Mallory, Grant W.

OBJECTIVE Historically, performing neurosurgery with the patient in the sitting position offered advantages such as improved visualization and gravity-assisted retraction. However, this position fell out of favor at many centers due to the perceived risk of venous air embolism (VAE) and other position-related complications. Some neurosurgical centers continue to perform sitting-position cases in select patients, often using modern monitoring techniques that may improve procedural safety. Therefore, this paper reports the risks associated with neurosurgical procedures performed in the sitting position in a modern series. METHODS The authors reviewed the anesthesia records for instances of clinically significant VAE and other complications for all neurosurgical procedures performed in the sitting position between January 1, 2000, and October 8, 2013. In addition, a prospectively maintained morbidity and mortality log of these procedures was reviewed for instances of subdural or intracerebral hemorrhage, tension pneumocephalus, and quadriplegia. Both overall and specific complication rates were calculated in relation to the specific type of procedure. RESULTS In a series of 1792 procedures, the overall complication rate related to the sitting position was 1.45%, which included clinically significant VAE, tension pneumocephalus, and subdural hemorrhage. The rate of any detected VAE was 4.7%, but the rate of VAE requiring clinical intervention was 1.06%. The risk of clinically significant VAE was highest in patients undergoing suboccipital craniotomy/craniectomy with a rate of 2.7% and an odds ratio (OR) of 2.8 relative to deep brain stimulator cases (95% confidence interval [CI] 1.2–70, p = 0.04). Sitting cervical spine cases had a comparatively lower complication rate of 0.7% and an OR of 0.28 as compared with all cranial procedures (95% CI 0.12–0.67, p < 0.01). Sitting cervical cases were further subdivided into extradural and intradural procedures. The rate of complications in intradural cases was significantly higher (OR 7.3, 95% CI 1.4–39, p = 0.02) than for extradural cases. The risk of VAE in intradural spine procedures did not differ significantly from sitting suboccipital craniotomy/craniectomy cases (OR 0.69, 95% CI 0.09–5.4, p = 0.7). Two cases (0.1%) had to be aborted intraoperatively due to complications. There were no instances of intraoperative deaths, although there was a single death within 30 days of surgery. CONCLUSIONS In this large, modern series of cases performed in the sitting position, the complication rate was low. Suboccipital craniotomy/craniectomy was associated with the highest risk of complications. When appropriately used with modern anesthesia techniques, the sitting position provides a safe means of surgical access.

Study Design Retrospective study. Objective This study reviews 1,768 consecutive cervical decompressions with or without instrumented fusion to identify patient-specific and procedural risk factors significantly correlated with the development of delayed cervical palsy (DCP). Methods Baseline demographic and procedural information was collected from the electronic medical record. Particular attention was devoted to reviewing each chart for recognized risk factors of postsurgical inflammatory neuropathy: autoimmune disease, blood transfusions, diabetes, and smoking. Results Of 1,669 patients, 56 (3.4%) developed a DCP. Although 71% of the palsies involved C5, 55% of palsies were multimyotomal and 18% were bilateral. Significant risk factors on univariate analysis included age ( p = 0.0061, odds ratio [OR] = 1.07, 95% confidence interval [CI] 1.008 to 1.050), posterior instrumented fusion ( p < 0.0001, OR = 3.30, 95% CI 1.920 to 5.653), prone versus semisitting/sitting position ( p = 0.0036, OR = 3.58, 95% CI 1.451 to 11.881), number of operative levels ( p < 0.0001, OR = 1.42, 95% CI 1.247 to 1.605), intraoperative transfusions ( p = 0.0231, OR = 2.57, 95% CI 1.152 to 5.132), and nonspecific autoimmune disease ( p = 0.0107, OR = 3.83, 95% CI 1.418 to 8.730). On multivariate analysis, number of operative levels ( p = 0.0053, OR = 1.27, 95% CI 1.075 to 1.496) and nonspecific autoimmune disease ( p = 0.0416, OR 2.95, 95% CI 1.047 to 7.092) remained significant. Conclusions Although this study partially supports a mechanical etiology in the pathogenesis of a DCP, we also describe a notable correlation with autoimmune risk factors. Bilateral and multimyotomal involvement provides additional support that some DCPs may result from an inflammatory response and thus an underlying multifactorial etiology for this complication.

Study Design. Laboratory/animal-based proof of principle study. Objective. To validate the accuracy of a magnetic resonance imaging (MRI)-guided stereotactic system for intraspinal electrode targeting and demonstrate the feasibility of such a system for controlling implantation of intraspinal electrodes. Summary of Background Data. Intraspinal microstimulation (ISMS) is an emerging preclinical therapy, which has shown promise for the restoration of motor function following spinal cord injury. However, targeting inaccuracy associated with existing electrode implantation techniques remains a major barrier preventing clinical translation of ISMS. Methods. System accuracy was evaluated using a test phantom comprised of nine target locations. Targeting accuracy was determined by calculating the root mean square error between MRI-generated coordinates and actual frame coordinates required to reach the target positions. System performance was further validated in an anesthetized pig model by performing MRI-guided intraspinal electrode implantation and stimulation followed by computed tomography of electrode location. Finally, system compatibility with a commercially available microelectrode array was demonstrated by implanting the array and applying a selection of stimulation amplitudes that evoked hind limb responses. Results. The root mean square error between actual frame coordinates and software coordinates, both acquired using the test phantom, was 1.09 ± 0.20 mm. Postoperative computed tomography in the anesthetized pig confirmed spatially accurate electrode placement relative to preoperative MRI. Additionally, MRI-guided delivery of a microwire electrode followed by ISMS evoked repeatable electromyography responses in the biceps femoris muscle. Finally, delivery of a microelectrode array produced repeatable and graded hind limb evoked movements. Conclusion. We present a novel frame-based stereotactic system for targeting and delivery of intraspinal instrumentation. This system utilizes MRI guidance to account for variations in anatomy between subjects, thereby improving upon existing ISMS electrode implantation techniques. Level of Evidence: N/A

OBJECT Endoscopic approaches to the anterior craniocervical junction are increasing in frequency. Choice of oral versus endoscopic endonasal approach to the odontoid often depends on the relationship of the C1–2 complex to the hard palate. However, it is not known how this relevant anatomy changes with age. We hypothesize that there is a dynamic relationship of C-2 and the hard palate, which changes with age, and potentially affects the choice of surgical approach. The aim of this study was to characterize the relationship of C-2 relative to the hard palate with respect to age and sex. METHODS Emergency department billing and trauma records from 2008 to 2014 were reviewed for patients of all ages who underwent cervical or maxillofacial CT as part of a trauma evaluation for closed head injury. Patients who had a CT scan that allowed adequate visualization of the hard palate, opisthion, and upper cervical spine (C-1 and C-2) were included. Patients who had cervical or displaced facial/skull base fractures, a history of rheumatoid arthritis, or craniofacial anomalies were excluded. The distance from McGregor's palatooccipital line to the midpoint of the inferior endplate of C-2 (McL–C2) was measured on midsagittal CT scans. Patients were grouped by decile of age and by sex. A 1-way ANOVA was performed with each respective grouping. RESULTS Ultimately, 483 patients (29% female) were included. The mean age was 46 ± 24 years. The majority of patients studied were in the 2nd through 8th decades of life (85%). Significant variation was found between McL–C2 and decile of age (p < 0.001) and sex (p < 0.001). The mean McL–C2 was 27 mm in the 1st decade of life compared with the population mean of 37 mm. The mean McL–C2 was also noted to be smaller in females (mean difference 4.8 mm, p < 0.0001). Both decile of age (p = 0.0009) and sex (p < 0.0001) were independently correlated with McL–C2 on multivariate analysis. CONCLUSIONS The relationship of C-2 and the hard palate significantly varies with respect to age and sex, descending relative to the hard palate a full centimeter on average in adulthood. These findings may have relevance in determining optimal surgical approaches for addressing pathology involving the anterior craniocervical junction.

OBJECT Nonpowder guns, defined as spring- or gas-powered BB or pellet guns, can be dangerous weapons that are often marketed to children. In recent decades, advances in compressed-gas technology have led to a significant increase in the power and muzzle velocity of these weapons. The risk of intracranial injury in children due to nonpowder weapons is poorly documented. METHODS A retrospective review was conducted at 3 institutions studying children 16 years or younger who had intracranial injuries secondary to nonpowder guns. RESULTS The authors reviewed 14 cases of intracranial injury in children from 3 institutions. Eleven (79%) of the 14 children were injured by BB guns, while 3 (21%) were injured by pellet guns. In 10 (71%) children, the injury was accidental. There was 1 recognized assault, but there were no suicide attempts; in the remaining 3 patients, the intention was indeterminate. There were no mortalities among the patients in this series. Ten (71%) of the children required operative intervention, and 6 (43%) were left with permanent neurological injuries, including epilepsy, cognitive deficits, hydrocephalus, diplopia, visual field cut, and blindness. CONCLUSIONS Nonpowder guns are weapons with the ability to penetrate a child’s skull and brain. Awareness should be raised among parents, children, and policy makers as to the risk posed by these weapons.

Study Design Retrospective study. Objective Efficient use of operating room time is important, as delays during induction or recovery increase time not spent operating while in the operating room. We identified factors that increase anesthetized, nonoperative time by utilizing a database of over 5,000 consecutive neurosurgical spine cases. Methods Surgical records were searched to identify all spine surgeries performed between January 2010 and July 2012. Anesthetized, nonoperative time was calculated from the anesthesia record and compared with both patient and procedure characteristics to determine any significant relationships Results There were 5,515 surgical cases with a mean age of 60.5 and mean body mass index (BMI) of 29.7; 3,226 (58%) were male subjects. There were 1,176 (21%) fusion cases, and level of pathology was predominantly lumbar (4,010 cases, 73%). Fusion cases had a significantly longer total anesthetized, nonoperative time (fusion: 98 minutes, nonfusion: 76 minutes, mean difference: 22 minutes, p < 0.0001). Significant factors affecting anesthetized, nonoperative time in nonfusion cases include age greater than 65 years (mean difference 5 minutes, p < 0.0001), American Society of Anesthesiologists (ASA) grade, and BMI (BMI < 25: 72 ± 1.2 minutes, BMI 25 to 29: 74 ± 0.6 minutes, BMI 30 to 39: 79 ± 0.6 minutes, BMI 40 + : 87 ± 1.8 minutes, p < 0.0001). Similarly, for fusion operations, age > 65 years significantly increased nonoperative time (mean difference 6 minutes, p < 0.01), as did increasing ASA (mean difference 9 minutes, p < 0.0001) and increasing BMI. Conclusion Patient and surgical factors, including ASA grade, BMI, level of pathology, and surgical approach, have noticeable effects on anesthetized, nonoperative times in spine surgery.

OBJECT While extent of resection has been shown to correlate with outcomes after myxopapillary ependymoma (MPE) resection, the effect of capsular violation has not been well studied. The role of adjuvant radiation also remains controversial. In this paper the authors' goals were to evaluate outcomes following resection of MPE based on intraoperative capsular violation and to explore the role of adjuvant radiotherapy in cases of capsular violation. METHODS A retrospective review of patients undergoing resection of MPE at 2 academic institutions between 1990 and 2013 was performed. Cases with dissemination at presentation, less than 12 months of follow-up, or incomplete records were excluded. Extent of resection was defined as en bloc if all visible tumor was removed without capsular violation, gross-total resection (GTR) if all visible tumor was removed, but with capsular violation, and subtotal resection (STR) if a known residual was left at the time of surgery. Postoperative MR images were reviewed to confirm the extent of resection. Primary outcomes were progression-free survival (PFS) and overall recurrence rates. The effects of extent of resection, capsular violation, and adjuvant radiotherapy on recurrence rates and PFS were analyzed using Kaplan-Meier statistics. Associations between recurrence and preoperative variables were evaluated using Fisher exact methods and t-tests where appropriate. RESULTS Of the 107 patients reviewed, 58 patients (53% were male) met inclusion criteria. The mean age at surgery was 40.8 years (range 7–68 years). The median follow-up was 51.5 months (range 12–243 months). Extent of resection was defined as en bloc in 46.5% (n = 27), GTR in 34.5% (n = 20), and STR in 18.9% (n = 11). No recurrences were noted in the en bloc group, compared with 15% (n = 3) and 45% (n = 5) in the GTR and STR groups. En bloc resection was achieved most frequently in tumors involving the conus. Twelve patients (20%) underwent adjuvant radiotherapy following either STR or GTR. The overall recurrence rate was 13.8% (n = 8), and the 5-year PFS was 81%. Capsular violation was associated with a higher recurrence rate (p = 0.005). Adjuvant radiotherapy showed a nonsignificant trend of lower recurrence rates (16.7% vs 31.6%, p = 0.43) and longer PFS at 5 years (83.3% vs 49.9%, p = 0.16) in cases of capsular violation. CONCLUSIONS A strong correlation between capsular violation and recurrence was found following removal of MPE and should be assessed when defining extent of resection in future studies. Although the use of adjuvant radiotherapy in cases of capsular violation showed a trend toward improved PFS, further investigation is needed to establish its role as salvage therapy also appears to be effective at halting disease progression.

Study Design Retrospective case series. Objective To determine the effect of obesity on the resource utilization and cost in 3270 consecutive patients undergoing elective noninstrumented decompressive surgeries for degenerative spine disease at Mayo Clinic Rochester between 2005 and 2012. Methods Groups were assessed for baseline differences (age, gender, and American Society of Anesthesiologists [ASA] classification, procedure type, and number of operative levels). Outcome variables included the transfusion requirements during surgery, the total anesthesia and surgical times, intensive care unit (ICU) admissions, standardized costs, as well as the ICU and hospital length of stay (LOS). Regression analysis was used to evaluate for strength of association between obesity and outcome variables. Results Baseline differences between the groups (nonobese: n = 1,853; obese: n = 1,417) were found with respect to age, ASA class, gender, procedure type, and number of operative levels. After correcting for differences, we found significant associations between obesity and surgical ( p < 0.0001) and anesthesia times ( p < 0.0001) and hospital LOS ( p < 0.0001). Additionally, ICU admission rates ( p = 0.02) and requirement for postoperative ventilation ( p = 0.048) were significantly higher in obese patients. Finally, mean difference in total cost ($1,632, p < 0.0001) was significantly higher for the obese cohort. Conclusion Obesity is associated with increased resource utilization and cost in patients undergoing a noninstrumented decompressive surgery for degenerative spine disease.

OBJECT Despite a promising outlook, existing intraspinal microstimulation (ISMS) techniques for restoring functional motor control after spinal cord injury are not yet suitable for use outside a controlled laboratory environment. Thus, successful application of ISMS therapy in humans will require the use of versatile chronic neurostimulation systems. The objective of this study was to establish proof of principle for wireless control of ISMS to evoke controlled motor function in a rodent model of complete spinal cord injury. METHODS The lumbar spinal cord in each of 17 fully anesthetized Sprague-Dawley rats was stimulated via ISMS electrodes to evoke hindlimb function. Nine subjects underwent complete surgical transection of the spinal cord at the T-4 level 7 days before stimulation. Targeting for both groups (spinalized and control) was performed under visual inspection via dorsal spinal cord landmarks such as the dorsal root entry zone and the dorsal median fissure. Teflon-insulated stimulating platinum-iridium microwire electrodes (50 μm in diameter, with a 30- to 60-μm exposed tip) were implanted within the ventral gray matter to an approximate depth of 1.8 mm. Electrode implantation was performed using a free-hand delivery technique (n = 12) or a Kopf spinal frame system (n = 5) to compare the efficacy of these 2 commonly used targeting techniques. Stimulation was controlled remotely using a wireless neurostimulation control system. Hindlimb movements evoked by stimulation were tracked via kinematic markers placed on the hips, knees, ankles, and paws. Postmortem fixation and staining of the spinal cord tissue were conducted to determine the final positions of the stimulating electrodes within the spinal cord tissue. RESULTS The results show that wireless ISMS was capable of evoking controlled and sustained activation of ankle, knee, and hip muscles in 90% of the spinalized rats (n = 9) and 100% of the healthy control rats (n = 8). No functional differences between movements evoked by either of the 2 targeting techniques were revealed. However, frame-based targeting required fewer electrode penetrations to evoke target movements. CONCLUSIONS Clinical restoration of functional movement via ISMS remains a distant goal. However, the technology presented herein represents the first step toward restoring functional independence for individuals with chronic spinal cord injury.

OBJECT The following study was conducted to identify risk factors for a postoperative CSF leak after vestibular schwannoma (VS) surgery. METHODS The authors reviewed a prospectively maintained database of all patients who had undergone resection of a VS at the Mayo Clinic between September 1999 and May 2013. Patients who developed a postoperative CSF leak within 30 days of surgery were compared with those who did not. Data collected included patient age, sex, body mass index (BMI), tumor size, tumor side, history of prior tumor treatment, operative time, surgical approach, and extent of resection. Both univariate and multivariate regression analyses were performed to evaluate all variables as risk factors of a postoperative CSF leak. RESULTS A total of 457 patients were included in the study, with 45 patients (9.8%) developing a postoperative CSF leak. A significant association existed between increasing BMI and a CSF leak, with those classified as overweight (BMI 25–29.9), obese (BMI 30–39.9), or morbidly obese (BMI ≥ 40) having a 2.5-, 3-, and 6-fold increased risk, respectively. Patients undergoing a translabyrinthine (TL) approach experienced a higher rate of CSF leaks (OR 2.5, 95% CI 1.3–4.6; p = 0.005), as did those who had longer operative times (OR 1.04, 95% CI 1.02–1.07; p = 0.0006). The BMI, a TL approach, and operative time remained independent risk factors on multivariate modeling. CONCLUSIONS Elevated BMI is a risk factor for the development of a postoperative CSF leak following VS surgery. Recognizing this preoperatively can allow surgeons to better counsel patients regarding the risks of surgery as well as perhaps to alter perioperative management in an attempt to decrease the likelihood of a leak. Patients undergoing a TL approach or having longer operative times are also at increased risk of developing a postoperative CSF leak.