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

Intraoperative use of low-field magnetic resonance imaging for brain tumors: A systematic review

Background

Low-field magnetic resonance imaging (LF-MRI) has become a valuable tool in the diagnosis of brain tumors due to its high spatial resolution and ability to acquire images in a short amount of time. However, the use of LF-MRI for intraoperative imaging during brain tumor surgeries has not been extensively studied. The aim of this systematic review is to investigate the impact of low-field intraoperative magnetic resonance imaging (LF-IMRI) on the duration of brain tumor surgery and the extent of tumor resection.

Methods

A comprehensive literature search was conducted using PubMed, Scopus, and Google Scholar from February 2000 to December 2022. The studies were selected based on the inclusion criteria and reviewed independently by two reviewers. The gathered information was organized and analyzed using Excel.

Results

Our review of 21 articles found that low-field intraoperative MRI (LF-IMRI) with a field below 0.3T was used in most of the studies, specifically 15 studies used 0.15T LF-IMRI. The T1-weighted sequence was the most frequently reported, and the average scanning time was 24.26 min. The majority of the studies reported a positive impact of LF-IMRI on the extent of tumor resection, with an increase ranging from 11% to 52.5%. Notably, there were no studies describing the use of ultra-low-field (ULF) intraoperative MRI.

Conclusion

The results of this systematic review will aid neurosurgeons and neuroradiologists in making informed decisions about the use of LF-MRI in brain tumor surgeries. Further, research is needed to fully understand the impact of LF-MRI in brain tumor surgeries and to optimize its use in the clinical setting. There is an opportunity to study the utility of ULF-MRI in brain tumor surgeries.

The Neurosurgeon's Armamentarium for Gliomas: An Update on Intraoperative Technologies to Improve Extent of Resection

Maximal safe resection is the standard of care in the neurosurgical treatment of high-grade gliomas. To aid surgeons in the operating room, adjuvant techniques and technologies centered around improving intraoperative visualization of tumor tissue have been developed. In this review, we will discuss the most advanced technologies, specifically fluorescence-guided surgery, intraoperative imaging, neuromonitoring modalities, and microscopic imaging techniques. The goal of these technologies is to improve detection of tumor tissue beyond what conventional microsurgery has permitted. We describe the various advances, the current state of the literature that have tested the utility of the different adjuvants in clinical practice, and future directions for improving intraoperative technologies.

Intraoperative imaging technology to maximise extent of resection for glioma: a network meta-analysis

BACKGROUND

Multiple studies have identified the prognostic relevance of extent of resection in the management of glioma. Different intraoperative technologies have emerged in recent years with unknown comparative efficacy in optimising extent of resection. One previous Cochrane Review provided low- to very low-certainty evidence in single trial analyses and synthesis of results was not possible. The role of intraoperative technology in maximising extent of resection remains uncertain. Due to the multiple complementary technologies available, this research question is amenable to a network meta-analysis methodological approach.

OBJECTIVES

To establish the comparative effectiveness and risk profile of specific intraoperative imaging technologies using a network meta-analysis and to identify cost analyses and economic evaluations as part of a brief economic commentary.

SEARCH METHODS

We searched CENTRAL (2020, Issue 5), MEDLINE via Ovid to May week 2 2020, and Embase via Ovid to 2020 week 20. We performed backward searching of all identified studies. We handsearched two journals, Neuro-oncology and the Journal of Neuro-oncology from 1990 to 2019 including all conference abstracts. Finally, we contacted recognised experts in neuro-oncology to identify any additional eligible studies and acquire information on ongoing randomised controlled trials (RCTs).

SELECTION CRITERIA

RCTs evaluating people of all ages with presumed new or recurrent glial tumours (of any location or histology) from clinical examination and imaging (computed tomography (CT) or magnetic resonance imaging (MRI), or both). Additional imaging modalities (e.g. positron emission tomography, magnetic resonance spectroscopy) were not mandatory. Interventions included fluorescence-guided surgery, intraoperative ultrasound, neuronavigation (with or without additional image processing, e.g. tractography), and intraoperative MRI.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the search results for relevance, undertook critical appraisal according to known guidelines, and extracted data using a prespecified pro forma.

MAIN RESULTS

We identified four RCTs, using different intraoperative imaging technologies: intraoperative magnetic resonance imaging (iMRI) (2 trials, with 58 and 14 participants); fluorescence-guided surgery with 5-aminolevulinic acid (5-ALA) (1 trial, 322 participants); and neuronavigation (1 trial, 45 participants). We identified one ongoing trial assessing iMRI with a planned sample size of 304 participants for which results are expected to be published around winter 2020. We identified no published trials for intraoperative ultrasound. Network meta-analyses or traditional meta-analyses were not appropriate due to absence of homogeneous trials across imaging technologies. Of the included trials, there was notable heterogeneity in tumour location and imaging technologies utilised in control arms. There were significant concerns regarding risk of bias in all the included studies. One trial of iMRI found increased extent of resection (risk ratio (RR) for incomplete resection was 0.13, 95% confidence interval (CI) 0.02 to 0.96; 49 participants; very low-certainty evidence) and one trial of 5-ALA (RR for incomplete resection was 0.55, 95% CI 0.42 to 0.71; 270 participants; low-certainty evidence). The other trial assessing iMRI was stopped early after an unplanned interim analysis including 14 participants; therefore, the trial provided very low-quality evidence. The trial of neuronavigation provided insufficient data to evaluate the effects on extent of resection. Reporting of adverse events was incomplete and suggestive of significant reporting bias (very low-certainty evidence). Overall, the proportion of reported events was low in most trials and, therefore, issues with power to detect differences in outcomes that may or may not have been present. Survival outcomes were not adequately reported, although one trial reported no evidence of improvement in overall survival with 5-ALA (hazard ratio (HR) 0.82, 95% CI 0.62 to 1.07; 270 participants; low-certainty evidence). Data for quality of life were only available for one study and there was significant attrition bias (very low-certainty evidence).

AUTHORS' CONCLUSIONS

Intraoperative imaging technologies, specifically 5-ALA and iMRI, may be of benefit in maximising extent of resection in participants with high-grade glioma. However, this is based on low- to very low-certainty evidence. Therefore, the short- and long-term neurological effects are uncertain. Effects of image-guided surgery on overall survival, progression-free survival, and quality of life are unclear. Network and traditional meta-analyses were not possible due to the identified high risk of bias, heterogeneity, and small trials included in this review. A brief economic commentary found limited economic evidence for the equivocal use of iMRI compared with conventional surgery. In terms of costs, one non-systematic review of economic studies suggested that, compared with standard surgery, use of image-guided surgery has an uncertain effect on costs and that 5-ALA was more costly. Further research, including completion of ongoing trials of ultrasound-guided surgery, is needed.

Navigated neuroendoscopy combined with intraoperative magnetic resonance cysternography for treatment of arachnoid cysts

Endoscopic cystocysternostomy or cystoventriculostomy is the treatment of choice in patients with symptomatic intracranial arachnoid cysts. There are no objective diagnostic tests for reliable intraoperative evaluation of the effectiveness of performed stomies. The aim of this prospective open-label study is to demonstrate for the first time the usefulness of intraoperative cysternography performed with the low-field 0.15-T magnetic resonance imager Polestar N20 during endoscopic cysternostomies. The study was performed in patients operated for middle fossa arachnoid cysts (n = 10), suprasellar cysts (n = 4), paraventricular or intraventricular cysts (n = 6), and a pineal cyst (n = 1). The operations were performed with use of a navigated neuroendoscope. Intraoperative magnetic resonance (iMR) cysternography was performed before and after the cystostomy. In each case, iMR cysternography was safe and could show clearly the cyst morphology and the effectiveness of performed endoscopic cystostomies. In six cases, iMR cysternography had a significant influence of the surgical decision (p = 0.027). The rate of inconsistency between the intraoperative observations and iMR imaging–based findings was 29%. A good contrast flow through the fenestrated cyst walls correlated with a good long-term clinical outcome (ρ = 0.54, p < 0.05) and good long-term radiological outcome (ρ = 0.72, p < 0.05). Intraoperative low-field MR cysternography is a safe and reliable method for assessment of the efficacy of performed endoscopic cystostomies and has significant influence on the surgical decision. It may be reliably used for prediction of the long-term clinical and radiological outcome.

Intraoperative imaging technology to maximise extent of resection for glioma

BACKGROUND

Extent of resection is considered to be a prognostic factor in neuro-oncology. Intraoperative imaging technologies are designed to help achieve this goal. It is not clear whether any of these sometimes very expensive tools (or their combination) should be recommended as standard care for people with brain tumours. We set out to determine if intraoperative imaging technology offers any advantage in terms of extent of resection over standard surgery and if any one technology was more effective than another.

OBJECTIVES

To establish the overall effectiveness and safety of intraoperative imaging technology in resection of glioma. To supplement this review of effects, we also wished to identify cost analyses and economic evaluations as part of a Brief Economic Commentary (BEC).

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (Issue 7, 2017), MEDLINE (1946 to June, week 4, 2017), and Embase (1980 to 2017, week 27). We searched the reference lists of all identified studies. We handsearched two journals, the Journal of Neuro-Oncology and Neuro-oncology, from 1991 to 2017, including all conference abstracts. We contacted neuro-oncologists, trial authors, and manufacturers regarding ongoing and unpublished trials.

SELECTION CRITERIA

Randomised controlled trials evaluating people of all ages with presumed new or recurrent glial tumours (of any location or histology) from clinical examination and imaging (computed tomography (CT) or magnetic resonance imaging (MRI), or both). Additional imaging modalities (e.g. positron emission tomography, magnetic resonance spectroscopy) were not mandatory. Interventions included intraoperative MRI (iMRI), fluorescence-guided surgery, ultrasound, and neuronavigation (with or without additional image processing, e.g. tractography).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the search results for relevance, undertook critical appraisal according to known guidelines, and extracted data using a prespecified pro forma.

MAIN RESULTS

We identified four randomised controlled trials, using different intraoperative imaging technologies: iMRI (2 trials including 58 and 14 participants, respectively); fluorescence-guided surgery with 5-aminolevulinic acid (5-ALA) (1 trial, 322 participants); and neuronavigation (1 trial, 45 participants). We identified one ongoing trial assessing iMRI with a planned sample size of 304 participants for which results are expected to be published around autumn 2018. We identified no trials for ultrasound.Meta-analysis was not appropriate due to differences in the tumours included (eloquent versus non-eloquent locations) and variations in the image guidance tools used in the control arms (usually selective utilisation of neuronavigation). There were significant concerns regarding risk of bias in all the included studies. All studies included people with high-grade glioma only.Extent of resection was increased in one trial of iMRI (risk ratio (RR) of incomplete resection 0.13, 95% confidence interval (CI) 0.02 to 0.96; 1 study, 49 participants; very low-quality evidence) and in the trial of 5-ALA (RR of incomplete resection 0.55, 95% CI 0.42 to 0.71; 1 study, 270 participants; low-quality evidence). The other trial assessing iMRI was stopped early after an unplanned interim analysis including 14 participants, therefore the trial provides very low-quality evidence. The trial of neuronavigation provided insufficient data to evaluate the effects on extent of resection.Reporting of adverse events was incomplete and suggestive of significant reporting bias (very low-quality evidence). Overall, reported events were low in most trials. There was no clear evidence of improvement in overall survival with 5-ALA (hazard ratio 0.83, 95% CI 0.62 to 1.07; 1 study, 270 participants; low-quality evidence). Progression-free survival data were not available in an appropriate format for analysis. Data for quality of life were only available for one study and suffered from significant attrition bias (very low-quality evidence).

AUTHORS' CONCLUSIONS

Intra-operative imaging technologies, specifically iMRI and 5-ALA, may be of benefit in maximising extent of resection in participants with high grade glioma. However, this is based on low to very low quality evidence, and is therefore very uncertain. The short- and long-term neurological effects are uncertain. Effects of image-guided surgery on overall survival, progression-free survival, and quality of life are unclear. A brief economic commentary found limited economic evidence for the equivocal use of iMRI compared with conventional surgery. In terms of costs, a non-systematic review of economic studies suggested that compared with standard surgery use of image-guided surgery has an uncertain effect on costs and that 5-aminolevulinic acid was more costly. Further research, including studies of ultrasound-guided surgery, is needed.

Intraoperative visualisation of functional structures facilitates safe frameless stereotactic biopsy in the motor eloquent regions of the brain

BACKGROUND

For stereotactic brain biopsy involving motor eloquent regions, the surgical objective is to enhance diagnostic yield and preserve neurological function. To achieve this aim, we implemented functional neuro-navigation and intraoperative magnetic resonance imaging (iMRI) into the biopsy procedure. The impact of this integrated technique on the surgical outcome and postoperative neurological function was investigated and evaluated.

METHOD

Thirty nine patients with lesions involving motor eloquent structures underwent frameless stereotactic biopsy assisted by functional neuro-navigation and iMRI. Intraoperative visualisation was realised by integrating anatomical and functional information into a navigation framework to improve biopsy trajectories and preserve eloquent structures. iMRI was conducted to guarantee the biopsy accuracy and detect intraoperative complications. The perioperative change of motor function and biopsy error before and after iMRI were recorded, and the role of functional information in trajectory selection and the relationship between the distance from sampling site to nearby eloquent structures and the neurological deterioration were further analyzed.

RESULTS

Functional neuro-navigation helped modify the original trajectories and sampling sites in 35.90% (16/39) of cases to avoid the damage of eloquent structures. Even though all the lesions were high-risk of causing neurological deficits, no significant difference was found between preoperative and postoperative muscle strength. After data analysis, 3mm was supposed to be the safe distance for avoiding transient neurological deterioration. During surgery, the use of iMRI significantly reduced the biopsy errors (p = 0.042) and potentially increased the diagnostic yield from 84.62% (33/39) to 94.87% (37/39). Moreover, iMRI detected intraoperative haemorrhage in 5.13% (2/39) of patients, all of them benefited from the intraoperative strategies based on iMRI findings.

CONCLUSIONS

Intraoperative visualisation of functional structures could be a feasible, safe and effective technique. Combined with intraoperative high-field MRI, it contributed to enhance the biopsy accuracy and lower neurological complications in stereotactic brain biopsy involving motor eloquent areas.

Current imaging techniques for the diagnosis of pituitary adenoma

Stepwise improvements in the imaging of pituitary adenomas in the last 100 years have had a tremendous impact on patient care. Pituitary tumors are now diagnosed earlier in the time course of the disease, improving chances of endocrine and visual recovery. There is improved pre-surgical planning due to a better understanding of the investment of the tumor around important surrounding parasellar structures. Approaches to tumors are now safer due to stereotactic navigation and residual disease can be radiographically followed for a lifetime and treated prior to irreversible neurological damage. Furthermore, adjuvant radiotherapy can be more precisely delivered to the tumor bed with the aid of higher resolution images. Thanks to these incremental improvements previously formidable macroadenomas, which carried a high risk for morbidity and residual disease, can now be treated safely and effectively. Here, we review modern imaging modalities used to diagnose pituitary adenomas, and identify areas for further improvement.

"Intrasellar Balloon Technique" in intraoperative MRI guided transsphenoidal endoscopic surgery for sellar region tumors. Usefulness on image interpretation and extent of resection evaluation. Technical note

BACKGROUND

Intraoperative magnetic resonance imaging (iMRI) is an effective and proven tool in transsphenoidal endoscopic surgery. However, image interpretation is not always easy and can be hindered by the presence of blood, tumor remains or the displacement of surrounding structures. In this article we present a novel technique based on using intrasellar ballons to reduce these difficulties and facilitate the surgeon's intraoperative assessment by iMRI.

METHODS

Eighteen patients with pituitary macroadenomas underwent transsphenoidal surgery during 2013-2014 under low-field iMRI control (PoleStar N20, 0.15 T). Intrasellar balloons were used in all of them to assess the presence of tumoral remnants. We compared the findings in iMRI and postoperative high-field MRI control scans and also analyzed the number of intermediate imaging controls needed during surgery using this technique.

RESULTS

In total, of the 18 patients, 14 underwent a complete resection. In the remaining four patients, a safe maximal resection was performed, leaving a remnant because of cavernous sinus invasion. In all cases, the balloons were a major help in distinguishing the anatomical structures from the tumoral remnants. Fewer imaging controls were required, and there were no false-positives or negative intraoperative findings. No complications related to the technique were registered.

CONCLUSION

The "intrasellar balloon technique" is a useful tool that facilitates surgeons' intraoperative decision making. It is an important contribution to overcome the limitations of low-field iMRI as it provides a precise delineation of the resection margins, reduces false-positives and -negatives, and decreases the number of intermediate imaging controls required.

Usefulness of intraoperative magnetic resonance ventriculography during endoscopic third ventriculostomy

BACKGROUND

Endoscopic third ventriculostomy (ETV) is the preferred method for the treatment of noncommunicating hydrocephalus. The different success rates of ETV indicate the difficulties in predicting the success of this procedure.

OBJECTIVE

To show the usefulness of intraoperative ventriculography performed by the low-field 0.15-T magnetic resonance imager Polestar N20 during ETV.

METHODS

The study was conducted in 11 patients with noncommunicating hydrocephalus caused by tumors or cysts of the third ventricle (n = 5), nontumoral stenosis of the sylvian aqueduct (n = 3), and fourth ventricle outlet obstruction (n = 3). Intraoperative magnetic resonance (iMR) ventriculography was performed before and after the ETV.

RESULTS

In each case, iMR-ventriculography was a safe procedure and determined the exact site of obstruction of cerebrospinal fluid flow. In all cases, iMR-ventriculography performed after ETV showed with the greatest accuracy the patency of the performed fenestrations, demonstrating in 9 patients good flow of the contrast from the third ventricle to the basal cisterns, restricted flow in 1 patient, and no flow in 1 patient. The results of ventriculography were consistent with the postoperative neurological status of operated-on patients. In 3 patients, the opinion of the surgeons about the patency of endoscopic fenestration, based on intraoperative observation of the third ventricle floor, was inconsistent with the results from iMR-ventriculography.

CONCLUSION

Low-field iMR-ventriculography is a safe procedure that can be successfully applied during ETV to determine the site of obstruction in hydrocephalus and the patency of performed ventricle fenestration.

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.

Intraoperative magnetic resonance-guided frameless stereotactic biopsies - initial clinical experience

BACKGROUND AND PURPOSE

We present our early experience in intraoperative magnetic resonance (iMRI)-guided stereotactic frameless biopsies with special regard to its safety, efficacy and diagnostic value.

MATERIAL AND METHODS

The records of patients who underwent frameless stereotactic iMRI-guided biopsies between June 2009 and April 2011 were analysed prospectively. All the operations were performed under local anaesthesia, with the use of a passive side-cutting biopsy needle. The needle was introduced into the pathological lesion with the help of optic neuronavigation system guidance. The iMRI scans served as reference images. We analysed the patients' demographic and epidemiological data, the preparation and surgery times, diagnostic values of collected specimens, lengths of the hospital stay (LOS) and the complication rate.

RESULTS

Fifteen iMRI-guided stereotactic biopsies were performed in the analysed period. The mean patient age was 52 ± 18 yrs, the median WHO score was 2 (range: 1-3), there were 9 (60%) males in the study group. The average preparation time was 53 ± 24 minutes and the operation time 69 ± 25 minutes. No major complications were noted. The median total length of hospital stay was 5 days. The histopathological diagnoses were as follows: glioblastoma multiforme - 6 cases, low-grade gliomas - 4 cases, lymphomas - 3 cases, and other pathologies - 2 cases. In all the cases biopsy material allowed specified histopathological diagnoses to be obtained.

CONCLUSIONS

Frameless stereotactic iMRI-guided brain tumour biopsy is a safe and diagnostically effective procedure. The use of iMRI might increase the diagnostic value and safety of stereotactic biopsy and positively influence its economic balance.