Abstract
The fundamental principle in the operative treatment of brain tumors involves achieving maximal safe resection in order to improve postoperative outcomes. At present, challenges in visualizing microscopic disease and residual tumor remain an impediment to complete tumor removal. Spectroscopic tools have the theoretical advantage of accurate tissue identification, coupled with the potential for manual intraoperative adjustments to improve visualization of remaining tumor tissue that would otherwise be difficult to detect. The current evidence and techniques for handheld spectroscopic tools in surgical neuro-oncology are explored here.
Introduction
The fundamental goal in the surgical treatment of brain tumors is achieving the greatest possible extent of resection while minimizing injury to surrounding pathways present in the adjacent brain. Indeed, numerous studies in the literature have demonstrated that the proportion of tumor removed is significantly associated with key postoperative outcome metrics, including overall survival (OS) and progression-free survival (PFS) (–). Despite this, however, complete tumor resection remains challenging due to the presence of microscopic disease and infiltrative tumor tissue that is difficult to visually differentiate from the surrounding brain. As such, numerous tools have been developed, for both pre- and intra-operative use [e.g., neuronavigation and intraoperative MRI (iMRI)], in order to assist in the identification and removal of neoplastic tissue (). More sophisticated MRI techniques, such as whole brain magnetic resonance spectroscopic imaging (MRSI), has allowed for more precise visualization of tumor than would otherwise be possible with standard MRI (). Multiple studies have highlighted the fact that microscopic involvement of high-grade gliomas (HGGs) extends well-beyond the contrast-enhancing lesion visible on T2-weighted MRI (, ). Other techniques, such as neurosurgical virtual reality and simulation have facilitated preoperative visualization and planning (). Although these instruments have demonstrated utility, intraoperative retraction and tumor resection often result in brain shift, making it challenging to assess the extent of resection in real time. Also, non-specific enhancement after iMRI may be confused with residual tumor. Fluorescence-guided surgery using 5-aminolevulinic acid (5-ALA) has been a crucial addition to the neurosurgeon's toolkit, allowing for direct fluorescence visualization of HGGs using wide-field surgical microscopy (). However, the infiltrative margin of HGGs and World Health Organization (WHO) grade II low grade gliomas (LGGs) have remained challenging to visualize, since sufficient levels of fluorescence often cannot be detected using traditionally employed visualization technologies (). Handheld tools were developed as an adjunct to intraoperative resection, under the premise that real-time use and the ability to adjust the angle of the instrument could facilitate detection of remaining tumor at the time of surgery. Among the most studied techniques has been the use of handheld Raman spectroscopy in the identification of cancer cells during surgery. Other devices aimed at improving visualization in fluorescence guidance surgery have recently been developed. The purpose of this review is to examine the technique and evidence for the utility of handheld spectroscopy tools in neuro-oncologic surgery.
Technique
Raman Spectroscopic Probes
Handheld Raman spectroscopic probes harness the traditionally employed Raman spectroscopic technique described decades ago (). Monochromatic light from a laser is used to shine on an object of interest, resulting in a change in vibrational energy states, which can be detected as electromagnetic radiation that is filtered through a monochromator (). This results in a molecular fingerprint that can be subsequently harnessed to differentiate various tissue types (). Neoplastic cells, for instance, have a molecular composition that is distinct from normal brain parenchyma and thus allows for their identification during surgery (, ). Glioblastoma (GBM) has been shown to exhibit a decreased lipid band and an increased protein band, while cholesterol bands were found to be absent in metastatic brain lesions (). One specific advantage of this technique is that water molecules do not interfere with the Raman scattering, thereby increasing its utility in surgical applications. In the operating room, the laser/collection cones, lens, and filter can be combined into a hand-held probe that is then connected to a camera and spectrometer device. This probe can be used intraoperatively during resection in order to both identify tumor cells outside of contrast-enhancing areas on anatomic MRI as well as residual tumor following debulking and resection (). Unlike the MRI neuronavigation, virtual reality, and other imaging techniques, the handheld probe allows the surgeon to make intraoperative adjustments in terms of positioning and angles following changes in the relative location of anatomic structures during surgery.
5-ALA Fluorescence Visualization
5-ALA is an oral pro-drug and the preoperative administration of this agent results in the accumulation of the fluorescent metabolite protoporphyrin IX in neoplastic lesions, which can be visualized during surgery (, ). This is accomplished via excitation of protoporphyrin IX-rich tissue with blue 440 nanometer wavelength light, resulting in the emission of a violet-colored signal (). Improved visualization of tumors consequently allows for a greater extent of resection than would otherwise be possible under white light. Numerous randomized, controlled trials have demonstrated a benefit to patient survival using this agent, resulting in it gaining recent FDA approval for the treatment of suspected HGGs in the United States (–). Despite this, however, the evidence for its utility in the treatment of LGGs is less robust, due to the difficulty in achieving adequate fluorescent signal using wide-field microscopic illumination from a long working distance (, ). In addition, visualization of the infiltrative tumor margin becomes more difficult with fluorescence due to the lower number of tumor cells residing away from the tumor bulk. Handheld probes offer distinct advantages in visualizing these tumors, due to both the ability to place the instrument in close proximity to the tissue, as well as potentially generate a precise, quantitative measurement of protoporphyrin IX concentrations (, ). These techniques involve utilizing a handheld probe coupled to spectrometer that can be manipulated within the intraoperative field (Figure 1) (, ).
Figure 1
Evidence
Raman Spectroscopy
Basic Science
An array of ex-vivo and animal model studies have demonstrated the value of handheld Raman spectroscopy in differentiating tumor from normal brain tissue. Ji et al. examined the ability of Raman microscopy to discriminate tumor samples from 22 biopsy specimens, and found that Raman spectroscopy detected tumor infiltration in near-perfect agreement with hematoxylin and eosin (H&E) staining (
Other studies have revolved around the identification of important biomarkers that could be employed in distinguishing various tumor types. For instance, Zhou et al. demonstrated the utility of Raman spectroscopy in differentiating malignant tissue in 87 samples, revealing the presence of peaks corresponding to lactic acid and ATP in certain tumor tissues when compared to controls (
Figure 2

Depiction of Raman-stimulated histology slides alongside traditional haematoxylin and eosin for a patient with a history of recurrent oligodendroglioma [With permission from Orringer et al. (
Clinical Studies
Comparatively few studies have examined the feasibility and utility of handheld Raman spectroscopy using real-time, in-vivo experimental design. Jermyn et al. employed a handheld probe in 17 patients with grade 2-4 gliomas and compared imaging findings with obtained biopsy specimens (
Table 1
| References | Journal | Number of samples | Tumor histology | Relevant outcome metric | Rate | Notes |
|---|---|---|---|---|---|---|
| CLINICAL AND BASIC SCIENCE STUDIES | ||||||
| Ji et al. ( | Sci Transl Med | 22 | Gliomas (both LGG and HGG) | Tumor infiltration (compared to H&E) | Sensitivity = 97.5% Specificity = 98.5% | – |
| Kalkanis et al. ( | J Neurooncol | 40 | GBM | Differentiation of GBM from gray matter and necrosis | 99.6 and 97.8% accuracy in training and validation cohorts, respectively | Utilized a training set with subsequent validation series |
| Aguiar et al. ( | Photomed Laser Surg | 172 | GBM, medulloblastoma, meningioma | Diagnosis of tumor types | Sensitivity = 97.4% Specificity = 100% | – |
| Orringer et al. ( | Nat Biomed Eng | 30 | Gliomas (both LGG and HGG) + meningioma, lymphoma, medulloblastoma, and metastases | Prediction of brain tumor subtypes (compared to H&E) | >92% accuracy | – |
| Hollon et al. ( | Cancer Res | 25 | All tumor types | Prediction of brain tumor subtypes (compared to H&E) | 92–96% accuracy | Pediatric brain tumor patients |
| Jermyn et al. ( | Sci Transl Med | 161 | Gliomas (WHO grades II-IV) | Detection of malignancy (vs. bright microscopy and MRI) | Sensitivity = 93% Specificity = 91% | In-vivo experimental design |
| Desroches et al. ( | Sci Rep | 280 | Gliomas (WHO grades II-IV) | Detection of malignancy (compared to H&E) | Sensitivity = 80% Specificity = 90% | Authors used handheld probe in swine brain biopsy model first, followed by human validation study |
Characteristics of selected studies reporting on the utility of Raman spectroscopy in tumor.
GBM, Glioblastoma multiforme; HGG, High grade glioma; LGG, Low grade glioma; MRI, Magnetic resonance imaging; WHO, World Health Organization.
Future Multimodal Techniques
Much of the recent literature on Raman spectroscopy in neurosurgical oncology revolves around the coupling of this technique to other, novel modalities in order to facilitate visualization. For instance, Neuschmelting et al. examined a combined approach of surface-enhanced Raman scattering and multispectral optoacoustic tomography in the detection of GBM cells in mouse brains. The authors reported that this new model exhibited a highly sensitive surface detection of infiltrating GBMs and could be transferrable to other animal models and potentially human trials (
Visualization in Fluorescence-Guided Surgeries
Basic Science
Numerous laboratory investigations have examined the feasibility and efficacy of handheld probes in detecting protoporphyrin IX. Kim et al. used a handheld, fiberoptic probe in order to quantify the fluorescence signal in ex vivo mouse brain tumors (
Clinical Studies
These handheld visualization devices have also been studied to assess their use and efficacy in the operating room. Haj-Hosseini et al. employed a handheld spectroscopic tool in order to make intraoperative measurements of white, gray, and known tumor tissue from patients undergoing GBM resection under 5-ALA fluorescence (
Figure 3

Intraoperative placement of the hand-held fluorescent probe on the cortical surface [With permission from Richter et al. (
Discussion
Tumor Identification Using Raman Probes
Overall, the use of handheld Raman spectroscopic imaging as an adjunct to neurosurgical resection is a promising development in brain tumor treatment and has been corroborated in a variety of clinical and basic science literature. The unique spectra allow for the differentiation of various tissue types. Numerous investigations have identified key biomarkers that can be employed to not only discriminate between tumor and normal parenchyma, but between various tumor types for both intra- and extra-axial lesions. Zhou et al., for instance, reported a detailed analysis of Raman spectra for an array of tumors, including GBM, acoustic neuroma, pituitary adenoma, and meningioma (
Intraoperative Advantages
Although numerous other modalities facilitate improved preoperative visualization of tumor, handheld spectroscopic tools offer the advantage of not only strong discriminatory capacity based on molecular footprint, but the ability to make physical adjustments intraoperatively. Unlike other visualization techniques, including intraoperative MRI, handheld probes can be angled away in order to inspect portions of the resection cavity that may not otherwise be visible. This may facilitate the identification of Raman-positive foci and removal of additional tumor. Karabeber et al. performed a study involving the surgical resection of GBM in mice, comparing resection with light microscopy, Raman microscopy, and hand-held Raman scanning (
5-ALA Visualization
Other handheld tools have been developed in order to facilitate both visualization and quantification of protoporphyrin IX concentrations for patients undergoing tumor resection with 5-ALA. While the detection of fluorescence using traditional wide-field microscopy has been challenging for LGGs and other tumor types, handheld probes offer several advantages that can improve the utility of 5-ALA for these tumors. First, the ability to place these probes in close proximity to the tissue helps ameliorate the light scatter and suboptimal angle between traditionally employed microscopes and the resection bed (
Clinical Relevance
There is substantial literature reporting the relationship between the extent of resection and subsequent postoperative outcomes in patients with brain tumors (
Conclusions
There is significant evidence demonstrating the utility of Raman spectroscopic imaging in identifying areas of malignancy in both human and animal specimens. Several studies have highlighted the use of concomitant algorithms in accurately diagnosing histologic tumor subtype and the feasibility of using handheld spectroscopy tools in the operative setting. In addition, numerous studies have demonstrated the efficacy of handheld probes in the operative quantification of protoporphyrin IX levels for patients undergoing 5-ALA fluorescence-guided resection. Further studies exploring the relationship between in-vivo spectroscopic use, extent of resection, and postoperative survival are needed to better assess the impact of these tools on patient outcomes.
Statements
Author contributions
All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.
Conflict of interest
CH is a consultant for NXDC and Synaptive Medical Inc. He will receive royalties from NXDC. He has also received speaker fees by Carl Zeiss and Leica. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
References
1.
BrownTJBrennanMCLiMChurchEWBrandmeirNJRakszawskiKLet al. Association of the extent of resection with survival in glioblastoma: a systematic review and meta-analysis. JAMA Oncol. (2016) 2:1460–9. 10.1001/jamaoncol.2016.1373
2.
XiaLFangCChenGSunC. Relationship between the extent of resection and the survival of patients with low-grade gliomas: a systematic review and meta-analysis. BMC Cancer. (2018) 18:48. 10.1186/s12885-017-3909-x
3.
KuhntDBeckerAGanslandtOBauerMBuchfelderMNimskyC. Correlation of the extent of tumor volume resection and patient survival in surgery of glioblastoma multiforme with high-field intraoperative MRI guidance. Neuro Oncol. (2011) 13:1339–48. 10.1093/neuonc/nor133
4.
SchulderMCarmelPW. Intraoperative magnetic resonance imaging: impact on brain tumor surgery. Cancer Control J Moffitt Cancer Cent. (2003) 10:115–24. 10.1177/107327480301000203
5.
CordovaJSShuHKLiangZGurbaniSSCooperLAHolderCAet al. Whole-brain spectroscopic MRI biomarkers identify infiltrating margins in glioblastoma patients. Neuro Oncol. (2016) 18:1180–9. 10.1093/neuonc/now036
6.
CordovaJSGurbaniSSOlsonJJLiangZCooperLAShuHGet al. A systematic pipeline for the objective comparison of whole-brain spectroscopic MRI with histology in biopsy specimens from grade III glioma. Tomogr Ann Arbor Mich. (2016) 2:106–16. 10.18383/j.tom.2016.00136
7.
ChanSContiFSalisburyKBlevinsNH. Virtual reality simulation in neurosurgery: technologies and evolution. Neurosurgery. (2013) 72 (Suppl 1):154–64. 10.1227/NEU.0b013e3182750d26
8.
HadjipanayisCGWidhalmGStummerW. What is the surgical benefit of utilizing 5-ALA for fluorescence-guided surgery of malignant gliomas?Neurosurgery. (2015) 77:663–73. 10.1227/NEU.0000000000000929
9.
WeiLRobertsDWSanaiNLiuJTC. Visualization technologies for 5-ALA-based fluorescence-guided surgeries. J Neurooncol. (2018) 141:495–505. 10.1007/s11060-018-03077-9
10.
RamanCV. Part II.—The Raman effect. Investigation of molecular structure by light scattering. Trans Faraday Soc. (1929) 25:781–92. 10.1039/TF9292500781
11.
DownesAElfickA. Raman spectroscopy and related techniques in biomedicine. Sensors. (2010) 10:1871–89. 10.3390/s100301871
12.
TuQChangC. Diagnostic applications of Raman spectroscopy. Nanomed Nanotechnol Biol Med. (2012) 8:545–58. 10.1016/j.nano.2011.09.013
13.
WillsHKastRStewartCRabahRPandyaAPoulikJet al.Raman spectroscopy detects and distinguishes neuroblastoma and related tissues in fresh and (banked) frozen specimens. J Pediatr Surg. (2009) 44:386–91. 10.1016/j.jpedsurg.2008.10.095
14.
DepciuchJKaznowskaEZawlikIWojnarowskaRCholewaMHeraudPet al. Application of Raman spectroscopy and infrared spectroscopy in the identification of breast cancer. Appl Spectrosc. (2016) 70:251–63. 10.1177/0003702815620127
15.
UckermannOGalliRMeinhardtMSteinerGSchackertGKirschM. Path-15. optical analysis of human brain tumors by raman spectroscopy. Neuro Oncol. (2017) 19(Suppl 6):vi173–vi173. 10.1093/neuonc/nox168.706
16.
JermynMDesrochesJMercierJSt-ArnaudKGuiotMCLeblondFet al. Raman spectroscopy detects distant invasive brain cancer cells centimeters beyond MRI capability in humans. Biomed Opt Express. (2016) 7:5129–37. 10.1364/BOE.7.005129
17.
TonnJ-CStummerW. Fluorescence-guided resection of malignant gliomas using 5-aminolevulinic acid: practical use, risks, and pitfalls. Clin Neurosurg. (2008) 55:20–26. Available online at: https://pdfs.semanticscholar.org/29de/0409643ebcdcc768ade61f30ca33d1296026.pdf
18.
LakomkinNHadjipanayisCG. Fluorescence-guided surgery for high-grade gliomas. J Surg Oncol. (2018) 118:356–61. 10.1002/jso.25154
19.
FerraroNBarbariteEAlbertTRBerchmansEShahAHBregyAet al. The role of 5-aminolevulinic acid in brain tumor surgery: a systematic review. Neurosurg Rev. (2016) 39:545–55. 10.1007/s10143-015-0695-2
20.
StummerWPichlmeierUMeinelTWiestlerODZanellaFReulenHJet al. Fluorescence-guided surgery with 5-aminolevulinic acid for resection of malignant glioma: a randomised controlled multicentre phase III trial. Lancet Oncol. (2006) 7:392–401. 10.1016/S1470-2045(06)70665-9
21.
StummerWTonnJCMehdornHMNestlerUFranzKGoetzCet al. Counterbalancing risks and gains from extended resections in malignant glioma surgery: a supplemental analysis from the randomized 5-aminolevulinic acid glioma resection study. Clinical article. J Neurosurg. (2011) 114:613–23. 10.3171/2010.3.JNS097
22.
DÃez ValleRTejada SolisSIdoate GastearenaMAGarcÃa de EulateRDomÃnguezEchávarri PAristu MendirozJ. Surgery guided by 5-aminolevulinic fluorescence in glioblastoma: volumetric analysis of extent of resection in single-center experience. J Neurooncol. (2011) 102:105–13. 10.1007/s11060-010-0296-4
23.
BelykhEMartirosyanNLYagmurluKMillerEJEschbacherJMIzadyyazdanabadiMet al. Intraoperative fluorescence imaging for personalized brain tumor resection: current state and future directions. Front Surg. (2016) 3:55. 10.3389/fsurg.2016.00055
24.
StummerWTonnJCGoetzCUllrichWSteppHBinkAet al. 5-Aminolevulinic acid-derived tumor fluorescence: the diagnostic accuracy of visible fluorescence qualities as corroborated by spectrometry and histology and postoperative imaging. Neurosurgery. (2014) 74:310–9; discussion 319–20. 10.1227/NEU.0000000000000267
25.
KairdolfBABourasAKaluzovaMSharmaAKWangMDHadjipanayisCGet al. Intraoperative spectroscopy with ultrahigh sensitivity for image-guided surgery of malignant brain tumors. Anal Chem. (2016) 88:858–67. 10.1021/acs.analchem.5b03453
26.
Haj-HosseiniNRichterJAndersson-EngelsSWårdellK. Optical touch pointer for fluorescence guided glioblastoma resection using 5-aminolevulinic acid. Lasers Surg Med. (2010) 42:9–14. 10.1002/lsm.20868
27.
JiMLewisSCamelo-PiraguaSRamkissoonSHSnuderlMVennetiSet al. Detection of human brain tumor infiltration with quantitative stimulated Raman scattering microscopy. Sci Transl Med. (2015) 7:309ra163. 10.1126/scitranslmed.aab0195
28.
KalkanisSNKastRERosenblumMLMikkelsenTYurgelevicSMNelsonKMet al. Raman spectroscopy to distinguish grey matter, necrosis, and glioblastoma multiforme in frozen tissue sections. J Neurooncol. (2014) 116:477–85. 10.1007/s11060-013-1326-9
29.
AguiarRPSilveiraLFalcãoETPachecoMTTZângaroRAPasqualucciCA. Discriminating neoplastic and normal brain tissues in vitro through Raman spectroscopy: a principal components analysis classification model. Photomed Laser Surg. (2013) 31:595–604. 10.1089/pho.2012.3460
30.
ZhouYLiuCWuBZhangCYuXChengGet al. Invited article: molecular biomarkers characterization for human brain glioma grading using visible resonance Raman spectroscopy. APL Photonics. (2018) 3:120802. 10.1063/1.5036637
31.
OrringerDAPandianBNiknafsYSHollonTCBoyleJLewisSet al. Rapid intraoperative histology of unprocessed surgical specimens via fibre-laser-based stimulated Raman scattering microscopy. Nat Biomed Eng. (2017) 1:0027. 10.1038/s41551-016-0027
32.
HollonTCLewisSPandianBNiknafsYSGarrardMRGartonHet al. Rapid intraoperative diagnosis of pediatric brain tumors using stimulated raman histology. Cancer Res. (2018) 78:278–89. 10.1158/0008-5472.CAN-17-1974
33.
JermynMMokKMercierJDesrochesJPichetteJSaint-ArnaudKet al. Intraoperative brain cancer detection with Raman spectroscopy in humans. Sci Transl Med. (2015) 7:274ra19. 10.1126/scitranslmed.aaa2384
34.
DesrochesJJermynMPintoMPicotFTremblayMAObaidSet al. A new method using Raman spectroscopy for in vivo targeted brain cancer tissue biopsy. Sci Rep. (2018) 8:1792. 10.1038/s41598-018-20233-3
35.
NeuschmeltingVHarmsenSBeziereNLockauHHsuHTHuangRet al. Dual-modality surface-enhanced resonance raman scattering and multispectral optoacoustic tomography nanoparticle approach for brain tumor delineation. Small. (2018) 14:e1800740. 10.1002/smll.201800740
36.
KarabeberHHuangRIaconoPSamiiJMPitterKHollandECet al. Guiding brain tumor resection using surface-enhanced raman scattering nanoparticles and a hand-held raman scanner. ACS Nano. (2014) 8:9755–66. 10.1021/nn503948b
37.
JermynMMercierJAubertinKDesrochesJUrmeyKKaramchandianiJet al. Highly accurate detection of cancer in situ with intraoperative, label-free, multimodal optical spectroscopy. Cancer Res. (2017) 77:3942–50. 10.1158/0008-5472.CAN-17-0668
38.
KimAKhuranaMMoriyamaYWilsonBC. Quantification of in vivo fluorescence decoupled from the effects of tissue optical properties using fiber-optic spectroscopy measurements. J Biomed Opt. (2010) 15:067006. 10.1117/1.3523616
39.
CorneliusJFPlackeJMKnippsJFischerIKampMSteigerHJ. Minispectrometer with handheld probe for 5-ALA based fluorescence-guided surgery of brain tumors: preliminary study for clinical applications. Photodiagn Photodyn Ther. (2017) 17:147–53. 10.1016/j.pdpdt.2016.12.007
40.
RichterJCOHaj-HosseiniNHallbeckMWårdellK. Combination of hand-held probe and microscopy for fluorescence guided surgery in the brain tumor marginal zone. Photodiagn Photodyn Ther. (2017) 18:185–92. 10.1016/j.pdpdt.2017.01.188
41.
ValdésPALeblondFKimAHarrisBTWilsonBCFanXet al. Quantitative fluorescence in intracranial tumor: implications for ALA-induced PpIX as an intraoperative biomarker. J Neurosurg. (2011) 115:11. 10.3171/2011.2.JNS101451
42.
ZhouYLiuCHSunYPuYBoydston-WhiteSLiuYet al. Human brain cancer studied by resonance Raman spectroscopy. J Biomed Opt. (2012) 17:116021. 10.1117/1.JBO.17.11.116021
43.
GrimbergenMCMvan SwolCFPvan MoorselaarRJAUffJMahadevan-JansenAStoneN. Raman spectroscopy of bladder tissue in the presence of 5-aminolevulinic acid. J Photochem Photobiol B. (2009) 95:170–6. 10.1016/j.jphotobiol.2009.03.002
Summary
Keywords
handheld technologies, gliomas, fluorescence-guided surgery, brain tumors, 5-ALA = 5-aminolevulinic acid, Raman spectroscopy
Citation
Lakomkin N and Hadjipanayis CG (2019) The Use of Spectroscopy Handheld Tools in Brain Tumor Surgery: Current Evidence and Techniques. Front. Surg. 6:30. doi: 10.3389/fsurg.2019.00030
Received
20 January 2019
Accepted
09 May 2019
Published
29 May 2019
Volume
6 - 2019
Edited by
Mark Preul, Barrow Neurological Institute (BNI), United States
Reviewed by
Jennifer Eschbacher, St. Joseph's Hospital and Medical Center, United States; Nikolay L. Martirosyan, University of Arizona, United States
Updates

Check for updates
Copyright
© 2019 Lakomkin and Hadjipanayis.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Constantinos G. Hadjipanayis constantinos.hadjipanayis@mountsinai.org
This article was submitted to Neurosurgery, a section of the journal Frontiers in Surgery
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.