A critical event frequent lead to reversible spinal cord injury during vertebral column resection surgery.

OBJECTIVE: To report a "critical phase" (between osteotomy completion and correction beginning) that will frequently lead to the reversible intraoperative neurophysiological monitoring (IOM) change during posterior vertebral column resection (PVCR) surgery. METHODS: The study sample consisted of 120 patients with severe spine deformity who underwent PVCR and deformity correction surgeries. Those patients were recruited consecutively from 2010 to 2018 January in our spine center. The detailed IOM data (the amplitude of MEP & SEP) and its corresponding surgical points were collected prospectively. Early and long-term postoperative neurologic outcomes were assessed for the following functions: motor, sensory, and pain at immediate postoperative and 1-year post-operation in this cases series. RESULTS: A total of 105 (105/120) patients presented varying degrees of IOM reduction in the critical phase; the mean IOM amplitude retention vs rescue rate was 27% ± 11.2 versus 58% ± 16.9, P < 0.01 (MEP) & 34% ± 8.3 versus 66% ± 12.4 P < 0.01 (SEP). Patients with postoperative spinal deficits often had a significantly longer IOM-alerting duration than the patients without (p < 0.01, Mann-Whitney U-test), and IOM-alerting duration greater than 39.5 min was identified as an independent predictor of the risk of postoperative spinal deficits. CONCLUSIONS: The reversible IOM events probably often appear in the critical phase during PVCR surgery. The new postoperative spinal deficits are possible for patients without satisfied IOM recovery or alerting duration greater than 39.5 min. Timely and suitable surgical interventions are useful for rescuing the IOM alerts.

Validity of evoked potential as biomarker for predicting early neural function changes after thoracic spinal decompression surgery in patients with neurological deficits.

OBJECTIVE: To evaluate the validity of intraoperative evoked potential (EP) including motor evoked potential (MEP) and somatosensory evoked potentials (SEP) as a biomarker for predicting neural function changes after thoracic spinal decompression (TSD) surgery. METHOD: A consecutive series of 336 TSD surgeries were reviewed between 2010 and 2021 from four spine center. All patients with TSD were divided into 3 groups according to different intraoperative EP results: group 1, EP alerts; group 2, no obvious EP deterioration; group 3, EP improvement compared with baselines. The lower limb Japanese Orthopedic Association (JOA) scores (as well as early and long-term JOA recovery rate) were utilized to quantitatively assess pre- and postoperative neural function change. RESULTS: Among the 3 subgroups according to the different EP changes, the early JOA recovery rate (RR%) in the EP improvement group was significantly better than the other two groups (51.3 ± 58.6* vs. 27.5 ± 31.2 and 33.3 ± 43.1; p < 0.01) after 3-month follow-up. The mean MEP and SEP amplitude were from 116 ± 57 µV to 347 ± 71 µV (p < 0.01) and from 1.86 ± 0.24 µV to 2.65 ± 0.29 µV (p < 0.01) between spinal cord pre-decompression and post-decompression. Moreover, multivariate logistic regression analysis revealed that risk factors of EP improvement were duration of symptom (p < 0.001, OR 10.9) and Preop. neurologic deficit degree (p = 0.013, OR 7.46). CONCLUSION: The intraoperative EP can predict postoperative neural function changes as a biomarker during TSD. Patient with EP improvement probably has better prognosis for early neural function recovery. The duration of symptom and preoperative neurologic deficit degree may be related to intraoperative EP improvement.

Transcranial MEP threshold voltages and current densities simulated with finite element modelling.

OBJECTIVE: The aim of this study was to compare stimulation thresholds and current densities in the brain for transcranial motor evoked potentials (tcMEPs) from the hands and feet with linked quadripolar (LQP), M3-M4 and C1-C2 electrode montages. METHODS: Twenty-five patients underwent cerebral vascular surgery with tcMEP monitoring. tcMEP voltage thresholds were compared between LQP (C1, M3, C2, M4), C1-C2, and M3-M4 montages. In a finite element model (FEM), hand, arm, and leg regions of interest (ROIs) on the cortical motor homunculus were segmented. Current densities in these ROIs at tcMEP thresholds were compared across tcMEP electrode montages. RESULTS: LQP tcMEP thresholds were 61.5 volts for hands and 95.2 volts for feet. Thresholds were higher for M3-M4 (hands, 89.4 V; feet, 141.3 V) and C1-C2 (hands: 137.3 V; feet: 194.7 V). Total current at threshold voltage was greater for LQP (hands, 210.9 mA; feet, 311.3 mA) compared to M3-M4 (hands, 166.8 mA; feet, 256.6 mA), but similar to C1-C2 (hands, 246.7 mA; feet, 341.1 mA). In FEM simulations, current density and local current density topography in the hand ROI at threshold were very similar for LQP, M3-M4 and C1-C2. CONCLUSIONS: TcMEP voltage thresholds were least for LQP, and lesser for M3-M4 compared to C1-C2. In FEM simulations, resistance to current to hand ROI was ordered the same (LQP < M3-M4 < C1-C2). The local distribution of current density in motor cortex with tcMEP was mainly determined by cortical geometry. SIGNIFICANCE: Current densities and resistance to current simulated with FEM may explain threshold requirements for tcMEP electrode montages.

Intraoperative neuromonitoring during surgery for lumbar stenosis.

The indications for neuromonitoring during lumbar stenosis surgery are defined by the risks associated with patient positioning, the approach, decompression of neural elements, deformity correction, and instrument implantation. The routine use of EMG and SEP alone during lumbar stenosis surgery is no longer supported by the literature. Lateral approach neuromonitoring with EMG only is also suspect. Lumbar stenosis patients often present with multiple co-morbidities which put them at risk during routine pre-surgical positioning. Frequently encountered morbid obesity and/or diabetes mellitus may play a role in monitorable and preventable brachial plexopathy after "superman" positioning or femoral neuropathy from groin pressure after prone positioning, for example. Deformity correction in lumbar stenosis surgery often demands advanced implementation of multiple neuromonitoring modalities: EMG, SEP, and MEP. Because the bulbocavernosus reflex detects the function of the conus medullaris and sacral somato afferent/efferent fibers of the cauda equina, it may also be recorded. The recommendation to record pedicle screw thresholds has become more nuanced as surgeon dependence on 3D imaging, navigation, and robotics has increased. Neuromonitoring in lumbar stenosis surgery has been subject mainly to uncontrolled case series; prospective cohort trials are also needed.

Monitoring spinal surgery for extramedullary tumors and fractures.

Meningiomas are the most common intradural extramedullary tumors, followed by nerve sheath tumors that can also grow extradurally. Metastases are the most frequent extradural tumors and most commonly affect the thoracic vertebrae. Spinal fractures with column dislocation and/or instability require surgical fixation. Spine surgery for an extramedullary tumor or fracture usually involves decompression of neural elements and instrumentation for stabilization. These procedures risk spinal cord and nerve root injury. The incidence of nerve root deficits after resection of nerve sheath tumors is particularly high since the tumor grows from the rootlets. Intraoperative neurophysiologic monitoring and mapping techniques have been introduced to prevent iatrogenic neurologic deficits. These include motor and sensory evoked potentials, electromyography, compound muscle action potentials, and the bulbocavernosus reflex. The combination of techniques chosen for a particular procedure depends on the surgical level and the character of the lesion.

The Minimal Subcortical Electronic Threshold Predicts the Motor Deficit and Survivals in Non-Awake Surgery for Gliomas Involving the Motor Pathway.

Purpose: Direct subcortical motor mapping is the golden criterion to detect and monitor the motor pathway during glioma surgery. Minimal subcortical monopolar threshold (MSCMT) means the minimal distance away from the motor pathway and is critical to decide to continue or interrupt glioma resection. However, the optimal cutoff value of MSCMT for glioma resection in non-awake patients has not been reported discreetly. In this study, we try to establish the safe cutoff value of MSCMT for glioma resection and analyzed its relationship with postoperative motor deficit and long-term survivals. Methods: We designed this prospective study with high-frequency electronic stimulus method. The cutoff MSCMT of postoperative motor deficits was statistically calculated by receiver operating characteristic (ROC) curve, and its relationship with motor deficit and survivals was analyzed by logistic and Cox regression, respectively. Results: The cutoff MSCMT to predict motor deficit after surgery was 3.9 mA on day 1, 3.7 mA on day 7, 5.2 mA at 3 months, and 5.2 mA at 6 months. MSCMT ≤3.9 mA and MSCMT ≤5.2 mA independently predicted postoperative motor deficits at four times after surgery (P < 0.05) but had no effect on the removal degree of tumor (P > 0.05). In high-grade gliomas, MSCMT ≤3.9 mA independently predicted shorter progression-free survival [odds ratio (OR) = 3.381 (1.416-8.076), P = 0.006] and overall survival [OR = 3.651 (1.336-9.977), P = 0.012]. Power model has the best fitness for paired monopolar and bipolar high-frequency thresholds. Conclusions: This study showed strong cause-effect relation between MSCMT and postoperative motor deficit and prognoses. The cutoff MSCMT was dug out to avoid postoperative motor deficit. Further studies are needed to establish the results above.

Utilization of intraoperative neuromonitoring during the Woodward procedure for treatment of Sprengel deformity.

BACKGROUND: Brachial plexus injury (BPI) leading to palsy of the upper extremities is the most serious complication of the Woodward procedure for treatment of Sprengel deformity. Intraoperative neuromonitoring (IONM) is widely used for detecting emerging spinal cord or peripheral nerve injury during spinal and shoulder surgery. However, to date, its utilization in pediatric patients with Sprengel deformity is limited. Furthermore, it remains unclear whether IONM can help prevent BPI during surgery. The purpose of the current study was to assess the feasibility and effectiveness of IONM for early identification and prevention of nerve injury during the Woodward procedure. METHODS: We retrospectively reviewed the records of patients who underwent the Woodward procedure for Sprengel deformity at our institution between January 2017 and January 2020. IONM, including somatosensory evoked potentials (SEP) and motor evoked potentials (MEPs), was performed in all patients. Detailed IONM data were collected and analyzed. Preoperative and postoperative cosmetic appearance (according to the Cavendish classification), shoulder joint abduction function, and radiologic evaluation of the scapula were reviewed. Surgical complications were recorded. RESULTS: Forty-six patients (19 girls, 27 boys) were included (mean age, 5.1 ± 2.1 years). Both SEP and MEP (amplitude of the abductor pollicis) were successfully performed (100%). MEP alerts occurred in 3 patients (6.5%). After scapula position adjustment, signals recovered in 2 patients and remained unchanged in 1 patient-this patient exhibited postoperative motor deficits that resolved completely by 4 months recovery. The SEP amplitudes decreased in all 3 patients but did not reach the warning criteria. Forty patients were classified as grade III and 6 as grade IV in the Cavendish classification, whereas 35 patients were classified as grade II and 11 as grade III in the Rigault scale. The preoperative Cavendish grade was III (III, IV) and the postoperative Cavendish grade was I (I, II) (χ2 = 88.098, P < .001). The preoperative Rigault grade was II (II, III) and the postoperative Rigault grade was I (I, II) (χ2 = 62.133, P < .001). The mean arc of shoulder joint abduction improved from 99° ± 8° to 167° ± 7° (t = -45.871, P < .001) after surgery. Except for temporary motor deficits detected in 1 patient, no other postoperative complications were observed through the time of final follow-up. CONCLUSION: IONM during the Woodward procedure for Sprengel deformity is feasible and effective in detecting intraoperative neurologic changes and may be effective in preventing BPI associated with surgery.

Utility of intraoperative neuromonitoring and outcomes of neurological complication in lower cervical and upper thoracic posterior-based three-column osteotomies for cervical deformity.

OBJECTIVE: For severe and rigid adult cervical deformity, posterior-based three-column osteotomies (3COs) are warranted, but neurological complications are relatively high with such procedures. The performance measures of intraoperative neuromonitoring (IONM) during cervicothoracic 3CO have yet to be studied, and there remains a paucity of literature regarding the topic. Therefore, the authors of this study examined the performance of IONM in predicting new neurological weakness following lower cervical and upper thoracic 3CO. In addition, they report the 6-month, 1-year, and 2-year outcomes of patients who experienced new postoperative weakness. METHODS: The authors performed a retrospective review of a single surgeon's experience from 2011 to 2018 with all patients who had undergone posterior-based 3CO in the lower cervical (C7) or upper thoracic (T1-4) spine. Medical and neuromonitoring records were independently reviewed. RESULTS: A total of 56 patients were included in the analysis, 38 of whom had undergone pedicle subtraction osteotomy and 18 of whom had undergone vertebral column resection. The mean age was 61.6 years, and 41.1% of the patients were male. Among the study cohort, 66.1% were myelopathic and 33.9% had preoperative weakness. Mean blood loss was 1565.0 ml, and length of surgery was 315.9 minutes. Preoperative and postoperative measures assessed were cervical sagittal vertical axis (6.5 and 3.8 cm, respectively; p < 0.001), cervical lordosis (2.3° and -6.7°, p = 0.042), and T1 slope (48.6° and 35.8°, p < 0.001). The complication rate was 49.0%, and the new neurological deficit rate was 17.9%. When stratifying by osteotomy level, there were significantly higher rates of neurological deficits at C7 and T1: C7 (37.5%), T1 (44.4%), T2 (16.7%), T3 (14.3%), and T4 (0.0%; p = 0.042). Most new neurological weakness was the nerve root pattern rather than the spinal cord pattern. Overall, there were 16 IONM changes at any threshold: 14 at 50%, 8 at 75%, and 13 if only counting patients who did not return to baseline (RTB). Performance measures for the various thresholds were accuracy (73.2% to 77.8%), positive predictive value (25.0% to 46.2%), negative predictive value (81.3% to 88.1%), sensitivity (18.2% to 54.5%), and specificity (77.8% to 86.7%). Sensitivity to detect a spinal cord pattern of weakness was 100% and 28.6% for a nerve root pattern of weakness. In patients with a new postoperative deficit, 22.2% were unchanged, 44.4% improved, and 33.3% had a RTB at the 2-year follow-up. CONCLUSIONS: Complication rates are high following posterior 3CO for cervical deformity. 3CO at C7 and T1 has the highest rates of neurological deficit. Current IONM modalities have modest performance in predicting postoperative deficits, especially for nerve root neuropraxia. A large prospective multicenter study is warranted.

Survivals of the Intraoperative Motor-evoked Potentials Response in Pediatric Patients Undergoing Spinal Deformity Correction Surgery: What Are the Neurologic Outcomes of Surgery?

STUDY DESIGN: This is a retrospective cases study from a prospective patient register. OBJECTIVE: To clarify the clinical implication regard to the survivals of motor-evoked potential (MEP) response. SUMMARY OF BACKGROUND DATA: Intraoperative neurophysiological monitoring has become an essential component for decreasing the incidence of neurological deficits during spine surgeries. Significant motor-evoked potential (MEP) loss but does not vanish completely is common especially in some high-risk and complicated pediatric spine deformity surgeries. METHODS: A total of 1820 young patients (mean age = 12.2 years) underwent spinal deformity correction were mainly analyzed. Intraoperative monitoring (somatosensory-evoked potential, MEP, free-run electromyography, free-run electromyography) and postoperative neurologic outcomes were mainly analyzed in this study. All patients with monitoring alerts were divided into two groups: group 1, intraoperative MEP recovery group; and group 2, no obvious MEP recovery group. Moreover, the patients would be followed up strictly if he/she showed IOM alerting. The surviving MEP response was identified as significant monitoring alerts (80%-95% MEP Amp. loss) associated with high-risk surgical maneuvers. RESULTS: The results showed that there were 32 pediatric patients (group 1, 21 cases and group 2, 11 cases) presenting significant MEP monitoring alerts (80%-95% loss) relative to baseline. The patients in group 1 presented the partial/entire signal recovery from MEP alerts and they did not show spinal cord deficits postoperation. The patients in group 2 without obvious intraoperative MEP recovery showed different levels of new spinal deficits, no patient showed postoperative complete paraplegia or permanent spinal cord/nerve root deficits. CONCLUSION: When the intraoperative MEP changes significant and persistent but without totally disappeared, the rate of postoperative neural complication is relatively low. The chance of recovery of these neurological deficits is very high. Therefore, this phenomenon may be used to predictive of nonpermanent paraplegia. LEVEL OF EVIDENCE: 3.

The Correlation Between Recordable MEPs and Motor Function During Spinal Surgery for Resection of Thoracic Spinal Cord Tumor.

BACKGROUND: Motor evoked potentials (MEPs) are commonly used during surgery for spinal cord tumor resection. However, it can be difficult to record reliable MEPs from the muscles of the lower extremities during surgery in patients with preoperative weakness due to spinal cord compression. In this study, motor function of patients' lower extremities and their association with intraoperative MEP recording were compared. PATIENTS AND METHODS: Patients undergoing thoracic spinal cord tumor resection were studied. Patients' motor function was checked immediately before the surgical procedure. MEP responses were recorded from the tibialis anterior and foot muscles, and the hand muscles were used as control. Electrical current with train of eight pulses, 200 to 500 V was delivered through 2 corkscrews placed at C3' and C4' sites. Anesthesia was maintained by total intravenous anesthesia using a combination of propofol and remifentanil after induction with intravenous propofol, remifentanil, and rocuronium. Rocuronium was not repeated. Bispectral Index was maintained between 40 to 50. RESULTS: From 178 lower limbs of 89 patients, myogenic MEPs could be recorded from 100% (105/105) of the patients with 5 of 5 motor strength in lower extremity; 90% (36/40) from the patients with 4/5 motor strength; only 25% (5/20) with 3/5; and 12.5% (1/8) with 2/5 motor strength; none (0/5) were able to be recorded if the motor strength was 1/5. SUMMARY: The ability to record myogenic MEPs is closely associated with the patient's motor function. They are difficult to obtain if motor function is 3/5 motor strength in the lower extremity. They are almost impossible to record if motor function is worse than 3/5.

Effects of Dexmedetomidine on motor- and somatosensory-evoked potentials in patients with thoracic spinal cord tumor: a randomized controlled trial.

BACKGROUND: We hypothesized that the addition of dexmedetomidine in a clinically relevant dose to propofol-remifentanil anesthesia regimen does not exert an adverse effect on motor-evoked potentials (MEP) and somatosensory-evoked potentials (SSEP) in adult patients undergoing thoracic spinal cord tumor resection. METHODS: Seventy-one adult patients were randomized into three groups. Propofol group (n = 25): propofol-remifentanil regimenand the dosage was adjusted to maintain the bispectral index (BIS) between 40 and 50. DP adjusted group (n = 23): Dexmedetomidine (0.5 µg/kg loading dose infused over 10 min followed by a constant infusion of 0.5 µg/kg/h) was added to the propofol-remifentanil regimen and propofol was adjusted to maintain BIS between 40 and 50. DP unadjusted group (n = 23): Dexmedetomidine (administer as DP adjusted group) was added to the propofol-remifentanil regimen and propofol was not adjusted. All patients received MEP, SSEP and BIS monitoring. RESULTS: There were no significant changes in the amplitude and latency of MEP and SSEP among different groups (P > 0.05). The estimated propofol plasma concentration in DP adjusted group (2.7 ± 0.3 µg/ml) was significantly lower than in propofol group (3.1 ± 0.2 µg/ml) and DP unadjusted group (3.1 ± 0.2 µg/ml) (P = 0.000). BIS in DP unadjusted group (35 ± 5) was significantly lower than in propofol group (44 ± 3) (P = 0.000). CONCLUSIONS: The addition of dexmedetomidine to propofol-remifentanil regimen does not exert an adverse effect on MEP and SSEP monitoring in adult patients undergoing thoracic spinal cord tumor resection. TRIAL REGISTRATION: The study was registered with the Chinese Clinical Trial Registry on January 31st, 2014. The reference number was ChiCTR-TRC-14004229.

Simple method to enhance terahertz radiation from femtosecond laser filament array with a step phase plate.

In this work, we experimentally demonstrate a 200% enhancement of terahertz (THz) wave amplitude generated by femtosecond laser filamentation in air. The experimental setup simply uses a semicircular phase plate to generate two parallel filaments. Temporally overlapped THz pulses from two filaments coherently add up, giving rise to significant enhancement of the THz pulse amplitude. It has been foreseen that further enhancement would be achieved if the design of phase plates could be optimized to generate a filament array. This simple method makes full use of the laser energy and could potentially open a new approach to remotely enhance the THz emission in air.

Rescue Bypass for Revascularization After Ischemic Complications in the Treatment of Giant or Complex Intracranial Aneurysms.

BACKGROUND: Surgical trapping or endovascular deconstruction commonly is used for the treatment of giant or complex intracranial aneurysms. Preoperative balloon test occlusion and cerebral blood flow studies and intraoperative neurophysiologic monitoring can indicate whether sufficient collateralization exists or whether revascularization is needed. Hemodynamic insufficiency can occur, however, despite passing these tests, necessitating posttreatment revascularization. METHODS: We conducted a retrospective review of patients who underwent surgical or endovascular parent vessel occlusion for the management of giant or complex intracranial aneurysms and subsequently required rescue bypass for symptoms of hemodynamic insufficiency. Pre- and postrevascularization functional status was measured with the modified Rankin Scale. RESULTS: During a 15-year period from 1997 to 2012, a rescue bypass was performed in 5 patients each harboring a giant or complex intracranial internal carotid artery (ICA) aneurysm that was treated with surgical trapping or endovascular deconstruction in a previous procedure. All bypasses were extracranial-to-intracranial and included cervical ICA to middle cerebral artery, subclavian to middle cerebral artery, and cervical ICA to supraclinoid ICA anastomoses via either a saphenous vein or radial artery graft. Functional outcome at time of last follow-up was improved in each patient (improvement in modified Rankin Scale of 1-3 points). CONCLUSIONS: Ischemic complications must always be anticipated in the treatment of giant or complex intracranial aneurysms, even if pre- and intraoperative blood flow studies indicate sufficient collateralization. Here we show that extracranial-to-intracranial bypass is an effective option to rescue unanticipated hemodynamic insufficiency after parent vessel occlusion. This study emphasizes the need for cerebrovascular surgeons to maintain proficiency in complex bypass techniques.

Safety and efficacy of motor mapping utilizing short pulse train direct cortical stimulation.

BACKGROUND/AIMS: A major goal of intracranial surgery is to maximize resection while minimizing neurological morbidity, particularly motor dysfunction. Direct cortical stimulation (DCS) is a common intraoperative adjunct used to identify functional motor cortex. In this study, we report on the safety/efficacy of short pulse train DCS (direct cortical stimulation motor-evoked potential, dcMEP) for motor mapping and monitoring during intracranial surgery. METHODS: A retrospective analysis of 29 patients undergoing elective craniotomy for lesions near the motor cortex was performed. dcMEP mapping (40-120 V, 500-1,000 Hz, 5-9 pulses/s, 1- to 3-ms interstimulus interval, monopolar, 50-µs pulse width) was performed either alone (n = 29) or in addition to standard DCS (n = 6). Outcome measures were positive MEPs and the presence of seizures during stimulation. dcMEP-based continuous corticospinal tract (CST) monitoring was also performed. Changes in stimulation threshold and new postoperative neurological deficits were recorded. RESULTS: dcMEP mapping success was 96% and was not affected by preoperative motor status. Intraoperative seizure rates for dcMEP were 3% and were not related to preoperative seizure status. CST monitoring success rate was 96%, and changes in stimulation threshold were predictive of new permanent motor deficits. CONCLUSIONS: dcMEP is an effective method for mapping motor function and may prove useful for continuous CST monitoring.

The use of motor evoked potential monitoring during cerebral aneurysm surgery to predict pure motor deficits due to subcortical ischemia.

Subcortical infarcts are most commonly the consequence of perforating artery occlusion and pure motor deficit is the most frequent syndrome resulting from an interruption of the corticospinal tract at the level of the corona radiate, the internal capsule or the brainstem. Motor evoked potential (MEP) monitoring is used as an adjunct to surgery as somatosensory evoked potentials (SEP) have been found to be insensitive to these lesions. Two different techniques have been used for monitoring MEPs during aneurysm surgery: transcranial electrical stimulation (TES) and direct cortical stimulation (DCS). TES may result in patient movement, interfering with microdissection. There is also concern that TES MEP may not detect subcortical motor pathway ischemia by stimulating deeper subcortical structures and may thereby bypass the ischemic area. DCS produces focal muscle activation, less movement and more superficial stimulation that should detect cortical and superficial subcortical ischemia, hence avoiding false-negatives. However, this technique also has disadvantages including subdural bleeding and injury to the brain. Using close-to-motor-threshold stimulation and focal stimulating electrode montages, TES and DCS MEPs do not vary significantly in their capacity to detect lesions of the motor cortex or its efferent pathways. Both techniques are prone to interference by anesthetic agents.

Microvascular decompression in hemifacial spasm resulting from a cerebellopontine angle lipoma: case report.

OBJECTIVE: Hemifacial spasm caused by a cerebellopontine angle lipoma is extremely rare. We describe a patient with left-sided hemifacial spasm caused by vascular compression of the facial and vestibulocochlear cranial nerves by the anteroinferior cerebellar artery embedded within a cerebellopontine angle lipoma. CLINICAL PRESENTATION: A 77-year-old man presented with a 10-year history of left-sided facial spasms that progressively worsened over time and significantly interfered with his ability to read, drive, and interact in social situations. Neurological examination showed obvious left hemifacial spasm, including orbicularis oculi and levator labii muscles. Magnetic resonance imaging revealed characteristic abnormal signal within the cerebellopontine angle cistern that was consistent with lipoma abutting the anteroinferior cerebellar artery. INTERVENTION: Surgical exploration with standard retrosigmoid craniectomy and subarachnoid dissection of the cerebellopontine angle was performed. The offending anteroinferior cerebellar artery branch was dissected away from the VIIth and VIIIth cranial nerves. Teflon felt was interposed between the artery and nerves after the artery was dissected off the surface of the lipoma. Electrophysiological monitoring showed resolution of the abnormal hemifacial spasm response during the procedure. No attempt was made to resect the lipoma, given the risk to injury of the brainstem and perforating blood vessels. Postoperatively, the patient's symptoms were completely resolved. CONCLUSION: This case demonstrates that relief of the vascular compression, when present, of the VIIth cranial nerve is sufficient for resolution of hemifacial spasm symptoms, even when associated with nearby, benign lesions.

Compound muscle action potentials and spontaneous electromyography can be used to identify and protect the femoral nerve during resection of large retroperitoneal tumors.

BACKGROUND: Resection of large retroperitoneal neoplasms may injure the femoral nerve, thereby causing a permanent neurological deficit. We used electrical neurophysiological monitoring to identify, map, and preserve the femoral nerve during surgical resection to reduce the risk of neurological deficit. METHODS: Seven patients with retroperitoneal neoplasms underwent eight resections. Compound muscle action potentials (CMAPs) were recorded from needle electrodes placed in the iliacus, quadriceps, and sartorius muscles. Spontaneous electromyography (EMG) was continuously monitored from the same muscle groups. A handheld monopolar stimulator was used to elicit evoked EMG responses to identify and map the course of the femoral nerve. A stimulating strength of 10 mA was used to map the nerve. The stimulation threshold was tested after neoplasm resection to predict postoperative femoral nerve function. RESULTS: Electrical stimulation with CMAP recording and a stimulating strength of 10 mA successfully localized the femoral nerve in six cases. Monitoring with a stimulating threshold between 0.6 and 1.6 mA predicted postoperative femoral nerve preservation after tumor resection in four of the six cases. CONCLUSION: Neurophysiological monitoring using CMAP and spontaneous EMG can protect the femoral nerve during resection of large retroperitoneal neoplasms.

Optimal placement of recording electrodes for quantifying facial nerve compound muscle action potential.

OBJECTIVE: To analyze optimal placement of recording-needle electrodes surrounding the eye and lip for facial nerve monitoring by identifying the maximum compound muscle action potential (CMAP) recorded by electrode pairs of different spatial configurations. STUDY DESIGN: Prospective clinical trial. SETTING: Ambulatory surgery at a tertiary care center. PATIENTS: Thirty adults undergoing chronic ear surgery such as tympanoplasty, mastoidectomy, ossicular chain reconstruction, stapedectomy, and cochlear implantation. INTERVENTION: Facial nerve monitoring. MAIN OUTCOME MEASURE: Suprathreshold (threshold + 0.2 V) CMAP responses are recorded from referential paired needle electrodes placed into orbicularis oculi (1.5-cm spacing; n = 15) and orbicularis oris (1.0-cm spacing; n = 15) muscles. Optimal recording electrode placement is inferred by identifying the maximum evoked CMAP amplitude. RESULTS: For the eye, placement of electrodes by the orbital rim and into the upper eyelid is significantly better (Friedman test; p < 0.01) than the other 2 configurations. For the lip, placement of electrodes into the oral commissure and either the upper or lower lip is satisfactory because there is no statistically significant difference among the configurations (Friedman test; p > 0.2). CONCLUSION: Recording electrode placement configurations that capture the largest CMAP responses are recommended as standard operating procedure for intraoperative facial nerve monitoring.

Continuous EMG recordings and intraoperative electrical stimulation for identification and protection of cervical nerve roots during foraminal tumor surgery.

OBJECTIVE: Spinal cord function is now routinely monitored with somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) during surgery for intraspinal cervical dumbbell and foraminal tumors. However, upper extremity nerve roots are also at risk during these procedures. Anatomic relations are frequently difficult to interpret because the nerve roots may be displaced by the tumor. We used electrical stimulation with compound muscle action potential (CMAP) recordings at multiple sites to identify the location and course of the involved nerve root and to provide real-time information regarding the functional status of the roots to predict postoperative outcome. METHODS: Ten patients were monitored during surgery for cervical dumbbell or foraminal tumors. SEPs and MEPs were monitored as a routine procedure. CMAPs were recorded from needle electrodes placed in the deltoid, biceps, triceps, and flexor carpi ulnaris muscles. Spontaneous electromyography (EMG) muscle activity was also continuously monitored. A handheld monopolar stimulation electrode was used to elicit evoked EMG responses to identify and trace the course of nerves in relation to the tumor. In four patients, the stimulation threshold was tested before and after tumor resection to predict postoperative nerve root function. RESULTS: Electrical stimulation with CMAP recording was successful in localizing nerve roots during tumor resection in all 10 patients. Monitoring predicted postoperative nerve root preservation after tumor removal in each case. It was possible to identify either by using low-level stimulation (<2.0 V) or by observing changes in spontaneous EMG amplitude if activation was present during surgical dissection. The monitoring of spontaneous muscle activity in response to direct or indirect surgical manipulation during tumor resection also provided continuous assessment of nerve root function and identified any physiologic disturbance induced by surgical manipulation. CONCLUSIONS: Electrical stimulation in the operating field and recording of CMAPs facilitated nerve root identification and predicted postoperative function during dissection and separation from ligamentous or neoplastic tissue in 10 patients. Electrical stimulation might also be useful to predict postoperative preservation of function when nerve root sacrifice is necessary and no motor response is detected intraoperatively.