The Role of Simultaneous Medical Conditions in Idiopathic Normal Pressure Hydrocephalus.

BACKGROUND: Idiopathic normal pressure hydrocephalus (iNPH) is a chronic neurologic syndrome that affects the elderly population in a context of concomitant medical conditions. The aim of this study was to understand the significance of comorbidities using 4 validated and specific clinical scores: Cumulative Illness Rating Scale (CIRS), American Society of Anesthesiologists (ASA) score, Comorbidity Index (CMI), and Charlson Comorbidity Index (CCI). METHODS: From 2015 until 2019, the Bologna PRO-Hydro multidisciplinary team selected 63 patients for shunt surgery. All comorbidity scores were collected during preoperative anesthesia evaluation. Positive shunt response was defined as an improvement in overall disability (assessed with modified Rankin Scale [mRS]), in risk of fall (assessed with Tinetti Permormance Orientated Mobility Assessment, Tinetti) and in INPH specific symptoms (assessed with INPH Grading Scale, INPHGS). RESULTS: Patients with elevated values of CIRS had worse performance in gait and balance at Tinetti scale, both before (P = 0.039) and after surgery (P = 0.005); patients with high values of CMI had inferior values of Tinetti at baseline (P = 0.027) and higher mRS after surgery (P = 0.009); ASA 2 patients had better postoperative Tinetti scores than ASA 3 patients (P = 0.027). A positive or negative shunt response was not significantly correlated with patients' preoperative comorbidity scores. CONCLUSIONS: Patients with multiple comorbidities have a worse preoperative condition compared to patients with less concomitant diseases, and the proposed comorbidity scores, CIRS in particular, are useful clinical tools for the anesthesiologist. Comorbidities, though, do not impact overall postoperative outcome.

Ventricular Volume Change as a Predictor of Shunt-Dependent Hydrocephalus in Aneurysmal Subarachnoid Hemorrhage.

BACKGROUND: Hydrocephalus is a common complication of aneurysmal subarachnoid hemorrhage (aSAH) that often requires acute placement of an external ventricular drain (EVD). The current systems available for determining which patients will require long-term cerebrospinal fluid diversion remain subjective. We investigated the ventricular volume change (ΔVV) after EVD clamping as an objective predictor of shunt dependence in patients with aSAH. METHODS: We performed a retrospective medical record review and image analysis of patients treated for aSAH at a single academic institution who had required EVD placement for acute hydrocephalus and had undergone 1 EVD weaning trial. Head computed tomography (CT) scans obtained before and after EVD clamping were analyzed using a custom semiautomated MATLAB program (MathWorks, Natick, Massachusetts, USA), which segments each CT scan into 5 tissue types using k-means clustering. Differences in the pre- and postclamp ventricular volumes were calculated. RESULTS: A total of 34 patients with an indwelling shunt met the inclusion criteria and were sex- and age-matched to 34 controls without a shunt. The mean ΔVV was 19.8 mL in the shunt patients and 3.8 mL in the nonshunt patients (P < 0.0001). The area under the receiver operating characteristic curve was 0.84. The optimal ΔVV threshold was 11.4 mL, with a sensitivity of 76.5% and specificity of 88.2% for predicting shunt dependence. The mean ΔVV was significantly greater for the patients readmitted for shunt placement compared with the patients not requiring cerebrospinal fluid diversion (18.69 mL vs. 3.84 mL; P = 0.005). Finally, 70% of the patients with delayed shunt dependence had ΔVV greater than the identified threshold. CONCLUSIONS: The ΔVV volume between head CT scans taken before and after EVD clamping was predictive of early and delayed shunt dependence.

Longitudinal CSF Iron Pathway Proteins in Posthemorrhagic Hydrocephalus: Associations with Ventricle Size and Neurodevelopmental Outcomes.

OBJECTIVE: Iron has been implicated in the pathogenesis of brain injury and hydrocephalus after preterm germinal matrix hemorrhage-intraventricular hemorrhage, however, it is unknown how external or endogenous intraventricular clearance of iron pathway proteins affect the outcome in this group. METHODS: This prospective multicenter cohort included patients with posthemorrhagic hydrocephalus (PHH) who underwent (1) temporary and permanent cerebrospinal fluid (CSF) diversion and (2) Bayley Scales of Infant Development-III testing around 2 years of age. CSF proteins in the iron handling pathway were analyzed longitudinally and compared to ventricle size and neurodevelopmental outcomes. RESULTS: Thirty-seven patients met inclusion criteria with a median estimated gestational age at birth of 25 weeks; 65% were boys. Ventricular CSF levels of hemoglobin, iron, total bilirubin, and ferritin decreased between temporary and permanent CSF diversion with no change in CSF levels of ceruloplasmin, transferrin, haptoglobin, and hepcidin. There was an increase in CSF hemopexin during this interval. Larger ventricle size at permanent CSF diversion was associated with elevated CSF ferritin (p = 0.015) and decreased CSF hemopexin (p = 0.007). CSF levels of proteins at temporary CSF diversion were not associated with outcome, however, higher CSF transferrin at permanent CSF diversion was associated with improved cognitive outcome (p = 0.015). Importantly, longitudinal change in CSF iron pathway proteins, ferritin (decrease), and transferrin (increase) were associated with improved cognitive (p = 0.04) and motor (p = 0.03) scores and improved cognitive (p = 0.04), language (p = 0.035), and motor (p = 0.008) scores, respectively. INTERPRETATION: Longitudinal changes in CSF transferrin (increase) and ferritin (decrease) are associated with improved neurodevelopmental outcomes in neonatal PHH, with implications for understanding the pathogenesis of poor outcomes in PHH. ANN NEUROL 2021;90:217-226.

Perceived and actual changes in gait balance after CSF shunting in idiopathic normal pressure hydrocephalus.

OBJECTIVES: We evaluated the perceived and actual changes in gait and balance function immediately after cerebrospinal fluid (CSF) shunting in patients with idiopathic normal pressure hydrocephalus (iNPH), including those with mild cases. MATERIALS AND METHODS: Ninety-nine iNPH patients were assessed using the timed Up and Go (TUG) and Functional Gait Assessment (FGA) before and 1-week after CSF shunting and their perceived changes were assessed on a Global Rate of Change (GRC) scale. Minimal clinically important differences (MCIDs) were calculated using a receiver operating characteristic (ROC) curve method using GRC scores. RESULTS: In all patients (n = 99), the TUG value postoperatively was significantly faster than the preoperative value (difference; 3.1 ± 4.6 s, p < 0.001), and the postoperative FGA score was significantly better than the preoperative score (difference; 3.8 ± 3.3 points, p < 0.001). In the TUG <15 s group (n = 51), the postoperative FGA score was significantly improved (difference; 3.3 ± 2.9 points, p < 0.001), whereas the TUG value was only slightly improved (difference; 0.6 ± 1.6 s, p = 0.008). The ROC curve MCIDs of GRC ≥2 points, which is the recommended level of improvement, were 1.7 s (16.5%) for the TUG and 4 points (20.0%) for the FGA in all patients (n = 99) and the TUG <15 s group (n = 51). CONCLUSIONS: FGA can be used to confirm treatment effects, including perceived and actual changes after CSF shunting, in patients with mild iNPH. Our results can help clinicians to determine the clinical significance of improvements in gait and balance function immediately after CSF shunting in individual patients with iNPH.

Shunt Failure-The First 30 Days.

BACKGROUND: Incontrovertible predictors of shunt malfunction remain elusive. OBJECTIVE: To determine predictors of shunt failure within 30 d of index surgery. METHODS: This was a single-center retrospective cohort study from January 2010 through November 2016. Using a ventricular shunt surgery research database, clinical and procedural variables were procured. An "index surgery" was defined as implantation of a new shunt or revision or augmentation of an existing shunt system. The primary outcome was shunt failure of any kind within the first 30 days of index surgery. Bivariate models were created, followed by a final multivariable logistic regression model using a backward-forward selection procedure. RESULTS: Our dataset contained 655 unique patients with a total of 1206 operations. The median age for the cohort at the time of first shunt surgery was 4.6 yr (range, 0-28; first and third quartile, .37 and 11.8, respectively). The 30-day failure rates were 12.4% when analyzing the first-index operation only (81/655), and 15.7% when analyzing all-index operations (189/1206). Small or slit ventricles at the time of index surgery and prior ventricular shunt operations were found to be significant covariates in both the "first-index" (P < .01 and P = .05, respectively) and "all-index" (P = .02 and P < .01, respectively) multivariable models. Intraventricular hemorrhage at the time of index surgery was an additional predictor in the all-index model (P = .01). CONCLUSION: This study demonstrates that only 3 variables are predictive of 30-day shunt failure when following established variable selection procedures, 2 of which are potentially under direct control of the surgeon.

A Comparison of Ventriculoperitoneal and Ventriculoatrial Shunts in a Population of 544 Consecutive Pediatric Patients.

BACKGROUND: Although ventriculoperitoneal shunts (VPS) remain the first-line option in most instances of pediatric hydrocephalus, the long-term efficacy of ventriculoatrial shunts (VAS) remains unknown. OBJECTIVE: To characterize the long-term outcomes and adverse occurrences associated with both VPS and VAS at our institution. METHODS: The authors retrospectively analyzed all cerebrospinal fluid (CSF) shunting procedures performed over a 13-yr period at a single institution. A total of 544 pediatric shunt patients were followed for at least 90 d (VPS: 5.9 yr; VAS: 5.3 yr). RESULTS: A total of 54% of VPS and 60% of VAS required at least 1 revision. VPS demonstrated superior survival overall; however, if electively scheduled VAS lengthening procedures are not considered true "failures," no statistical difference is noted in overall survival (P = .08). VPS demonstrated significantly greater survival in patients less than 7 yr of age (P = .001), but showed no difference in older children (P = .4). VAS had a significantly lower rate of infection (P < .05) and proximal failure (P < .001). CONCLUSION: VAS can be a useful alternative to VPS when the abdomen is unsuitable, particularly in older children. Although VPS demonstrates superior overall survival, it should be understood that elective VAS lengthening procedures are often necessary, especially in younger patients. If elective lengthening procedures are not considered true failures, then the devices show similar survival.

Background Risk Factors Associated with Shunt Intervention for Possible Idiopathic Normal Pressure Hydrocephalus: A Nationwide Hospital-Based Survey in Japan.

BACKGROUND: Patients with idiopathic normal-pressure hydrocephalus (iNPH) are typically older adults with multiple comorbidities that are associated with a reduction in the efficacy of iNPH treatment via cerebrospinal fluid (CSF) shunt placement. OBJECTIVE: The present study aimed to investigate the effectiveness of CSF shunt for iNPH using data from a nationwide epidemiological survey in Japan. METHODS: We examined 1,423 patients (581 women) aged ≥60 years (median age [25%-75%]: 77 [73-80] years) who were diagnosed with iNPH following a hospital visit in 2012. Patients who experienced an improvement of at least one modified Rankin Scale (mRS) grade after the CSF shunt were classified as "improvement" while the remaining patients were classified as "non-improvement." The efficacy of the shunt intervention (n = 842) was analyzed using a binomial logistic regression analysis. RESULTS: An analysis of risk factors associated with shunt placement in patients with mRS grade 2 revealed an association between comorbid chronic ischemic lesions (odds ratio [OR], 2.28; 95% confidence interval [CI], 1.11-4.67; p = 0.025) and cervical spondylosis (OR, 3.62; 95% CI, 1.15-11.34; p = 0.027). Patients with mRS grade 3 at study entry had an association with comorbid Alzheimer's disease (OR, 3.02; 95% CI, 1.44-6.31; p = 0.003). CONCLUSIONS: The results presented here showed that any age-related risk is minimal and should not be cause for rejection of surgical treatment options. Clinical decisions regarding CSF shunt should be individualized to each patient, with adequate consideration of the relative risks and benefits, including maximizing a healthy life expectancy.

A systematic review of shunt-related extraneural metastases of primary central nervous system tumors.

Extraneural metastasis (ENM) of primary central nervous system (CNS) tumors is an uncommon occurrence. Case reports and case series describe ENM after shunting, but this phenomenon has not been well characterized. In this review we aim to better understand the risk factors and clinical implications of ENM associated with shunting. A literature search of cases of ENM related to shunt placement in patients with primary CNS tumors reported through January 2018 was performed using PubMed and Google Scholar. We identified 106 cases of ENM of primary CNS tumors related to shunt placement. The three most common tumor histologies resulting in ENM were germinoma (24%), medulloblastoma (21%), and glioblastoma (11%). Of the patients with ENM, 48% had leptomeningeal spread and 37% had brain or spinal cord metastasis. Mean survival time from shunt placement was 13 months. Ventriculoatrial-shunted cases had higher rates of widespread metastasis and shorter average survival time from shunt placement (2 months) than the average of all types of shunts. Given the known association with ENM, careful consideration should be given to shunt placement in patients with primary CNS tumors, especially germinomas, medulloblastomas, and glioblastomas. Appropriate surveillance should be instituted after shunt placement, and leptomeningeal or neural metastasis should prompt the consideration of potential ENM. When considering distal shunt options, our review suggests that ventriculoatrial shunts should be avoided if possible. For truly obstructive pathologies, the risk of ENM is a further indication to consider other treatment options such as endoscopic third ventriculostomy rather than shunt placement.

The Quest for Predicting Sustained Shunt Response in Normal-Pressure Hydrocephalus: An Analysis of the Callosal Angle's Utility.

BACKGROUND: Diagnosing normal-pressure hydrocephalus (NPH) and selecting patients who will experience a sustained benefit from fluid diversion surgery remains challenging. This study seeks to evaluate the association between the callosal angle (CA) and the long-term postoperative response to ventriculoperitoneal shunt surgery in a different subgroup population than previously studied to assess its generalizability. METHODS: We studied 72 patients with idiopathic NPH who underwent ventriculoperitoneal shunt surgery and had at least 18 months of follow-up between 2000 and 2016. We recorded their pre- and postoperative symptoms according to the NPH Eide scale and their comorbidities with the Kiefer index. Their CA, as well as Evans' Index, ventricular height, and transependymal signal were measured. Multivariable statistical models were used to determine which factors were associated with postoperative improvement while we controlled for the presence of the NPH triad. RESULTS: Fifty-nine patients (82%) demonstrated a successful response to surgery at their first postoperative follow-up. However, this declined to 54 patients (75%) at 1 year and 45 (62.5%) patients at their last follow-up. When we controlled for the presence of the triad of symptoms, the CA significantly predicted a good, sustained response to surgery; for every degree decrease in the CA, a patient is 4% more likely to experience benefit from surgery. CONCLUSIONS: The CA is a useful preoperative prognostic tool for predicting which patients will experience a sustained benefit from surgery. Further studies are required to clarify this disease in the context of old age, comorbidity, and possible concomitant neurodegenerative diseases.

Patient out-of-pocket spending in cranial neurosurgery: single-institution analysis of 6569 consecutive cases and literature review.

OBJECTIVE With drastic changes to the health insurance market, patient cost sharing has significantly increased in recent years. However, the patient financial burden, or out-of-pocket (OOP) costs, for surgical procedures is poorly understood. The goal of this study was to analyze patient OOP spending in cranial neurosurgery and identify drivers of OOP spending growth. METHODS For 6569 consecutive patients who underwent cranial neurosurgery from 2013 to 2016 at the authors' institution, the authors created univariate and multivariate mixed-effects models to investigate the effect of patient demographic and clinical factors on patient OOP spending. The authors examined OOP payments stratified into 10 subsets of case categories and created a generalized linear model to study the growth of OOP spending over time. RESULTS In the multivariate model, case categories (craniotomy for pain, tumor, and vascular lesions), commercial insurance, and out-of-network plans were significant predictors of higher OOP payments for patients (all p < 0.05). Patient spending varied substantially across procedure types, with patients undergoing craniotomy for pain ($1151 ± $209) having the highest mean OOP payments. On average, commercially insured patients spent nearly twice as much in OOP payments as the overall population. From 2013 to 2016, the mean patient OOP spending increased 17%, from $598 to $698 per patient encounter. Commercially insured patients experienced more significant growth in OOP spending, with a cumulative rate of growth of 42% ($991 in 2013 to $1403 in 2016). CONCLUSIONS Even after controlling for inflation, case-mix differences, and partial fiscal periods, OOP spending for cranial neurosurgery patients significantly increased from 2013 to 2016. The mean OOP spending for commercially insured neurosurgical patients exceeded $1400 in 2016, with an average annual growth rate of 13%. As patient cost sharing in health insurance plans becomes more prevalent, patients and providers must consider the potential financial burden for patients receiving specialized neurosurgical care.

Shunt freedom and clinical resolution of idiopathic intracranial hypertension after bariatric surgery in the pediatric population: report of 3 cases.

Idiopathic intracranial hypertension (IIH), formerly known as pseudotumor cerebri, is a disease of elevated intracranial pressure that is thought to develop due to impaired CSF absorption related to elevated venous sinus pressure in the setting of increased intraabdominal and thoracic pressures. Symptoms can be disabling and, if left untreated, can lead to permanent visual loss. Previous treatments directed toward vision preservation include CSF diversion through shunting and optic nerve sheath fenestration. Recently, attention has been turned toward surgical weight loss strategies as an alternative to shunt treatment. The authors present a report of 3 patients with adolescent-onset IIH that was treated at the authors' institution (Duke University) in whom bariatric surgery was pursued successfully. The patients had previously undergone CSF shunting at ages 12, 15, and 23 years. They were shunt dependent for a collective average of 3.3 years prior to bariatriwc surgery. All patients reported "low-pressure" or postural headaches after bariatric surgery that correlated with dramatic reduction in their weight. Two of the 3 patients had their shunts removed and continued to be shunt free 1.5 years later at last follow-up; the third patient remained shunt dependent with the pressure set at 200 mm H2O. Given the significant complications inherent to multiple shunt revisions, earlier intervention for weight loss, including bariatric surgery, in these patients might have prevented complications and the associated health care burden. The authors recommend a multidisciplinary approach for IIH treatment with early consideration for weight loss interventions in select patients.

Quality of Life in Individuals Surgically Treated for Congenital Hydrocephalus During Infancy: A Single-Institution Experience.

BACKGROUND: Congenital hydrocephalus (CH) is a frequently encountered birth anomaly that can hinder long-term neurologic maturity and social well-being of affected children. This study was undertaken to assess quality of life (QOL) 10-15 years after surgical treatment for primary CH during infancy at a tertiary care hospital in a developing country. METHODS: This retrospective cohort study included individuals who presented to Aga Khan University Hospital, Karachi, Pakistan, between 1995 and 2005 at <1 year old and underwent surgery for primary CH. The Hydrocephalus Outcome Questionnaire was used to assess outcomes with respect to QOL. RESULTS: Of 118 patients, 90 patients participated in the study. Mean age at first admission was 6.2 months. Mean length of follow-up was 5.4 years. Of these, 28 patients had died after surgery. Shunt infection (P = 0.012) and delayed milestones (P = 0.003) were found to be statistically significant factors affecting mortality in the patients who died. The mean overall health score was 0.67 ± 0.30. Age <6 months at the time of first surgery was a poor predictor of overall health on the Hydrocephalus Outcome Questionnaire (P = 0.039). CONCLUSIONS: In our analysis, we assessed the QOL associated with CH. We hope that these results will provide insight for future prospective work with the ultimate goal of improving long-term QOL in children with CH.

Predictors of Shunt Insertion in Aneurysmal Subarachnoid Hemorrhage.

OBJECTIVE: Hydrocephalus is a common complication of aneurysmal subarachnoid hemorrhage (aSAH), requiring permanent cerebrospinal fluid (CSF) diversion in up to two thirds of patients. Factors that predict permanent CSF diversion are not well established. METHODS: An exploratory analysis of 149 patients enrolled in the CARAS (Cerebral Aneurysm Renin Angiotensin System) study was performed in an effort to identify factors predictive of permanent CSF diversion after aSAH; only the 135 patients surviving the initial hospitalization were included in the present study. CARAS was a prospective, multicenter study investigating the impact of genetic polymorphisms in patients with aSAH and enrolled patients from September 2012 to January 2015. RESULTS: One hundred and forty-nine patients with aSAH were enrolled in CARAS, with 135 (90.6%) patients surviving the initial hospitalization. Sixty-four of these patients (47.4%) required permanent CSF diversion. Multivariable analysis identified the following as independent risk factors: sympathomimetic illicit drug use, external ventricular drain (EVD) insertion, and hyponatremia. A scoring system based on EVD insertion (2 points), Hunt and Hess grade (1 point if grade ≥4) and modified Fisher computed tomography grade (1 point if grade 4) produced an area under the curve of 0.8 (P < 0.001). CONCLUSIONS: Sympathomimetic illicit drug use, EVD insertion, and hyponatremia are the strongest predictors of shunt insertion in patients with aSAH. Moreover, a scoring system based on EVD insertion, Hunt and Hess grade, and modified Fisher computed tomography grade can reliably predict the need for shunt placement in patients with aSAH.

Rate of shunt revision as a function of age in patients with shunted hydrocephalus due to myelomeningocele.

OBJECTIVE It is generally accepted that cerebrospinal fluid shunts fail most frequently in the first years of life. The purpose of this study was to describe the risk of shunt failure for a given patient age in a well-defined cohort with shunted hydrocephalus due to myelomeningocele (MMC). METHODS The authors analyzed data from their institutional spina bifida research database including all patients with MMC and shunted hydrocephalus. For the entire population, the number of shunt revisions in each year of life was determined. Then the number of patients at risk for shunt revision during each year of life was calculated, thus enabling them to calculate the rate of shunt revision per patient in each year of life. In this way, the timing of all shunt revision operations for the entire clinic population and the likelihood of having a shunt revision during each year of life were calculated. RESULTS A total of 655 patients were enrolled in the spina bifida research database, 519 of whom had a diagnosis of MMC and whose mean age was 17.48 ± 11.7 years (median 16 years, range 0-63 years). Four hundred seventeen patients had had a CSF shunt for the treatment of hydrocephalus and thus are included in this analysis. There were 94 shunt revisions in the 1st year of life, which represents a rate of 0.23 revisions per patient in that year. The rate of shunt revision per patient-year initially decreased as age increased, except for an increase in revision frequency in the early teen years. Shunt revisions continued to occur as late as 43 years of age. CONCLUSIONS These data substantiate the idea that shunt revision surgeries in patients with MMC are most common in the 1st year of life and decrease thereafter, except for an increase in the early teen years. A persistent risk of shunt failure was observed well into adult life. These findings underscore the importance of routine follow-up of all MMC patients with shunted hydrocephalus and will aid in counseling patients and families.

Chiari-related hydrocephalus: assessment of clinical risk factors in a cohort of 297 consecutive patients.

OBJECTIVE Patients treated for Chiari I malformation (CM-I) with posterior fossa decompression (PFD) may occasionally and unpredictably develop postoperative hydrocephalus. The clinical risk factors predictive of this type of Chiari-related hydrocephalus (CRH) are unknown. The authors' objective was to evaluate their experience to identify risk factors that may predict which of these patients undergoing PFD will develop CRH after surgery. METHODS The authors performed a retrospective clinical chart review of all patients who underwent PFD surgery and duraplasty for CM-I at the Primary Children's Hospital in Utah from June 1, 2005, through May 31, 2015. Patients were dichotomized based on the need for long-term CSF diversion after PFD. Analysis included both univariate and multivariable logistic regression analyses. RESULTS The authors identified 297 decompressive surgeries over the period of the study, 22 of which required long-term postoperative CSF diversion. On multivariable analysis, age < 6 years old (OR 3.342, 95% CI 1.282-8.713), higher intraoperative blood loss (OR 1.003, 95% CI 1.001-1.006), and the presence of a fourth ventricular web (OR 3.752, 95% CI 1.306-10.783) were significantly associated with the need for long-term CSF diversion after decompressive surgery. CONCLUSIONS Younger patients, those with extensive intraoperative blood loss, and those found during surgery to have a fourth ventricular web were at higher risk for the development of CRH. Clinicians should be alert to evidence of CRH in this patient population after PFD surgery.

A novel technique to treat acquired Chiari I malformation after supratentorial shunting.

PURPOSE: The acquired Chiari I malformation with abnormal cranial vault thickening is a rare late complication of supratentorial shunting. It poses a difficult clinical problem, and there is debate about the optimal surgical strategy. Some authors advocate supratentorial skull enlarging procedures while others prefer a normal Chiari decompression consisting of a suboccipital craniectomy, with or without C1 laminectomy and dural patch grafting. METHODS: We illustrate three cases of symptomatic acquired Chiari I malformation due to inward cranial vault thickening. RESULTS: We describe a new surgical approach that appears to be effective in these patients. This approach includes the standard Chiari decompression combined with posterior fossa augmentation by thinning the occipital planum. CONCLUSION: Internal volume re-expansion of the posterior fossa by thinning the occipital planum appears to be an effective novel surgical strategy in conjunction with the standard surgical therapy of Chiari decompression.