Correlation between intraoperative ultrasound and postoperative MRI in pediatric tumor surgery

Intraoperative MRI versus intraoperative ultrasound in pediatric brain tumor surgery: is expensive better than cheap? A review of the literature

PURPOSE

The extent of brain tumor resection (EOR) is a fundamental prognostic factor in pediatric neuro-oncology in association with the histology. In general, resection aims at gross total resection (GTR). Intraoperative imaging like intraoperative US (iOUS) and MRI have been developed in order to find any tumoral remnant but with different costs. Aim of our work is to review the current literature in order to better understand the differences between costs and efficacy of MRI and iOUS to evaluate tumor remnants intraoperatively.

METHODS

We reviewed the existing literature on PubMed until 31st December 2021 including the sequential keywords "intraoperative ultrasound and pediatric brain tumors", "iUS and pediatric brain tumors", "intraoperative magnetic resonance AND pediatric brain tumors", and "intraoperative MRI AND pediatric brain tumors.

RESULTS

A total of 300 papers were screened through analysis of title and abstract; 254 were excluded. After selection, a total of 23 articles were used for this systematic review. Among the 929 patients described, a total of 349(38%) of the cases required an additional resection after an iMRI scan. GTR was measured on 794 patients (data of 69 patients lost), and it was achieved in 552(70%) patients. In case of iOUS, GTR was estimated in 291 out of 379 (77%) cases. This finding was confirmed at the post-operative MRI in 256(68%) cases.

CONCLUSIONS

The analysis of the available literature demonstrates that expensive equipment does not always mean better. In fact, for the majority of pediatric brain tumors, iOUS is comparable to iMRI in estimating the EOR.

Essential Management of Pediatric Brain Tumors

Brain tumors are the most common solid tumors in children and are associated with high mortality. The most common childhood brain tumors are grouped as low-grade gliomas (LGG), high grade gliomas (HGG), ependymomas, and embryonal tumors, according to the World Health Organization (WHO). Advances in molecular genetics have led to a shift from pure histopathological diagnosis to integrated diagnosis. For the first time, these new criteria were included in the WHO classification published in 2016 and has been further updated in the 2021 edition. Integrated diagnosis is based on molecular genomic similarities of the tumor subclasses, and it can better explain the differences in clinical courses of previously histopathologically identical entities. Important advances have also been made in pediatric neuro-oncology. A growing understanding of the molecular-genetic background of tumorigenesis has improved the diagnostic accuracy. Re-stratification of treatment protocols and the development of targeted therapies will significantly affect overall survival and quality of life. For some pediatric tumors, these advances have significantly improved therapeutic management and prognosis in certain tumor subgroups. Some therapeutic approaches also have serious long-term consequences. Therefore, optimized treatments are greatly needed. Here, we discuss the importance of multidisciplinary collaboration and the role of (pediatric) neurosurgery by briefly describing the most common childhood brain tumors and their currently recognized molecular subgroups.

Intraoperative Ultrasound-Assisted Extent of Resection Assessment in Pediatric Neurosurgical Oncology

Central nervous system tumors represent the most frequent solid malignancy in the pediatric population. Maximal safe surgical resection is a mainstay of treatment, with significant prognostic impact for the majority of histotypes. Intraoperative ultrasound (ioUS) is a widely available tool in neurosurgery to assist in intracerebral disease resection. Despite technical caveats, preliminary experiences suggest a satisfactory predictive ability, when compared to magnetic resonance imaging (MRI) studies. Most of the available evidence on ioUS applications in brain tumors derive from adult series, a scenario that might not be representative of the pediatric population. We present our preliminary experience comparing ioUS-assisted resection assessment to early post-operative MRI findings in 154 consecutive brain tumor resections at our pediatric neurosurgical unit. A high concordance was observed between ioUS and post-operative MRI. Overall ioUS demonstrated a positive predictive value of 98%, a negative predictive value of 92% in assessing the presence of tumor residue compared to postoperative MRI. Overall, sensibility and specificity were 86% and 99%, respectively. On a multivariate analysis, the only variable significantly associated to unexpected tumor residue on postoperative MRI was histology. Tumor location, patient positioning during surgery, age and initial tumor volume were not significantly associated with ioUS predictive ability. Our data suggest a very good predictive value of ioUS in brain tumor resective procedures in children. Low-grade glioma, high-grade glioma and craniopharyngioma might represent a setting deserving specific endeavours in order to improve intraoperative extent of resection assessment ability.

Extent of Glioma Resection on Intraoperative Ultrasound Correlates Well with Postoperative MRI Results

Background: Maximal surgical resection is thought to confer survival benefit for both high- and low-grade gliomas. Intraoperative imaging assists with achieving maximal surgical resection. Different intraoperative imaging modalities have been implemented, but intra-operative MRI has a high cost that may limit its uptake in resource scarce healthcare systems. Objectives: This study aims to evaluate intraoperative ultrasound as a surrogate for intra and post-operative MRI for assessing the extent of resection of glioma. Methods: A partially prospective comparative study, which compares a prospective cohort group with a historical control group. We evaluated 74 glioma patients, who all underwent surgery in a regional UK Neurosurgical centre between October 2013 and October 2017. The study population was divided into 2 groups based on the use of ultrasound to guide the resection. We compared the size of the lesion prior and after excision to evaluate the extent of resection and undertook comparison with post-operative MRI. Results: The mean extent of resection on the ultrasound images was 96.1 % and 97.7 % on the postoperative MR. Using Spearman’s correlation; extent of resection on the ultrasound images was strongly correlated with the extent of resection on the postoperative MR images (P=value <0.001). The use of intraoperative ultrasound was associated with a significant increase in the number of patients in whom 95% or greater extent of resection was achieved (Fisher’s exact test P= value 0.033). Conclusion: Intra-operative ultrasonography could provide a reliable and cheaper alternative to intraoperative MRI to improve the extent of resection in glioma surgery.

5-ALA fluorescence-guided surgery in pediatric brain tumors-a systematic review

BACKGROUND

5-Aminolevulinic acid (5-ALA)-guided resection of gliomas in adults enables better differentiation between tumor and normal brain tissue, allowing a higher degree of resection, and improves patient outcomes. In recent years, several reports have emerged regarding the use of 5-ALA in other brain tumor entities, including pediatric brains tumors. Since gross total resection (GTR) of many brain tumors in children is crucial and the role of 5-ALA-guided resection of these tumors is not clear, we sought to perform a comprehensive literature review on this topic.

METHODS

A systematic literature review of EMBASE and MEDLINE/PubMed databases revealed 19 eligible publications encompassing 175 5-ALA-guided operations on pediatric brain tumors. To prevent bias, publications were revised independently by two authors.

RESULTS

We found that 5-ALA-guided resection enabled the surgeons to identify the tumor more easily and was considered helpful mainly in cases of glioblastoma (GBM, 21/27, 78%), anaplastic ependymoma WHO grade III (10/14, 71%), and anaplastic astrocytoma (4/6, 67%). In contrast, cases of pilocytic astrocytomas (PAs) and medulloblastomas 5-ALA-guided surgery did not show consistent fluorescent signals and 5-ALA was considered helpful only in 12% and 22% of cases, respectively. Accumulation of fluorescent porphyrins seems to depend on WHO tumor grading. One important finding is that when 5-ALA-guided resections were considered helpful, the degree of resection was higher than is cases where it was not helpful. The rate of adverse events related to 5-ALA was negligible, especially new postoperative sequelae.

CONCLUSION

5-ALA could play a role in resection of pediatric brain tumors. However, further prospective clinical trials are needed.

The impact of fluorescein-guided technique in the surgical removal of CNS tumors in a pediatric population: results from a multicentric observational study

BACKGROUND

Surgery has a fundamental role in central nervous system (CNS) tumors in the pediatric population, as aggressive resection correlates with prognosis. Due to its accumulation in areas with damaged blood brain barrier, sodium fluorescein (SF) could be a valid tool to improve the extent of resection in tumors enhancing at preoperative MRI. This study is aimed to systematically assess the utility of SF in a pediatric population.

METHODS

Patient data were collected in two centers, one in Italy and the other in Germany. At the induction of anesthesia, SF was administered intravenously (5 mg/kg). Surgery was performed using a YELLOW560 filter. Fluorescence intensity was graduated as bright, moderate or absent based on surgeon's opinion; furthermore, SF use was judged as "helpful," "not helpful" or "not essential" in tumor removal.

RESULTS

Twenty-four patients for 27 surgical procedures were identified. In 21 of 27 (77.8%) procedures fluorescence was reported as bright or moderate, in two of 27 (7.4%) absent and in four of 27 (14.8%) data were unavailable. Intraoperative fluorescence was reported in 21 of 25 (84%) surgeries whose corresponding preoperative MRI had shown contrast enhancement. In 14 of 27 (51.8%) surgical procedures SF was considered "helpful"; in two of 27 (7.4%) not "helpful"; in seven of 27 (25.9%) "not essential." In four of 27 (14.8%) data were unavailable. No adverse effect to SF was registered.

CONCLUSIONS

SF could be considered a valid and safe tool to improve visualization of tumors enhancing at preoperative MRI also in pediatric patients. Future prospective studies are needed to confirm these preliminary data.

New Hope in Brain Glioma Surgery: The Role of Intraoperative Ultrasound. A Review

Maximal safe resection represents the gold standard for surgery of malignant brain tumors. As regards gross-total resection, accurate localization and precise delineation of the tumor margins are required. Intraoperative diagnostic imaging (Intra-Operative Magnetic Resonance-IOMR, Intra-Operative Computed Tomography-IOCT, Intra-Operative Ultrasound-IOUS) and dyes (fluorescence) have become relevant in brain tumor surgery, allowing for a more radical and safer tumor resection. IOUS guidance for brain tumor surgery is accurate in distinguishing tumor from normal parenchyma, and it allows a real-time intraoperative visualization. We aim to evaluate the role of IOUS in gliomas surgery and to outline specific strategies to maximize its efficacy. We performed a literature research through the Pubmed database by selecting each article which was focused on the use of IOUS in brain tumor surgery, and in particular in glioma surgery, published in the last 15 years (from 2003 to 2018). We selected 39 papers concerning the use of IOUS in brain tumor surgery, including gliomas. IOUS exerts a notable attraction due to its low cost, minimal interruption of the operational flow, and lack of radiation exposure. Our literature review shows that increasing the use of ultrasound in brain tumors allows more radical resections, thus giving rise to increases in survival.

Neuroendoscopic Intraoperative Ultrasound-Guided Technique for Biopsy of Paraventricular Tumors

Different tumors can be encountered in the paraventricular regions, and whereas their deep location often make them difficult to access surgically, they may be amenable to chemotherapy and/or radiotherapy. Therefore, tumor biopsy and histologic diagnosis are mandatory to optimize treatment. Different technical procedures have been recommended; the neuroendoscopic approach is accepted and widely used, in particular with an enlarged ventricular system. However, specifically with paraventricular tumors, tissue sampling may be challenging. In such a scenario, the use of intraoperative ultrasonography technique can add some advantages regarding diagnostic accuracy and procedure safety. Accordingly, in this study we describe a novel technical procedure in 7 selected patients in whom tumor tissue biopsy was performed in a coupled neuroendoscopic and ultrasound-guided environment. We define a neuroendoscopic intraoperative ultrasound technique. The main advantages of this technique are the identification of the tumor that may not been clearly identified underneath the ventricular ependymal through the neuroendoscopic window alone, and furthermore, that this technique gives the possibility to detect the depth of the needle advance∖ment in the selected tissue while labeling the lesion beneath the ventricular ependyma. Moreover, intraoperative ultrasonography can reveal in a real-time fashion intracranial hemorrhages that may occur after tissue biopsy, therefore providing a useful tool to achieve valid and directed hemostasis when needed.

Efficacy of intraoperative ultrasonography in neurosurgical tumor resection

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

The impact of intraoperative magnetic resonance in routine pediatric neurosurgical practice-a 6-year appraisal

BACKGROUND

The intraoperative magnetic resonance scanner (ioMR) was introduced in our unit in 2009, and has been used routinely since then.

OBJECTIVE

This study aims to describe indications, radiological features, and clinical outcomes of the patients operated on with ioMRI and analyze our experience.

METHODS

A retrospective analysis of a prospective surgical database has been performed, including surgical procedure, intent, radiological reports, need for second-look surgery, and complications, supplemented by further review of the clinical notes and the scans.

RESULTS

From 2009 to 2015, 255 surgical procedures with ioMR were performed: 175 were craniotomies for tumor excision, 65 were epilepsy related, and 15 were biopsies or cyst drainages. The mean age was 9.4 years. One ioMR was performed in 79.5% patients; the mean duration of the MR was 41 min. In 172 cases (67.4%), no actions followed the ioMR. When the aim of the surgery was debulking of the tumor, the percentage of patients in which the ioMR was followed by resection was higher than when complete resection was the aim (56 vs 27.5%). The complication rate was not increased when compared with our previous results (infection 1%, neurological deficits 12%).

CONCLUSION

This is the largest published series of ioMRI-aided pediatric neurosurgery to date. We have demonstrated that it can be used safely and routinely in pediatric neurosurgical procedures at any age, assisting the surgeon in achieving the best extent of resection and aiding in intra-operative decision-making for tumor- and non-tumor-related intracranial pathology.