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Deep brain stimulation for medically refractory epilepsy

Thomas L. Ellis and Andrew Stevens

Epilepsy is a chronic neurological disorder that affects 0.5–1% of the population. Up to one-third of patients will have incompletely controlled seizures or debilitating side effects of anticonvulsant medications. Although some of these patients may be candidates for resection, many are not. The desire to find alternative treatments for epilepsy has led to a resurgence of interest in the use of deep brain stimulation (DBS), which has been used quite successfully in movement disorders. Small pilot studies and open-label trials have yielded results that may support the use of DBS in selected patients with refractory seizures. Because of the diversity of regions involved with seizure initiation and propagation, a variety of targets for stimulation have been examined. Moreover, stimulation parameters such as amplitude, frequency, pulse duration, and continuous versus intermittent on vary from one study to the next. More studies are necessary to determine if there is an appropriate population of seizure patients for DBS, the optimal target, and the most efficacious stimulation parameters.

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Open reduction and internal fixation for angulated, unstable odontoid synchondrosis fractures in children: a safe alternative to halo fixation?

Report of 2 cases

Daniel H. Fulkerson, Steven W. Hwang, Akash J. Patel, and Andrew Jea

External orthosis is the accepted and historical management of odontoid synchondrosis fractures; however, this conservative therapy carries a significant complication and fracture nonunion rate among young children. The purpose of this study was to evaluate the authors' own experience in the context of the literature, to explore surgical fixation as a primary treatment for unstable fractures. The authors retrospectively reviewed 2 cases of unstable odontoid synchondrosis fractures treated at their institution; both showed radiographic progression of deformity and subsequently underwent an open surgical reduction and fusion. A literature review was conducted to compare the authors' management strategy with those in published data. External orthosis for treatment of odontoid synchondrosis fractures has a strong history of success. However, in the literature, patients treated with a halo orthosis had a 43.3% rate of complications and an 11.4% risk of nonunion. There are radiographic findings that suggest instability, such as severe angulation and displacement of the odontoid process. Both patients in the present report underwent successful fusion without complication, as documented on CT scans obtained 3 months after surgery. Given the high rate of fusion attained with conservative therapy, it is recommended for most synchondrosis fractures. However, there is a recognized subgroup of synchondrosis fractures with severe angulation (> 30°) and displacement suggestive of significant ligamentous injury. In these patients, surgical fixation may be a safe and efficacious alternative to halo orthosis as the primary treatment.

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Insertion of magnetically controlled growing rods in a patient with a diaphragmatic pacemaker: case report

Andrew C. Vivas, Steven W. Hwang, and Joshua M. Pahys

Phrenic stimulators offer an alternative to standard mechanical ventilation as well as the potential for ventilator independence in select patients with chronic respiratory failure. Young patients (< 10 years old) with high cervical spinal cord injuries often develop paralytic scoliosis due to loss of muscle tone caudal to their spinal cord lesion. Growing rod systems allow for stabilization of spinal deformity while permitting continued growth of the spine and thoracic cavity. Magnetically controlled growing rods (MCGRs) offer the advantage of noninvasive expansion, as opposed to the operative expansion required in traditional growing rod systems. To the authors’ knowledge, this is the first reported case of MCGRs in a patient with a diaphragmatic pacemaker (DP). A 7-year-old boy with ventilator dependence after a high cervical spinal cord injury presented to the authors’ institution with paralytic scoliosis that progressed to > 120°. The patient had previously undergone insertion of phrenic nerve stimulators for diaphragmatic pacing. The decision was made to insert MCGRs bilaterally to stabilize his deformity, because the planned lengthening surgeries that are necessary with traditional growing rods would be poorly tolerated in this patient. The patient’s surgery and postoperative course were uneventful. The DP remained functional after insertion and lengthening of the MCGRs by using the external magnet. The DP had no effect on the expansion capability of the MCGRs. In conclusion, the MCGRs appear to be compatible with the DP. Further studies are needed to validate the long-term safety and compatibility of these 2 devices.

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Thromboprophylaxis

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Cost-effectiveness analysis: comparing single-level cervical disc replacement and single-level anterior cervical discectomy and fusion

Clinical article

Sheeraz A. Qureshi, Steven McAnany, Vadim Goz, Steven M. Koehler, and Andrew C. Hecht

Object

In recent years, there has been increased interest in the use of cervical disc replacement (CDR) as an alternative to anterior cervical discectomy and fusion (ACDF). While ACDF is a proven intervention for patients with myelopathy or radiculopathy, it does have inherent limitations. Cervical disc replacement was designed to preserve motion, avoid the limitations of fusion, and theoretically allow for a quicker return to activity. A number of recently published systematic reviews and randomized controlled trials have demonstrated positive clinical results for CDR, but no studies have revealed which of the 2 treatment strategies is more cost-effective. The purpose of this study was to evaluate the cost-effectiveness of CDR and ACDF by using the power of decision analysis. Additionally, the authors aimed to identify the most critical factors affecting procedural cost and effectiveness and to define thresholds for durability and function to focus and guide future research.

Methods

The authors created a surgical decision model for the treatment of single-level cervical disc disease with associated radiculopathy. The literature was reviewed to identify possible outcomes and their likelihood following CDR and ACDF. Health state utility factors were determined from the literature and assigned to each possible outcome, and procedural effectiveness was expressed in units of quality-adjusted life years (QALYs). Using ICD-9 procedure codes and data from the Nationwide Inpatient Sample, the authors calculated the median cost of hospitalization by multiplying hospital charges by the hospital-specific cost-to-charge ratio. Gross physician costs were determined from the mean Medicare reimbursement for each current procedural terminology (CPT) code. Uncertainty as regards both cost and effectiveness numbers was assessed using sensitivity analysis.

Results

In the reference case, the model assumed a 20-year duration for the CDR prosthesis. Cervical disc replacement led to higher average QALYs gained at a lower cost to society if both strategies survived for 20 years ($3042/QALY for CDR vs $8760/QALY for ACDF). Sensitivity analysis revealed that CDR needed to survive at least 9.75 years to be considered a more cost-effective strategy than ACDF. Cervical disc replacement becomes an acceptable societal strategy as the prosthesis survival time approaches 11 years and the $50,000/QALY gained willingness-to-pay threshold is crossed. Sensitivity analysis also indicated that CDR must provide a utility state of at least 0.796 to be cost-effective.

Conclusions

Both CDR and ACDF were shown to be cost-effective procedures in the reference case. Results of the sensitivity analysis indicated that CDR must remain functional for at least 14 years to establish greater cost-effectiveness than ACDF. Since the current literature has yet to demonstrate with certainty the actual durability and long-term functionality of CDR, future long-term studies are required to validate the present analysis.

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Superficial siderosis of the central nervous system from a bleeding pseudomeningocele

Case illustration

Max K. Kole, David Steven, Andrew Kirk, and Stephen P. Lownie

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Trigeminal neuropathic pain as a complication of anterior temporal lobectomy: report of 2 cases

Impreet Gill, Andrew G. Parrent, and David A. Steven

Cranial nerve (CN) deficits following anterior temporal lobectomy (ATL) are an uncommon but well-recognized complication. The usual CNs implicated in post-ATL complications include the oculomotor, trochlear, and facial nerves. To the authors’ knowledge, injury to the trigeminal nerve leading to neuropathic pain has not been previously described in the literature. This paper presents 2 cases of trigeminal neuropathic pain following temporal lobe resections for pharmacoresistant epilepsy. The possible pathophysiological mechanisms are discussed and the microsurgical anatomy of surgically relevant structures is reviewed.

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Computed tomography morphometric analysis for lateral mass screw placement in the pediatric subaxial cervical spine

Clinical article

George Al-Shamy, Jacob Cherian, Javier A. Mata, Akash J. Patel, Steven W. Hwang, and Andrew Jea

Object

Lateral mass screws are routinely placed throughout the subaxial cervical spine in adults, but there are few clinical or radiographic studies regarding lateral mass fixation in children. The morphology of pediatric cervical lateral masses may be associated with greater difficulty in obtaining adequate purchase. The authors examined the lateral masses of the subaxial cervical spine in pediatric patients to define morphometric differences compared with adults, establish guidelines for lateral mass instrumentation in children, and define potential limitations of this technique in the pediatric age group.

Methods

Morphometric analysis was performed on CT of the lateral masses of C3–7 in 56 boys and 14 girls. Measurements were obtained in the axial, coronal, and sagittal planes.

Results

For most levels and measurements, results in boys and girls did not differ significantly; the few values that were significantly different are not likely to be clinically significant. On the other hand, younger (< 8 years of age) and older children (≥ 8 years of age) differed significantly at every level and measurement except for facet angularity. Sagittal diagonal, a measurement that closely estimates screw length, was found to increase at each successive caudal level from C-3 to C-7, similar to the adult population. A screw acceptance analysis found that all patients ≥ 4 years of age could accept at least a 3.5 × 10 mm lateral mass screw.

Conclusions

Lateral mass screw fixation is feasible in the pediatric cervical spine, particularly in children age 4 years old or older. Lateral mass screw fixation is feasible even at the C-7 level, where pedicle screw placement has been advised in lieu of lateral mass screws because of the small size and steep trajectory of the C-7 lateral mass. Nonetheless, all pediatric patients should undergo high-resolution, thin-slice CT preoperatively to assess suitability for lateral mass screw fixation.

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Incidence patterns for primary malignant spinal cord gliomas: a Surveillance, Epidemiology, and End Results study

Clinical article

Steven Hsu, Marisa Quattrone, Quinn Ostrom, Timothy C. Ryken, Andrew E. Sloan, and Jill S. Barnholtz-Sloan

Object

Primary malignant spinal glioma represents a significant clinical challenge due to the devastating effect on clinical outcomes in the majority of cases. As they are infrequently encountered in any one center, there has been limited population-based data analysis on the incidence patterns of these aggressive tumors. The objective of this study was to use publically available Surveillance, Epidemiology and End Results (SEER) program data to examine the overall incidence and incidence patterns over time with regard to age at diagnosis, sex, race, primary site of tumor, and histological subtype in patients in whom primary malignant spinal cord gliomas were diagnosed between 1973 and 2006.

Methods

The study population of interest was limited to primary, malignant, pathologically confirmed spinal cord gliomas based on data drawn from the SEER 9 standard registries for patients diagnosed between 1973 and 2006. Variables of interest included age at diagnosis, sex, race, primary site of tumor, and histological subtype of tumor. The SEER*Stat 6.5.2 program was used to calculate frequencies, age-adjusted incidence rates with 95% CIs, and annual percentage change (APC) statistics with a 2-sided p value. In addition, linear correlation coefficients (R2) were calculated for the time association stratified by variables of interest.

Results

The overall age-adjusted incidence rate for primary malignant spinal gliomas was 0.12 per 100,000, which increased significantly over the study period (APC = 1.74; p = 0.0004; R2 = 0.36). The incidence was highest in patients diagnosed at ages 35–49 (0.17 per 100,000), males (0.14 per 100,000), whites (0.13 per 100,000), and those with ependymomas (0.07 per 100,000). Over the study period, the incidence of ependymomas increased significantly (APC = 3.17; p < 0.0001; R2 = 0.58) as did the incidence of these tumors in whites (APC = 2.13; p = 0.0001) and for both males (APC = 1.90, p value < 0.0001) and females (APC = 1.60, p < 0.0001). The authors found no significant changes in the incidence over time by age of diagnosis.

Conclusions

This study demonstrates an increasing overall incidence of primary, malignant spinal cord glioma over the past 3 decades. Notably, for ependymoma the incidence has increased, whereas the incidence of most other glioma subtypes remained stable. This may be due to improved diagnostic and surgical techniques, changes in histological classification criteria, and changes in neuropathology diagnostic criteria. Although primary, malignant spinal cord gliomas are rare, an improved understanding of the incidence will assist investigators and clinicians in planning potential studies and preparing for allocation of resources to care for these challenging patients.

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The dynamics of brain and cerebrospinal fluid growth in normal versus hydrocephalic mice

Laboratory investigation

Jason G. Mandell, Thomas Neuberger, Corina S. Drapaca, Andrew G. Webb, and Steven J. Schiff

Object

Hydrocephalus has traditionally been quantified by linear measures of ventricular size, with adjunct use of cortical mantle thickness. However, clinical outcome depends on cognitive function, which is more directly related to brain volume than these previous measures. The authors sought to quantify the dynamics of brain and ventricular volume growth in normal compared with hydrocephalic mice.

Methods

Hydrocephalus was induced in 14-day-old C57BL/6 mice by percutaneous injection of kaolin into the cisterna magna. Nine hydrocephalic and 6 normal mice were serially imaged from age 2–12 weeks with a 14.1-T MR imaging unit. Total brain and ventricle volumes were calculated, and linear discriminant analysis was applied.

Results

Two very different patterns of response were seen in hydrocephalic mice compared with mice with normative growth. In one pattern (3 mice) brain growth was normal despite accumulation of CSF, and in the second pattern (6 mice) abnormal brain enlargement was accompanied by increased CSF volume along with parenchymal edema. In this latter pattern, spontaneous ventricular rupture led to normalization of brain volume, implying edema from transmantle pressure gradients. These 2 patterns of hydrocephalus were significantly discriminable using linear discriminant analysis (p < 0.01). In contrast, clinically relevant measurements of head circumference or frontal and occipital horn ratios were unable to discriminate between these patterns.

Conclusions

This study is, to the authors' knowledge, the first serial quantification of the growth of brain and ventricle volumes in normal versus hydrocephalic development. The authors' findings demonstrate the feasibility of constructing normative curves of brain and fluid growth as complements to normative head circumference curves. By measuring brain volumes, distinct patterns of brain growth and enlargement can be observed, which are more likely linked to cognitive development and clinical outcome than fluid volumes alone.