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Hiroki Ushirozako, Go Yoshida, Sho Kobayashi, Tomohiko Hasegawa, Yu Yamato, Tatsuya Yasuda, Tomohiro Banno, Hideyuki Arima, Shin Oe, Yuki Mihara, Daisuke Togawa, and Yukihiro Matsuyama

OBJECTIVE

Intraoperative neuromonitoring may be valuable for predicting postoperative neurological complications, and transcranial motor evoked potentials (TcMEPs) are the most reliable monitoring modality with high sensitivity. One of the most frequent problems of TcMEP monitoring is the high rate of false-positive alerts, also called “anesthetic fade.” The purpose of this study was to clarify the risk factors for false-positive TcMEP alerts and to find ways to reduce false-positive rates.

METHODS

The authors analyzed 703 patients who underwent TcMEP monitoring under total intravenous anesthesia during spinal surgery within a 7-year interval. They defined an alert point as final TcMEP amplitudes ≤ 30% of the baseline. Variations in body temperature (maximum − minimum body temperature during surgery) were measured. Patients with false-positive alerts were classified into 2 groups: a global group with alerts observed in 2 or more muscles of the upper and lower extremities, and a focal group with alerts observed in 1 muscle.

RESULTS

False-positive alerts occurred in 100 cases (14%), comprising 60 cases with global and 40 cases with focal alerts. Compared with the 545 true-negative cases, in the false-positive cases the patients had received a significantly higher total propofol dose (1915 mg vs 1380 mg; p < 0.001). In the false-positive cases with global alerts, the patients had also received a higher mean propofol dose than those with focal alerts (4.5 mg/kg/hr vs 4.2 mg/kg/hr; p = 0.087). The cutoff value of the total propofol dose for predicting false-positive alerts, with the best sensitivity and specificity, was 1550 mg. Multivariate logistic analysis revealed that a total propofol dose > 1550 mg (OR 4.583; 95% CI 2.785–7.539; p < 0.001), variation in body temperature (1°C difference; OR 1.691; 95% CI 1.060–2.465; p < 0.01), and estimated blood loss (500-ml difference; OR 1.309; 95% CI 1.155–1.484; p < 0.001) were independently associated with false-positive alerts.

CONCLUSIONS

Intraoperative total propofol dose > 1550 mg, larger variation in body temperature, and greater blood loss are independently associated with false-positive alerts during spinal surgery. The authors believe that these factors may contribute to the false-positive global alerts that characterize anesthetic fade. As it is necessary to consider multiple confounding factors to distinguish false-positive alerts from true-positive alerts, including variation in body temperature or ischemic condition, the authors argue the importance of a team approach that includes surgeons, anesthesiologists, and medical engineers.

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Shahan Momjian, Rémi Tyrand, Basile N. Landis, and Colette Boëx

OBJECTIVE

Intraoperative neuromonitoring of the chemical senses (smell and taste) has never been performed. The objective of this study was to determine if olfactory-evoked potentials could be obtained intraoperatively under general anesthesia.

METHODS

A standard olfactometer was used in the surgical theater with hydrogen sulfide (4 ppm, 200 msec). Olfactory-evoked potentials were recorded in 8 patients who underwent neurosurgery for resection of cerebral lesions. These patients underwent routine target-controlled propofol and sufentanil general anesthesia. Frontal, temporal, and parietal scalp subdermal electrodes were recorded ipsilaterally and contralaterally at the site of the surgery. Evoked potentials were computed if at least 70 epochs (0.5–100 Hz) satisfying the artifact rejection criterion (threshold 45 μV) could be extracted from signals of electrodes.

RESULTS

Contributive recordings were obtained for 5 of 8 patients (3 patients had fewer than 70 epochs with an amplitude < 45 μV). Olfactory-evoked potentials showed N1 responses (mean 442.8 ± 40.0 msec), most readily observed in the patient who underwent midline anterior fossa neurosurgery. No component of later latencies could be recorded consistently.

CONCLUSIONS

The study confirms that olfactory-evoked potentials can be measured in response to olfactory stimuli under general anesthesia. This demonstrates the feasibility of recording olfactory function intraoperatively and opens the potential for neuromonitoring of olfactory function during neurosurgery.

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Amro Al-Habib, Wajda Alhothali, Abdulrahman Albakr, Sherif Elwatidy, Ghaida Alawaji, Hissah Alabdulsalam, Fahad Albadr, Metab Alkubeyyer, Abdullah Abu Jamea, Waleed Awwad, Anhar Ullah, Faisal Fakhouri, and Abdulrazag Ajlan

OBJECTIVE

Although evaluating tissue elasticity has various clinical applications, spinal cord elasticity (SCE) in humans has never been well documented. In this study, the authors aimed to evaluate the impact of compression on human SCE in vivo.

METHODS

The authors prospectively assessed SCE using intraoperative shear wave elastography (SWE). All consecutive patients undergoing spinal cord (SC) decompression (laminectomy or corpectomy) between June 2018 and June 2019 were included. After intraoperative exposure of the patient’s dura mater, at least three SWE measurements of the SC and its coverings were performed. Intraoperative neurological monitoring in the form of motor and somatosensory evoked potentials was utilized. Cases were divided into two groups based on the state of SC compression following bone removal (laminectomy or corpectomy): patients with adequate decompression (the decompressed SC group [DCG]) following bone removal and patients with remining compression, e.g., compressing tumor or instability (the compressed SC group [COG]).

RESULTS

A total of 25 patients were included (8 females and 17 males) with a mean age of 48.28 ± 21.47 years. Most cases were degenerative diseases (10 cases) followed by tumors (6 cases), and the compression was observed at cervical (n = 14), thoracic (n = 9), and conus medullaris (n = 2) levels. The COG (6 cases) expressed significantly higher elasticity values, i.e., greater stiffness (median 93.84, IQR 75.27–121.75 kPa) than the decompressed SC in DCG (median 9.35, IQR 6.95–11.22 kPa, p < 0.001). Similarly, the compressed dura mater in the COG was significantly stiffer (mean ± SD 121.83 ± 70.63 kPa) than that in the DCG (29.78 ± 18.31 kPa, p = 0.042). Following SC decompression in COG, SCE values were significantly reduced (p = 0.006; adjusted for multiple comparisons). Intraoperative monitoring demonstrated no worsening from the baseline.

CONCLUSIONS

The current study is to the authors’ knowledge the first to quantitatively demonstrate increased stiffness (i.e., elasticity value) of the human SC and dura mater in response to external compression in vivo. It appears that SCE is a dynamic phenomenon and is reduced following decompression. Moreover, the evaluation of human SCE using the SWE technique is feasible and safe. Information from future studies aiming to further define SCE could be valuable in the early and accurate diagnosis of the compressed SC.

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Scott L. Zuckerman, Hani Chanbour, Fthimnir M. Hassan, Christopher S. Lai, Yong Shen, Nathan J. Lee, Mena G. Kerolus, Alex S. Ha, Ian A. Buchanan, Eric Leung, Meghan Cerpa, Ronald A. Lehman Jr., and Lawrence G. Lenke

OBJECTIVE

When treating patients with adult spinal deformity (ASD), radiographic measurements evaluating coronal alignment above C7 are lacking. The current objectives were to: 1) describe the new orbital–coronal vertical axis (ORB-CVA) line that evaluates coronal alignment from cranium to sacrum, 2) assess correlation with other radiographic variables, 3) evaluate correlations with patient-reported outcomes (PROs), and 4) compare the ORB-CVA with the standard C7-CVA.

METHODS

A retrospective cohort study of patients with ASD from a single institution was undertaken. Traditional C7-CVA measurements were obtained. The ORB-CVA was defined as the distance between the central sacral vertical line and the vertical line from the midpoint between the medial orbital walls. The ORB-CVA was correlated using traditional coronal measurements, including C7-CVA, maximum coronal Cobb angle, pelvic obliquity, leg length discrepancy (LLD), and coronal malalignment (CM), defined as a C7-CVA > 3 cm. Clinical improvement was analyzed as: 1) group means, 2) minimal clinically important difference (MCID), and 3) minimal symptom scale (MSS) (Oswestry Disability Index < 20 or Scoliosis Research Society–22r Instrument [SRS-22r] pain + function domains > 8).

RESULTS

A total of 243 patients underwent ASD surgery, and 175 had a 2-year follow-up. Of the 243 patients, 90 (37%) had preoperative CM. The mean (range) ORB-CVA at each time point was as follows: preoperatively, 2.9 ± 3.1 cm (−14.2 to 25.6 cm); 1 year postoperatively, 2.0 ± 1.6 cm (−12.4 to 6.7 cm); and 2 years postoperatively, 1.8 ± 1.7 cm (−6.0 to 11.1 cm) (p < 0.001 from preoperatively to 1 and 2 years). Preoperative ORB-CVA correlated best with C7-CVA (r = 0.842, p < 0.001), maximum coronal Cobb angle (r = 0.166, p = 0.010), pelvic obliquity (r = 0.293, p < 0.001), and LLD (r = 0.158, p = 0.006). Postoperatively, the ORB-CVA correlated only with C7-CVA (r = 0.629, p < 0.001) and LLD (r = 0.153, p = 0.017). Overall, 155 patients (63.8%) had an ORB-CVA that was ≥ 5 mm different from C7-CVA. The ORB-CVA correlated as well and sometimes better than C7-CVA with SRS-22r subdomains. After multivariate logistic regression, a greater ORB-CVA was associated with increased odds of complication, whereas C7-CVA was not associated with any of the three clinical outcomes (complication, readmission, reoperation). A larger difference between the ORB-CVA and C7-CVA was significantly associated with readmission and reoperation after univariate and multivariate logistic regression analyses. A threshold of ≥ 1.5-cm difference between the preoperative ORB-CVA and C7-CVA was found to be predictive of poorer outcomes.

CONCLUSIONS

The ORB-CVA correlated well with known coronal measurements and PROs. ORB-CVA was independently associated with increased odds of complication, whereas C7-CVA was not associated with any outcomes. A ≥ 1.5-cm difference between the preoperative ORB-CVA and C7-CVA was found to be predictive of poorer outcomes.

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Ali Kooshkabadi, Brian Jankowitz, Phillip A. Choi, Gregory M. Weiner, and Stephanie Greene

The authors present the case of a boy who was successfully managed through the spontaneous thrombosis of a cavernous internal carotid artery (ICA) aneurysm, the subsequent occlusion of the ICA, its recanalization, and ultimate endovascular sacrifice, using only two angiograms because of the diagnostic capability of CT angiography. Spontaneous recanalization of the ICA following occlusion in the setting of a giant aneurysm has not been previously reported.

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Jorge Tirado-Caballero, Andres Muñoz-Nuñez, Santiago Rocha-Romero, Mónica Rivero-Garvía, Emilio Gomez-González, and Javier Marquez-Rivas

Intracranial pressure (ICP) measurements are imperative for the proper diagnosis and treatment of several neurological disorders. Telemetric sensors have shown their utility for ICP estimation in short-term monitoring in humans. However, their long-term reliability is uncertain. The authors present the case of a 37-year-old woman diagnosed with benign intracranial hypertension and obesity. The patient underwent gastric bypass surgery for ICP control. In order to monitor ICP before and after bariatric surgery, a Neurovent-P-tel sensor was implanted in the left frontal lobe. After gastric bypass, normal ICP values were recorded, and the patient’s visual fields improved. However, the patient experienced incapacitating daily headaches. The authors decided to implant a Codman Microsensor ICP transducer in the right frontal lobe to assess the long-term reliability of the Neurovent-P-tel measurements. A comparison of the recordings at 24 and 48 hours showed good correlation and reliability during long-term monitoring with the Neurovent-P-tel, with minimal zero drift after 11 months of implantation.

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Nicolas W. Villelli, David M. Lewis, Thomas J. Leipzig, Andrew J. DeNardo, Troy D. Payner, and Charles G. Kulwin

OBJECTIVE

Intraoperative angiography can be a valuable tool in the surgical management of vascular disorders in the CNS. This is typically accomplished via femoral artery puncture; however, this can be technically difficult in patients in the prone position. The authors describe the feasibility of intraoperative angiography via the popliteal artery in the prone patient.

METHODS

Three patients underwent intraoperative spinal angiography in the prone position via vascular access through the popliteal artery. Standard angiography techniques were used, along with ultrasound and a micropuncture needle for initial vascular access. Two patients underwent intraoperative angiography to confirm the obliteration of dural arteriovenous fistulas. The third patient required unexpected intraoperative angiography when a tumor was concerning for a vascular malformation in the cervical spine.

RESULTS

All 3 patients tolerated the procedure without complication. The popliteal artery was easily accessed without any adaptation to typical patient positioning for these prone-position cases. This proved particularly beneficial when angiography was not part of the preoperative plan.

CONCLUSIONS

Intraoperative angiography via the popliteal artery is feasible and well tolerated. It presents significant benefit when obtaining imaging studies in patients in a prone position, with the added benefit of easy access, familiar anatomy, and low concern for catheter thrombosis or kinking.

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Farouk Olubajo, Tatyana Yermakova, J. Robin Highley, and Vasileios Arzoglou

Idiopathic hypertrophic spinal pachymeningitis (IHSP), a rare diffuse inflammatory thickening of the dura mater, and Guillain-Barré syndrome (GBS) are known entities but they have never been reported as concomitant diagnoses. To their knowledge, the authors present the first reported case in the international literature with supportive evidence for both IHSP (based on MRI, intraoperative, and histological findings) and GBS (based on history, clinical examination, and electrophysiological findings). They review the literature on IHSP and the diagnostic criteria for GBS, with the view of identifying a possible causative connection.

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Mark P. Garrett, Richard W. Williamson, Michael A. Bohl, C. Roger Bird, and Nicholas Theodore

OBJECTIVE

For a diagnosis of brain death (BD), ancillary testing is performed if patient factors prohibit a complete clinical examination and apnea test. The American Academy of Neurology (AAN) guidelines identify cerebral angiography (CA), cerebral scintigraphy, electroencephalography, and transcranial Doppler ultrasonography as accepted ancillary tests. CA is widely considered the gold standard of these, as it provides the most reliable assessment of intracranial blood flow. CT angiography (CTA) is a noninvasive and widely available study that is also capable of identifying absent or severely diminished intracranial blood flow, but it is not included among the AAN's accepted ancillary tests because of insufficient evidence demonstrating its reliability. The objective of this study was to assess the statistical performance of CTA in diagnosing BD, using clinical criteria alone or clinical criteria plus CA as the gold-standard comparisons.

METHODS

The authors prospectively enrolled 22 adult patients undergoing workup for BD. All patients had cranial imaging and clinical examination results consistent with BD. In patients who met the AAN clinical criteria for BD, the authors performed CA and CTA so that both tests could be compared with the gold-standard clinical criteria. In cases that required ancillary testing, CA was performed as a confirmatory study, and CTA was then performed to compare against clinical criteria plus CA. Radiographic data were evaluated by an independent neuroradiologist. Test characteristics for CTA were calculated.

RESULTS

Four patients could not complete the standard BD workup and were excluded from analysis. Of the remaining 18 patients, 16 met AAN criteria for BD, 9 of whom required ancillary testing with CA. Of the 16 patients, 2 who also required CA ancillary testing were found to have persistent intracranial flow and were not declared brain dead at that time. These patients also underwent CTA; the results were concordant with the CA results. Six patients who were diagnosed with BD on the basis of clinical criteria alone also underwent CA, with 100% sensitivity. For all 18 patients included in the study, CTA had a sensitivity of 75%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 33%.

CONCLUSIONS

Clinical examination with or without CA remains the gold standard in BD testing. Studies assessing the statistical performance of CTA in BD testing should compare CTA to these gold standards. The statistical performance of CTA in BD testing is comparable to several of the nationally accepted ancillary tests. These data add to the growing medical literature supporting the use of CTA as a reliable ancillary test in BD testing.

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Oliver Ganslandt, Stylianos Mourtzoukos, Andreas Stadlbauer, Björn Sommer, and Rudolf Rammensee

OBJECTIVE

There is no established method of noninvasive intracranial pressure (NI-ICP) monitoring that can serve as an alternative to the gold standards of invasive monitoring with external ventricular drainage or intraparenchymal monitoring. In this study a new method of NI-ICP monitoring performed using algorithms to determine ICP based on acoustic properties of the brain was applied in patients undergoing invasive ICP (I-ICP) monitoring, and the results were analyzed.

METHODS

In patients with traumatic brain injury and subarachnoid hemorrhage who were undergoing treatment in a neurocritical intensive care unit, the authors recorded ICP using the gold standard method of invasive external ventricular drainage or intraparenchymal monitoring. In addition, the authors simultaneously measured the ICP noninvasively with a device (the HS-1000) that uses advanced signal analysis algorithms for acoustic signals propagating through the cranium. To assess the accuracy of the NI-ICP method, data obtained using both I-ICP and NI-ICP monitoring methods were analyzed with MATLAB to determine the statistical significance of the differences between the ICP measurements obtained using NI-ICP and I-ICP monitoring.

RESULTS

Data were collected in 14 patients, yielding 2543 data points of continuous parallel ICP values in recordings obtained from I-ICP and NI-ICP. Each of the 2 methods yielded the same number of data points. For measurements at the ≥ 17–mm Hg cutoff, which was arbitrarily chosen for this preliminary analysis, the sensitivity and specificity for the NI-ICP monitoring were found to be 0.7541 and 0.8887, respectively. Linear regression analysis indicated that there was a strong positive relationship between the measurements. Differential pressure between NI-ICP and I-ICP was within ± 3 mm Hg in 63% of data-paired readings and within ± 5 mm Hg in 85% of data-paired readings. The receiver operating characteristic–area under the curve analysis revealed that the area under the curve was 0.895, corresponding to the overall performance of NI-ICP monitoring in comparison with I-ICP monitoring.

CONCLUSIONS

This study provides the first clinical data on the accuracy of the HS-1000 NI-ICP monitor, which uses advanced signal analysis algorithms to evaluate properties of acoustic signals traveling through the brain in patients undergoing I-ICP monitoring. The findings of this study highlight the capability of this NI-ICP device to accurately measure ICP noninvasively. Further studies should focus on clinical validation for elevated ICP values.