Abstract BACKGROUND AND IMPORTANCE Skull base surgery involves the microdissection and intraoperative monitoring of cranial nerves, including cranial nerve XI (CN XI). Manipulation of CN XI can evoke brisk trapezius contraction, which in turn may disturb the surgical procedure and risk patient safety. Here we describe a method for temporarily silencing CN XI via direct intraoperative application of 1% lidocaine. CLINICAL PRESENTATION A 41-yr-old woman presented with symptoms of elevated intracranial pressure and obstructive hydrocephalus secondary to a hemangioblastoma of the right cerebellar tonsil. A far-lateral suboccipital craniotomy was performed for resection of the lesion. During the initial stages of microdissection, vigorous trapezius contraction compromised the course of the operation. Following exposure of the cranial and cervical portions of CN XI, lidocaine was applied to the course of the exposed nerve. Within 3 min, trapezius electromyography demonstrated neuromuscular silencing, and further manipulation of CN XI did not cause shoulder movements. Approximately 30 min after lidocaine application, trapezius contractions returned, and lidocaine was again applied to re-silence CN XI. Gross total resection of the hemangioblastoma was performed during periods of CN XI inactivation, when trapezius contractions were absent. CONCLUSION Direct application of lidocaine to CN XI temporarily silenced neuromuscular activity and prevented unwanted trapezius contraction during skull base microsurgery. This method improved operative safety and efficiency by significantly reducing patient movement due to the unavoidable manipulation of CN XI. Accessory nerve, Foramen magnum, Neuromonitoring, Skull base neurosurgery, Lidocaine ABBREVIATIONS ABBREVIATIONS CN XI cranial nerve XI SSEP somatosensory evoked potential During surgical procedures of the skull base, cranial nerve and brainstem white matter pathway functions are routinely monitored. Physiological monitoring requires adequate depth of anesthesia without neuromuscular blockade. As a result, intraoperative mechanical stimulation of motor cranial nerves can lead to muscle contractions.1 Cranial nerve XI (CN XI) is frequently encountered during procedures involving the lateral foramen magnum region.2-5 Mechanical contact of this nerve can lead to vigorous shoulder movement due to contraction of the trapezius. This shoulder movement, in turn, disturbs delicate microdissection, risking patient safety and slowing the progress of the operation. The ability to temporarily silence CN XI, while maintaining monitoring of other cranial nerves and brainstem pathways, is thus desirable. In this report, we describe a technique used by the senior author to temporarily prevent shoulder movement due to CN XI stimulation during surgery of the lateral magnum region. This technique, which involves direct topical application of lidocaine onto the exposed CN XI, is a safe and temporary means to prevent unwanted trapezius contraction during skull base microsurgery. Video and electromyography (EMG) documentation of the method and the resultant CN XI silencing are provided. CLINICAL PRESENTATION A 41-yr-old woman was transferred to our hospital after presenting with symptoms and signs of elevated intracranial pressure. Magnetic resonance imaging revealed a mass involving the right cerebellar tonsil and foramen magnum region (Figure 1). Imaging features were consistent with a hemangioblastoma, which caused obstructive hydrocephalus. FIGURE 1. View largeDownload slide Preoperative coronal A and axial B T1-weighted, gadolinium-enhanced magnetic resonance imaging sequences depicting a hemangioblastoma involving the right cerebellar tonsil. The mass compressed the distal fourth ventricle, causing obstructive hydrocephalus. FIGURE 1. View largeDownload slide Preoperative coronal A and axial B T1-weighted, gadolinium-enhanced magnetic resonance imaging sequences depicting a hemangioblastoma involving the right cerebellar tonsil. The mass compressed the distal fourth ventricle, causing obstructive hydrocephalus. A right-sided, subocciptal far-lateral craniotomy was undertaken to resect the lesion (Figure 2). Our Institutional Committee on Human Research approved this related technical note; patient consent was not required for this “minimal risk” study, per institutional policy. During the surgical procedure, neuromonitoring of CN VII, CN XI, and CN XII function, and brainstem white matter pathways (ie, somatosensory evoked potential [SSEP] monitoring), was performed. To monitor CN XI function, subdermal needle electrodes (1.5 cm, 29 gauge; Medtronic-Xomed, Dublin, Ireland) were placed into the trapezius muscle, and electrophysiologic recordings were made with a 32-channel system (Cadwell Cascade; Cadwell Laboratories Inc, Kennewick, Washington).6 Following exposure of the brainstem and rostral spinal cord, the subarachnoid space was dissected in order to identify the ipsilateral vertebral artery and the posterior inferior cerebellar artery. Care was taken to avoid mechanical stimulation of CN XI during dissection. However, direct contact of CN XI could not be completely avoided during this stage of the procedure. Mechanical stimulation of CN XI resulted in sudden forceful movements of the patient's shoulder, which in turn jarred the operative field. FIGURE 2. View largeDownload slide Intraoperative microscopic images obtained during far lateral craniotomy for resection of a right cerebellar tonsillar hemangioblastoma. A, The exposed right cerebellum and cervico-medullary junction. B, Gentle retraction of the cerebellar tonsil with a suction device, allowing initial exposure of the cerebellar tonsillar hemangioblastoma (asterisk). Note close apposition of the right CN XI (arrow) and right posterior inferior cerebellar artery (chevron), which were situated anterolateral to the hemangioblastoma (in B). C, The surgical field following resection of the lesion. FIGURE 2. View largeDownload slide Intraoperative microscopic images obtained during far lateral craniotomy for resection of a right cerebellar tonsillar hemangioblastoma. A, The exposed right cerebellum and cervico-medullary junction. B, Gentle retraction of the cerebellar tonsil with a suction device, allowing initial exposure of the cerebellar tonsillar hemangioblastoma (asterisk). Note close apposition of the right CN XI (arrow) and right posterior inferior cerebellar artery (chevron), which were situated anterolateral to the hemangioblastoma (in B). C, The surgical field following resection of the lesion. To temporarily block unwanted trapezius contraction during microdissection, the operating surgeon (MWD) used a previously undescribed method for silencing CN XI (Video, Supplemental Digital Content). Using a 30-gauge needle attached to a 1-mL syringe, small drops (approximately 20-500 μL drops) of 1% lidocaine hydrochloride (Hospira Inc, Lake Forest, Illinois) were applied to the surface of the cranial and cervical portions of CN XI. During lidocaine application, a suction instrument was positioned adjacent to and below the site of application to prevent unwanted run-off of lidocaine into the subarachnoid space. Approximately 2 min after lidocaine application, further manipulation of CN XI caused no observable trapezius contraction, and the dissection was resumed. Consistent with CN XI silencing, trapezius EMG demonstrated a significant decrease in the frequency and amplitude of motor unit action potentials within 3 min of lidocaine application (Figure 3). No EMG changes were observed at the orbicularis muscles (CN VII) or genioglossus (CN XII; data not shown). After approximately 30 min, mechanical stimulation again evoked shoulder movements. Lidocaine was then reapplied as previously described to reduce trapezius activation. No sudden or adverse changes in the patient's vital signs (eg, heart rate, blood pressure, oxygenation) were observed following lidocaine application. Additionally, SSEP monitoring was unaffected by lidocaine application. FIGURE 3. View largeDownload slide Electromyographic recordings of mechanically elicited CN XI activity. Traces 1 to 5 depict recordings made over a 10-min period that coincided with the application of topical lidocaine to CN XI. Trace 1 was recorded immediately prior to lidocaine application; note large amplitude tonic activity indicative of “C” trains (average amplitude, approximately 850 μV). Three minutes after lidocaine application (trace 2), EMG amplitudes were decreased by approximately 80%. Five minutes after lidocaine application (trace 3), motor unit action potentials (MUAPs) were created in frequency. Eight minutes after lidocaine application (trace 4) MUAPs were highly synchronized. Ten minutes after lidocaine significant (trace 5), MUAPs remained highly synchronized, and spontaneous irregular discharges were largely absent. The average MUAP amplitude at this point was approximately 100 μV, as compared to approximately 850 μV before lidocaine application. FIGURE 3. View largeDownload slide Electromyographic recordings of mechanically elicited CN XI activity. Traces 1 to 5 depict recordings made over a 10-min period that coincided with the application of topical lidocaine to CN XI. Trace 1 was recorded immediately prior to lidocaine application; note large amplitude tonic activity indicative of “C” trains (average amplitude, approximately 850 μV). Three minutes after lidocaine application (trace 2), EMG amplitudes were decreased by approximately 80%. Five minutes after lidocaine application (trace 3), motor unit action potentials (MUAPs) were created in frequency. Eight minutes after lidocaine application (trace 4) MUAPs were highly synchronized. Ten minutes after lidocaine significant (trace 5), MUAPs remained highly synchronized, and spontaneous irregular discharges were largely absent. The average MUAP amplitude at this point was approximately 100 μV, as compared to approximately 850 μV before lidocaine application. During the periods of CN XI silencing, further dissection and tumor removal were safely and efficiently performed. Gross total resection of the tumor was achieved, and the patient exhibited intact neurological function postoperatively, including full strength of shoulder movement and head rotation. Her postoperative course was uncomplicated. DISCUSSION We have described a method for safely silencing an isolated motor cranial nerve during skull base neurosurgery. Direct lidocaine application to CN XI halted the unwanted shoulder movements that commonly result from unavoidable manipulation of this nerve during surgery. This technique, which the senior author has used in over 20 surgical cases, improved operative safety and efficiency by temporarily halting jarring contractions of the trapezius muscle. Monitoring of motor cranial nerve function allows the operating surgeon to minimize the risk of iatrogenic injury to these structures.7 The functions of these cranial nerves are assessed by EMG measurements of muscles such as the inferior rectus (for CN III), masseter and temporalis (CN V), orbicularis oculi and orbicularis oris (CN VII), laryngeal musculature (CN IX and CN X, via endotracheal tube), trapezius (CN XI), and genioglossus (CN XII). The largest of these muscles is the trapezius, which originates at the occiput and the spinous processes of cervical and thoracic vertebra, and inserts into the scapula, clavicle, and acromion. Contraction of the patient's trapezius produces substantial movement of the upper trunk, even when the patient is secured to the operating table and placed in a head fixation device. During surgery of the foramen magnum region, particularly when accessed by a far lateral craniotomy, these movements cause sudden shifts of the patient and operative field. Additionally, the ipsilateral shoulder can collide with the operating surgeon. Thus, these movements risk patient safety and compromise operative efficiency. Our experiences suggest that unwanted, iatrogenic trapezius contraction can be safely prevented by the direct application of 1% lidocaine to the exposed surface of CN XI. Trapezius inactivation occurs shortly after lidocaine application (2-3 min), and persists for approximately 20 to 30 min, during which time the operating surgeon can perform microdissection around CN XI without eliciting unwanted patient movements. When trapezius contractions return, lidocaine can be reapplied to CN XI, if necessary. Of note, during lidocaine application, low-pressure suction is maintained directly below and adjacent to CN XI, in order to minimize lidocaine run-off into the subarachnoid space (where, theoretically, it could affect central control of hemodynamics, eg, blood pressure or heart rhythm).8 The senior author has used this method in over 20 cases, which involved both intra- and extra-axial pathologies, and he has noted no instances of related CN XI injury or other cranial nerve injury. While lidocaine application minimizes disturbances caused by patient shoulder movement, it also transiently affects the neuromonitoring of CN XI. As such, the operating surgeon must be mindful to ensure that reductions in trapezius EMG signals are due to lidocaine application (as demonstrated in Figure 3), rather than iatrogenic injury to the nerve. Generally, lidocaine should be applied only during stages of the procedure when CN XI manipulation is unavoidable and intentional, and the operating surgeon should use great caution when manipulating CN XI during the period of nerve inactivation. Additionally, the surgeon and neurophysiologist should expect trapezius EMG signals to return within approximately 20 to 30 min of lidocaine application; if signals do not return to baseline levels, other causes must be immediately considered. Finally, while the senior author has not observed silencing of other cranial nerves, such as CN VII or CN VIII, following application of lidocaine to CN XI, this technique could theoretically compromise monitoring of those structures. The assisting neurophysiologist should thus closely monitor and anticipate potential changes to neuromonitoring signals from these other structures. If neuromonitoring of neighboring nerves be compromised by application of lidocaine to CN XI, the surgeon should attempt to dilute the lidocaine with irrigant, and may consider suspending further dissection until those signals return. CONCLUSION Direct application of lidocaine to CN XI transiently silenced neuromuscular activity and prevented unwanted trapezius contraction during skull base microsurgery. In the senior author's experience, this technique is a safe and effective method for reducing trapezius contractions that result from surgical manipulation of CN XI. By reducing unwanted shoulder movement, silencing of CN XI improves operative safety and efficiency. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Holland NR . Intraoperative electromyography . J Clin Neurophysiol . 2002 ; 19 ( 5 ): 444 - 453 . Google Scholar CrossRef Search ADS PubMed 2. Bruneau M , George B . Foramen magnum meningiomas: detailed surgical approaches and technical aspects at Lariboisière Hospital and review of the literature . Neurosurg Rev . 2007 ; 31 ( 1 ): 19 - 33 . Google Scholar CrossRef Search ADS PubMed 3. de Oliveira E Rhoton AL , Peace D . Microsurgical anatomy of the region of the foramen magnum . Surg Neurol . 1985 ; 24 ( 3 ): 293 - 352 . Google Scholar CrossRef Search ADS PubMed 4. Bassiouni H , Ntoukas V , Asgari S , Sandalcioglu EI , Stolke D , Seifert V . Foramen magnum meningiomas: clinical outcome after microsurgical resection via a posterolateral suboccipital retrocondylar approach . Neurosurgery . 2006 ; 59 ( 6 ): 1177 - 1187 . Google Scholar CrossRef Search ADS PubMed 5. Nanda A , Vincent DA , Vannemreddy PS , Baskaya MK , Chanda A . Far-lateral approach to intradural lesions of the foramen magnum without resection of the occipital condyle . J Neurosurg . 2002 ; 96 ( 2 ): 302 - 309 . Google Scholar CrossRef Search ADS PubMed 6. Romstöck J , Strauss C , Fahlbusch R . Continuous electromyography monitoring of motor cranial nerves during cerebellopontine angle surgery . J Neurosurg . 2000 ; 93 ( 4 ): 586 - 593 . Google Scholar CrossRef Search ADS PubMed 7. Karlikaya G , Citçi B , Güçlü B , Türe H , Türe U , Bingöl CA . Spinal accessory nerve monitoring in posterior fossa surgery . J Clin Neurophysiol . 2008 ; 25 ( 6 ): 346 - 350 . Google Scholar CrossRef Search ADS PubMed 8. Kobet KA . Cerebral spinal fluid recovery of lidocaine and bupivicaine following respiratory arrest subsequent to retrobulbar block . Ophthalmic Surg . 1987 ; 18 ( 1 ): 11 - 13 . Google Scholar PubMed Supplemental digital content is available for this article at www.operativeneurosurgery-online.com Supplemental Digital Content. Video. Intraoperative video recording depicting application of topical lidocaine to the exposed segment of CN XI. Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)
Operative Neurosurgery – Oxford University Press
Published: May 18, 2018
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