- Email: [email protected]
Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery
Journal of Clinical Neuroscience xxx (xxxx) xxx
Contents lists available at ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery Spyridoula Tsetsou a, William Butler b, Lawrence Borges b, Emad N. Eskandar b,d, Katie P. Fehnel b,c, Reiner B. See a, Mirela V. Simon a,⇑ a
Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States Deparmernt of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States Department of Neurosurgery, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States d Department of Neurosurgery, Albert Einstein College of Medicine, New York, NY, United States b c
a r t i c l e
i n f o
Article history: Received 28 October 2019 Accepted 11 January 2020 Available online xxxx Keywords: Spinal cord mapping Direct spinal cord stimulation Corticospinal tract
a b s t r a c t Object: Spinal cord surgeries carry a high risk for significant neurological impairments. The initial techniques for spinal cord mapping emerged as an aid to identify the dorsal columns and helped select a safe myelotomy site in intramedullary tumor resection. Advancements in motor mapping of the cord have also been made recently, but exclusively with tumor surgery. We hereby present our experiences with dynamic mapping of the corticospinal tract (CST) in other types of spinal cord procedures that carry an increased risk of postoperative motor deficit, and thus could directly benefit from this technique. Case reports: Two patients with intractable unilateral lower extremity pain due to metastatic disease of the sacrum and a thoraco-lumbar chordoma, respectively underwent thoracic cordotomy to interrupt the nociceptive pathways. A third patient with progressive leg weakness underwent cord untethering and surgical repair of a large thoracic myelomeningocele. In all three cases, multimodality intraoperative neurophysiologic testing included somatosensory and motor evoked potentials monitoring as well as dynamic mapping of the CST. Conclusion: CST mapping allowed safe advancement of the cordotomy probe and exploration of the meningocele sac with untethering of the anterior-lateral aspect of the cord respectively, resulting in postoperative preservation or improvement of motor strength from the pre-operative baseline. Stimulus thresholds varied likely with the distance between the stimulating probe and the CST as well as with the baseline motor strength in the mapped myotomes. Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction Spinal cord contains important sensory and motor tracts (Fig. 1) that are difficult to locate and visualize reliably, especially in presence of lesions distorting the local anatomy. Thus, neurophysiologic techniques for identification of sensory [1–6] and motor [6–13] (table 1) pathways have been primarily employed for safe resection of intramedullary tumors. However, they can also inform other surgeries, e.g. those requiring an anterior and/or lateral approach, by offering safe guidance via dynamic delineation of the nearby motor tracts. We report our experience with motor mapping in two such high-risk procedures: open cordotomy for oncologic pain
⇑ Corresponding author. E-mail address: [email protected] (M.V. Simon).
management (two patients) and untethering of the anterior thoracic cord during myelomeningocele repair (one patient). 2. Case reports Standard multimodality neurophysiologic techniques (upper and lower limbs somatosensory evoked potentials (SSEP), transcranially evoked muscle motor evoked potentials (tcmMEP) and motor mapping [11–13]) as well as standardized anesthesia protocol [3,5] were used. 2.1. Case # 1 A 49-year-old female with lung adenocarcinoma and sacral metastasis presented with intractable right leg pain. She underwent T3-4 cordotomy for interruption of the nociceptive pathways (Figs. 2 and 3). However, selective disruption of the latter is
https://doi.org/10.1016/j.jocn.2020.01.054 0967-5868/Ó 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
2
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
challenging, given their proximity to important tracts including the lateral and anterior CST (Figs. 1 and 2). A safe path of entry for the Jacobson probe was created with the help of cathodal stimulation via a handheld monopolar stimulator. After mapping of the lateral cord, the stimulator was slowly advanced towards the location of the spinothalamic tracts (STT), while continuously stimulating tissue at 0.4 mA. At an early point along its trajectory, high amplitude direct muscle motor evoked potentials (dmMEP) were triggered in all left leg muscles. The probe advancement was immediately stopped, and the stimulus intensity was decreased. The lowest current that triggered dmMEP in isolated muscle groups was 0.15 mA (Fig. 3). The stimulator trajectory was readjusted until no dmMEP were triggered, and advancement continued while stimulating at 0.2 mA. Postoperatively, the patient had resolution of pain and preservation of the strength in the left leg.
2.2. Case # 2 A 67-year-old female with a history of spine chordoma, bilateral lower extremities weakness and intractable right leg pain underwent the same procedure as above. In her case, isolated robust left quadriceps dmMEP were triggered at 1 mA. The threshold was higher than expected and assumed to be related to the longer distance between the tip of the stimulator and the CST fibers. As such, the stimulus intensity was decreased to 0.4 mA when only intermittent responses were seen. The surgeon readjusted the trajectory and the advancement of the probe continued until reproducible high amplitude dmMEP were again seen, this time in the right AH muscle. This was consistent with the surgeon’s assessment that the probe reached the anterior midline septum (Fig. 4). At the end of the procedure, the left quadriceps tcmMEP were significantly decreased. Postoperatively, the patient was pain free, but did show temporary worsening of the left hip flexion. At one month follow, the strength had returned to the pre-operative baseline.
2.3. Case #3
Fig. 1. Spinal cord anatomy A-Cross-section of the spinal cord, distribution of the long tracts. LCST = lateral corticospinal tract; ACST = anterior corticospinal tract; ASTT = anterior spinothalamic tract; LSTT = lateral spinothalamic tract; GF = gracilis fasciculus; CF = cuneate fasciculus; 1 = rubrospinal tract; 2 = reticulospinal tract; 3 = olivospinal tract; 4 = vestibulospinal tract; 5 = posterior spinocerebellar tract; 6 = anterior spinocerebellar tract Somatotopic organization of fibers in different tracts: S = sacral; L = lumbar; T = thoracic; C = cervical. B-Lateral and anterior CST. 90% of the fibers decussate in the medullary pyramids to form the contralateral lateral CST (Lat CST) that descends in the spinal cord in the lateral funiculus. 10% of the fibers do not cross and descend through the ipsilateral anterior funiculus as ipsilateral anterior CST (Ant CST); very few fibers, through the ipsilateral lateral funiculus to form ipsilateral lateral CST.
A 74-year-old male presented with subacute worsening of chronic leg weakness (left > right). Neuroimaging demonstrated vertebral spine segmentation anomalies and a defect of the anterior thoracic spine at T3-T7 with an extruded meningocele in the mediastinum containing a tethered right ventro-lateral cord (Fig. 5). The patient underwent right thoracotomy, with partial T4 corpectomy and microsurgical release of the tethered spinal cord. The meningocele sac was identified and opened. A gliotic band extending towards an opened defect of spinal canal tethered the ventro-lateral cord. Significant adhesions impaired delineating a clear plane of separation between the spinal cord, fibrous tissue and the meningocele sac. The meningocele exploration, identification and untethering of the right anterior-lateral cord was safely achieved by using continuous electrical stimulation via a handheld monopolar probe. The lowest current that triggered dmMEP in the right leg muscles was 1.5 mA. This intensity was further used for negative mapping during exploration of the thecal sac and demarcation of the anterior cord from regions of the fibrous band. The patient showed mild improvement in the right leg muscle strength in the immediate postoperative period and further improvement at one month follow up. Table 2 summarizes the specifics of motor mapping and monitoring and their relationship with the pre and post-operative motor strength in all three patients.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
3
Table 1 Techniques of motor mapping of the spinal cord as described in the literature. Author
Probe
Stimulation settings
Stimulus intensity range (thresholds)
Recording
Duffau et al, 1998 [7]
Bayonet bipolar microprobe, prongs 5 mm apart, 1 mm tips Handheld stimulator
Repetitive biphasic pulses at 60 Hz, 1 ms pulse width, for 1 s
Observed triggered clinical motor responses
Not specified
1–0.4 mA (0.4, 0.9 and 1 mA) 2 mA (2 mA)
QuinonesHinojosa et al, 2002 [1] Gandhi, et al, 2015 [9]
Ojemann, bipolar stimulator, prongs 5 mm apart
Repetitive pulses at 60 Hz, 1 ms pulse width, for 1 s
1–0.75 mA (0.75, 1 mA)
Kartush concentric bipolar stimulating prob, 2 mm width
Repetitive biphasic pulses at 60.11 Hz, 1.0 ms pulse width, for 1–2 s
0.1 1.0 mA (0.1, 1 mA)
Costa et al, 2015 [10]
Epidural electrode
Repetitive pulses at 3–5 Hz, 0.3 ms pulse width, 30–100 averaged trials
up to 30 mA (up to 30 mA)
Barzilai et al, 2017 [11]
Continuous monopolar cathodal stimulation via CUSA Bipolar concentric
Repetitive trains, 3–5 pulses/train, 0.2–0.5 ms pulse width, ISI 3 ms, ITI 0.5–1 s Dual trains, 3–5 pulses//train, 0.5 ms pulse width, ISI 2–4 ms, ITI 60 ms
0.3–2.5 mA (0.3 to 2.5 mA)
Intermittent monopolar cathodal stimulation with handheld stimulator
Repetitive trains, 5 pulses/train, 0.5 ms pulse width, ISI 4 ms, ITI 0.5 s
0.2–0.5 mA (0.5 mA)
Deletis et al, 2001 [8]
Deletis et al, 2018 [12]
Simon et al, 2018 [13]
0.3–5 mA (0.3 to 5 mA)
Collision technique: decrease in D waves amplitudes orthodotromically triggered by transcranial electrical stimulation, due to their collision with D waves antidromically triggered by direct intramedullary stimulation of CST (anti-D wave) Triggered electrophysiologic muscle responses recorded on free run EMG recordings from APB-ADM, TA-Gas, AH-ADM pedis LFF 30 Hz, HFF 1 kHz Sens 200 mV/div, Timebase 1 s Triggered electrophysiologic muscle responses recorded on free run EMG recordings from hand, TA, medial Gas, AH, EHL LFF 30 Hz, HFF 500 Hz Sens 200 uV/div, Timebase 10 ms/div Anti-D wave recorded from scalp electrodes Fz-FPz, Cz-FPz, with a latency shorter than that of the gracilis SSEPs LFF 10–300 Hz, HFF 1 kHz Sens 1–2.5 uV/div, Timebase 5 ms/div Triggered mMEP Recorded in a variety of muscle channels: Delt, Bic, Tric, APB, ADM, AT, AH, Quad Triggered mMEP Recorded in a variety of muscle channels: delt, Bic, Tric, EDC, APB, ADM, TA, AH, Quad, Gas LFF 5 Hz, HFF 2 kKz Triggered mMEP Recorded in a variety of muscle channels: Quad, Ham, TA, Gas, AH, AS LFF 30 Hz, HFF 2 kHz Sens 20 uV/div, Timebase 10 ms/div
ADM = adductor digiti minimi, AH = abductor hallucis, APB = abductor pollicis brevis, AS = anal sphincter, Bic = biceps, CST = corticospinal tract, Delt = deltoid, EDC = extensor digitorum communis, EHL = extensor hallucis longus, EMG = electromyography, Gas = gastrocnemius, Ham = hamstring, HFF = high frequency filter, ISI = interstimulus interval, ITI = intertrial interval, LFF = low frequency filter, mMEP = muscle Motor Evoked Potentials, Quad = quadriceps, Sens = sensitivity, SSEPs = somatosensory evoked potentials, TA = tibialis anterior, Tric = triceps.
Fig. 2. Open left cordotomy. Excerpts from Tomycz L, Forbes J, Ladner T, et al. Open thoracic cordotomy as a treatment option for severe, debilitating pain. J Neurol Surg A Cent Eur Neurosurg 2014;75(2):126–32. with permission Ó Georg Thieme Verlag KG. A-After hemilaminectomy and durotomy, the dentate ligament (DL) is identified, cut and pulled; under its traction, the cord is mildly rotated posteriorly by 45° to gain better access to the anterolateral aspect of the cord, and thus to the nociceptive pathways to be transected. The shaded area (better shown in B) indicates their location within the lateral and anterior funiculi. B-Region targeted during the procedure (shaded) and the tracts of interest: LSTT = lateral spinothalamic tract; LCST = lateral corticospinal tract; 1 = ventral spinocerebellar tract; 2 = vestibulospinal tract; 3 = ascending sympathetic fibers for distal vasomotor and sudomotor innervation; 4 = descending parasympathetic fibers innervating the bowel and bladder; 5 = anterior spinothalamic tract and 6 = anterior corticospinal tract.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
4
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
Fig. 3. Patient 1 left cordotomy: path of entry. A-The surgeon approached the cord from the left dorso-lateral quadrant. The cord was gently rotated to the right, to get exposure to the left antero-lateral quadrant. A handheld monopolar stimulator (asterix) was used to stimulate the cord. No compound muscle action potentials (CMAPs) were triggered when stimulating medial to the dorsal root entry zone, where dorsal columns are located (black arrow). As the surgeon marched from the dorsal cord towards ipsilateral and more anterior aspect, stimulation at 0.4 mA triggered CMAPs in left leg muscles, signaling proximity of the LCST. B-As the stimulator was slowly advanced through a negatively mapped area, isolated CMAPs were suddenly triggered as low as 0.15 mA, primarily in the left abductor halluces (AH) muscle (red arrow); this prompted readjustment of the probe’s trajectory until no further responses were triggered. C-Diagram showing the trajectory of the stimulator (blue arrow) to create a safe path of entry for the Jacobson probe.
3. Discussion Supratentorial CST mapping thresholds depend on the type of stimulation probe and paradigm used [14], distance between the stimulation site and fibers location [15,16] as well as on the
excitability of motor pathways distal to the stimulation. The latter is directly influenced by anesthesia and pathology [17,18]. We used cathodal monopolar multipulse train technique for two reasons. First, the radial current spread from the tip of a cathodal monopolar probe allows optimal depolarization of different
Fig. 4. Patient 2, dynamic motor mapping. The red arrows point to CMAPs triggered in left quadriceps muscle at 1 mA (~20:52) and 0.4 mA (~20:53) and then in the right abductor hallucis (AH) muscle at 0.4 mA (~20:55). Notice the difference in amplitudes and morphologies between the right AH and left quadriceps CMAPs triggered at same intensity.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
5
Fig. 5. Thecal sac exploration and untethering of the ventrolateral cord. A-T2 Sagittal cervico-thoracic spine MRI sequence showing segmentation defect of the anterior thoracic spine and extruded myelomeningocele in the mediastinum. A-Neurophysiologic recordings: Left: robust muscle motor evoked potentials (mMEP) in the right anterior tibialis (AT), abductor halluces (AH) and gastrocnemius (Gas) muscles when stimulating the right ventrolateral aspect of the cord at 1.5 mA. Right: right posterior tibial somatosensory evoked potentials (SSEPs) during the case. A- Dynamic motor mapping during exploration of the thecal sac and cord untethering, displayed chronologically, with earlier traces on the top.
orientated motor nerves at lowest thresholds [14,19,20], and thus increases the specificity of stimulation. Second, the multipulse paradigm triggers time-locked mMEP that are easier to quantify and suitable for continuous mapping [11,21] under general anesthesia [22].
As expected, our threshold varied, likely with the distance between the stimulation site and the motor fibers. Additionally, mapping and monitoring of diseased myotomes required higher direct and transcranial currents respectively. In retrospect, the
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
6
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
Table 2 Motor mapping and monitoring and their relationship with pre and post-operative motor exam. Type of surgery (spine level)
Preoperative legs motor exam
Muscle channels
1 Left cordotomy (T3-4) Right: 2 to 3 Left: 5
BR, Hand, IPS, Quad, TA AH, Gas, Ham, AS 2 Left cordotomy (T2-3) Right: 4+ to 5 BR, Hand, IPS, Quad, Left: 4+ prox TA, AH, Gas, Ham 0 distal
3 Myelomeningocele repair and cord untethering (T3-T7)
Right: 3 to 4 Left: 2 to 4
Threshold tcmMEP (V) Double trains, 3–6 pulses/train, 0.05 ms pulse width, ITI 300 ms
tcmMEP Threshold dmMEP (mA) 6 pulses/train, 0.5 ms pulse changes width, ISI 4 ms, train frequency 2 Hz
Right: 400 Left: 250
0.15 left AH > AT > Gas
Right: 300 all mm Left: 400 (only IPS, Quad obtained)
Right: 400 all Hand, IPS, Quad, TA, AH, Gas, Ham, Left: 400 (only AH, AS) AS
Postoperative legs motor exam
Right: No Left: No
Right: 2–3 Left: 5
0.4 right AH 1 left Quad
Right: No Left: >80% drop in left quad tcmMEP
1.5 right TA, AH and Gas
Right: No Left: No
Right: 4+ to 5 Left: 2–3 proximal (POD#1) 4+ proximal (POD#30) 0 distal Right: 4 to 4+ (POD, #1), 5 (POD#30) Left: 2 to 4
BR = brachioradialis, IPS = iliopsoas, Quad = quadriceps, TA = tibialis anterior, AH = abductor halluces, Gas = gastrocnemius, Ham = hamstring, AS = anal sphincter, tcmMEP = transcranially evoked muscle motor evoked potentials, dmMEP = direct triggered muscle Motor Evoked Potentials.
post-procedure worsening of the left quadriceps tcmMEP, and of its strength (case #2) raises the questions whether the dynamic mapping in this patient should have been performed at higher currents. Direct stimulation of the dorsal columns can trigger mMEP antidromically via a sensory reflex [12]. As such, a legitimate question is whether we nonselectively stimulated the motor pathways. Unlike in cases of intramedullary tumor resection, the surgical approach in both open cordotomy and ventral cord untethering and the absence of infiltrative pathology allowed a reliable appreciation of the location of the stimulation in relationship to the location of the CST and DC within the spinal cord. Stimulation at threshold further contributed to the selectiveness of mapping. Whenever dmMEP were triggered, the current was decreased to an on/off response. We consistently triggered mMEP at very small currents, that were often isolated to one myotome distal to the spinal level at which stimulation took place. Our results are in accord with findings by other authors [9,11–13] showing that stimulation of isolated CST fascicles is possible and support the hypothesis that CST maintains a somatotopic organization at the spinal cord level.
4. Conclusion To our knowledge this is the first report of continuous CST mapping in spinal cord surgeries other than tumor resection. We’ve found good correlation between tcmMEP monitoring, CST mapping and post-operative motor outcome. The mapping thresholds showed variability that seemed to depend not only on the distance between the stimulating probe and CST fibers but also on the patient’s motor function baseline. Our results need confirmation in a larger study that will allow a systematic analysis of these thresholds and of their significance.
Study funding This work did not receive any funding.
Disclosures The authors report no disclosures to the manuscript.
References [1] Quinones-Hinojosa A, Gulati M, Lyon R, et al. Spinal cord mapping as an adjunct for resection of intramedullary tumors: surgical technique with case illustrations. Neurosurgery 2002;51:1199–207. [2] Yanni DS, Ulkatan S, Deletis V, et al. Utility of neurophysiological monitoring using dorsal column mapping in intramedullary spinal cord surgery. J Neurosurg Spine 2010;12(6):623. [3] Simon MV, Chiappa KH, Borges L. Phase reversal of somatosensory evoked potentials triggered by Gracilis tract stimulation: a new technique for neurophysiologic dorsal column mapping. Neurosurgery 2012;70(3):E783–8. [4] Mehta AI, Mohrhaus CA, Husain AM, et al. Dorsal column mapping for intramedullary spinal cord tumor resection decreases dorsal column dysfunction. J Spinal Disord Tech 2012;25(4):205–9. [5] Nair MD, Kumaraswamy DV, Braver FD, et al. Dorsal column mapping via phase reversal method: the refined technique and clinical applications. Neurosurgery 2014;74(4):437–63. [6] Scibilia A, Terranova C, Rizzo V, et al. Intraoperative neurophysiological mapping and monitoring in spinal tumor surgery: sirens or indispensable tools?. Neurosurg Focus 2016;41(2):E18. [7] Duffau H, Capelle L, Sichez J. Direct spinal cord electrical stimulations during surgery of intramedullary tumoral and vascular lesions. Stereotact Funct Neurosurg 1998;71(4):180–9. [8] Deletis V, Camargo BD. Interventional neurophysiological mapping during spinal cord procedures. Stereotact Funct Neurosurg 2001;77(1):25–8. [9] Gandhi R, Curtis CM, Cohen-Gadol AA. High-resolution direct microstimulation mapping of spinal cord motor pathways during resection of an intramedullary tumor. J Neurosurg Spine 2015;22(2):205–10. [10] Costa P, Deletis V. Cortical activity after stimulation of the corticospinal tract in the spinal cord. Clin Neurophysiol 2016;127(2):1726–33. [11] Barzilai O, Lidar Z, Constantini S, et al. Continuous mapping of the corticospinal tracts in intramedullary spinal cord tumor surgery using an electrified ultrasonic aspirator. J Neurosurg Spine 2017;27(2):161–8. [12] Deletis V, Seidel K, Sala F, et al. Intraoperative identification of the corticospinal tract and dorsal column of the spinal cord by electrical stimulation. J Neurol Neurosurg Psychiatry 2018;89(7):754–61. [13] Simon MV, Borges L. Intramedullary spinal cord tumor resection. In: Simon MV, editor. Intraperative neurophysiology: a comprehensive guide to monitoring and mapping. New York: Springer Publishing Company/Demos Medical; 2018. p. 389–424. [14] Szelényi A, Senft C, Jardan M, et al. Intra-operative subcortical electrical stimulation: a comparison of two methods. Clin Neurophysiol 2011;122 (7):1470–5. [15] Kamada K, Todo T, Ota T, et al. The motor-evoked potential threshold evaluated by tractography and electrical stimulation. J Neurosurg 2009;111 (4):785–95. [16] Nossek E, Korn A, Shahar T, et al. Intraoperative mapping and monitoring of the corticospinal tracts with neurophysiological assessment and 3dimensional ultrasonography-based navigation. J Neurosurg 2011;114 (3):738–46. [17] Journee HL, Berends HI, Kruyt MC. The percentage of amplitude decrease warning criteria for transcranial MEP monitoring. J Clin Neurophysiol 2017;34 (1):22–31. [18] Dineen J, Simon MV. Neurophysiologic tests in the operating room. In: Simon MV, editor. Intraoperative neurophysiology: a comprehensive guide to monitoring and mapping. New York: Springer Publishing Company/Demos Medical; 2018. p. 1–57. [19] Lorente de No’ R. A study of nerve physiology. Stud Rockefeller Inst Med Res Repr 1947;132:1–548.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx [20] Rudin DO, Eisenman G. The action potential of spinal axons in vitro 3. J Gen Physiol 1954;37:505–38. [21] Raabe A, Beck J, Schucht P, et al. Continuous dynamic mapping of the corticospinal tract during surgery of motor eloquent brain tumors: evaluation of a new method. J Neurosurg 2014;120(5):1015–24.
7
[22] Taniguchi M, Cedzich C, Schramm J. Modification of cortical stimulation for motor evoked potentials under general anesthesia: Technical description. Neurosurgery 1993;32(2):219–26.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
Contents lists available at ScienceDirect
Journal of Clinical Neuroscience journal homepage: www.elsevier.com/locate/jocn
Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery Spyridoula Tsetsou a, William Butler b, Lawrence Borges b, Emad N. Eskandar b,d, Katie P. Fehnel b,c, Reiner B. See a, Mirela V. Simon a,⇑ a
Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States Deparmernt of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States Department of Neurosurgery, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States d Department of Neurosurgery, Albert Einstein College of Medicine, New York, NY, United States b c
a r t i c l e
i n f o
Article history: Received 28 October 2019 Accepted 11 January 2020 Available online xxxx Keywords: Spinal cord mapping Direct spinal cord stimulation Corticospinal tract
a b s t r a c t Object: Spinal cord surgeries carry a high risk for significant neurological impairments. The initial techniques for spinal cord mapping emerged as an aid to identify the dorsal columns and helped select a safe myelotomy site in intramedullary tumor resection. Advancements in motor mapping of the cord have also been made recently, but exclusively with tumor surgery. We hereby present our experiences with dynamic mapping of the corticospinal tract (CST) in other types of spinal cord procedures that carry an increased risk of postoperative motor deficit, and thus could directly benefit from this technique. Case reports: Two patients with intractable unilateral lower extremity pain due to metastatic disease of the sacrum and a thoraco-lumbar chordoma, respectively underwent thoracic cordotomy to interrupt the nociceptive pathways. A third patient with progressive leg weakness underwent cord untethering and surgical repair of a large thoracic myelomeningocele. In all three cases, multimodality intraoperative neurophysiologic testing included somatosensory and motor evoked potentials monitoring as well as dynamic mapping of the CST. Conclusion: CST mapping allowed safe advancement of the cordotomy probe and exploration of the meningocele sac with untethering of the anterior-lateral aspect of the cord respectively, resulting in postoperative preservation or improvement of motor strength from the pre-operative baseline. Stimulus thresholds varied likely with the distance between the stimulating probe and the CST as well as with the baseline motor strength in the mapped myotomes. Ó 2020 Elsevier Ltd. All rights reserved.
1. Introduction Spinal cord contains important sensory and motor tracts (Fig. 1) that are difficult to locate and visualize reliably, especially in presence of lesions distorting the local anatomy. Thus, neurophysiologic techniques for identification of sensory [1–6] and motor [6–13] (table 1) pathways have been primarily employed for safe resection of intramedullary tumors. However, they can also inform other surgeries, e.g. those requiring an anterior and/or lateral approach, by offering safe guidance via dynamic delineation of the nearby motor tracts. We report our experience with motor mapping in two such high-risk procedures: open cordotomy for oncologic pain
⇑ Corresponding author. E-mail address: [email protected] (M.V. Simon).
management (two patients) and untethering of the anterior thoracic cord during myelomeningocele repair (one patient). 2. Case reports Standard multimodality neurophysiologic techniques (upper and lower limbs somatosensory evoked potentials (SSEP), transcranially evoked muscle motor evoked potentials (tcmMEP) and motor mapping [11–13]) as well as standardized anesthesia protocol [3,5] were used. 2.1. Case # 1 A 49-year-old female with lung adenocarcinoma and sacral metastasis presented with intractable right leg pain. She underwent T3-4 cordotomy for interruption of the nociceptive pathways (Figs. 2 and 3). However, selective disruption of the latter is
https://doi.org/10.1016/j.jocn.2020.01.054 0967-5868/Ó 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
2
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
challenging, given their proximity to important tracts including the lateral and anterior CST (Figs. 1 and 2). A safe path of entry for the Jacobson probe was created with the help of cathodal stimulation via a handheld monopolar stimulator. After mapping of the lateral cord, the stimulator was slowly advanced towards the location of the spinothalamic tracts (STT), while continuously stimulating tissue at 0.4 mA. At an early point along its trajectory, high amplitude direct muscle motor evoked potentials (dmMEP) were triggered in all left leg muscles. The probe advancement was immediately stopped, and the stimulus intensity was decreased. The lowest current that triggered dmMEP in isolated muscle groups was 0.15 mA (Fig. 3). The stimulator trajectory was readjusted until no dmMEP were triggered, and advancement continued while stimulating at 0.2 mA. Postoperatively, the patient had resolution of pain and preservation of the strength in the left leg.
2.2. Case # 2 A 67-year-old female with a history of spine chordoma, bilateral lower extremities weakness and intractable right leg pain underwent the same procedure as above. In her case, isolated robust left quadriceps dmMEP were triggered at 1 mA. The threshold was higher than expected and assumed to be related to the longer distance between the tip of the stimulator and the CST fibers. As such, the stimulus intensity was decreased to 0.4 mA when only intermittent responses were seen. The surgeon readjusted the trajectory and the advancement of the probe continued until reproducible high amplitude dmMEP were again seen, this time in the right AH muscle. This was consistent with the surgeon’s assessment that the probe reached the anterior midline septum (Fig. 4). At the end of the procedure, the left quadriceps tcmMEP were significantly decreased. Postoperatively, the patient was pain free, but did show temporary worsening of the left hip flexion. At one month follow, the strength had returned to the pre-operative baseline.
2.3. Case #3
Fig. 1. Spinal cord anatomy A-Cross-section of the spinal cord, distribution of the long tracts. LCST = lateral corticospinal tract; ACST = anterior corticospinal tract; ASTT = anterior spinothalamic tract; LSTT = lateral spinothalamic tract; GF = gracilis fasciculus; CF = cuneate fasciculus; 1 = rubrospinal tract; 2 = reticulospinal tract; 3 = olivospinal tract; 4 = vestibulospinal tract; 5 = posterior spinocerebellar tract; 6 = anterior spinocerebellar tract Somatotopic organization of fibers in different tracts: S = sacral; L = lumbar; T = thoracic; C = cervical. B-Lateral and anterior CST. 90% of the fibers decussate in the medullary pyramids to form the contralateral lateral CST (Lat CST) that descends in the spinal cord in the lateral funiculus. 10% of the fibers do not cross and descend through the ipsilateral anterior funiculus as ipsilateral anterior CST (Ant CST); very few fibers, through the ipsilateral lateral funiculus to form ipsilateral lateral CST.
A 74-year-old male presented with subacute worsening of chronic leg weakness (left > right). Neuroimaging demonstrated vertebral spine segmentation anomalies and a defect of the anterior thoracic spine at T3-T7 with an extruded meningocele in the mediastinum containing a tethered right ventro-lateral cord (Fig. 5). The patient underwent right thoracotomy, with partial T4 corpectomy and microsurgical release of the tethered spinal cord. The meningocele sac was identified and opened. A gliotic band extending towards an opened defect of spinal canal tethered the ventro-lateral cord. Significant adhesions impaired delineating a clear plane of separation between the spinal cord, fibrous tissue and the meningocele sac. The meningocele exploration, identification and untethering of the right anterior-lateral cord was safely achieved by using continuous electrical stimulation via a handheld monopolar probe. The lowest current that triggered dmMEP in the right leg muscles was 1.5 mA. This intensity was further used for negative mapping during exploration of the thecal sac and demarcation of the anterior cord from regions of the fibrous band. The patient showed mild improvement in the right leg muscle strength in the immediate postoperative period and further improvement at one month follow up. Table 2 summarizes the specifics of motor mapping and monitoring and their relationship with the pre and post-operative motor strength in all three patients.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
3
Table 1 Techniques of motor mapping of the spinal cord as described in the literature. Author
Probe
Stimulation settings
Stimulus intensity range (thresholds)
Recording
Duffau et al, 1998 [7]
Bayonet bipolar microprobe, prongs 5 mm apart, 1 mm tips Handheld stimulator
Repetitive biphasic pulses at 60 Hz, 1 ms pulse width, for 1 s
Observed triggered clinical motor responses
Not specified
1–0.4 mA (0.4, 0.9 and 1 mA) 2 mA (2 mA)
QuinonesHinojosa et al, 2002 [1] Gandhi, et al, 2015 [9]
Ojemann, bipolar stimulator, prongs 5 mm apart
Repetitive pulses at 60 Hz, 1 ms pulse width, for 1 s
1–0.75 mA (0.75, 1 mA)
Kartush concentric bipolar stimulating prob, 2 mm width
Repetitive biphasic pulses at 60.11 Hz, 1.0 ms pulse width, for 1–2 s
0.1 1.0 mA (0.1, 1 mA)
Costa et al, 2015 [10]
Epidural electrode
Repetitive pulses at 3–5 Hz, 0.3 ms pulse width, 30–100 averaged trials
up to 30 mA (up to 30 mA)
Barzilai et al, 2017 [11]
Continuous monopolar cathodal stimulation via CUSA Bipolar concentric
Repetitive trains, 3–5 pulses/train, 0.2–0.5 ms pulse width, ISI 3 ms, ITI 0.5–1 s Dual trains, 3–5 pulses//train, 0.5 ms pulse width, ISI 2–4 ms, ITI 60 ms
0.3–2.5 mA (0.3 to 2.5 mA)
Intermittent monopolar cathodal stimulation with handheld stimulator
Repetitive trains, 5 pulses/train, 0.5 ms pulse width, ISI 4 ms, ITI 0.5 s
0.2–0.5 mA (0.5 mA)
Deletis et al, 2001 [8]
Deletis et al, 2018 [12]
Simon et al, 2018 [13]
0.3–5 mA (0.3 to 5 mA)
Collision technique: decrease in D waves amplitudes orthodotromically triggered by transcranial electrical stimulation, due to their collision with D waves antidromically triggered by direct intramedullary stimulation of CST (anti-D wave) Triggered electrophysiologic muscle responses recorded on free run EMG recordings from APB-ADM, TA-Gas, AH-ADM pedis LFF 30 Hz, HFF 1 kHz Sens 200 mV/div, Timebase 1 s Triggered electrophysiologic muscle responses recorded on free run EMG recordings from hand, TA, medial Gas, AH, EHL LFF 30 Hz, HFF 500 Hz Sens 200 uV/div, Timebase 10 ms/div Anti-D wave recorded from scalp electrodes Fz-FPz, Cz-FPz, with a latency shorter than that of the gracilis SSEPs LFF 10–300 Hz, HFF 1 kHz Sens 1–2.5 uV/div, Timebase 5 ms/div Triggered mMEP Recorded in a variety of muscle channels: Delt, Bic, Tric, APB, ADM, AT, AH, Quad Triggered mMEP Recorded in a variety of muscle channels: delt, Bic, Tric, EDC, APB, ADM, TA, AH, Quad, Gas LFF 5 Hz, HFF 2 kKz Triggered mMEP Recorded in a variety of muscle channels: Quad, Ham, TA, Gas, AH, AS LFF 30 Hz, HFF 2 kHz Sens 20 uV/div, Timebase 10 ms/div
ADM = adductor digiti minimi, AH = abductor hallucis, APB = abductor pollicis brevis, AS = anal sphincter, Bic = biceps, CST = corticospinal tract, Delt = deltoid, EDC = extensor digitorum communis, EHL = extensor hallucis longus, EMG = electromyography, Gas = gastrocnemius, Ham = hamstring, HFF = high frequency filter, ISI = interstimulus interval, ITI = intertrial interval, LFF = low frequency filter, mMEP = muscle Motor Evoked Potentials, Quad = quadriceps, Sens = sensitivity, SSEPs = somatosensory evoked potentials, TA = tibialis anterior, Tric = triceps.
Fig. 2. Open left cordotomy. Excerpts from Tomycz L, Forbes J, Ladner T, et al. Open thoracic cordotomy as a treatment option for severe, debilitating pain. J Neurol Surg A Cent Eur Neurosurg 2014;75(2):126–32. with permission Ó Georg Thieme Verlag KG. A-After hemilaminectomy and durotomy, the dentate ligament (DL) is identified, cut and pulled; under its traction, the cord is mildly rotated posteriorly by 45° to gain better access to the anterolateral aspect of the cord, and thus to the nociceptive pathways to be transected. The shaded area (better shown in B) indicates their location within the lateral and anterior funiculi. B-Region targeted during the procedure (shaded) and the tracts of interest: LSTT = lateral spinothalamic tract; LCST = lateral corticospinal tract; 1 = ventral spinocerebellar tract; 2 = vestibulospinal tract; 3 = ascending sympathetic fibers for distal vasomotor and sudomotor innervation; 4 = descending parasympathetic fibers innervating the bowel and bladder; 5 = anterior spinothalamic tract and 6 = anterior corticospinal tract.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
4
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
Fig. 3. Patient 1 left cordotomy: path of entry. A-The surgeon approached the cord from the left dorso-lateral quadrant. The cord was gently rotated to the right, to get exposure to the left antero-lateral quadrant. A handheld monopolar stimulator (asterix) was used to stimulate the cord. No compound muscle action potentials (CMAPs) were triggered when stimulating medial to the dorsal root entry zone, where dorsal columns are located (black arrow). As the surgeon marched from the dorsal cord towards ipsilateral and more anterior aspect, stimulation at 0.4 mA triggered CMAPs in left leg muscles, signaling proximity of the LCST. B-As the stimulator was slowly advanced through a negatively mapped area, isolated CMAPs were suddenly triggered as low as 0.15 mA, primarily in the left abductor halluces (AH) muscle (red arrow); this prompted readjustment of the probe’s trajectory until no further responses were triggered. C-Diagram showing the trajectory of the stimulator (blue arrow) to create a safe path of entry for the Jacobson probe.
3. Discussion Supratentorial CST mapping thresholds depend on the type of stimulation probe and paradigm used [14], distance between the stimulation site and fibers location [15,16] as well as on the
excitability of motor pathways distal to the stimulation. The latter is directly influenced by anesthesia and pathology [17,18]. We used cathodal monopolar multipulse train technique for two reasons. First, the radial current spread from the tip of a cathodal monopolar probe allows optimal depolarization of different
Fig. 4. Patient 2, dynamic motor mapping. The red arrows point to CMAPs triggered in left quadriceps muscle at 1 mA (~20:52) and 0.4 mA (~20:53) and then in the right abductor hallucis (AH) muscle at 0.4 mA (~20:55). Notice the difference in amplitudes and morphologies between the right AH and left quadriceps CMAPs triggered at same intensity.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
5
Fig. 5. Thecal sac exploration and untethering of the ventrolateral cord. A-T2 Sagittal cervico-thoracic spine MRI sequence showing segmentation defect of the anterior thoracic spine and extruded myelomeningocele in the mediastinum. A-Neurophysiologic recordings: Left: robust muscle motor evoked potentials (mMEP) in the right anterior tibialis (AT), abductor halluces (AH) and gastrocnemius (Gas) muscles when stimulating the right ventrolateral aspect of the cord at 1.5 mA. Right: right posterior tibial somatosensory evoked potentials (SSEPs) during the case. A- Dynamic motor mapping during exploration of the thecal sac and cord untethering, displayed chronologically, with earlier traces on the top.
orientated motor nerves at lowest thresholds [14,19,20], and thus increases the specificity of stimulation. Second, the multipulse paradigm triggers time-locked mMEP that are easier to quantify and suitable for continuous mapping [11,21] under general anesthesia [22].
As expected, our threshold varied, likely with the distance between the stimulation site and the motor fibers. Additionally, mapping and monitoring of diseased myotomes required higher direct and transcranial currents respectively. In retrospect, the
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
6
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
Table 2 Motor mapping and monitoring and their relationship with pre and post-operative motor exam. Type of surgery (spine level)
Preoperative legs motor exam
Muscle channels
1 Left cordotomy (T3-4) Right: 2 to 3 Left: 5
BR, Hand, IPS, Quad, TA AH, Gas, Ham, AS 2 Left cordotomy (T2-3) Right: 4+ to 5 BR, Hand, IPS, Quad, Left: 4+ prox TA, AH, Gas, Ham 0 distal
3 Myelomeningocele repair and cord untethering (T3-T7)
Right: 3 to 4 Left: 2 to 4
Threshold tcmMEP (V) Double trains, 3–6 pulses/train, 0.05 ms pulse width, ITI 300 ms
tcmMEP Threshold dmMEP (mA) 6 pulses/train, 0.5 ms pulse changes width, ISI 4 ms, train frequency 2 Hz
Right: 400 Left: 250
0.15 left AH > AT > Gas
Right: 300 all mm Left: 400 (only IPS, Quad obtained)
Right: 400 all Hand, IPS, Quad, TA, AH, Gas, Ham, Left: 400 (only AH, AS) AS
Postoperative legs motor exam
Right: No Left: No
Right: 2–3 Left: 5
0.4 right AH 1 left Quad
Right: No Left: >80% drop in left quad tcmMEP
1.5 right TA, AH and Gas
Right: No Left: No
Right: 4+ to 5 Left: 2–3 proximal (POD#1) 4+ proximal (POD#30) 0 distal Right: 4 to 4+ (POD, #1), 5 (POD#30) Left: 2 to 4
BR = brachioradialis, IPS = iliopsoas, Quad = quadriceps, TA = tibialis anterior, AH = abductor halluces, Gas = gastrocnemius, Ham = hamstring, AS = anal sphincter, tcmMEP = transcranially evoked muscle motor evoked potentials, dmMEP = direct triggered muscle Motor Evoked Potentials.
post-procedure worsening of the left quadriceps tcmMEP, and of its strength (case #2) raises the questions whether the dynamic mapping in this patient should have been performed at higher currents. Direct stimulation of the dorsal columns can trigger mMEP antidromically via a sensory reflex [12]. As such, a legitimate question is whether we nonselectively stimulated the motor pathways. Unlike in cases of intramedullary tumor resection, the surgical approach in both open cordotomy and ventral cord untethering and the absence of infiltrative pathology allowed a reliable appreciation of the location of the stimulation in relationship to the location of the CST and DC within the spinal cord. Stimulation at threshold further contributed to the selectiveness of mapping. Whenever dmMEP were triggered, the current was decreased to an on/off response. We consistently triggered mMEP at very small currents, that were often isolated to one myotome distal to the spinal level at which stimulation took place. Our results are in accord with findings by other authors [9,11–13] showing that stimulation of isolated CST fascicles is possible and support the hypothesis that CST maintains a somatotopic organization at the spinal cord level.
4. Conclusion To our knowledge this is the first report of continuous CST mapping in spinal cord surgeries other than tumor resection. We’ve found good correlation between tcmMEP monitoring, CST mapping and post-operative motor outcome. The mapping thresholds showed variability that seemed to depend not only on the distance between the stimulating probe and CST fibers but also on the patient’s motor function baseline. Our results need confirmation in a larger study that will allow a systematic analysis of these thresholds and of their significance.
Study funding This work did not receive any funding.
Disclosures The authors report no disclosures to the manuscript.
References [1] Quinones-Hinojosa A, Gulati M, Lyon R, et al. Spinal cord mapping as an adjunct for resection of intramedullary tumors: surgical technique with case illustrations. Neurosurgery 2002;51:1199–207. [2] Yanni DS, Ulkatan S, Deletis V, et al. Utility of neurophysiological monitoring using dorsal column mapping in intramedullary spinal cord surgery. J Neurosurg Spine 2010;12(6):623. [3] Simon MV, Chiappa KH, Borges L. Phase reversal of somatosensory evoked potentials triggered by Gracilis tract stimulation: a new technique for neurophysiologic dorsal column mapping. Neurosurgery 2012;70(3):E783–8. [4] Mehta AI, Mohrhaus CA, Husain AM, et al. Dorsal column mapping for intramedullary spinal cord tumor resection decreases dorsal column dysfunction. J Spinal Disord Tech 2012;25(4):205–9. [5] Nair MD, Kumaraswamy DV, Braver FD, et al. Dorsal column mapping via phase reversal method: the refined technique and clinical applications. Neurosurgery 2014;74(4):437–63. [6] Scibilia A, Terranova C, Rizzo V, et al. Intraoperative neurophysiological mapping and monitoring in spinal tumor surgery: sirens or indispensable tools?. Neurosurg Focus 2016;41(2):E18. [7] Duffau H, Capelle L, Sichez J. Direct spinal cord electrical stimulations during surgery of intramedullary tumoral and vascular lesions. Stereotact Funct Neurosurg 1998;71(4):180–9. [8] Deletis V, Camargo BD. Interventional neurophysiological mapping during spinal cord procedures. Stereotact Funct Neurosurg 2001;77(1):25–8. [9] Gandhi R, Curtis CM, Cohen-Gadol AA. High-resolution direct microstimulation mapping of spinal cord motor pathways during resection of an intramedullary tumor. J Neurosurg Spine 2015;22(2):205–10. [10] Costa P, Deletis V. Cortical activity after stimulation of the corticospinal tract in the spinal cord. Clin Neurophysiol 2016;127(2):1726–33. [11] Barzilai O, Lidar Z, Constantini S, et al. Continuous mapping of the corticospinal tracts in intramedullary spinal cord tumor surgery using an electrified ultrasonic aspirator. J Neurosurg Spine 2017;27(2):161–8. [12] Deletis V, Seidel K, Sala F, et al. Intraoperative identification of the corticospinal tract and dorsal column of the spinal cord by electrical stimulation. J Neurol Neurosurg Psychiatry 2018;89(7):754–61. [13] Simon MV, Borges L. Intramedullary spinal cord tumor resection. In: Simon MV, editor. Intraperative neurophysiology: a comprehensive guide to monitoring and mapping. New York: Springer Publishing Company/Demos Medical; 2018. p. 389–424. [14] Szelényi A, Senft C, Jardan M, et al. Intra-operative subcortical electrical stimulation: a comparison of two methods. Clin Neurophysiol 2011;122 (7):1470–5. [15] Kamada K, Todo T, Ota T, et al. The motor-evoked potential threshold evaluated by tractography and electrical stimulation. J Neurosurg 2009;111 (4):785–95. [16] Nossek E, Korn A, Shahar T, et al. Intraoperative mapping and monitoring of the corticospinal tracts with neurophysiological assessment and 3dimensional ultrasonography-based navigation. J Neurosurg 2011;114 (3):738–46. [17] Journee HL, Berends HI, Kruyt MC. The percentage of amplitude decrease warning criteria for transcranial MEP monitoring. J Clin Neurophysiol 2017;34 (1):22–31. [18] Dineen J, Simon MV. Neurophysiologic tests in the operating room. In: Simon MV, editor. Intraoperative neurophysiology: a comprehensive guide to monitoring and mapping. New York: Springer Publishing Company/Demos Medical; 2018. p. 1–57. [19] Lorente de No’ R. A study of nerve physiology. Stud Rockefeller Inst Med Res Repr 1947;132:1–548.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054
S. Tsetsou et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx [20] Rudin DO, Eisenman G. The action potential of spinal axons in vitro 3. J Gen Physiol 1954;37:505–38. [21] Raabe A, Beck J, Schucht P, et al. Continuous dynamic mapping of the corticospinal tract during surgery of motor eloquent brain tumors: evaluation of a new method. J Neurosurg 2014;120(5):1015–24.
7
[22] Taniguchi M, Cedzich C, Schramm J. Modification of cortical stimulation for motor evoked potentials under general anesthesia: Technical description. Neurosurgery 1993;32(2):219–26.
Please cite this article as: S. Tsetsou, W. Butler, L. Borges et al., Dynamic mapping of the corticospinal tract in open cordotomy and myelomeningocele surgery, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2020.01.054