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Intraoperative mapping of pre-central motor cortex and subcortex: a proposal for
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supplemental cortical and novel subcortical maps to Penfield’s motor homunculus
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Prajwal Ghimire1*, Jose Pedro Lavrador1, Asfand Baig Mirza1, Noemia Pereira3, Hannah
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Keeble3, Marco Borri2, Luciano Furlanetti1, Christian Brogna1, Jozef Jarosz2, Richard
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Gullan1, Francesco Vergani1, Ranjeev Bhangoo1, Keyoumars Ashkan1
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1. Department of Neurosurgery, King’s College Hospital NHS Foundation Trust, London,
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UK
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2. Department of Neuroradiology, King’s College Hospital NHS Foundation Trust,
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London, UK
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3. Neuromonitoring Team, Inomed Neurocare UK Ltd., UK
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Corresponding Author:
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Mr Prajwal Ghimire
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MBBS MRCSEd. MSc
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Department of Neurosurgery
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King’s College Hospital NHS Foundation Trust
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London, UK
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Word Count:
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Abstract: 250
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Manuscript: 2500 (excluding references, figures, tables, acknowledgements)
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References: 40
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Abstract:
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Introduction:
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Penfield’s motor homunculus describes a caricaturised yet useful representation of the map of
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various body parts on the pre-central cortex. We propose a supplemental map of the clinically
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represented areas of human body in pre-central cortex and a novel subcortical corticospinal
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tract map that are accurate and essential for safe surgery in patients with eloquent brain lesions.
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Materials and methods:
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A single-institution retrospective cohort study of patients who underwent craniotomy for motor
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eloquent lesions with intraoperative motor neuromonitoring (cortical and subcortical) between
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2015 and 2020 was performed. All positive cortical and subcortical stimulation points were
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taken into account and cartographic maps were produced to demonstrate cortical and
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subcortical areas of motor representation and their configuration. A literature review in
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PubMed was performed.
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Results:
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180 patients (58.4% male, 41.6% female) were included in the study with 81.6% asleep and
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18.4% awake craniotomies for motor eloquent lesions (gliomas 80.7%, metastases 13.8%) with
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intraoperative cortical and subcortical motor mapping. Based on the data, we propose a
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supplemental clinical cortical and a novel subcortical motor map to the original Penfield’s
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motor homunculus, including demonstration of localisation of intercostal muscles both in the
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cortex and subcortex which has not been previously described.
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Conclusion:
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The supplementary clinical cortical and novel subcortical motor maps of the homunculus
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presented here have been derived from a large cohort of patients undergoing direct cortical and
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subcortical brain mapping. The information will have direct relevance for improving the safety
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and outcome of patients undergoing resection of motor eloquent brain lesions.
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Key Words:
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Motor homunculus, subcortical map, craniotomy, corticospinal tract, motor cortex
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Introduction:
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Homunculus as described by Penfield and Boldrey in 1937 after bipolar direct cortical
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stimulation (DCS) in 126 awake patients has provided the foundation for intraoperative motor
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mapping in patients undergoing craniotomy for brain lesions1. Since then, there has been a
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range of studies on motor mapping of corticospinal tract (CST) using neuro-physiological, viral
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tracing, microstructural, cadaveric and intraoperative human and animal studies2,3,4,5. More
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recently, there has been further studies using advanced imaging techniques such as
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deterministic as well as probabilistic tractography to produce a map of the CST, including U
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fibre connections, highlighting the complex fibre connections and overlap6,7. Human
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connectome project has further provided an advanced interface to characterise the
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configuration of cortical and subcortical CST8. Difference in the size of representation of body-
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parts within the primary motor cortex has been recognized and is thought to be likely related
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to each regions’ functional specialisation and fine motor functions1,7,9.
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Advancements in the DCS and subcortical mapping techniques (monopolar stimulation,
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dynamic continuous monitoring), allow accurate measurement of the distance from CST during
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intraoperative stimulation to achieve safe lesion resection and avoid inadvertent injury to
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CST central to preserving the quality of life of the patients10,11,12. Bello et al described
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subcortical mapping in 57 patients where individual areas of hand, arm and leg were identified
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during resection of gliomas and accurate identification of CST enhanced surgical performance
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and safety maintaining a high rate of functional preservation13. Increasingly, a combination of
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pre-operative (functional magnetic resonance imaging(fMRI), diffusion tensor imaging(DTI),
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navigated transcranial magnetic stimulation(nTMS)) and intra-operative (neuronavigation,
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intra-operative ultrasound (ioUS), augmented reality microscope, 5-aminolevulinic acid (5-
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ALA)) tools are combined with direct intra-operative brain mapping to aid surgical planning
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for maximal safe resection10,11,12,13,14,15. Despite these studies and the data gathered, no updated
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homunculus nor subcortical map, based on intra-operative direct cortical/ subcortical
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stimulation, has been proposed since the original 1937 work (Supplemental Table 1).
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In this study, we propose a supplemental motor cortical map and a novel motor subcortical map
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of the configuration of the corticospinal tract initially described by Penfield and Boldrey1,9 that
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gives an insight into the cortical and subcortical representation of the body parts; critical for
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surgery in eloquent brain and for better clinical outcomes.
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Materials and Methods:
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A single-centre retrospective study was performed between January 2015 and January 2020 to
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collect intraoperative data on 180 patients who underwent craniotomy for eloquent brain
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lesions with intraoperative cortical and subcortical motor neuromonitoring at our quaternary
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referral neurosurgical centre. Patients were consented for intraoperative neuromonitoring
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including motor mapping. Prior to the surgery, all patients underwent a range of pre-operative
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brain mapping investigations to include fMRI, DTI and nTMS to evaluate the feasibility of
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lesion resection, determine the best surgical approach and help consent the patient based on
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individual’s risk profile. At surgery, 3 dimensional (3D) reconstructed structural MRI,
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tractography from DTI, fMRI hotspots and 3D reconstructed nTMS motor stimulation points
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were projected onto the brain with augmented reality using ZEISS KINEVO® 900
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microscope(CARL ZEISS Meditec AG, Jena, Germany) for the patients. These helped as
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starting points to define the relationship between the lesions and eloquent motor brain areas,
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guiding intra-operative mapping with cortical/ subcortical stimulation. Thereafter, all positive
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documented cortical and subcortical points of stimulation confirmed with intraoperative
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neuromonitoring were recorded and plotted over cartographical maps by utilizing the
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intraoperative numerically labelled pictures and correlating with intra-operative neuro-
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navigation MRI, corrected for intra-operative brain shift using the ioUS, and immediate post-
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operative anatomical T1 post gadolinium MRI. The overlap of stimulated points were also
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noted. Demographic, clinical and surgical data were collected from patients’ medical records.
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A PubMed literature review on subcortical motor mapping was performed to provide insights
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into the current position on the subcortical motor representation of human body in the literature.
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The demographic and clinical data were analysed with Microsoft Excel 2020.
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Functional Magnetic Resonance Imaging (fMRI)
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Three different tasks were performed: lip smacking, finger-tapping and foot rocking
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(Supplemental Figure 1). The cortical activated areas were used to constrain the probabilistic
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tractography.
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Diffusion tensor imaging (DTI) and deterministic tractography
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DTI sequences were obtained to reconstruct CST. The parameters utilised for obtaining
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diffusion tensor imaging were b-value: 1,500; diffusion directions: 64; diffusion mode; multi-
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directional diffusion weighting; field of view: 32 cm; voxel size,2.5*2.5*2.5 mm;
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TR/TE:9,500/86; scan time:11:35 minutes. The deterministic tractography was modelled in 3D
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with StealthViz Medtronic Software (Minneapolis, Minnesota, USA)12. The dissection of the
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corticospinal tract was performed according to the regions of interest (ROIs) between the motor
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cortex and the ipsilateral half of the medulla oblongata below the middle cerebellar peduncle
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(Figure 1). Constrained probabilistic tractography for complex motor function and
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cortical/subcortical CST was performed with MRTrix3 opensource Software16(Supplemental
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Figure 2).
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Navigated transcranial magnetic stimulation (nTMS)
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Preoperative nTMS was utilised for pre-operative motor mapping, using Nexstim TMS, v.4.3.1
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(Nexstim, Helsinki, Finland)17. nTMS was obtained with single-pulse sequence delivered using
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a figure-of-eight coil, and the motor mapping was performed at 105% of the determined resting
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motor threshold17. The nTMS preoperative positive motor responses were transformed in 3D
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objects (StealthViz Medtronic software, Minneapolis, Minnesota, USA) superimposed to the
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3D tractography model of the CST on the Medtronic Stealth Station S7/S8 neuronavigation
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software/machine (Minneapolis, Minnesota, USA) (Supplemental Figure 3).
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Cortical mapping
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Cortical motor evoked potentials (cMEPs) were recorded with direct electrical monopolar
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stimulations of primary motor cortex (Figure 2). Train of five pulses, positive pulse form,
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inter-stimuli interval of 4.0 ms, pulse width of 0.5 ms, 1Hz and anodal pole were the parameters
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for stimulations. Continuous cMEPs were monitored using a four-contact strip electrode
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positioned over the motor cortex recording stable MEPs at the motor threshold. Muscles
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monitored during intraoperative neuromonitoring were orbicularis oris, masseter, tongue,
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cricothyroid, deltoid, brachioradialis/flexor carpi ulnaris (BR/FCU), abductor pollicis
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brevis/abductor digiti minimi (APB/ADM), first dorsal interosseous (FDI), intercostals,
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quadriceps femoris, tibialis anterior, abductor hallucis.
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Subcortical mapping
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Subcortical motor evoked potentials (scMEPs) were recorded using modified monopolar
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suction probe and monopolar probe (Parameters were same as cMEP recording with cathodal
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pole)10,12(Figure 3). Muscles monitored were same as on cortical mapping.
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Intraoperative ultrasound
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Ultrasound images were obtained intraoperatively prior to corticotomy and at the end of
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resection with Esaote Ultrasound Machine (Esaote, Genova, Italy) to delineate the margins of
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the tumour and post resection cavity. It provided the configuration, depth and location of the
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lesion with respect to the motor cortex and subcortical CST identified with subcortical
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stimulation and helped to correct for any intra-operative brain shift (Supplemental Figure 4).
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Results:
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Table 1 summarises the demographics. The motor threshold during stimulation represented
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the estimated distance from the clinically detected anatomical bundle of fibres of CST
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(1mA=1mm). Cortical motor threshold of DCT of motor cortex/CST was recorded as mean of
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7.2 mA (Range:0.8 mA – 25mA, n=180). Cortical and subcortical mean stimulation threshold
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for leg (c8.4mA, range:2-17mA,n=14; sc5.8mA, range:3-13,n=11), foot (c7mA, range:5-
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12mA,n=17; sc6.5mA, range:2-14mA,n=12), intercostal muscles (c10mA, range:6-
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14mA,n=6; sc6mA, range:4-12mA,n=7), arm (c7.6mA, range:0.8-13mA,n=21; sc4.3mA,
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range:2-6mA,n=6), hand (c8.7mA, range:0.8-20mA,n=47; sc6.6mA, range:5-8.5mA,n=20)
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and face (c7.4 mA, range:2-11 mA, n=24; sc5.7 mA, range:0.5-8, n=12) were recorded during
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the procedures (Table 2,Table 3). The stimulated cortical and subcortical points were then
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plotted in the diagrammatic representation of cortex and subcortex with individual area
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stimulated. The points were then assembled into cartographic maps to demonstrate a clinical
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cortical and subcortical map of intraoperative corticospinal tract (Figure 4, Figure 5).
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Cortical and subcortical stimulation of Intercostal Muscles
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As a contribution to the previous described homunculus, we present, for the first time in the
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literature, a detailed representation at both cortical and subcortical level of the intercostal
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muscles demonstrated during routine neurophysiological mapping and monitoring
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(Supplemental Table 2). An example of isolated subcortical stimulation recording (scMEP)
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during intraoperative subcortical mapping with electrode placed in the intercostal muscles is
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shown in Supplemental Figure 5. These findings aided in the illustration of the proposed
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maps.
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Literature Review
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A PubMed literature review was performed, in order to investigate if a subcortical motor map
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was previously described, with the MeSH items ((Subcortical stimulation) OR (subcortical
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mapping) OR (subcortical intraoperative neuromonitoring) AND Motor AND corticospinal
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tract)) with filters of “articles with abstracts, adult (19+ years), English language articles,
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human studies”. It resulted in identification of 141 articles. The articles were reviewed to
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identify data on subcortical mapping of specific motor areas of patients who underwent
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craniotomy for brain lesions (Supplemental Table 1). There was no article identified
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suggesting a map for the subcortical motor areas.
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Proposed homunculus Maps
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Proposal of Supplemental map of Cortical motor Region(Clinical cortical motor Homunculus)
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The proposed supplemental cortical map consists of new addition of cortical representation of
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intercostal muscles in the existing Penfield’s motor homunculus (Figure 4).
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Proposal of map of intraoperative subcortical Corticospinal Tract (isCST) (Clinical
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Subcortical motor homunculus)
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The proposed subcortical novel map of the corticospinal tract along the corona radiata (Figure
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5) provides an insight into the configuration of CST fibres and highlights the significant
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differences between the cortical orientation and subcortical orientation of the CST fibres.
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Discussion:
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Understanding the topography of the motor pathway at both cortical and subcortical levels is
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crucial for neurosurgeons during surgery for motor eloquent brain lesions if risk of deficits is
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to be minimised. Penfield’s 1937 description of the arrangement of the motor function onto the
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homunculus, although a simplified map, provides a representative image of the motor
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arrangement of function onto the precentral cortex1. Since then, human clinical studies and
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cadaver anatomical studies have provided further insight into the complexity of the motor
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cortex and overlap of function3,7. There has been recognition of dynamic, rather than the
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traditional static, representation of the body parts on the motor cortex, especially for complex
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motor movement18,19 as well as significant overlapping of motor representation in the
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supplementary motor area (SMA), premotor, primary motor and parietal cortex20. Furthermore,
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contrary to the traditional orientation of body parts on motor cortex , multiple directions of the
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representation of have now been described: Lateral-anterior-ventral direction along the
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precentral gyrus and central sulcus, reflecting a shift from lower- to upper-body muscles21.
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Catani recently described a detailed reappraisal of the original Penfield’s findings, suggesting
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overlaps between the trasitional areas and cross over to the somatosensory cortex along with
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description of role of U fibres7. Non-human primate studies, using viral tracers, have added
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additional dimensions to this complexity by defining phylogenetically new M1 and old M1
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cortex4. Despite the spectrum of the new knowledge and techniques, from the practical point
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of view, the original Penfield’s motor homunculus remains central as a starting point when
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planning surgery for lesions in and around motor cortex, and DCS continues as the gold
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standard for intra-operative refinement. Thus, Duffau and colleagues, through DCS studies,
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were recently even able to demonstrate the concept of negative motor response whereby
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movement arrest was induced at specific stimulation points in the pre-central gyrus22. In this
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context, our supplementary motor homunculus presented here, provides a useful addition by
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clearly demonstrating the motor cortical area for the intercostal muscles, previously not
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described in detail. We first reported mapping of intercostal muscles as a technical note23. This
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has now been replicated and mapped in detail in this paper (Supplemental Table 2).
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Understanding the cortical topography of intercostal muscles is important to avoid inadvertent
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damage during the surgery which could lead to paralysis of respiratory muscles and the well-
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recognised post-operative respiratory complications.
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Unlike the motor cortex, our understanding of the detailed functional anatomy of the white
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matter motor tracts is at an earlier stage. Cadaveric anatomical and imaging studies have shown
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that corticospinal tract (CST) predominantly begins in the pre-central gyrus (M1), making its
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way caudally through the corona radiata into the internal capsule, condensing the fibres with a
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unique formation and thus producing a swirl-like configuration with the twist of the fibres
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subcortically24,25,26,27,28,29.The CST undergoes a rotation whereby the most medially located
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fibres at the cortical level (topographically – lower limb) become posterior at the level of the
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internal capsule and lateral at the level of the cerebral peduncle24,29,30,31. Primate studies have
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demonstrated the complexity of organisation of the CST fibres corresponding to the functional
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body areas and its dynamic nature32. Understanding the detailed anatomy of these tracts is
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therefore essential for safe surgery for lesions in or around the subcortical motor pathways. In
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the recent years, DTI has proved useful as a starting point to understand the relationship
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between the CST and the lesions with DTI based maps of subcortex emerging as useful tools
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for pre-operative planning6,29,33,34,35. The accuracy of the image-based technology, however,
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remains less than what is required for confident safe surgery and intra-operative direct
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stimulation of subcortical motor pathways remain the gold standard. Despite the limited
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number of papers published on subcortical stimulation (Supplemental Table 1), accurate
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intraoperative identification of cortical and subcortical boundaries has been challenging with
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no clear subcortical map, along the same line as the cortical motor homunculus, has been
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described. We therefore aimed to address it using the data from our large cohort of patients as
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demonstrated in our novel subcortical map. In this illustration and based on our intra-operative
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direct stimulation of CST, the motor areas of leg shifted from medial to the posterior, motor
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areas of hand/forearm shifted from superior to the centre of the condensed bundle and the face
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representation shifted from lateral to the anterior aspect of the condensed bundle demonstrating
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the change in CST configuration during the descent of fibres within the corona radiata. There
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were further changes in configuration prior to reaching the internal capsule: the leg area shifted
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from posterior to the midline position with the face area shifting anteriorly and the arm area
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shifting posteriorly as progressing into the known configuration of fibres in the genu and
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posterior limb of internal capsule. The subcortical map thus generated, we hope will aid in a
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better understanding of the functional anatomy of the CST and aid in safe surgery for motor
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eloquent lesions.
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As our understanding of the biology of brain lesions, particularly gliomas, evolve and concepts
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such as survivorship and preservation of quality of life, quite rightly, gain centre-stage, there
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is an ever-increasing need for maximal safe resection. This remains a challenge for lesions in
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and around the motor pathways. Understanding the cortical and subcortical functional anatomy
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is therefore crucial and it is best derived from intra-operative direct stimulation of motor
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pathways. Our findings from a large cohort of patients presented as an updated motor
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homunculus and a novel subcortical map will aid neurosurgeons in their quest to achieve the
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best outcome possible for these patients.
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Conclusion:
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Penfield’s motor homunculus represented a landmark in understating the functional anatomy
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of the motor cortex with real implications for surgery in motor eloquent brain. After an almost
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a century, however, there is now time for a reappraisal. Our data from a large cohort of patients
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undergoing modern intra-operative stimulation of motor pathways, the gold standard for brain
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mapping, generated a supplementary updated motor homunculus and a novel subcortical motor
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map. Our finding will aid surgical planning for lesions in or around the motor pathways, to
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reduce the risks and increase the extent of resection.. Further multicentre studies are required
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to validate the map towards routine utilisation in clinical practice.
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Acknowledgements:
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Authors would like to acknowledge pioneering work on direct cortical stimulation by Penfield
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and Boldrey. We are sitting on the shoulders of the giants producing this paper. Authors would
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like to acknowledge the support provided by the Department of Neurosurgery and Department
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of Neuroradiology at King’s College Hospital, London, UK and the intraoperative
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neurophysiology Team at Inomed Neurocare UK, London, UK. This paper partly represents
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independent research on BRCMAP project funded by the NIHR- Welcome Trust, King’s
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Clinical Research Facility and the National Institute for Health Research (NIHR) Biomedical
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Research Centre at South London and Maudsley NHS Foundation Trust and King’s College
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London. We would like to thank PG, Ms Aashika Sharma Lamichhane and Mrs Pilar Camino
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Alcon for their work in hand painting, illustrating and software processing of Figure 4 and 5.
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Author Contributions:
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PG drafted the manuscript. ABM carried out the collection of the patient data. PG, JPL and
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KA participated in the design of the study and in drafting discussion. MB, JPL, JJ participated
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in obtaining advanced imaging including fMRI, DTI and its analytical modelling. NP, HK
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participated in performing intraoperative neuromonitoring and its data analysis. PG, JPL, LF,
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CB, FV, KA participated in obtaining and analysing intraoperative data. RB, RG, FV and KA
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conceived of the study and participated in its design and coordination and helped to draft the
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manuscript. All authors read and approved the final manuscript.
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Funding: No funding was obtained for the study
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Competing interests: The authors report no competing interests.
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Supplementary Materials: Supplemental Table 1, 2; Supplemental Figure 1,2,3,4,5
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Captions:
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Tables
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Table 1: Demographics of the patient data
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Table 2: Cortical Stimulation of motor cortex areas with their thresholds
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Table 3: Subcortical Stimulation of motor subcortex areas with their thresholds
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Supplemental Table 1: Literature Review of Subcortical intraoperative mapping
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demonstrating each mapped area
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Supplemental Table 2: Case series of cortical and subcortical intercostal muscles Stimulation
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(MEP)
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Figures:
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Figure 1(a,b,c,d): Pre-operative 3D reconstruction of Corticospinal tract (blue, green) with
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tumour (red) utilising the pre-operative DTI and modelling using neuronavigation (Medtronic
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Stealth S7, StealthViz Software) (70y female with left precentral metastatic tumour (primary
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lung small cell carcinoma who underwent gross total resection)
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Figure 2: Cortical stimulation with monopolar probe stimulating different areas of motor
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cortex (a) 1,2,3: hand and forearm 4,5: foot and leg (b) 6,7,8,9,10,11,13,14- hand knob (ADM,
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FDI, APB, forearm, deltoid) 1,2,5- post central gyrus (c)1,2: intercostal muscles 3,4: deltoid 5:
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foot (d) 1,2: arm, forearm, hand 3,4,5: hand, face 6,7: face
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Figure 3: Subcortical stimulation with intraoperative MEPs demonstrating subcortical
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mapping of the corticospinal tract (a,b) with contact numbering corresponding to the
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mapping/stimulation positive areas with motor thresholds (1-15); 1- upper limb (8mA), face
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(5mA); 2- upper limb (8mA), face (6mA); 3- upper limb (7mA), face (2mA); 4- upper limb
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(5mA), face (2mA); 5- upper limb (7mA), face (4mA); 6- face (2mA); 7- upper limb (6mA), face
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(5mA); 8- upper limb (8mA); 9- face (6mA); 10- upper limb (7mA), lower limb (10mA), face
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(6mA); 11- face (8mA); 12- upper limb, face (13mA); 13- upper limb (8mA), face (7mA); 14-
566
upper limb (12mA), face (11mA); 15- upper limb (19mA), face (17mA)
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Figure 4: Proposed Provisional Supplemental Cortical Motor Homunculus including the
568
cortical somatotopy of intercostal muscles: (a) cortical motor representation (b,c): Primary
569
motor cortex reconstructed with Meshlab opensource software36 with the data available from
570
The Human Brainnectome Atlas37
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Figure 5: Illustration demonstrating intraoperative subcortical Corticospinal Tract (isCST) (the
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novel “Clinical subcortical motor homunculus”)
573
574
18
Supplementary Figure 1 (a,b,c): fMRI demonstrating complex motor function mapping (a-
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foot rock task, b-Finger tapping, c-lip smacking) demonstrating cortical complex motor
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function representation of CST (36y left-handed female with recurrent right frontal
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transformed WHO Grade III IDH 1 mutant MGMT methylated anaplastic gemistocytic
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astrocytoma who underwent subtotal resection)
579
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Supplementary Figure 2 (a,b,c,d): Pre-operative 3D Reconstruction of Cortical and
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subcortical corticospinal tract (foot: blue circle, hand: orange circle, face: yellow circle
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representation) utilizing Constrained Probabilistic tractography and modelling (MRTrix
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opensource software16) (36y left-handed female with recurrent right frontal transformed WHO
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Grade III IDH 1 mutant MGMT methylated anaplastic gemistocytic astrocytoma who
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underwent subtotal resection)
586
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Supplemental Figure 3 (a,b,c): Integration of nTMS motor stimulation points with DTI
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reconstruction with neuronavigation (StealthStation Medtronic S7 machine, StealthViz
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software) (White -Tumour, Red – CST (Face + Upper Limb), Green – CST (Lower Limb),
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Yellow dots – TMS Motor map, Blue Tractography – CST (contralateral to the lesion))(22y
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male with right cystic-solid parietal WHO grade I IDH wildtype, ATRX wildtype, MGMT
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unmethylated pilocytic astrocytoma who underwent gross total resection)
593
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Supplementary Figure 4 (a,b,c): Intraoperative pre-resection ultrasound (ioUS)
595
demonstrating right frontal tumour and its relation to the pre-central cortex at the cortical and
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subcortical level ; (d): Intraoperative image with cortical mapping (Tag 1 – Lower Limb, Tag
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2 – Lower Limb and Intercostal Muscles, Tag 3 – Intercostal Muscles, Tag 4 – Forearm, Strip
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Number 1 – Monitoring the Foot, Strip Number 2 – Monitoring the Hand)(Black arrow: tumour
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location, blue arrow: cortical motor cortex and subcortical CST)(36y left-handed female with
600
recurrent right frontal transformed WHO Grade III IDH 1 mutant MGMT methylated
601
anaplastic gemistocytic astrocytoma who underwent subtotal resection)
602
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Supplementary Figure 5: Isolated Subcortical stimulation of intercostal muscles during
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intraoperative subcortical mapping
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19
Figure 1(a,b,c,d): Pre-operative 3D reconstruction of Corticospinal tract (blue, green) with
609
tumour (red) utilising the pre-operative DTI and modelling using neuronavigation (Medtronic
610
Stealth S7, StealthViz Software) (70y female with left precentral metastatic tumour (primary
611
lung small cell carcinoma who underwent gross total resection)
612
613
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615
616
617
618
619
620
621
20
Figure 2: Cortical stimulation with monopolar probe stimulating different areas of motor
622
cortex (a) 1,2,3: hand and forearm 4,5: foot and leg (b) 6,7,8,9,10,11,13,14- hand knob (ADM,
623
FDI, APB, forearm, deltoid) 1,2,5- post central gyrus (c)1,2: intercostal muscles 3,4: deltoid 5:
624
foot (d) 1,2: arm, forearm, hand 3,4,5: hand, face 6,7: face
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628
629
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632
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21
Figure 3: Subcortical stimulation with intraoperative MEPs demonstrating subcortical
641
mapping of the corticospinal tract (a,b) with contact numbering corresponding to the
642
mapping/stimulation positive areas with motor thresholds (1-15); 1- upper limb (8mA), face
643
(5mA); 2- upper limb (8mA), face (6mA); 3- upper limb (7mA), face (2mA); 4- upper limb
644
(5mA), face (2mA); 5- upper limb (7mA), face (4mA); 6- face (2mA); 7- upper limb (6mA), face
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(5mA); 8- upper limb (8mA); 9- face (6mA); 10- upper limb (7mA), lower limb (10mA), face
646
(6mA); 11- face (8mA); 12- upper limb, face (13mA); 13- upper limb (8mA), face (7mA); 14-
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upper limb (12mA), face (11mA); 15- upper limb (19mA), face (17mA)
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23
Figure 4: Proposed Provisional Supplemental Cortical Motor Homunculus including the
709
cortical somatotopy of intercostal muscles: (a) cortical motor representation (b,c): Primary
710
motor cortex reconstructed with Meshlab opensource software36 with the data available from
711
The Human Brainnectome Atlas37
712
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24
Figure 5: Illustration demonstrating intraoperative subcortical Corticospinal Tract (isCST) (the
725
novel “Clinical subcortical motor homunculus”)
726
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728
25
729
Table 1: Demographics of the patient data
730
731
Demographics
Data
Mean Age (years) (with Range)
50 (16-79)
Laterality of the lesion
Right
Left
N (%)
97 (53.8%)
83 (46.2%)
Gender
Male
Female
N (%)
105 (58.4%)
75 (41.6%)
Pathology of the lesion
Glioma
-High Grade (III,IV)
-Low Grade (I,II)
Meningioma
Metastasis
Vascular malformations
104 (57.7%)
41 (23%)
8 (4.4%)
25 (13.8%)
2 (1.1%)
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
26
Table 2: Cortical Stimulation of motor cortex areas with their thresholds
748
Cortical Stimulation
MT
Intraoperative Representation (Tag Numbers)
Leg
12mA
1,2,3: hand and forarm
4, 5: foot and leg
Intercostal Muscles
12mA
1,2-intercostals
3,4-deltoid
5 -Foot
Arm
10mA
1,2 – arm, forearm, hand
3,4,5 – hand and face
6,7 – face
Hand
6mA
6,7,8,9,10,11,13,14- hand knob (ADM, FDI, APB,
forearm, deltoid)
1,2,5- post central gyrus
Face
10mA
5,6,7- Face
Black Arrow: Tumour causing expansion of motor/pre-motor cortex, ADM: abductor digiti minimi ,FDI: first
749
dorsal interossei , APB: abductor pollicis brevis , MT: motor threshold
750
27
Table 3: Subcortical Stimulation of motor subcortex areas with their thresholds
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Subcortical
Stimulation
MT
Representative Demonstration
Leg
4mA
1,2,3- hand
5- face
6- foot
7,8,9- UL, LL
6,7,8- 5-7mA
9- 4mA
Intercostal muscles
4mA
1,2,3,10- hand, forearm (10 mA)
4,5- foot, leg (12 mA)
6- Intercostal Muscles
7,8- foot, leg
9- hand, forearm (5 mA)
Arm
Hand
Face
20mA
1,2,3- Intercostal muscles (cortical)
4- Deltoids (arm)
5- foot
6,8- Hand
7- UL, LL, Face, Intercostal muscles
9- Intercostal muscles (subcortical) 12mA
10- Hand (subcortical)
Green- Superimposed CST model with operating microscope
UL: upper limbs, LL: lower limbs, MT: motor threshold, CST: corticospinal tract
753
754