Establishment of Different Intraoperative Monitoring and Mapping Techniques and Their Impact on Survival, Extent of Resection, and Clinical Outcome in Patients with High-Grade Gliomas-A Series of 631 Patients in 14 Years.

BACKGROUND: The resection of brain tumors can be critical concerning localization, but is a key point in treating gliomas. Intraoperative neuromonitoring (IONM), awake craniotomy, and mapping procedures have been incorporated over the years. Using these intraoperative techniques, the resection of eloquent-area tumors without increasing postoperative morbidity became possible. This study aims to analyze short-term and particularly long-term outcomes in patients diagnosed with high-grade glioma, who underwent surgical resection under various technical intraoperative settings over 14 years. METHODS: A total of 1010 patients with high-grade glioma that underwent resection between 2004 and 2018 under different monitoring or mapping procedures were screened; 631 were considered eligible for further analyses. We analyzed the type of surgery (resection vs. biopsy) and type of IONM or mapping procedures that were performed. Furthermore, the impact on short-term (The National Institute of Health Stroke Scale, NIHSS; Karnofsky Performance Scale, KPS) and long-term (progression-free survival, PFS; overall survival, OS) outcomes was analyzed. Additionally, the localization, extent of resection (EOR), residual tumor volume (RTV), IDH status, and adjuvant therapy were approached. RESULTS: In 481 patients, surgery, and in 150, biopsies were performed. The number of biopsies decreased significantly with the incorporation of awake surgeries with bipolar stimulation, IONM, and/or monopolar mapping (p < 0.001). PFS and OS were not significantly influenced by any intraoperative technical setting. EOR and RTV achieved under different operative techniques showed no statistical significance (p = 0.404 EOR, p = 0.186 RTV). CONCLUSION: Based on the present analysis using data from 14 years and more than 600 patients, we observed that through the implementation of various monitoring and mapping techniques, a significant decrease in biopsies and an increase in the resection of eloquent tumors was achieved. With that, the operability of eloquent tumors without a negative influence on neurological outcomes is suggested by our data. However, a statistical effect of monitoring and mapping procedures on long-term outcomes such as PFS and OS could not be shown.

Feasibility of multimodal intraoperative neurophysiological monitoring for extramedullary spinal cord tumor surgery in elderly patients.

BACKGROUND/PURPOSE: Extramedullary spinal cord tumors (EMSCTs) are mostly benign tumors which are increasingly diagnosed and operatively treated in the elderly. While there are hints that multimodal intraoperative neurophysiological monitoring (IONM) could be influenced by age and age-related comorbidities, no study has ever systematically evaluated its feasibility and value for EMSCT surgery in elderly patients. METHODS: We retrospectively evaluated all patients with microsurgical EMSCT resection under continuous multimodal IONM with SSEPs, MEPs and electromyography between 2016 and 2020. Epidemiological, clinical, imaging and operative/IONM records as well as detailed individual outcomes were analyzed and compared for the cohort < / ≥ 65 years. RESULTS: Mean age was 45 years in cohort < 65 years (n = 109) and 76 years in cohort ≥ 65 years (n = 64), while baseline/operative characteristics did not significantly differ. Mean baseline SSEPs' latencies (left-right average) were significantly higher in the cohort ≥ 65 years for both median (20.9 ms vs. 22.1 ms; p < 0.01) and tibial nerve (42.9 ms vs. 46.1 ms; p < 0.01) without significant differences for SSEPs' amplitudes. Stimulation intensity to elicit intraoperative MEPs was significantly higher in the cohort ≥ 65 years (surrogate-marker: left-right-averaged quotient ID1-muscle/abductor-hallucis-muscle; 1.6 vs. 2.1; p < 0.001). Intraoperatively, SSEP and MEP monitoring were feasible in 99%/100% and 99%/98% for the cohort < / ≥ 65 years without significant differences in rates for significant IONM changes during surgery or postoperatively new sensorimotor deficits. Sensitivity of IONM was 29%/43%, specificity 99%/98%, positive and negative predictive values 67%/75% and 95%/93% for the cohort < / ≥ 65 years. Overall, age was no risk factor for IONM feasibility or rate of significant IONM changes. DISCUSSION: Multimodal IONM is feasible/reliable for EMSCT surgery in elderly patients. An age-related prolongation of SSEPs' latencies and demand for higher stimulation intensities for MEPs' elicitation has to be considered.

Dorsal column mapping in resection of intramedullary spinal cord tumors: a prospective comparison of two methods and neurological follow-up.

PURPOSE: In surgery for intramedullary spinal cord tumors (imSCT), distortion of the anatomy challenges the visual identification of dorsal columns (DC) for midline myelotomy. Dorsal column mapping (DCM) and spinal cord stimulation (SCS) can identify DC neurophysiologically. We compare application and feasibility of both methods. METHODS: Patients with surgically treated imSCT were prospectively included between 04/2017 and 06/2019. The anatomical midline (AM) was marked. SSEPs at the DC after stimulation of tibial/median nerve with an 8-channel DCM electrode and cortical SSEP phase reversal at C3/C4 after SCS using a bipolar concentric probe were recorded. Procedural and technical aspects were compared. Standardized neurological examinations were performed preoperatively, 1 week postoperatively and after more than 12 months. RESULTS: The DCM electrode detected the midline in 9/13 patients with handling limitations in the remaining patients. SCS was applicable in all patients with determination of the midline in 9/13. If both recordings could be acquired (6/13), concordance was 100%. If baseline SSEPs were poor, both methods were limited. SCS was less time-consuming (p = 0.001), cheaper, and easier to handle. In 92% of cases, the AM and neurophysiologic midlines were concordant. After myelotomy, 3 patients experienced > 50% reduction in amplitude of SSEPs. Despite early postoperative worsening of DC function, long-term follow-up showed significant recovery and improvement in quality of life. CONCLUSION: DCM and SCS may help confirm and correct the AM for myelotomy in imSCT, leading to a favorable long-term neurological outcome in this cohort. SCS evolved to be superior concerning applicability, cost-effectiveness, and time expenditure.

Acute Hiccups Detected by Electromyographic Recordings During Resection of a Vestibular Schwannoma.

BACKGROUND AND IMPORTANCE: Intraoperative neuromonitoring (IONM) is routinely used to monitor cranial nerve function during resection of vestibular schwannomas. Sudden movements in the surgical field can be a disturbing factor for the surgeon. IONM can help determine the cause of unexpected patient movements. CLINICAL PRESENTATION: We report the case of a 54-year-old patient who underwent retromastoid craniotomy and resection of a vestibular schwannoma. Toward the end of dissection of the tumor from the lower cranial nerves and brainstem, the patient showed repetitive shoulder elevation. Electroencephalography showed burst suppression, confirming deep sedation and excluding voluntary movements. Free-running electromyography recorded spontaneous, simultaneous, bilateral vocal cord activity that was synchronous with upper body movement. There was simultaneous but smaller activity in the right genioglossus muscle and levator veli palatini, indicative for far-field activity. These IONM findings allowed us to classify the clinical observations as intraoperative hiccups. CONCLUSION: Hiccups during general anesthesia are rare but should be considered as a differential diagnosis of sudden upper body movement. To the best of our knowledge, this is the first reported case of acute hiccups during resection of a vestibular schwannoma. IONM reliably distinguished it from an increase in intraoperative consciousness or accessory nerve activation resulting in shoulder movements.

Intramedullary spinal cord cavernous malformations-association between intraoperative neurophysiological monitoring changes and neurological outcome.

BACKGROUND: Microsurgical resection of spinal cord cavernous malformations can be assisted by intraoperative neurophysiological monitoring (IONM). While the clinical outcome after surgical resection has been discussed in several case series, the association of intraoperative IONM changes and detailed neurological outcome, however, has not been analyzed so far. METHODS: Seventeen patients with spinal cavernomas underwent surgery between 02/2004 and 06/2020. Detailed neurological and clinical outcome as well as IONM data including motor-evoked potential (MEP) and somatosensory-evoked potential (SSEP) monitoring were retrospectively analyzed. Intraoperative IONM changes were compared to outcome at 3-month and 1-year follow-up in order to identify surrogate parameters for an impending neurological deficit. RESULTS: Compared to the preoperative state, McCormick score at 1-year follow-up remained unchanged in 12 and improved in five patients, none worsened, while detailed neurological examination revealed a new or worsened sensorimotor deficit in 4 patients. The permanent 80% amplitude reduction of MEP and 50% amplitude reduction of SSEP showed the best diagnostic accuracy with a sensitivity of 100% and 67% respectively and a specificity of 73% and 93% respectively. The relative risk for a new neurological deficit at 1-year follow-up, when reversible IONM-deterioration was registered compared to irreversible IONM deterioration, was 0.56 (0.23-1.37) for MEP deterioration and 0.4 (0.18-0.89) for SSEP deterioration. CONCLUSIONS: Reversible IONM changes were associated with a better neurological outcome at follow-up compared to irreversible IONM deterioration during SCCM surgery. Our study favors the permanent 80% amplitude reduction criterion for MEP and 50% amplitude reduction criterion for SSEP for further prospective evaluation of IONM significance and the effectiveness of corrective maneuvers during SCCM surgeries.

Evaluation of a new cortical strip electrode for intraoperative somatosensory monitoring during perirolandic brain surgery.

OBJECTIVE: During neurosurgical procedures, strip electrodes should have low impedance and sufficient adherence on the brain surface. We evaluated the signal quality, safety, and performance of a novel strip electrode (WISE Cortical Strip, WCS®), with conductive electrode contacts created with platinum nanoparticles embedded in a polymer base. METHODS: In a multicenter interventional, non-inferiority study, we compared WCS to a conventional strip electrode (Ad-Tech). We recorded impedance and somatosensory evoked potentials (SEP) and determined the signal-to-noise ratio (SNR). We performed direct stimulation of the motor cortex. An external clinical event committee rated safety and adverse events and users rated usability. RESULTS: During 32 brain surgeries in the paracentral region, WCS was rated safe and effective in signal transmission. Two seizure events were classified as probably related to the stimulation with WCS. The users rated WCS adhesion to the brain as satisfactory but reported difficulties sliding the WCS under the dura. The median (IQR) impedance of WCS was lower than for Ad-Tech: 2.7 (2.3-3.7) vs 5.30 (4.3-6.6) kΩ (p < 0.005). The SNR of SEP was non-inferior for WCS compared to Ad-Tech. CONCLUSIONS: The impedance of WCS was lower than Ad-Tech without safety limitations. In small craniotomies not exposing the motor cortex its use may be limited. SIGNIFICANCE: Low impedance electrodes facilitate recordings with high SNR.

Intraoperative mapping and monitoring during brain tumor surgeries.

Many different methodologies and paradigms are available to guide surgery of supratentorial tumors with the aim to preserve quality of life of the patients and to increase the extent of tumor resection. Neurophysiologic monitoring techniques (such as different evoked potentials) may help to continuously assess functional integrity of the observed systems and warn about vascular injury. For neurophysiologic mapping methods, the focus is not only to preserve cortical sites, but also to prevent injury to subcortical pathways. Therefore, cortical mapping is not enough but should be combined with subcortical mapping to identify tracts. This may be done by alternating resection and stimulation, or by continuous mapping via an electrified surgical tool such as a stimulating suction tip. Increasingly refined techniques are evolving to improve mapping of complex motor networks as well as language and higher cortical functions. Finally, in deciding between an awake vs asleep intraoperative setting, various factors need to be considered, such as the surgical goal, patient expectation and cooperation, treating team expertise, and neurooncologic aspects including histopathology. Therefore, the choice of protocol depends on the clinical context and the experience of the interdisciplinary team treating the patients.

Surgery and intraoperative neurophysiologic monitoring for aneurysm clipping.

This chapter describes the feasibility, utilization, and value of intraoperative neurophysiologic monitoring (IONM) in cerebrovascular cases. Practical advice on the integration of these adjunct methods into the modern neurosurgical operating room is based on our own neurophysiologic and neurosurgical experience. Most IONM is done for anterior circulation aneurysms. Somatosensory and motor evoked potentials are the modalities of choice covering vascular territories of the internal, anterior, and middle cerebral arteries. While monitoring both hemispheres with the unoperated side as control, monitoring focus is laid upon those territories at risk and bearing the aneurysm. The specificity of IONM is close to 1, and sensitivity ranges from 0.2 to 1, depending on the categorization of transient changes. The overall likelihood of worsened neurologic outcome after any intraoperative signal deterioration (transient or permanent) is 0.4.

Long latency responses in tongue muscle elicited by various stimulation sites in anesthetized humans - New insights into tongue-related brainstem reflexes.

BACKGROUND: Long Latency Responses (LLR) in tongue muscles are a scarcely described phenomenon, the physiology of which is uncertain. OBJECTIVES: The aim of this exploratory, observational study was to describe tongue-LLR elicited by direct trigeminal nerve (DTNS), dorsal column (DoColS), transcranial electric (TES) and peripheral median nerve (MNS) stimulation in a total of 93 patients undergoing neurosurgical procedures under general anesthesia. METHODS: Bilateral tongue responses were derived concurrently after each of the following stimulations: (1) DTNS applied with single monophasic or train-of-three pulses, ≤5 mA; (2) DoColS applied with a train-of-three pulses, ≤10 mA; (3) TES consisting of an anodal train-of-five stimulation, ≤250 mA; (4) MNS at wrist consisting of single or train-of-three monophasic pulses, ≤50 mA. Polyphasic tongue muscle responses exceeding the latencies of tongue compound muscle action potentials or motor evoked potentials were classified as LLR. RESULTS: Tongue-LLR were evoked from all stimulation sites, with latencies as follows: (1) DTNS: solely ipsilateral 20.2 ± 3.3 msec; (2) DoColS: ipsilateral 25.9 ± 1.6 msec, contralateral 25.1 ± 4.2 msec; (3) TES: contralateral 55.3 ± 10.2 msec, ipsilateral 54.9 ± 12.0 msec; (4) MNS: ipsilateral 37.8 ± 4.7 msec and contralateral 40.3 ± 3.5 msec. CONCLUSION: The tongue muscles are a common efferent in brainstem pathways targeted by trigeminal and cervical sensory fibers. DTNS can elicit the "trigemino-hypoglossal-reflex". For the MNS elicited tongue-LLR, we propose the term "somatosensory-evoked tongue-reflex". Although the origin of the TES related tongue-LLR remains unclear, these data will help to interpret intraoperative tongue recordings.

Bilateral and Optimistic Warning Paradigms Improve the Predictive Power of Intraoperative Facial Motor Evoked Potentials during Vestibular Schwannoma Surgery.

Facial muscle corticobulbar motor evoked potentials (FMcoMEPs) are used to monitor facial nerve integrity during vestibular schwannoma resections to increase maximal safe tumor resection. Established warning criteria, based on ipsilateral amplitude reduction, have the limitation that the rate of false positive alarms is high, in part because FMcoMEP changes occur on both sides, e.g., due to brain shift or pneumocephalus. We retrospectively compared the predictive value of ipsilateral-only warning criteria and actual intraoperative warnings with a novel candidate warning criterion, based on "ipsilateral versus contralateral difference in relative stimulation threshold increase, from baseline to end of resection" (BilatMT ≥ 20%), combined with an optimistic approach in which a warning would be triggered only if all facial muscles on the affected side deteriorated. We included 60 patients who underwent resection of vestibular schwannoma. The outcome variable was postoperative facial muscle function. Retrospectively applying BilatMT, with the optimistic approach, was found to have a significantly better false positive rate, which was much lower (9% at day 90) than the traditionally used ipsilateral warning criteria (>20%) and was also lower than actual intraoperative warnings. This is the first report combining the threshold method with an optimistic approach in a bilateral multi-facial muscle setup. This method could substantially reduce the rate of false positive alarms in FMcoMEP monitoring.

Transcranial versus Direct Cortical Stimulation for Motor-Evoked Potentials during Resection of Supratentorial Tumors under General Anesthesia (The TRANSEKT-Trial): Study Protocol for a Randomized Controlled Trial.

BACKGROUND: Monitoring of motor function during surgery for supratentorial tumors under general anesthesia applies either transcranial electrical stimulation (TES) or direct cortical stimulation (DCS) to elicit motor-evoked potentials. To date, there is no guideline that favor one method over the other. Therefore, we designed this randomized study to compare between both methods regarding the prediction of postoperative motor deficits and extent of tumor resection. METHODS: This is a multicenter (six centers in Germany and one in Switzerland), double blind, parallel group, exploratory, randomized controlled clinical trial. Patients without or with mild paresis, who are scheduled for surgical resection of motor-eloquent brain tumors under general anesthesia will be randomized to surgical resection under TES or surgical resection under DCS. The primary endpoint is sensitivity and specificity in prognosis of motor function 7 days after surgery. The main secondary endpoint is the extent of tumor resection. The study is planned to include 120 patients within 2 years. DISCUSSION: The present exploratory study should compare TES and DCS regarding sensitivity and specificity in predicting postoperative motor deficit and extent of tumor resection to calculate the required number of patients in a confirmatory trial to test the superiority of one method over the other.

Detection of impending perfusion deficits by intraoperative computed tomography (iCT) in aneurysm surgery of the anterior circulation.

BACKGROUND: The aim of our study was to evaluate the additional benefit of intraoperative computed tomography (iCT), intraoperative computed tomography angiography (iCTA), and intraoperative computed tomography perfusion (iCTP) in the intraoperative detection of impending ischemia to established methods (indocyanine green videoangiography (ICGVA), microDoppler, intraoperative neuromonitoring (IONM)) for initiating timely therapeutic measures. METHODS: Patients with primary aneurysms of the anterior circulation between October 2016 and December 2019 were included. Data of iCT modalities compared to other techniques (ICGVA, microDoppler, IONM) was recorded with emphasis on resulting operative conclusions leading to inspection of clip position, repositioning, or immediate initiation of conservative treatment strategies. Additional variables analyzed included patient demographics, aneurysm-specific characteristics, and clinical outcome. RESULTS: Of 194 consecutive patients, 93 patients with 100 aneurysms received iCT imaging. While IONM and ICGVA were normal, an altered vessel patency in iCTA was detected in 5 (5.4%) and a mismatch in iCTP in 7 patients (7.5%). Repositioning was considered appropriate in 2 patients (2.2%), where immediate improvement in iCTP could be documented. In a further 5 cases (5.4%), intensified conservative therapy was immediately initiated treating the reduced CBP as clip repositioning was not considered causal. In terms of clinical outcome at last FU, mRS0 was achieved in 85 (91.4%) and mRS1-2 in 7 (7.5%) and remained mRS4 in one patient with SAH (1.1%). CONCLUSIONS: Especially iCTP can reveal signs of impending ischemia in selected cases and enable the surgeon to promptly initiate therapeutic measures such as clip repositioning or intraoperative onset of maximum conservative treatment, while established tools might fail to detect those intraoperative pathologic changes.

Intraspinal epidermoid and dermoid cysts-tumor resection with multimodal intraoperative neurophysiological monitoring and long-term outcome.

BACKGROUND: Intraspinal epidermoid/dermoid cysts are very rare, benign tumors arising from pathological displacement of epidermal cells into the spinal canal. Literature data about the long-term outcome after microsurgical resection with multimodal intraoperative neurophysiological monitoring (IONM) are lacking. We analyzed one of the largest case series with special regard to intraoperative characteristics and long-term outcome after IONM-aided surgery. METHOD: All 12 patients (m:f = 1.4:1) who underwent microsurgical tumor resection with multimodal IONM for intraspinal epidermoid/dermoid tumors between 1998 and 2019 in our university hospital were included. We retrospectively investigated the patients' characteristics, imaging/surgical parameters, and postoperative long-term outcomes. RESULTS: Symptomatic tumor manifestation was seen during adulthood in 4 patients (median age 33.0 years) and during childhood in 8 patients (median age 4.3 years). Spinal dysraphism was the most often comorbidity (75%). The most frequent symptoms at diagnosis were spastic pareses (75%), ataxia (58%), and vegetative disorders (42%). Tumors were most often lumbosacral (L1-L5 42%, L5-S3 50%) and intradural-extramedullary (92%). For microsurgical resection, IONM with EMG, SSEPs, and TcMEPs of the limbs and pudendal nerve/anal sphincter was always applied and feasible; intraoperative corrective actions were initiated in three cases due to transient IONM deterioration. None of the patients showed a postoperative deterioration of the neurological status with a gross total resection rate of 92%. Pain situation, McCormick grade, and mJOA Score were improved at long-term follow-up (median 4.8 years). CONCLUSIONS: IONM-aided resection of intraspinal epidermoid/dermoid tumors is feasible both in adult and pediatric cases and enables a satisfying clinical and surgical outcome.

Prognostic value of a bilateral motor threshold criterion for facial corticobulbar MEP monitoring during cerebellopontine angle tumor resection.

In intraoperative neuromonitoring (IONM), facial nerve motor function (FaNMF) is assessed by facial muscle corticobulbar motor evoked potentials (FMcoMEP). Mostly only amplitude decrease is used as warning criterion. We related a refined criterion for FMcoMEP consisting of a bilateral final-to-baseline motor threshold ratio with standard criteria and postoperative FaNMF. 79 patients (45 females; 48 ± 16 years) undergoing IONM-guided cerebellopontine angle tumor surgery were retrospectively analyzed. An intraoperative final-to-baseline motor threshold increase ≥ 20% ipsi- versus contralaterally (bFBMT20) was correlated to postoperative FaNMF at day 1 (D1), 7 (D7) and 3 months (3 M). An ipsilateral-only final-to-baseline motor threshold increase ≥ 20 mA (iAMT20) and amplitude decrement ≥ 50% (iAR50) served as reference. Tumors included vestibular schwannomas (68%), meningiomas (19%) and others (13%). Mean tumor diameter was 2.7 ± 1.1 cm. Postoperatively, HB-increase ≥ 2 was seen in 27% (D1), 17% (D7), and 6% (3 M) of patients, respectively. FMcoMEP were obtained in 75/79 cases. Pathological bFBMT20, iAMT20 and iAR50 were seen in 17, 17, and 46 cases, respectively. Area under the ROC curve for bFBMT20 (iAMT20) was 0.894 (0.868) at D1; 0.903 (0.822) at D7 and 0.941 (0.959) at 3 M. iAR50 performed worse at all time points. Diagnostic odds ratios were highest for bfBMT20 compared to iAMT20 and iAR50 for D1 (172.5 vs. 8.7 vs. 0.45) and D7 (51.4 vs. 6.1 vs. 0.8). The refined parameter bFBMT20 provides a valuable contribution to the prognostic assessment of FaNMF. Due to its bihemispheric character, it might thus circumvent false-positive events which affect FMcoMEP bilaterally.

Intraoperative Erb's Point-Vertex recording increases brainstem auditory evoked potential wave V amplitude.

OBJECTIVE: Recording derivations for intraoperative brainstem auditory evoked potential (BAEP) monitoring consist of a preauricular electrode referenced to Cz'. These derivations are prone to unfavorable signal amplitude. This study analyses whether an alternative noncephalic electrode positioned over ipsilateral Erb's point, thereby generating a new Erb's point-vertex recording derivation, improves BAEP recordings. METHODS: Electrodes were placed preauricularly (A1/A2) and at left and right Erb's point (EP1/EP2). They were referenced to Cz'. Click sound stimulation (80-95 dB above hearing level) was applied. At intraoperative baseline conditions, latencies and amplitudes of waves I-V of all derivations were analyzed. RESULTS: Data of 30 patients (54 ± 15 years/17 females) with normal hearing or mild symmetrical presbycusis undergoing infratentorial surgeries (15 microvascular decompressions) were analyzed. Using EP1-Cz'/EP2-Cz' derivations compared to A1-Cz'/A2-Cz', amplitudes for wave IV (left +65%, p < 0.001; right +43%, p = 0.002) and wave V (left +54%, p < 0.001; right +48%, p < 0.001) were significantly increased. Only in the left (EP1) derivation, there was a tendency towards less reproducibility of wave I, resulting in a decrease of amplitude (-35%, p = 0.005). CONCLUSIONS: Adding an Erb's point electrode derivation resulted in larger amplitudes of waves IV to V. whereas conventional preauricular or mastoid derivation is preferential for wave I assessment. SIGNIFICANCE: Increased wave amplitudes facilitate detection of pathologically reduced wave forms (wave V in particular) which represents a significant advancement.

Indication and technical implementation of the intraoperative neurophysiological monitoring during spine surgeries-a transnational survey in the German-speaking countries.

BACKGROUND: Intraoperative neurophysiological monitoring is widely used in spine surgery (sIONM). But guidelines are lacking and its use is mainly driven by individual surgeons' preferences and medicolegal advisements. To gain an overview over the current status of sIONM implementation, we conducted a transnational survey in the German-speaking countries. METHODS: We developed a Web interface-based survey assessing prevalence, indication, technical implementation, and general satisfaction regarding sIONM in German, Austrian, and Swiss spine centers. The electronic survey was performed between November 2017 and April 2018, including both neurosurgical and orthopedic spine centers. RESULTS: A total of 463 German, 60 Austrian, and 52 Swiss spine centers were contacted with participation rates of 64.1% (Germany), 68.3% (Austria), and 55.8% (Switzerland). Some 75.9% participating neurosurgical spine centers and only 14.7% of the orthopedic spine centers applied sIONM. Motor- and somatosensory-evoked potentials (93.7% and 94.3%, respectively) were the most widely available modalities, followed by direct wave (D wave; 66.5%). Whereas sIONM utilization was low in spine surgeries for degenerative, traumatic, and extradural tumor diseases, it was high for scoliosis and intradural tumor surgeries. Overall, the general satisfaction within the institutional setting regarding technical skills, staff, performance, and reliability of sIONM was rated as "high" by more than three-quarters of the centers. However, shortage of skilled staff was claimed to be a negative factor by 41.1% of the centers and reimbursement was considered to be insufficient by 83.5%. CONCLUSIONS: sIONM availability was high in neurosurgical but low in orthopedic spine centers. Main modalities were motor/somatosensory-evoked potentials and main indications were scoliosis and intradural spinal tumor surgeries. A more frequent sIONM use, however, was mainly limited by the shortage of skilled staff and restricted reimbursement.

Intraoperative neurophysiological monitoring during resection of infratentorial lesions: the surgeon's view.

OBJECTIVE Methods of choice for neurophysiological intraoperative monitoring (IOM) within the infratentorial compartment mostly include early brainstem auditory evoked potentials, free-running electromyography, and direct cranial nerve (CN) stimulation. Long-tract monitoring with somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) is rarely used. This study investigated the incidence of IOM alterations during posterior fossa surgery stratified for lesion location. METHODS Standardized CN and SEP/MEP IOM was performed in 305 patients being treated for various posterior fossa pathologies. The IOM data were correlated with lesion locations and histopathological types as well as other possible confounding factors. RESULTS Alterations in IOM were observed in 158 of 305 cases (51.8%) (CN IOM alterations in 130 of 305 [42.6%], SEP/MEP IOM alterations in 43 of 305 [14.0%]). In 15 cases (4.9%), simultaneous changes in long tracts and CNs were observed. The IOM alterations were followed by neurological sequelae in 98 of 305 cases (32.1%); 62% of IOM alterations resulted in neurological deficits. Sensitivity and specificity for detection of CN deficits were 98% and 77%, respectively, and 95% and 85%, respectively, for long-tract deficits. Regarding location, brainstem and petroclival lesions were closely associated with concurrent CN IOM and SEP/MEP alterations. CONCLUSIONS The incidence of IOM alterations during surgery in the posterior fossa varied widely between different lesion locations and histopathological types. This analysis provides crucial information on the necessity of IOM in different surgical settings. Because MEP/SEP and CN IOM alterations were commonly observed during posterior fossa surgery, the authors recommend the simultaneous use of both modalities based on lesion location.

Spinal cord hemangioblastomas: significance of intraoperative neurophysiological monitoring for resection and long-term outcome.

OBJECTIVE Spinal cord hemangioblastomas are rare benign tumors developing either sporadically or as part of von Hippel-Lindau (VHL) disease. Generally, resection is the treatment of choice. However, the significance of intraoperative neurophysiological monitoring (IONM) for resection and postoperative outcome is still controversial. The authors analyzed the surgical and clinical courses of patients who had undergone resection of spinal cord hemangioblastoma, with special attention to preoperative imaging, the use of IONM, and short- and long-term outcomes. METHODS A series of 24 patients (male/female 1:1, lesion sporadic/associated with VHL 2.4:1) who had undergone 26 operations for the resection of 27 spinal cord hemangioblastomas was analyzed. All patients had undergone pre- and postoperative contrast-enhanced MRI. In all cases, microsurgical tumor removal had been performed under continuous IONM of both somatosensory and transcranial motor evoked potentials as well as electromyographic recording. Clinical characteristics, imaging findings, and operative records were retrospectively analyzed. Outcome parameters included short- and long-term status as regards sensorimotor deficits and a questionnaire on general performance, patient satisfaction, and Oswestry Disability Index (ODI) at the end of the follow-up period. The impact of IONM findings on postoperative deficits and outcome parameters as well as risk factors affecting functional prognosis was statistically assessed. RESULTS Preoperative symptoms (mean duration 16.2 ± 22.0 months) included sensory changes (100.0%), pain (66.7%), spinal ataxia (66.7%), motor deficit (41.7%), and bladder/bowel dysfunction (12.5%). Average age at the first operation was 36.8 ± 12.8 years. Most tumors (21 intramedullary, 6 intra- and/or extramedullary) were located dorsally (92.6%) and cervically (77.8%) and were accompanied by peritumoral edema and/or syringomyelia (81.5%). Tumor resection was achieved via laminectomy for 15 tumors, hemilaminectomy for 5, laminoplasty for 6, and interlaminar approach for 1. Gross-total resection was accomplished for 26 tumors (96.3%) with no local tumor recurrence during follow-up. Intraoperative neurophysiological monitoring was nonpathological in 11 operations (42.3%) and pathological in 15 (57.7%). Patients with nonpathological IONM had significantly fewer new sensorimotor deficits (p = 0.005). Long-term follow-up evaluation (mean 7.9 ± 4.0 years postoperatively, 7 patients lost to follow-up) revealed a stable or improved McCormick myelopathy grade in 88.2% of the patients, and 88.2% reported a stable or improved overall outcome according to Odom's criteria. Long-term general performance was excellent with 88.2% having a WHO/Eastern Cooperative Oncology Group (ECOG) Performance Status grade ≤ 1, 76.5% a Karnofsky Performance Scale score ≥ 80, and 70.6% a Barthel Index (BI) of 100. The mean ODI (11.4% ± 12.5%) indicated only minimal disability. There was a significant correlation between pathological IONM findings and a worse long-term status according to the BI and ODI (p = 0.011 and 0.024, respectively). Additionally, VHL disease was a risk factor affecting functional prognosis (p = 0.044). CONCLUSIONS Microsurgical removal of spinal cord hemangioblastomas with IONM facilitates a satisfying long-term outcome for patients. Nonpathological IONM findings are associated with a lower risk of new sensorimotor deficits and correlate with a better overall long-term outcome. von Hippel-Lindau disease is a risk factor for a worse long-term prognosis.