✓The mathematical modeling of hydrocephalus is a relatively young field. The discipline evolved from Hakim's initial description of the brain as a water-filled sponge. Nagashima and colleagues subsequently translated this description into a computer-driven model by defining five important system rules. A number of researchers have since criticized and refined the method, providing additional system constraints or alternative approaches. Such efforts have led to an increased understanding of ventricular shape change and the development of periventricular lucency on imaging studies. However, severe limitations exist, precluding the use of the mathematical model to influence the operative decisions of practicing surgeons. In this paper, the authors explore the history, limitations, and future of the mathematical model of hydrocephalus.
Michelle J. Clarke and Fredric B. Meyer
Ross C. Puffer, Ryan Planchard, Grant W. Mallory, and Michelle J. Clarke
Health care-related costs after lumbar spine surgery vary depending on procedure type and patient characteristics. Age, body mass index (BMI), number of spinal levels, and presence of comorbidities probably have significant effects on overall costs. The present study assessed the impact of patient characteristics on hospital costs in patients undergoing elective lumbar decompressive spine surgery.
This study was a retrospective review of elective lumbar decompression surgeries, with a focus on specific patient characteristics to determine which factors drive postoperative, hospital-related costs. Records between January 2010 and July 2012 were searched retrospectively. Only elective lumbar decompressions including discectomy or laminectomy were included. Cost data were obtained using a database that allows standardization of a list of hospital costs to the fiscal year 2013–2014. The relationship between cost and patient factors including age, BMI, and American Society of Anesthesiologists (ASA) Physical Status Classification System grade were analyzed using Student t-tests, ANOVA, and multivariate regression analyses.
There were 1201 patients included in the analysis, with a mean age of 61.6 years. Sixty percent of patients in the study were male. Laminectomies were performed in 557 patients (46%) and discectomies in 644 (54%). Laminectomies led to an increased hospital stay of 1.4 days (p < 0.001) and increased hospital costs by $1523 (p < 0.001) when compared with discectomies. For laminectomies, age, BMI, ASA grade, number of levels, and durotomy all led to significantly increased hospital costs and length of stay on univariate analysis, but ASA grade and presence of a durotomy did not maintain significance on multivariate analysis for hospital costs. For a laminectomy, patient age ≥ 65 years was associated with a 0.6-day increased length of stay and a $945 increase in hospital costs when compared with patient age < 65 years (p < 0.001). A durotomy during a laminectomy increased length of stay by 1.0 day and increased hospital costs by $1382 (p < 0.03). For discectomies, age, ASA grade, and durotomy were significantly associated with increased hospital costs on univariate analysis, but BMI was not. Only age and presence of a durotomy maintained significance on multivariate analysis. There was a significant increase in hospital length of stay in patients undergoing discectomy with increasing age, BMI, ASA grade, and presence of a durotomy on univariate analysis. However, only age and presence of a durotomy maintained significance on multivariate analysis. For discectomies, age ≥ 65 years was associated with a 0.7-day increased length of stay (p < 0.001) and an increase of $931 in postoperative hospital costs (p < 0.01) when compared with age < 65 years.
Patient factors such as age, BMI, and comorbidities have significant and measurable effects on the postoperative hospital costs of elective lumbar decompression spinal surgeries. Knowledge of how these factors affect costs will become important as reimbursement models change.
Ross C. Puffer, William E. Clifton, Grant W. Mallory, and Michelle J. Clarke
Delayed cervical palsy (DCP) is a known complication following cervical spine surgery. While most DCPs eventually improve, they can result in significant temporary disability. Postoperative complications affect hospital length of stay (LOS) as well as overall hospital cost. The authors sought to determine the hospital cost of DCP after cervical spine fusion operations.
A retrospective review of patients undergoing cervical fusion for degenerative disease at the Mayo Clinic from 2008 to 2012 was performed. Patients who developed DCPs not attributable to intraoperative trauma were included. All nonoperative-related costs were compared with similar costs in a control group matched according to age, sex, and surgical approach. All costs and services were reflective of the standard costs for the current year. Raw cost data were presented using ratios due to institutional policy against publishing cost data.
There were 27 patients (18 men, 9 women) who underwent fusion and developed a DCP over the study period. These patients were compared with 24 controls (15 men, 9 women) undergoing fusion in the same time period. There was no difference between patients and controls in mean age (62.4 ± 3.1 years vs 63.8 ± 2.5 years, respectively; p = 0.74), LOS (4.2 ± 3.3 days vs 3.8 ± 4.5 days, respectively; p = 0.43), or operating room–related costs (1.08 ± 0.09 vs 1.0 ± 0.07, respectively; p = 0.58). There was a significant difference in nonoperative hospital-related costs between patients and controls (1.67 ± 0.15 vs 1.0 ± 0.09, respectively; p = 0.04). There was a significantly higher utilization of postoperative imaging (CT or MRI) in the DCP group (14/27, 52%) when compared with the matched cohort (4/24, 17%; p = 0.018), and a significantly higher utilization of physiatry services (24/27 [89%] vs 15/24 [63%], respectively; p = 0.046).
While DCPs did not significantly prolong the length of hospitalization, they did increase hospital-related costs. This method could be further extrapolated to model costs of other complications as well.
Deena M. Nasr, Waleed Brinjikji, Michelle J. Clarke, and Giuseppe Lanzino
Spinal epidural arteriovenous fistulas (SEDAVFs) constitute a rare but treatable cause of vascular myelopathy and are a different subtype from the more common Type I spinal dural AVFs. The purpose of this study was to review a consecutive series of SEDAVFs from a single institution and report on the clinical presentations, functional status, and treatment outcomes.
The authors identified all SEDAVFs treated at their institution from 2005 to 2015. SEDAVFs were defined as spinal AVFs in which the fistulous connection occurred in the epidural venous plexus. The clinical presentation, functional status, immediate treatment outcomes, and long-term neurological outcomes were analyzed.
Twenty-four patients with SEDAVFs were included in this study. The patients' mean age at presentation was 66.9 years. The most common presenting symptoms were pain and numbness (22 patients, 91.7%), followed by lower-extremity weakness (21 patients, 87.5%). The mean duration of symptoms prior to diagnosis was 11.8 months. Eighteen patients (75.0%) were treated with endovascular therapy alone, 4 (16.7) with surgery, and 2 (8.3%) with a combination of techniques. There was 1 major treatment-related complication (4.2%). Fifteen patients (62.5%) had improvement in disability, and 12 patients (54.5%) had improvement in sensory symptoms.
SEDAVFs often present with lower-extremity motor dysfunction and sensory symptoms. With the availability of newer liquid embolic agents, these lesions can be effectively treated with endovascular techniques. Surgery is also effective at treating these lesions, especially in situations where endovascular embolization fails or is not safe and in patients presenting with mass effect from compressive varices.
Michelle J. Clarke, Andrew B. Foy, Nicholas Wetjen, and Corey Raffel
Subependymal giant cell astrocytomas (SEGAs) are a common manifestation of tuberous sclerosis (TS). These evolving tumors have a propensity to cause obstructive hydrocephalus, usually due to obstruction at the level of the foramen of Monro. Differentiating SEGAs from subependymal nodules (SENs) before obstruction occurs may improve the morbidity associated with these tumors. In this study the authors' aim was to determine imaging characteristics of proven tumors in a single-center pediatric population.
The authors retrospectively reviewed all records and images obtained in patients with TS in whom results of biopsy sampling had proven that their tumors were SEGAs. Time to presentation, signs and symptoms at presentation, and imaging characteristics of the evolving tumors were noted. Twelve patients with 14 SEGAs proven by the results of biopsy sampling were reviewed. Resection was recommended for symptomatic and neuroimaging evidence of hydrocephalus (41%), tumor growth without evidence of hydrocephalus (33%), and for poorly controlled seizures (25%). The mean diameter of the tumors at the time of resection was 1.9 cm (range 0.3–4 cm), and no tumor recurred. Because of the pathological and radiographic continuum of SENs and SEGAs, it remains difficult to predict whether and when a given lesion will progress. Tumor growth and contrast enhancement are the most common signs of progression on neuroimages, and may be seen prior to the development of obstructive hydrocephalus.
Patients with SENs and SEGAs should undergo follow-up neuroimaging at yearly intervals, and if lesions show signs of progression (contrast enhancement or growth), these intervals should be shortened and consideration given to early resection.
Report of two cases
Michelle J. Clarke, Cormac O. Maher, Georgia Nothdurft, and Fredric Meyer
✓ Low-pressure hydrocephalus is an extremely rare condition. Authors of the few previous reports on this subject have suggested that symptoms are gradual in onset and successfully treated. In this report the authors presented two unique cases of very low pressure hydrocephalus in which the patients experienced rapid deterioration requiring negative-pressure cerebrospinal fluid drainage to achieve the best possible neurological function; outcomes in both patients ultimately were poor. The constellation of findings suggests that this may be a distinct clinical entity.
Abbas Amirjamshidi and Kazem Abbassioun
Christopher S. Graffeo, Avital Perry, Ross C. Puffer, Lucas P. Carlstrom, Wendy Chang, Grant W. Mallory, and Michelle J. Clarke
Type II odontoid fracture is a common injury among elderly patients, particularly given their predisposition toward low-energy falls. Previous studies have demonstrated a survival advantage following early surgery among patients older than 65 years, yet octogenarians represent a medically distinct and rapidly growing population. The authors compared operative and nonoperative management in patients older than 79 years.
A single-center prospectively maintained trauma database was reviewed using ICD-9 codes to identify octogenarians with C-2 cervical fractures between 1998 and 2014. Cervical CT images were independently reviewed by blinded neurosurgeons to confirm a Type II fracture pattern. Prospectively recorded outcomes included Glasgow Coma Scale (GCS) score, Abbreviated Injury Scale (AIS) score, Injury Severity Score (ISS), additional cervical fracture, and cord injury. Primary end points were mortality at 30 days and at 1 year. Statistical tests included the Student t-test, chi-square test, Fisher's exact test, Kaplan-Meier test, and Cox proportional hazard.
A total of 111 patients met inclusion criteria (94 nonoperative and 17 operative [15 posterior and 2 anterior]). Mortality data were available for 100% of patients. The mean age was 87 years (range 80–104 years). Additional cervical fracture, spinal cord injury, GCS score, AIS score, and ISS were not associated with either management strategy at the time of presentation. The mean time to death or last follow-up was 22 months (range 0–129 months) and was nonsignificant between operative and nonoperative groups (p = 0.3). Overall mortality was 13% in-hospital, 26% at 30 days, and 41% at 1 year. Nonoperative and operative mortality rates were not significant at any time point (12% vs 18%, p = 0.5 [in-hospital]; 27% vs 24%, p = 0.8 [30-day]; and 41% vs 41%, p = 1.0 [1-year]). Kaplan-Meier analysis did not demonstrate a survival advantage for either management strategy. Spinal cord injury, GCS score, AIS score, and ISS were significantly associated with 30-day and 1-year mortality; however, Cox modeling was not significant for any variable. Additional cervical fracture was not associated with increased mortality. The rate of nonhome disposition was not significant between the groups.
Type II odontoid fracture is associated with high morbidity among octogenarians, with 41% 1-year mortality independent of intervention—a dramatic decrease from actuarial survival rates for all 80-, 90-, and 100-year-old Americans. Poor outcome is associated with spinal cord injury, GCS score, AIS score, and ISS.
Jennifer S. McDonald, Michelle J. Clarke, Gregory A. Helm, and David F. Kallmes
The presence of a “July effect,” where the influx of new residents and fellows at teaching hospitals every July may negatively affect patient care and outcomes, is widely debated. The authors used the Nationwide Inpatient Sample (NIS) to identify all cases of spinal surgery and examine outcomes among patients who underwent surgery in July compared with those who underwent surgery in other months.
Spinal surgery hospitalizations from 2001 to 2008 were identified in the NIS by extracting relevant ICD-9 codes. Rates of in-hospital mortality, discharge to a long-term care facility, and postoperative complications were compared between admission months and between teaching and nonteaching hospitals using the Wilcoxon rank-sum test, Fisher exact test, and multivariate regression analysis.
Compared with patients admitted in other months, patients who were admitted to teaching hospitals in July for spinal surgery showed a similar likelihood of in-hospital mortality (OR 0.94 [95% CI 0.78–1.11], p = 0.46), reaction to implanted device/instrumentation (OR 0.88 [95% CI 0.77–1.02], p = 0.09), and postoperative wound dehiscence (OR 1.12 [95% CI 0.94–1.33], p = 0.25). A significantly higher likelihood of discharge to a long-term care facility (OR 1.03 [95% CI 1.00–1.07], p = 0.0467) and postoperative infection (OR 1.11 [95% CI 1.05–1.17], p = 0.0341) was observed in teaching hospitals in July compared with other months; however, incidence rates were similar regardless of admission month. Higher-risk patients (Charlson score ≥ 2) admitted to teaching hospitals in July had a similar likelihood of all outcomes regardless of admission month.
This study of nationwide hospitalizations demonstrates that the influx of new residents and fellows in July has a negligible effect on periprocedural outcomes following spinal surgery.