The diagnostic accuracy of neuromonitoring for detecting postoperative bowel and bladder dysfunction in spinal oncology surgery: a case series.

PURPOSE: Postoperative bowel and bladder dysfunction (BBD) poses a significant risk following surgery of the sacral spinal segments and sacral nerve roots, particularly in neuro-oncology cases. The need for more reliable neuromonitoring techniques to enhance the safety of spine surgery is evident. METHODS: We conducted a case series comprising 60 procedures involving 56 patients, spanning from September 2022 to January 2024. We assessed the diagnostic accuracy of sacral reflexes (bulbocavernosus and external urethral sphincter reflexes) and compared them with transcranial motor evoked potentials (TCMEP) incorporating anal sphincter (AS) and external urethral sphincter (EUS) recordings, as well as spontaneous electromyography (s-EMG) with AS and EUS recordings. RESULTS: Sacral reflexes demonstrated a specificity of 100% in predicting postoperative BBD, with a sensitivity of 73.33%. While sensitivity slightly decreased to 64.71% at the 1-month follow-up, it remained consistently high overall. TCMEP with AS/EUS recordings did not identify any instances of postoperative BBD, whereas s-EMG with AS/EUS recordings showed a sensitivity of 14.29% and a specificity of 97.14%. CONCLUSION: Sacral reflex monitoring emerges as a robust adjunct to routine neuromonitoring, offering surgeons valuable predictive insights to potentially mitigate the occurrence of postoperative BBD.

Direct (D)-Wave Monitoring Enhancement With Subdural Electrode Placement: A Case Series.

PURPOSE: Direct-wave (D-wave) neuromonitoring is a direct measure of corticospinal tract integrity that detects potential injury during spinal cord surgery. Epidural placement of electrodes used for D-wave measurements can result in high electrical impedances resulting in substantial signal noise that can compromise signal interpretation. Subdural electrode placement may offer a solution. METHODS: Medical records for consecutive patients with epidural and subdural D-wave monitoring were reviewed. Demographic and clinical information including preoperative and postoperative motor strength were recorded. Neuromonitoring charts were reviewed to characterize impedances and signal amplitudes of D-waves recorded epidurally (before durotomy) and subdurally (following durotomy). Nonparametric statistics were used to compare epidural and subdural D-waves. RESULTS: Ten patients (50% women, median age 50.5 years) were analyzed, of which five patients (50%) were functionally independent (modified McCormick grade ≤ II) preoperatively. D-waves were successfully acquired by subdural electrodes in eight cases and by epidural electrodes in three cases. Subdural electrode placement was associated with lower impedance values ( P = 0.011) and a higher baseline D-wave amplitude ( P = 0.007) relative to epidural placement. No association was observed between D-wave obtainability and functional status, and no adverse events relating to subdural electrode placement were encountered. CONCLUSIONS: Subdural electrode placement allows successful D-wave acquisition with accurate monitoring, clearer waveforms, and a more optimal signal-to-noise ratio relative to epidural placement. For spinal surgeries where access to the subdural compartment is technically safe and feasible, surgeons should consider subdural placement when monitoring D-waves to optimize clinical interpretation.

Influence of Preoperative Motor Score and Patient Comorbidities on Transcranial Motor-Evoked Potential Acquisition in Intracranial Surgery: A Retrospective Cohort Study.

BACKGROUND AND OBJECTIVES: Intraoperative neurophysiological monitoring plays a pivotal role in modern neurosurgery, aiding in real-time assessment of eloquent neural structures to mitigate iatrogenic neural injury. This study represents the largest retrospective series to date in monitoring corticospinal tract integrity during intracranial surgery with transcranial motor-evoked potentials (TCMEPs), focusing on the influence of demographic factors, comorbidities, and preoperative motor deficits on the reliability of intraoperative neurophysiological monitoring. While the impact of patient-specific factors affecting TCMEP monitoring in spine surgery is well-documented, similar insights for intracranial surgery are lacking. METHODS: A total of 420 craniotomy patients were retrospectively analyzed from electronic medical records from December 2017 to February 2023, excluding patients without preoperative Medical Research Council scores or medical histories. Using intrinsic hand muscles as a robust data set, 840 hand TCMEPs acquired during intracranial surgery were assessed. Demographic and clinical factors, including preoperative motor scores, were analyzed to identify associations with TCMEP acquisition and amplitude. Nonparametric statistics and multivariate regression analysis were employed. RESULTS: TCMEPs were successfully acquired in 734 (87.7%) patient hands, even in the presence of preoperative motor deficits in 13.9% of total patient hands. Preoperative motor scores did not predict the ability to acquire baseline TCMEPs (P = .6). Notably, older age (P < .001) and hypertension (P = .01) were independent predictors of lower TCMEP acquisition rates. Preoperative motor scores significantly influenced TCMEP amplitudes, with higher scores correlating with higher amplitudes (1771 [SD = 1550] eve vs 882 [SD = 856] µV, P < .0001). Older age (P < .001) and chronic kidney disease (P = .04) were also associated with reduced TCMEP amplitudes. CONCLUSION: Our investigation into TCMEPs during intracranial surgery demonstrated a notably high acquisition rate in hand muscles, irrespective of preoperative motor deficits. Preoperative motor scores reliably correlated with TCMEP amplitudes in a linear fashion while advanced age and renal disease emerged as independent predictors of lower TCMEP amplitudes.

Intraoperative Monitoring of the External Urethral Sphincter Reflex: A Novel Adjunct to Bulbocavernosus Reflex Neuromonitoring for Protecting the Sacral Neural Pathways Responsible for Urination, Defecation and Sexual Function.

PURPOSE: Intraoperative bulbocavernosus reflex neuromonitoring has been utilized to protect bowel, bladder, and sexual function, providing a continuous functional assessment of the somatic sacral nervous system during surgeries where it is at risk. Bulbocavernosus reflex data may also provide additional functional insight, including an evaluation for spinal shock, distinguishing upper versus lower motor neuron injury (conus vs. cauda syndromes) and prognosis for postoperative bowel and bladder function. Continuous intraoperative bulbocavernosus reflex monitoring has been utilized to provide the surgeon with an ongoing functional assessment of the anatomical elements involved in the S2-S4 mediated reflex arc including the conus, cauda equina and pudendal nerves. Intraoperative bulbocavernosus reflex monitoring typically includes the electrical activation of the dorsal nerves of the genitals to initiate the afferent component of the reflex, followed by recording the resulting muscle response using needle electromyography recordings from the external anal sphincter. METHODS: Herein we describe a complementary and novel technique that includes recording electromyography responses from the external urethral sphincter to monitor the external urethral sphincter reflex. Specialized foley catheters embedded with recording electrodes have recently become commercially available that provide the ability to perform intraoperative external urethral sphincter muscle recordings. RESULTS: We describe technical details and the potential utility of incorporating external urethral sphincter reflex recordings into existing sacral neuromonitoring paradigms to provide redundant yet complementary data streams. CONCLUSIONS: We present two illustrative neurosurgical oncology cases to demonstrate the utility of the external urethral sphincter reflex technique in the setting of the necessary surgical sacrifice of sacral nerve roots.

Neuromonitoring Identifies Occlusion of Femoral Artery in STA-MCA Bypass Procedure: A Case Report.

Intraoperative neurophysiological monitoring (IONM) is a technique used to assess the somatosensory and gross motor systems during surgery. While it is primarily used to detect and prevent surgically induced nervous system trauma, it can also detect and prevent injury to the nervous system that is the result of other causes such as trauma or ischemia that occur outside of the operative field as a result of malpositioning or other problematic physiologic states. We present a case study where a neuromonitoring alert altered the surgical procedure, though the alert was not correlated to the site of surgery. A 69-year-old male with a history of bilateral moyamoya disease and a left middle cerebral artery infarct underwent a right-sided STA-MCA bypass and encephaloduroarteriosynangiosis (EDAS) with multimodal IONM. During the procedure, the patient experienced a loss of motor evoked potential (MEP) recordings in the right lower extremity. Blood pressure was elevated, which temporarily restored the potentials, but they were lost again after the angiography team attempted to place an arterial line in the right femoral artery. The operation was truncated out of concern for left hemispheric ischemia, and it was later discovered that the patient had an acute right external iliac artery occlusion caused by a fresh thrombus in the common femoral artery causing complete paralysis of the limb. This case highlights the importance of heeding IONM alerts and evaluating for systemic causes if the alert is not thought to be of surgical etiology. IONM can detect adverse systemic neurological sequelae that is not necessarily surgically induced.

Adjustable, Dynamic Subcortical Stimulation Technique for Brain Tumor Resection: A Case-Series.

BACKGROUND AND OBJECTIVES: Subcortical stimulation (SCS) is the gold standard neuromonitoring technique for intraoperative identification of descending white matter tracts. Dynamic SCS confers several advantages over more commonly used static devices; however, current commercially available devices for dynamic SCS have not been widely adopted. METHODS: We fashioned a dynamic SCS device using a stainless-steel suction and commonly available materials and assessed its efficacy in a series of 14 patients with brain tumors. The device was used to provide continuous SCS during tumor resection. Preoperative and postoperative motor function were characterized, and preoperative and postoperative imaging were analyzed to determine extent of tumor resection and proximity to motor-eloquent structures. Inferential statistics were used to correlate study parameters. RESULTS: Fourteen patients (12 male and 2 female, median age 52.5 years) were analyzed. The lowest intraoperative SCS intensities were 10 to 15 mA (3 surgeries), 5 to 10 mA (4 surgeries), and <5 mA (2 surgeries). SCS with this device did not elicit motor evoked potentials in 5 surgeries because of distance from the corticospinal tract (CST) and served as negative controls. Three patients (21.4%) experienced new postoperative motor deficits immediately after surgery that resolved by discharge. We observed no instances of mechanical CST injury resulting in permanent postoperative motor deficits using this technique and no correlation between lower SCS intensity and the presence of new motor impairments after surgery. No patient experienced an intraoperative seizure. CONCLUSION: The novel dynamic SCS device is easily adoptable and allows accurate intraoperative identification of the CST, facilitating safe resection of tumors near motor-eloquent structures.

Intraoperative awake language mapping correlates to preoperative connectomics imaging: An instructive case.

Connectomics enables the study of structural-functional relationships in the brain, and machine learning technologies have enabled connectome maps to be developed for individual brain tumor patients. We report our experience using connectomics to plan and guide an awake craniotomy for a tumor impinging on the language area. Preoperative connectomics imaging demonstrated proximity of the tumor to parcellations of the language area. Intraoperative awake language mapping was performed, revealing speech arrest and paraphasic errors at areas of the tumor boundary correlating to functional regions that explained these findings. This instructive case highlights the potential benefits of implementing connectomics into neurosurgical planning.

Neuromonitoring Guided Vessel Identification in Iatrogenic Arterial Injury During Meningioma Resection.

Neuromonitoring is commonly used in neurosurgery and allows intraoperative assessment of functional pathways in the brain during surgery. Monitoring alerts can guide surgical decision making in real-time allowing surgeons to mitigate or avoid potential iatrogenic injury and subsequent postoperative neurologic sequelae that may result from cerebral ischemia or malperfusion. Here we present a case of a patient undergoing a right pterional craniotomy for the resection of a tumor which crosses midline with multimodal intraoperative neuromonitoring including somatosensory evoked potentials, transcranial motor evoked potentials, and visual evoked potentials. During the final portion of tumor resection, arterial bleeding was noted of unknown origin shortly followed by loss of right lower extremity motor evoked potential recordings. Motor evoked potential recordings in the right upper, and left upper and lower extremities were stable, as well as all somatosensory evoked potentials and visual evoked potentials. This distinct pattern of right lower extremity motor-evoked potential loss suggested compromise of the contralateral anterior cerebral artery and guided the surgeons to a rapid intervention. The patient awoke from surgery with moderate postoperative weakness in the affected limb that resolved to preoperative status by postoperative day 2, and back to normal strength prior to three-month follow-up. In this case the neuromonitoring data suggested compromise to the contralateral anterior cerebral artery which guided the surgeons to investigate and identify the site of vascular injury. The present case reinforces the utility of neuromonitoring in emergent surgical situations to guide surgical decision making.

Short and long-term prognostic value of intraoperative motor evoked potentials in brain tumor patients: a case series of 121 brain tumor patients.

PURPOSE: Iatrogenic neurologic deficits adversely affect patient outcomes following brain tumor resection. Motor evoked potential (MEP) monitoring allows surgeons to assess the integrity of motor-eloquent areas in real-time during tumor resection to lessen the risk of iatrogenic insult. We retrospectively associate intraoperative transcranial and direct cortical MEPs (TC-MEPs, DC-MEPs) to early and late post-operative motor function to prognosticate short- and long-term motor recovery in brain tumor patients undergoing surgical resection in peri-eloquent regions. METHODS: We reviewed 121 brain tumor patients undergoing craniotomies with DC-MEP and/or TC-MEP monitoring. Motor function scores were recorded at multiple time-points up to 1 year postoperatively. Sensitivity, specificity, and positive and negative predictive values (PPV, NPV) were calculated at each time point. RESULTS: The sensitivity, specificity, PPV, and NPV of TC-MEP in the immediate postoperative period was 17.5%, 100%, 100%, and 69.4%, respectively. For DC-MEP monitoring, the respective values were 25.0%, 100%, 100%, and 68.8%. By discharge, sensitivity had increased for both TC-MEP and DC MEPs to 43.8%, and 50.0% respectively. Subset analysis on patients without tumor recurrence/progression at long term follow-up (n = 62 pts, 51.2%) found that all patients with stable monitoring maintained or improved from preoperative status. One patient with transient intraoperative TC-MEP loss and permanent DC-MEP loss suffered a permanent deficit. CONCLUSION: Brain tumor patients who undergo surgery with intact MEP monitoring and experience new postoperative deficits likely suffer transient deficits that will improve over the postoperative course in the absence of disease progression.

Evolution of flash visual evoked potentials to monitor visual pathway integrity during tumor resection: illustrative cases and literature review.

Flash visual evoked potentials (fVEPs) provide a means to interrogate visual system functioning intraoperatively during tumor resection in which the optic pathway is at risk for injury. Due to technical limitations, fVEPs have remained underutilized in the armamentarium of intraoperative neurophysiological monitoring (IONM) techniques. Here we review the evolution of fVEPs as an IONM technique with emphasis on the enabling technological and intraoperative improvements. A combined approach with electroretinography (ERG) has enhanced feasibility of fVEP neuromonitoring as a practical application to increase safety and reduce error during tumor resection near the prechiasmal optic pathway. The major advance has been towards differentiating true cases of damage from false findings. We use two illustrative neurosurgical cases in which fVEPs were monitored with and without ERG to discuss limitations and demonstrate how ERG data can clarify false-positive findings in the operating room. Standardization measures have focused on uniformity of photostimulation parameters for fVEP recordings between neurosurgical groups.

Direct Wave Intraoperative Neuromonitoring for Spinal Tumor Resection: A Focused Review.

At present, surgical resection of primary intramedullary spinal cord tumors is the mainstay of treatment. However, given the dimensional constraints of the narrow spinal canal and dense organization of the ascending and descending tracts, intramedullary spinal cord tumor resection carries a significant risk of iatrogenic neurological injury. Intraoperative neurophysiological monitoring (IONM) and mapping techniques have been developed to evaluate the functional integrity of the essential neural pathways and optimize the surgical strategies. IONM can also inform on impending harm to at-risk structures and can correlate with postoperative functional recovery if damage has occurred. Direct waves (D-waves) will provide immediate feedback on the integrity of the lateral corticospinal tract. In the present review, we have provided an update on the utility of D-waves for spinal cord tumor resection. We have highlighted the neuroanatomical and neurophysiological insights from the use of D-wave monitoring, the technical considerations and limitations of the D-wave technique, and multimodal co-monitoring with motor-evoked potentials and somatosensory-evoked potentials. Together with motor-evoked potentials, D-waves can help to guide the extent of tumor resection and provide intraoperative warning signs and alarm criteria to direct the surgical strategy. D-waves can also serve as prognostic biomarkers for long-term recovery of postoperative motor function. We propose that the use of D-wave IONM can contribute key findings for clinical decision-making during spinal cord tumor resection.

A Cost-Effective, Adjustable, Dynamic Subcortical Stimulation Device - Technical Note.

Brain mapping and neuromonitoring remain the gold standard for identifying and preserving functional neuroanatomic regions during safe, maximal brain tumor resection. Subcortical stimulation (SCS) can identify white matter tracts and approximate their distance from the leading edge of an advancing resection cavity. Dynamic (continuous) devices permitting simultaneous suction and stimulation have recently emerged as time-efficient alternatives to traditional static (discontinuous) techniques. However, the high cost, fixed cap size, and fixed tube diameter of commercially available suction devices preclude universal adoption. Our objective is to modify available suction devices into monopolar probes for subcortical stimulation mapping. We describe our technique using a novel, cost-effective, dynamic SCS technique as part of our established neuromonitoring protocol. We electrified and insulated a conventional variable suction device using an alligator clip and red rubber catheter, respectively. We adjusted the catheter's length to expose metal on both sides, effectively converting the suction device into a monopolar stimulation probe capable of cortical and subcortical monopolar stimulation that does not differ from commercially available discontinuous or continuous devices. We fashioned a dynamic SCS suction probe using inexpensive materials compatible with all suction styles and sizes. Qualitative and quantitative analysis in future prospective case series is needed to assess efficacy and utility.

Subdural Direct Wave Intraoperative Neurophysiological Monitoring in Intramedullary Spinal Cord Tumor Resection: Case Report.

Direct wave (D-wave) intraoperative neurophysiological monitoring (IONM) is used during intramedullary spinal cord tumor (IMSCT) resection to assess corticospinal tract (CST) integrity. There are several obstacles to obtaining consistent and reliable D-wave monitoring and modifications to standard IONM procedures may improve surgical resection. We present the case of a subependymoma IMSCT resection at the T2-T6 spinal levels where subdural D-wave monitoring was implemented. A 47-year-old male was presented with a five-year history of numbness in his right foot eventually worsening to sharp upper back pain with increased lower extremity spasticity. MRI revealed an expansile non-contrast enhancing multi-loculated cystic lesion spanning T2-T6 as well as a separate T1-T2 lesion. A T2-T6 laminoplasty was performed for intramedullary resection of the lesion. A spinal electrode was placed in the epidural space caudal to the surgical site to monitor CST function; however, action potentials could not be obtained. Post durotomy, the electrode was placed in the subdural space under direct visualization. This resulted in a reliable D-wave recording, which assisted surgical decision-making during the procedure upon D-wave and limb motor evoked potential attenuation. Surgical intervention led to the recovery of the D-wave recording. Subdural D-wave monitoring serves as an alternative in patients where reliable D-waves from the epidural space are unable to be obtained. Further investigation is required to improve the recording technique, including exploring various types of contacts and lead placement locations.

Supplementary Motor Area Syndrome After Brain Tumor Surgery: A Systematic Review.

BACKGROUND: Supplementary motor area syndrome (SMAS) may occur after frontal tumor surgery, with variable presentation and outcomes. We reviewed the literature on postoperative SMAS after brain tumor resection. METHODS: PubMed, Web of Science, Scopus, and Cochrane were searched following the PRISMA guidelines to include studies reporting SMAS after brain tumor resection. RESULTS: We included 31 studies encompassing 236 patients. Most tumors were gliomas (94.5%), frequently of low grade (61.4%). Most lesions were located on the left hemisphere (64.4%), involving the supplementary motor area (61.4%) and the cingulate gyrus (20.8%). Tractography and functional magnetic resonance imaging evaluation were completed in 45 (19.1%) and 26 (11%) patients. Gross total resection was achieved in 46.3% patients and complete SMA resection in 69.4%. A total of 215 procedures (91.1%) used intraoperative neuromonitoring mostly consisting of direct cortical/subcortical stimulation (56.4%), motor (33.9%), and somatosensory (25.4%) evoked potentials. Postoperative SMAS symptoms occurred within 24 hours after surgery, characterized by motor deficits (97%), including paresis (68.6%) and hemiplegia (16.1%), and speech disorders (53%), including hesitancy (24.2%) and mutism (22%). Average SMAS duration was 45 days (range, 1-365 days), with total resolution occurring in 188 patients (79.7%) and partial improvement in 46 (19.5%). Forty-eight patients (20.3%) had persisting symptoms, mostly speech hesitancy (60.4%) and fine motor disorders (45.8%). CONCLUSIONS: Postoperative SMAS may occur within the first 24 hours after mesial frontal tumor surgery. Preoperative mapping and intraoperative neuromonitoring may assist resection and predict outcomes. Neuroplasticity and interhemispheric connectivity play a major role in resolution.

Temporary vessel occlusion in cerebral aneurysm surgery guided by direct cortical motor evoked potentials.

BACKGROUND: Temporary clipping is an important tool in the vascular neurosurgeon's armamentarium. We routinely utilize intraoperative neurophysiological monitoring (IONM) for complex brain aneurysm surgery cases, relying on direct cortical motor evoked potential (DCMEP) alerts to guide the duration of temporary clipping. Previous studies have argued for relatively short and intermittent temporary clipping strategies. In this study, we sought to assess the maximal permissive temporary clipping time during complex aneurysm surgery. To do this, we assessed patient outcome in relation to temporary clip duration guided by DCMEP. METHODS: We queried our prospectively collected neuromonitoring database for anterior circulation aneurysm cases where temporary clipping was utilized by a single cerebrovascular surgeon between 2018 and 2021. Operative and IONM reports were reviewed. Patients in whom the duration of temporary clipping could not be determined were excluded. The operative strategy permissively allowed continuous temporary clipping as long as no neuromonitoring alerts were encountered. Maximal permissive parent artery occlusion time (Clipmax) was recorded as the longest duration of tolerated temporary vessel clipping without decrement in DCMEP. RESULTS: A total of 41 complex anterior circulation aneurysm clipping cases met criteria for this study. The mean Clipmax for all cases was just over 19 min and did not differ between ruptured and unruptured aneurysms. Initial alert times were not found to be predictive of final permissive temporary clip duration after re-perfusion. In 100% (41/41) of cases, the aneurysm was completely clip occluded without residual on catheter angiogram. Stable or improved modified Rankin Score was achieved in 98% (40/41) of cases at 3-month follow-up. CONCLUSIONS: This study demonstrates that using DCMEP can facilitate relatively long but safe temporary clipping durations in complex anterior circulation aneurysm surgery. In the endovascular era with only a limited subset of technically challenging aneurysms needing open surgical treatment, extended permissive temporary clipping guided by DCMEPs can significantly enhance a surgeon's ability to achieve excellent technical and clinical outcomes.

Transcranial magnetic stimulation for post-operative neurorehabilitation in neuro-oncology: a review of the literature and future directions.

INTRODUCTION: Transcranial magnetic stimulation (TMS) is a neuromodulation technology capable of targeted stimulation and inhibition of cortical areas. Repetitive TMS (rTMS) has demonstrated efficacy in the treatment of several neuropsychiatric disorders, and novel uses of rTMS for neurorehabilitation in patients with acute and chronic neurologic deficits are being investigated. However, studies to date have primarily focused on neurorehabilitation in stroke patients, with little data supporting its use for neurorehabilitation in brain tumor patients. METHODS: We performed a review of the current available literature regarding uses of rTMS for neurorehabilitation in post-operative neuro-oncologic patients. RESULTS: Data have demonstrated that rTMS is safe in the post-operative neuro-oncologic patient population, with minimal adverse effects and no documented seizures. The current evidence also demonstrates potential effectiveness in terms of neurorehabilitation of motor and language deficits. CONCLUSIONS: Although data are overall limited, both safety and effectiveness have been demonstrated for the use of rTMS for neurorehabilitation in the neuro-oncologic population. More randomized controlled trials and specific comparisons of contralateral versus ipsilateral rTMS protocols should be explored. Further work may also focus on individualized, patient-specific TMS treatment protocols for optimal functional recovery.

Isolating the Superficial Peroneal Nerve Motor Branch to the Peroneus Longus Muscle with Concentric Stimulation during Diagnostic Motor Nerve Biopsy.

Motor nerve biopsies are performed in the workup of neuropathies of unknown origin when motor neuron disease is suspected. Biopsy of a motor branch of the superficial peroneal nerve innervating the peroneus longus muscle has been described as a convenient alternative to other commonly biopsied motor nerves. To date, neuromonitoring techniques have not been described for this procedure. We describe the surgical neurophysiology techniques necessary for preservation of motor function and associated data during muscle biopsy of a motor branch of the superficial peroneal nerve innervating the peroneus longus muscle. We present a case of a patient who underwent uncomplicated biopsy of the motor branch of the superficial peroneal nerve innervating the peroneus longus muscle during workup for suspected motor neuropathy. The surgical neurophysiology techniques and data are presented in detail. No postsurgical sensory or motor deficit was related to the procedure. Surgical neurophysiology is critical to confirm the appropriate motor branch to the peroneus longus muscle and facilitates safe and accurate motor nerve biopsy.

Sarcomatous Change of Cerebellopontine Angle Ependymoma Following Radiosurgery: A Case Report.

Sarcomatous change in ependymal tumors is rare and has been poorly described. We report on a cerebellopontine angle lesion that demonstrated rapid progression two years after radiosurgery in a 73-year-old female patient. Histopathological diagnosis at clinical progression showed an ependymoma with sarcomatous change ("ependymosarcoma") that was believed to be due to radiation. The patient underwent a complex tumor resection without complications using an exhaustive multi-modal neuromonitoring paradigm throughout the dissection and resection of the tumor. Given the limited available data on these rare tumors, we review their presentation, imaging, and histopathology in the context of the previous literature, and also discuss the management of these lesions in the cerebellopontine angle.