reported with iMRI use. This article discusses the history, indications, and future directions for iMRI during TSS.

Neuronavigation-guided endoscopy for intraventricular tumors in adult patients without hydrocephalus

Introduction

Intraventricular endoscopic operations are usually undertaken in patients with an enlarged ventricular system that provides good access to the ventricles, proper anatomic orientation and safety of maneuvers within the ventricles.

Aim

The preliminary assessment of the feasibility of endoscopic procedures in cases occurring without hydrocephalus.

Material and methods

Eleven patients with intraventricular tumor diagnosed in neuroimaging studies were included in the study. None of these cases was accompanied by hydrocephalus. Surgery was performed with a rigid neuroendoscope using a neuronavigation system. The purpose of the operation was tumor removal or histological verification.

Results

The colloid cyst of the third ventricle was removed in 5 patients. In 1 patient a glial-derived tumor adjacent to the interventricular foramen was partially resected. In 1 case a tumor of the lateral ventricle was totally removed, and in another case the resection of such a tumor was partial. In 2 cases, a biopsy of the tumor of the posterior portion of the third ventricle was undertaken, while in 1 case the biopsy was abandoned due to the risk of injury of structures surrounding interventricular foramen. There were no intraoperative or postoperative complications. None of the patients developed hydrocephalus in the long-term follow-up. The results of treatment in the study group did not differ from those obtained in patients operated on with hydrocephalus.

Conclusions

The presence of hydrocephalus is not necessary to perform endoscopic surgery. However, in each case it should be preceded by a thorough analysis of the feasibility of the endoscopic procedure and should be supported by a neuronavigation system.

Intraoperative low-field MR-guided frameless stereotactic biopsy for intracerebral lesions

BACKGROUND

To present our intraoperative low-field magnetic resonance imaging (ioMRI) technique for stereotactic brain biopsy in various intracerebral lesions.

METHOD

Seventy-eight consecutive patients underwent stereotactic biopsies with the PoleStar N-20/N-30 ioMRI system and data were evaluated retrospectively. Biopsy technique included ioMRI before surgery, followed by insertion of the biopsy cannula in the lesion, and ioMRI before and after biopsy. Statistical analysis was performed to compare subgroups using Excel and SPSS statistic software.

RESULTS

In all patients, stereotactic biopsy was possible, with a mean intraoperative surgery time of 86.2 ± 28.6 min and a mean hospital stay of 11.6 ± 4.6 days. In 97.4 % (n = 76), histology was conclusive, representing 58 brain tumors and 18 other pathologies. Five patients were biopsied previously without conclusive diagnosis, and all biopsies were conclusive this time. Mean cross-sectional lesion size in MRI T1 with contrast (n = 64) was 6.9 ± 5.7 cm(2), and in lesions without T1 contrast enhancement (n = 14), T2 mean cross-sectional lesion size was 5.5 ± 3.9 cm(2). Mean distance from the cortex surface to the lesion was 3.4 ± 1.2 cm. One patient suffered from a postoperative wound dehiscence; neither clinically or radiologically significant hemorrhage after surgery, nor intraoperative complications occurred.

CONCLUSIONS

Low-field ioMR-guided frameless stereotactic biopsy accurately diagnosed different intracerebral lesions without major complications for the patients, and within an acceptable surgery time and hospital stay. In repeated non-conclusive biopsies in particular, low-field ioMRI offers a technique for arriving at a diagnosis.

Recent advances in pituitary tumor management

PURPOSE OF REVIEW

Advances in the neurosurgical management of pituitary tumors have included the refinement of surgical access and significant progress in navigation technology to help further reduce morbidity and improve outcome. Similarly, stereotactic radiosurgery has evolved to become an integral part in pituitary tumors not amenable to medical or surgical treatment.

RECENT FINDINGS

The evolution of minimally invasive surgery has evolved toward endoscopic versus microscopic trans-sphenoidal approaches for pituitary tumors. Debate exists regarding each approach, with advocates for both championing their cause. Stereotactic and fractional radiosurgery have been shown to be a safe and effective means of controlling tumor growth and ensuring hormonal stabilization, with longer-term data available for GammaKnife compared with CyberKnife.

SUMMARY

The advances in trans-sphenoidal surgical approaches, navigation technological improvements and the current results of stereotactic radiosurgery are discussed.

Stereotactic brain biopsy with a low-field intraoperative magnetic resonance imager

BACKGROUND

Techniques for stereotactic brain biopsy have evolved in parallel with the imaging modalities used to visualize the brain.

OBJECTIVE

To describe our technique for performing stereotactic brain biopsy using a compact, low-field, intraoperative magnetic resonance imager (iMRI).

METHODS

Thirty-three patients underwent stereotactic brain biopsies with the PoleStar N-20 iMRI system (Medtronic Navigation, Louisville, Colorado). Preoperative iMRI scans were obtained for biopsy target identification and trajectory planning. A skull-mounted device (Navigus, Medtronic Navigation) was used to guide an MRI-compatible cannula to the target. An intraoperative image was acquired to confirm accurate cannula placement within the lesion. Serial images were obtained to track cannula movement and to rule out hemorrhage. Frozen sections were obtained in all but 1 patient with a brain abscess.

RESULTS

Diagnostic tissue was obtained in 32 of 33 patients. In all cases, imaging demonstrated cannula placement within the lesion. Histological diagnoses included 22 primary brain tumors and 10 nonneoplastic lesions. In 61% of the cases, initial trajectory was corrected on the basis of the intraoperative scans. In 1 patient, biopsy was nondiagnostic despite accurate cannula placement. No patient suffered a clinically or radiographically significant hemorrhage during or after surgery. There were no intraoperative complications.

CONCLUSION

Stereotactic biopsy with a low-field iMRI is an accurate way to obtain specimens with a high diagnostic yield. This accuracy, combined with the acceptable additional procedural time, may obviate the need for frozen section. The ability to correct biopsy cannula placement during surgery eliminates the chance of misdiagnosis because of faulty targeting, as well as the risks associated with inconclusive frozen sections and "blind" replacement of the cannula.

Dual-room 1.5-T intraoperative magnetic resonance imaging suite with a movable magnet: implementation and preliminary experience

We hereby report our initial clinical experience of a dual-room intraoperative magnetic resonance imaging (iMRI) suite with a movable 1.5-T magnet for both neurosurgical and independent diagnostic uses. The findings from the first 45 patients who underwent scheduled neurosurgical procedures with iMRI in this suite (mean age, 41.3 ± 12.0 years; intracranial tumors, 39 patients; cerebral vascular lesions, 5 patients; epilepsy surgery, 1 patient) were reported. The extent of resection depicted at intraoperative imaging, the surgical consequences of iMRI, and the clinical practicability of the suite were analyzed. Fourteen resections with a trans-sphenoidal/transoral approach and 31 craniotomies were performed. Eighty-two iMRI examinations were performed in the operating room, while during the same period of time, 430 diagnostic scans were finished in the diagnostic room. In 22 (48.9%) of 45 patients, iMRI revealed accessible residual tumors leading to further resection. No iMRI-related adverse event occurred. Complete lesion removal was achieved in 36 (80%) of all 45 cases. It is concluded that the dual-room 1.5-T iMRI suite can be successfully integrated into standard neurosurgical workflow. The layout of the dual-room suite can enable the maximum use of the system and save costs by sharing use of the 1.5-T magnet between neurosurgical and diagnostic use. Intraoperative MR imaging may provide valuable information that allows intraoperative modification of the surgical strategy.

Implementation of the ultra low field intraoperative MRI PoleStar N20 during resection control of pituitary adenomas

OBJECTIVE

To describe our experience with the application of an intraoperative ultra low field magnetic resonance imaging system (ioMRI) PoleStar N20, Medtronic Surgical Navigation Technologies, Louisville, USA during resection control of pituitary adenomas.

METHODS

Forty-four patients were operated on a pituitary adenoma (1 microadenoma, 43 macroadenomas; mean size 26.0 ± 9.7 mm). The ioMRI system was used for navigation and resection control after transseptal, transsphenoidal microsurgical tumour removal using standard instruments and standard microscope. If any accessible tumour remnant was suspected surgery was continued for navigation guided re-exploration and if necessary continued resection.

RESULTS

The applications of the scanner integrated navigation system, with a 3-planar reconstruction of the coronal scan, enabled the surgeon to safely approach and remove the tumour. The quality of preoperative tumour visualization with the ultra low field ioMRI in patients with macroadenomas is very good and has a good congruency with the preoperative 1.5 T MRI. For microadenomas the preoperative visualization is poor and very difficult to interpret. In seven patients ioMRI resection control showed residual tumours leading to further resection. After final tumour resection the ioMRI scan documented adequate decompression of the optic pathway in all patients. However, the intraoperative image interpretation was equivocal in four patients in whom it was difficult to distinguish between small intrasellar tumour remnants and perioperative changes.

CONCLUSIONS

The PoleStar N20 is a safe, helpful and feasible tool for navigation guided pituitary tumour approach. Image interpretation is requires some experience, but decompression of the optic system can be reliable shown in cases with pituitary macroadenomas. This system is of limited value for resection control of pituitary microadenomas.

Intraoperative MRI for stereotactic biopsy

This work aims at demonstrating the value of intraoperative magnetic resonance imaging (ioMRI) as a routine tool for stereotactic brain biopsy. Biopsies were done using the PoleStar N-20 ioMRI (Medtronic Navigation, Louisville, Colorado, USA) under general anesthesia. Images were acquired after patient positioning and after insertion of an MRI-compatible biopsy cannula. A Navigus guide (Medtronic Navigation) was used to align and direct the cannula. Retargeting was done as necessary, to improve placement within the target and to avoid critical structures, using the system's integrated infrared navigation tool. Cannula placement was tracked using serial images. ioMRI-guided biopsy was done in 39 patients, of whom 28 had neoplasms and 11 had non-neoplastic conditions. Additional OR time related to the use of ioMRI (including positioning of the patient and magnet, and imaging acquisition) averaged 1.1h. In 53% of the surgeries the biopsy cannula was repositioned based on intraoperative imaging. A histologic diagnosis was obtained in all but one patient, with ioMRI confirming proper cannula placement in all cases. There were no significant hemorrhages on clinical or imaging grounds nor any other complications. IoMRI can be routinely used for stereotactic biopsy in a regular neurosurgical operating environment. While general anesthesia is used and there is some additional time incurred from this technology the improved diagnostic yield and ability to avoid complications make ioMRI an ideal technical adjunct for brain biopsy.

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.

Subthalamic nucleus deep brain stimulator placement using high-field interventional magnetic resonance imaging and a skull-mounted aiming device: technique and application accuracy

OBJECT

The authors discuss their method for placement of deep brain stimulation (DBS) electrodes using interventional MR (iMR) imaging and report on the accuracy of the technique, its initial clinical efficacy, and associated complications in a consecutive series of subthalamic nucleus (STN) DBS implants to treat Parkinson disease (PD).

METHODS

A skull-mounted aiming device (Medtronic NexFrame) was used in conjunction with real-time MR imaging (Philips Intera 1.5T). Preoperative imaging, DBS implantation, and postimplantation MR imaging were integrated into a single procedure performed with the patient in a state of general anesthesia. Accuracy of implantation was assessed using 2 types of measurements: the "radial error," defined as the scalar distance between the location of the intended target and the actual location of the guidance sheath in the axial plane 4 mm inferior to the commissures, and the "tip error," defined as the vector distance between the expected anterior commissure-posterior commissure (AC-PC) coordinates of the permanent DBS lead tip and the actual AC-PC coordinates of the lead tip. Clinical outcome was assessed using the Unified Parkinson's Disease Rating Scale part III (UPDRS III), in the off-medication state.

RESULTS

Twenty-nine patients with PD underwent iMR imaging-guided placement of 53 DBS electrodes into the STN. The mean (+/- SD) radial error was 1.2 +/- 0.65 mm, and the mean absolute tip error was 2.2 +/- 0.92 mm. The tip error was significantly smaller than for STN DBS electrodes implanted using traditional frame-based stereotaxy (3.1 +/- 1.41 mm). Eighty-seven percent of leads were placed with a single brain penetration. No hematomas were visible on MR images. Two device infections occurred early in the series. In bilaterally implanted patients, the mean improvement on the UPDRS III at 9 months postimplantation was 60%.

CONCLUSIONS

The authors' technical approach to placement of DBS electrodes adapts the procedure to a standard configuration 1.5-T diagnostic MR imaging scanner in a radiology suite. This method simplifies DBS implantation by eliminating the use of the traditional stereotactic frame and the subsequent requirement for registration of the brain in stereotactic space and the need for physiological recording and patient cooperation. This method has improved accuracy compared with that of anatomical guidance using standard frame-based stereotaxy in conjunction with preoperative MR imaging.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

Software requirements for interventional MR in restorative and functional neurosurgery

Interventional MRI (iMRI) holds great promise for optimally guiding and monitoring restorative and functional neurosurgical procedures. This technology has already been used to guide ablative therapies and insert deep brain stimulation electrodes, and many future applications are envisioned. An optimized software interface is crucial for efficiently integrating the imaging data acquired during these procedures. MR systems are largely dedicated to image prescription and acquisition, whereas neuronavigation systems typically operate with previously acquired static data. An optimal software interface for iMRI requires fusion of many of the capabilities offered by these individual devices and further requires the development of tools to handle the integration and presentation of dynamically updated data.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

TRANSSPHENOIDAL PITUITARY MACROADENOMAS RESECTION GUIDED BY POLESTAR N20 LOW-FIELD INTRAOPERATIVE MAGNETIC RESONANCE IMAGING

OBJECTIVE

To evaluate the applicability of low-field intraoperative magnetic resonance imaging (iMRI) during transsphenoidal surgery of pituitary macroadenomas.

METHODS

Fifty-five transsphenoidal surgeries were performed for macroadenomas (modified Hardy's Grade II–IV) resections. All of the surgical processes were guided by real-time updated contrast T1-weighted coronal and sagittal images, which were acquired with 0.15 Tesla PoleStar N20 iMRI (Medtronic Navigation, Louisville, CO). The definitive benefits as well as major drawbacks of low-field iMRI in transsphenoidal surgery were assessed with respect to intraoperative imaging, tumor resection control, comparison with early postoperative high-field magnetic resonance imaging, and follow-up outcomes.

RESULTS

Intraoperative imaging revealed residual tumor and guided extended tumor resection in 17 of 55 cases. As a result, the percentage of gross total removal of macroadenomas increased from 58.2% to 83.6%. The accuracy of imaging evaluation of low-field iMRI was 81.8%, compared with early postoperative high-field MRI (Correlation coefficient, 0.677; P <0.001). A significantly lower accuracy was identified with low-field iMRI in 6 cases with cavernous sinus invasion (33.3%) in contrast to the 87.8% found with other sites (Fisher's exact test, P <0.001).

CONCLUSION

The PoleStar N20 low-field iMRI navigation system is a promising tool for safe, minimally invasive, endonasal, transsphenoidal pituitary macroadenomas resection. It enables neurosurgeons to control the extent of tumor resection, particularly for suprasellar tumors, ensuring surgical accuracy and safety, and leading to a decreased likelihood of repeat surgeries. However, this technology is still not satisfying in estimating the amount of the parasellar residual tumor invading into cavernous sinus, given the false or uncertain images generated by low-field iMRI in this region, which are difficult to discriminate between tumor remnant and blood within the venous sinus.

Feasibility of Polestar N20, an ultra-low-field intraoperative magnetic resonance imaging system in resection control of pituitary macroadenomas: lessons learned from the first 40 cases

OBJECTIVE

To evaluate the feasibility of PoleStar N20 (Medtronic Surgical Navigation Technologies, Louisville, KY), an ultra-low-field intraoperative magnetic resonance imaging (iMRI) system during resection control of pituitary macroadenomas and to compare intraoperative images with postoperative 1.5-T MRI images obtained 3 months after the procedure.

METHODS

Forty patients with a pituitary macroadenoma (mean size, 26.9 +/- 9.1 mm) underwent a surgical procedure to remove the tumor. The iMRI system was implemented in a standardized microsurgical procedure (endonasal, transseptal, transsphenoidal approach) using standard microsurgical instruments. Intraoperative imaging was performed for tumor visualization/navigation and resection control. If an accessible tumor remnant was suspected, surgery was continued for reexploration and, if necessary, continued resection. Total anesthesia time and operation time were compared with a historical cohort of 100 patients who underwent a surgical procedure on pituitary adenomas without iMRI. Sensitivity and specificity of the iMRI to detect residual tumor tissue was assessed in 33 patients (82.5%) after comparison with standard postoperative 1.5-T MRI 3 months after the procedure.

RESULTS

Preoperative tumor visualization with the ultra-low-field iMRI showed a very good congruency with the preoperative 1.5-T MRI scans. A three-dimensional reconstruction of the coronal scan enabled the surgeon to safely approach the tumor using the integrated navigation system. In seven patients (17.5%), iMRI resection control showed accessible residual tumors leading to further resection. After tumor resection, the final iMRI scan documented adequate decompression of the optic pathway in all patients. Implementation of iMRI led to a significant increase of anesthesia time (246.0 +/- 50.7 versus 163.4 +/- 41.2 min) and operation time (116.9 +/- 43.9 versus 78.2 +/- 33.0 min; P < 0.05, t test). Sensitivity of the iMRI was 88.9, 85.7, 93.3, and 100% for the suprasellar, intrasellar, and right and left parasellar regions, respectively, and the specificity was 90.5% in the suprasellar and 100% in the intra- and parasellar regions on both sides. In four patients, the intraoperative interpretation of iMRI was equivocal; thus, it was difficult to distinguish between very small tumor remnants and perioperative changes.

CONCLUSION

Ultra-low-field 0.15-T iMRI is a safe, helpful, and feasible tool for navigation and tumor resection control in patients with pituitary macroadenomas. Total anesthesia and operation times are prolonged, but iMRI adequately documents the extent of tumor resection. In this series, the PoleStar system increased the rate of resection without disrupting the neurosurgical workflow.

Radiotherapy of nonfunctioning and gonadotroph adenomas

Transsphenoidal surgery is the treatment of choice for NFPA but is seldom curative. The management of patients in whom residual tumor is detected after surgery is not clear-cut. Radiation therapy is effective in controlling tumor mass in the majority of patients, but is associated with long term complications that call for restriction of its use to patients at high risk for tumor growth. New radiation techniques may prove to be safer while retaining the effectiveness of conventional radiotherapy, however longer follow-up is necessary to confirm this assumption. For now, it appears to be safe to withhold radiation and carefully follow patients with small tumor remnants, whereas large remnants from invasive tumors should be considered for radiotherapy. Nevertheless, there are no prospective controlled studies that support this empirical approach.

Intracranial surgery with a compact, low-field-strength magnetic resonance imager

Intraoperative magnetic resonance imaging (iMRI) has been a reality for more than a decade. As technology has begun to mature, the focus on practicality and user-friendliness has sharpened. In addition, the need for well-designed and well-executed outcome studies remains so that expensive new instruments such as iMRI can be justified. We present our experience with the PoleStar system, a compact, low-field-strength iMRI designed to make intraoperative imaging a routine component of intracranial neurosurgery. The advantages and limitations of this approach are discussed in the context of different clinical applications.

How to overcome the limitations to determine the resection margin of pituitary tumours with low-field intra-operative MRI during trans-sphenoidal surgery: usefulness of Gadolinium-soaked cotton pledgets

OBJECTIVE

Intra-operative MRI (iMRI) is used as an immediate intra-operative quality control, allowing surgeons to extend resections in situations involving residual tumour remnants. Despite these advantages, low-field iMRI has some limitations with regards to image quality and artefacts. The aim of this study is to report our experience with bone wax and Gadolinium-soaked cotton pledgets in obtaining precise tumour resection margins using low-field iMRI.

PATIENTS AND METHODS

The study group included 63 consecutive patients who underwent endonasal trans-sphenoidal surgery with use of intra-operative low-field iMRI (0.15 T, PoleStar N20, Medtronic Navigation, Louisville, CO, U.S.A.). The indications for intra-operative MRI use included a suprasellar or retrosellar extension (n = 23), cavernous sinus invasion (n = 21), a tumour located in the vicinity of critical anatomic structures (such as the internal carotid artery, n = 10), recurrent or revision procedures (n = 5), and pre-operative imaging revealing unusual anatomy (n = 4).

RESULTS

Overall, among the 51 patients with intended complete tumour removal, iMRI revealed definite tumour remnants or suspicious findings in 13 patients (25.5%), leading to an extended resection and allowing completion of the resection in 10 patients. There was an increased rate of complete tumour removal from 74.5% (38 out of 51) to 94.1% (48 out of 51). The iMRI scan for complete tumour removal was more efficient in the group receiving Gadolinium-soaked cotton pledgets (85.2-100%) than in the group receiving bone wax or the conventional method (62.5-87.5%). The results of iMRI and the estimation by the surgeon concerning the extent of resection revealed a discrepancy in five patients (15.6%) in the Gadolinium-soaked cotton pledgets application group, and in 14 (45.2%) of the bone wax application group.

CONCLUSIONS

More valuable information for determining the resection margin can be obtained with the use of contrast-soaked cottonoid packing in the tumour resection cavity during iMRI scanning. We believe that the use of this simple method reduces the false-positive results and also overcomes the disadvantages of low-field iMRI.

Advances in brain tumor surgery

Advances in the fields of molecular and translational research, oncology, and surgery have emboldened the medical community to believe that intrinsic brain tumors may be treatable. Intraoperative imaging and brain mapping allow operations adjacent to eloquent cortex and more radical resection of tumors with increased confidence and safety. Despite these advances, the infiltrating edge of a neoplasm and distant microscopic satellite lesions will never be amendable to a surgical cure. Indeed, it is continued research into the delivery of an efficacious chemobiologic agent that will eventually allows us to manage this primary cause of treatment failure.

CLINICAL EVALUATION AND FOLLOW-UP OUTCOME OF DIFFUSION TENSOR IMAGING-BASED FUNCTIONAL NEURONAVIGATION

OBJECTIVE

To evaluate diffusion tensor imaging (DTI)-based functional neuronavigation in surgery of cerebral gliomas with pyramidal tract (PT) involvement with respect to both perioperative assessment and follow-up outcome.

METHODS

A prospective, randomized controlled study was conducted between 2001 and 2005. A consecutive series of 238 eligible patients with initial imaging diagnosis of cerebral gliomas involving PTs were randomized into study (n = 118) and control (n = 120) groups. The study cases underwent DTI and three-dimensional magnetic resonance imaging scans. The maps of fractional anisotropy were calculated for PT mapping. Both three-dimensional magnetic resonance imaging data sets and fractional anisotropy maps were integrated by rigid registration, after which the tumor and adjacent PT were segmented and reconstructed for presurgical planning and intraoperative guidance. The control cases were operated on using routine neuronavigation.

RESULTS

There was a trend for high-grade gliomas (HGGs) in the study group to be more likely to achieve gross total resection (74.4 versus 33.3%, P &lt; 0.001). There was no significant difference of low-grade gliomas resection between the two groups. Postoperative motor deterioration occurred in 32.8% of control cases, whereas it occurred in only 15.3% of the study cases (P &lt; 0.001). The 6-month Karnofsky Performance Scale score of study cases was significantly higher than that of control cases (86 ± 20 versus 74 ± 28 overall, P &lt; 0.001; 93 ± 10 versus 86 ± 17 for low-grade gliomas, P = 0.013; and 77 ± 27 versus 53 ± 32 for HGGs, P = 0.001). For 81 HGGs, the median survival of study cases was 21.2 months (95% confidence interval, 14.1–28.3 mo) compared with 14.0 months (95% confidence interval, 10.2–17.8 mo) of control cases (P = 0.048). The estimated hazard ratio for the effect of DTI-based functional neuronavigation was 0.570, representing a 43.0% reduction in the risk of death.

CONCLUSION

DTI-based functional neuronavigation contributes to maximal safe resection of cerebral gliomas with PT involvement, thereby decreasing postoperative motor deficits for both HGGs and low-grade gliomas while increasing high-quality survival for HGGs.

Surgical Therapies in Brain Metastasis

Brain metastases are the most common intracranial tumors in adults and source of the most common neurological complications of systemic cancer. The treatment approach to brain metastases differs essentially from treatment of systemic metastases due to the unique anatomical and physiological characteristics of the brain. Surgery and radiosurgery are important components in the complex treatment of brain metastases and can prolong survival and improve the quality of life (QOL). Aggressive intervention may be indicated for selected patients with well-controlled systemic cancer and good performance status in whom central nervous system (CNS) disease poses the greatest threat to functionality and survival. In this review the respective roles of surgery and radiosurgery, patient selection, general prognostic factors and tailoring of optimal surgical management strategies for cerebral metastases are discussed.

Real-time neuronavigation with high-quality 3D ultrasound SonoWand in pediatric neurosurgery

Intraoperative ultrasound (IOUS) serves as a basic imaging tool in neurosurgery. However, its low quality and difficulty in interpreting the images make its use as a resection control tool and navigation system cumbersome. We present our experience using a high-resolution 3D IOUS system combined with a navigation system in pediatric cranial surgery. We retrospectively reviewed 16 pediatric neurosurgical procedures in which a high-resolution 3D IOUS combined with a navigation system was used. The system enables basic navigation based on preoperative computed tomography or magnetic resonance imaging scans. In addition, IOUS images serve as a data set for updated intraoperative navigation. The indications for IOUS were preoperative navigation to define the skin incision and exact craniotomy site, and for real-time neuronavigation and resection control during tumor removal. The added time per case was short and no technical difficulties were encountered. High-resolution 3D IOUS combined with navigation systems has advantages for the pediatric neurosurgical population, including both real-time basic navigation and improved resection control.

Classical and real-time neuronavigation in pediatric neurosurgery

INTRODUCTION

Neuronavigation has become a cornerstone of neurosurgery. Navigation systems are categorized into two main groups: those based on preoperative imaging and those based on real-time intraoperative acquired images.

OBJECTIVES

The preoperative imaging systems, either computed tomography (CT)- or magnetic resonance imaging (MRI)-based, are straight-forward systems that are routinely used in most institutions. Image accuracy, however, decreases secondary to brain and lesion shifts that occur during surgery. Intraoperative, real-time navigation systems overcome anatomical shifts by updating the image base of the navigation during surgery, thus, maintaining precise navigation capabilities throughout the surgical procedure.

CONCLUSIONS

In this article, we review the main neuronavigation systems and their applications, emphasizing their unique advantages and usage within the pediatric population.

Image-guidance for surgical procedures

Contemporary imaging modalities can now provide the surgeon with high quality three- and four-dimensional images depicting not only normal anatomy and pathology, but also vascularity and function. A key component of image-guided surgery (IGS) is the ability to register multi-modal pre-operative images to each other and to the patient. The other important component of IGS is the ability to track instruments in real time during the procedure and to display them as part of a realistic model of the operative volume. Stereoscopic, virtual- and augmented-reality techniques have been implemented to enhance the visualization and guidance process. For the most part, IGS relies on the assumption that the pre-operatively acquired images used to guide the surgery accurately represent the morphology of the tissue during the procedure. This assumption may not necessarily be valid, and so intra-operative real-time imaging using interventional MRI, ultrasound, video and electrophysiological recordings are often employed to ameliorate this situation. Although IGS is now in extensive routine clinical use in neurosurgery and is gaining ground in other surgical disciplines, there remain many drawbacks that must be overcome before it can be employed in more general minimally-invasive procedures. This review overviews the roots of IGS in neurosurgery, provides examples of its use outside the brain, discusses the infrastructure required for successful implementation of IGS approaches and outlines the challenges that must be overcome for IGS to advance further.

Intraoperative magnetic resonance imaging-guided neurosurgery at 3-T

OBJECTIVE

Between 1997 and 2004, more than 700 neurosurgical procedures were performed in a 1.5-T magnetic resonance-guided therapy suite. During this period, the concept of high-field intraoperative magnetic resonance imaging (MRI) was validated, as was a new surgical guidance tool, the Navigus (Image-guided Neurologics, Melbourne, FL), and its methodology, prospective stereotaxy. Clinical protocols were refined to optimize surgical techniques. That implementation, the "Minnesota suite," has recently been revised, and a new suite with a 3-T MRI scanner has been developed.

METHODS

On the basis of experience at the initial 1.5-T suite, a new suite was designed to house a 3-T MRI scanner with wide surgical access at the rear of the scanner (opposite the patient couch). Use of electrocautery, a fiberoptic headlamp, a power drill, and MRI-compatible neurosurgical cutlery was anticipated by inclusion of waveguides and radiofrequency filter panels that penetrate the MRI suite's radiofrequency shield. An MRI-compatible head holder was adapted for use on the scanner table. A few items exhibiting limited ferromagnetism were used within the magnetic field, taking strict precautions.

RESULTS

During the initial procedures (all magnetic resonance-guided neurobiopsies), the new suite functioned as anticipated. Although metallic artifact related to titanium needles is more challenging at 3 T than at 1.5 T, it can be contained even at 3 T. Similar to 1.5 T, such artifact is best contained when the device is oriented along B0, the main magnetic field. Surgical needles, disposable scalpels, and disposable razors, despite being minimally ferromagnetic, were easily controlled by the surgeon.

CONCLUSION

An intraoperative magnetic resonance-guided neurosurgical theater has been developed with a 3-T MRI scanner. Intraoperative imaging is feasible at this field strength, and concerns regarding specific absorption rate can be allayed. Infection control procedures can be designed to permit neurosurgery within this environment. Despite the increase in magnetic field strength, safety can be maintained.

Cranial surgery with an expanded compact intraoperative magnetic resonance imager

✓In this article the authors report the implementation of an expanded compact intraoperative magnetic resonance (iMR) imager that is designed to overcome significant limitations of an earlier unit.

The PoleStar N20 iMR imager has a stronger magnetic field than its predecessor (0.15 tesla compared with 0.12 tesla), a wider gap between magnet poles, and an ergonomically improved gantry design. The additional time needed in the operating room (OR) for use of iMR imaging and the number of sessions per patient were recorded. Stereotactic accuracy of the integrated navigational tool was assessed using a water-covered phantom.

Of the 55 patients who have undergone surgery in the PoleStar N20 device, diagnoses included glioma in 13, meningioma in 12, pituitary adenoma in nine, other skull base lesions in seven, and miscellaneous other diagnoses. The extra time required for use of the system averaged 1.1 hours (range 0.5–2 hours). Imaging sessions averaged 2.3 per surgery (range one–six sessions).

Measurement of stereotactic accuracy revealed that T1-weighted images were the most accurate. Thinner slices yielded measurably greater accuracy, although this was of questionable clinical significance (all sequences ≤ 4 mm had a mean error of ≤ 1.8 mm). The position of the phantom in the center compared with the periphery of the magnetic field did not affect accuracy (mean error 0.9 mm for each).

The PoleStar N20 appears to make intraoperative neuroimaging with a low-field-strength magnet much more practical than it was with the first-generation device. Greater ease of positioning resulted in a decrease in added time in the OR and encouraged a larger number of imaging sessions.

Intraoperative portable 0.12-tesla MRI in pediatric neurosurgery

OBJECTIVES

Intraoperative MRI (iMRI) is used mainly in the adult neurosurgical population. The main indications for iMRI usage are resection control and updated intraoperative navigation capabilities. In this paper we present our experience using this technique in children. Specific advantages of iMRI for this age group are discussed.

METHODS AND RESULTS

We retrospectively reviewed 31 pediatric neurosurgical procedures in which a portable iMRI system was used. The indications for iMRI usage were preoperative navigation, resection control during tumor removal, shunt placements, and needle biopsy. In 7 children the use of the iMRI changed the course of the surgical procedure. Operative morbidity and mortality were not increased with use of the iMRI.

CONCLUSIONS

iMRI systems have advantages for the pediatric neurosurgical population, including both real-time basic navigation and improved resection control.

Intraoperative magnetic resonance imaging at 0.12 T: is it enough?

Low magnetic field strength MRI provides the anatomic information needed for intracranial procedures in which intraoperative imaging is needed. Stereotactic accuracy is proven. The distinct advantage of this technologic approach is that it allows the neurosurgical team to operate an iMRI system with minimal disruption to the OR routine. Technical improvements are likely to increase the power and versatility of low field strength iMRI. Logic dictates that ergonomics and economics will make this the iMRI technique desired by most neurosurgeons.

Use of a compact intraoperative low-field magnetic imager in pediatric neurosurgery

OBJECT

The majority of investigations on the utility of and indications for intraoperative magnetic resonance imaging (iMRI) have been in adult patients. We report our initial experience utilizing low-field iMRI in pediatric patients.

METHODS

We performed 21 procedures on 20 patients aged 2 months to 18 years (mean 8.9 years) utilizing the PoleStar -10 iMRI system. The procedures included 15 craniotomies, 2 shunts, and 1 each of the following surgeries: transsphenoidal, craniotomy/transsphenoidal, cranioplasty, and endoscopic biopsy and fenestration. Treated lesions included low-grade astrocytoma (5), craniopharyngioma (3), cortical dysplasia (3), hydrocephalus (2), and others (8). The number of scans ranged from 2 to 5 with a mean of 3.2. Intraoperative imaging and navigation provided valuable information on the extent of resection and catheter placement. In eight procedures it influenced the surgical strategy. No untoward events attributable to the system occurred.

CONCLUSIONS

The low-field PoleStar -10 iMRI system can safely assist pediatric neurosurgeons treating a variety of diseases. In addition to neuronavigation it provides information on extent of resection, real-time guided catheter placement, and avoidance of complications.

Intracranial neuronavigation with intraoperative magnetic resonance imaging

PURPOSE OF REVIEW

This is an invited review regarding the use of intraoperative magnetic resonance imaging in the neurosurgical setting. The medical literature evaluating the intraoperative use of magnetic resonance imaging for neurosurgery has increased steadily since the implementation of this technique 10 years ago. The present review discusses recent findings and the current use of intraoperative magnetic resonance imaging in neurosurgery with special emphasis on the quality of available evidence.

RECENT FINDINGS

Intraoperative use of magnetic resonance imaging is a safe technique that enables the neurosurgeon to update data sets for navigational systems, to evaluate the extent of tumor resection and modify surgery if necessary, to guide instruments to the site of the lesion, and to evaluate the presence of intraoperative complications at the end of surgery. Although recent findings support the safety and efficacy of intraoperative magnetic resonance imaging for the above-mentioned purposes, there is no convincing evidence regarding its prognostic significance in the neurosurgical setting.

SUMMARY

Although the use of intraoperative magnetic resonance imaging in neurosurgery has increased significantly within the last 10 years, currently there are less than two dozen dedicated intraoperative units in the United States. The popularization of this technique depends on both economic justification and high-quality scientific evidence supporting its prognostic importance regarding patient outcome.

Utilization of Low-Field MR Scanners

The evident advantage of high-field MR (magnetic resonance) scanners is their higher signal-to-noise ratio, which results in improved imaging. While no reliable efficacy studies exist that compare the diagnostic capabilities of low- versus high-field scanners, the adoption and acceptance of low-field MRI (magnetic resonance imaging) is subject to biases. On the other hand, the cost savings associated with low-field MRI hardware are obvious. The running costs of a non-superconductive low-field scanner show even greater differences in favor of low-field scanners. Patient anxiety and safety issues also reflect the advantages of low-field scanners. Recent technological developments in the realm of low-field MR scanners will lead to higher image quality, shorter scan times, and refined imaging protocols. Interventional and intraoperative use also supports the installation of low-field MR scanners. Utilization of low-field systems has the potential to enhance overall cost reductions with little or no loss of diagnostic performance.

PoleStar N-10 Low-field Compact Intraoperative Magnetic Resonance Imaging System with Mobile Radiofrequency Shielding

The PoleStar N-10 intraoperative magnetic resonance imaging system is manufactured by Odin Medical Technologies, Yokneam, Israel, and is marketed by Medtronic Surgical Navigation Technologies, 826 Coal Creek Circle, Coal Creek Corporate Center One, Louisville, CO 80027; telephone: 720/890-3200. The cost of the PoleStar N-10 ranges from $900,000 to $1,050,000, depending on options. The price of the mobile radiofrequency shielding option is $80,000.

Intraoperative imaging in glioblastoma resection

The use of intraoperative imaging (IOI) in neurosurgical practice is proving to be yet another important advance in the evolution of brain tumor resection, particularly for the most common adult primary brain tumor--glioblastoma (GBM). The number of surgeons using IOI continues to increase, and the experience to date affords an opportunity to assess the value of the various techniques used for IOI.