Long-term follow-up data from the Shunt Design Trial

Cerebrospinal Fluid Shunt Infections

Cerebrospinal fluid (CSF) shunt infections are a particularly challenging clinical problem. This review article addresses epidemiology and microbiology of CSF shunt infections. Clinical care is reviewed in detail, including recent guidelines and systematic review articles. Finally, current research into prevention and treatment is highlighted, with a discussion on the mechanisms of infection.

Measuring CSF shunt flow with MRI using flow enhancement of signal intensity (FENSI)

PURPOSE

To develop and validate a noninvasive imaging technique for accurately assessing very slow CSF flow within shunt tubes in pediatric patients with hydrocephalus, aiming to identify obstructions that might impede CSF drainage.

THEORY AND METHODS

A simulation of shunt flow enhancement of signal intensity (shunt-FENSI) signal is used to establish the relationship between signal change and flow rate. The quantification of flow enhancement of signal intensity data involves normalization, curve fitting, and calibration to match simulated data. Additionally, a phase sweep method is introduced to accommodate the impact of magnetic field inhomogeneity on the flow measurement. The method is tested in flow phantoms, healthy adults, intensive care unit patients with external ventricular drains (EVD), and shunt patients. EVDs enable shunt-flow measurements to be acquired with a ground truth measure of CSF drainage.

RESULTS

The flow-rate-to-signal simulation establishes signal-flow relationships and takes into account the T1 of draining fluid. The phase sweep method accurately accounts for phase accumulation due to frequency offsets at the shunt. Results in phantom and healthy human participants reveal reliable quantification of flow rates using controlled flows and agreement with the flow simulation. EVD patients display reliable measures of flow rates. Shunt patient results demonstrate feasibility of the method and consistent flow rates for functional shunts.

CONCLUSION

The results demonstrate the technique's applicability, accuracy, and potential for diagnosing and noninvasively monitoring hydrocephalus. Limitations of the current approach include a high sensitivity to motion and strict requirement of imaging slice prescription.

Image Quality and Related Outcomes of the ShuntScope-Guided Catheter Implantation in Adult Hydrocephalus: Experience of 63 Procedures

BACKGROUND

 Ventricular catheter (VC) placement in the selected subset of adult hydrocephalus can be highly challenging due to abnormal anatomical configuration or the need for trans-aqueductal stent placement. Transluminal endoscopy with the ShuntScope has been invented to increase the success rate of catheter placement. This study evaluates the image qualities of ShuntScope and related surgical outcomes in adults.

METHODS

 A retrospective analysis of all adult patients undergoing VC placement using the ShuntScope from November 2011 to July 2022 in the authors' department was performed. Demographic, clinical, and radiologic data were evaluated. The visualization quality of the intraoperative endoscopy was stratified into excellent, medium, and poor, and compared to the postoperative catheter tip placement. Follow-up evaluation included the surgical revision rate due to proximal catheter misplacement.

RESULTS

 A total of 63 ShuntScope-assisted surgeries have been performed on 60 adults. The mean age of the patients was 48.43 years. The most common underlying pathology was a tumor- or cyst-related cerebrospinal fluid (CSF) impairment in 38.33%, followed by a pseudotumor cerebri in 21.66%. The achieved image quality was excellent in 39.68%, medium in 47.62%, and poor in 12.7%. Ideal catheter placement was achieved in 79.37%. There were no intraoperative complications associated with the use of the ShuntScope. The revision rate due to suboptimal proximal VC placement was 4.76% during a mean follow-up period of 27.75 months. A statistical correlation between the image quality and accuracy of the catheter position was observed (p < 0.001).

CONCLUSION

 The ShuntScope can be considered an important addition to standard surgical tools in treating a selected subset of adult hydrocephalus. Direct visualization might even help achieve correct placement of the catheter in the cases with blurred vision and limited visual overview.

Obstetric and anesthetic management in parturients with ventriculoperitoneal shunt: a case series

Further study is needed to determine the safest mode of delivery and anesthetic management for parturients with ventriculoperitoneal shunts (VP). Prior recommendation for delivery in women with ventriculoperitoneal shunts was cesarean delivery. However, both vaginal delivery and neuraxial anesthesia have been shown to be safe in women with appropriately functioning VP shunts. We present a case series of parturients with VP shunt. Parturients with VP shunts were identified and VP shunt placement indications, neurologic symptoms during pregnancy, delivery mode, anesthetic type, and postpartum complications were reviewed. Forty patients were identified, and fifteen women with twenty deliveries were included. Two women experienced neurological symptoms during pregnancy and one required postpartum shunt revision for blurry vision and ataxia. There were ten cesarean deliveries and ten vaginal deliveries (eight normal spontaneous, one vacuum assisted, and one forceps assisted). Assisted vaginal deliveries were performed to decrease Valsalva including the patient with neurological symptoms related to shunt malfunction. Of the vaginal deliveries, six (60%) had epidural analgesia. Anesthesia for cesarean delivery included neuraxial anesthesia (n = 5) and general anesthesia (n = 5). In our cohort, women with VP shunt received neuraxial blockade without complication. Neuraxial techniques should be offered to women with appropriately functioning VP shunt.

Antibiotic-Impregnated Ventriculoperitoneal Shunts Decrease Bacterial Shunt Infection: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Antibiotic-impregnated shunts seem to be beneficial in preventing bacterial infections and decreasing mortality by effectively inhibiting microbial growth in the shunt system and reducing the risk of shunt-associated infections. This study aimed to evaluate the efficacy of antibiotic-impregnated shunt catheters (AISC) in reducing the incidence of bacterial shunt infection in patients with hydrocephalus.

METHODS

The protocol was registered on PROSPERO. A meta-analysis was conducted by searching 3 databases (PubMed, Scopus, CENTRAL) for relevant randomized controlled trials and observational studies. We included all studies published until November 2022 in any language. The primary outcome was the rate of bacterial infections, whereas the rate of shunt failure was our secondary endpoint. Odds ratios (OR) with 95% CI were calculated using a random-effects model.

RESULTS

A total of 27 articles with 27 266 shunt operations were included in this study. The results indicated that using AISC is significantly associated with reduction in infections (OR = 0.42; 95% CI: 0.33-0.54). Regarding shunt failure, there was a tendency in favor of AISC use (OR = 0.73; 95% CI: 0.51-1.06).

CONCLUSION

Our study provided evidence that AISC is significantly associated with the reduction in the rate of bacterial ventriculoperitoneal-shunt infection. In addition, there was a tendency toward AISC to decrease shunt failure compared with the standard shunt.

Paediatric hydrocephalus

Hydrocephalus is classically considered as a failure of cerebrospinal fluid (CSF) homeostasis that results in the active expansion of the cerebral ventricles. Infants with hydrocephalus can present with progressive increases in head circumference whereas older children often present with signs and symptoms of elevated intracranial pressure. Congenital hydrocephalus is present at or near birth and some cases have been linked to gene mutations that disrupt brain morphogenesis and alter the biomechanics of the CSF-brain interface. Acquired hydrocephalus can develop at any time after birth, is often caused by central nervous system infection or haemorrhage and has been associated with blockage of CSF pathways and inflammation-dependent dysregulation of CSF secretion and clearance. Treatments for hydrocephalus mainly include surgical CSF shunting or endoscopic third ventriculostomy with or without choroid plexus cauterization. In utero treatment of fetal hydrocephalus is possible via surgical closure of associated neural tube defects. Long-term outcomes for children with hydrocephalus vary widely and depend on intrinsic (genetic) and extrinsic factors. Advances in genomics, brain imaging and other technologies are beginning to refine the definition of hydrocephalus, increase precision of prognostication and identify nonsurgical treatment strategies.

Antibiotic impregnated catheters and intrathecal antibiotics for CSF shunt infection prevention in children undergoing low-risk CSF shunt surgery

BACKGROUND

Cerebrospinal fluid (CSF) shunts allow children with hydrocephalus to survive and avoid brain injury (J Neurosurg 107:345-57, 2007; Childs Nerv Syst 12:192-9, 1996). The Hydrocephalus Clinical Research Network implemented non-randomized quality improvement protocols that were shown to decrease infection rates compared to pre-operative prophylactic intravenous antibiotics alone (standard care): initially with intrathecal (IT) antibiotics between 2007-2009 (J Neurosurg Pediatr 8:22-9, 2011), followed by antibiotic impregnated catheters (AIC) in 2012-2013 (J Neurosurg Pediatr 17:391-6, 2016). No large scale studies have compared infection prevention between the techniques in children. Our objectives were to compare the risk of infection following the use of IT antibiotics, AIC, and standard care during low-risk CSF shunt surgery (i.e., initial CSF shunt placement and revisions) in children.

METHODS

A retrospective observational cohort study at 6 tertiary care children's hospitals was conducted using Pediatric Health Information System + (PHIS +) data augmented with manual chart review. The study population included children ≤ 18 years who underwent initial shunt placement between 01/2007 and 12/2012. Infection and subsequent CSF shunt surgery data were collected through 12/2015. Propensity score adjustment for regression analysis was developed based on site, procedure type, and year; surgeon was treated as a random effect.

RESULTS

A total of 1723 children underwent initial shunt placement between 2007-2012, with 1371 subsequent shunt revisions and 138 shunt infections. Propensity adjusted regression demonstrated no statistically significant difference in odds of shunt infection between IT antibiotics (OR 1.22, 95% CI 0.82-1.81, p = 0.3) and AICs (OR 0.91, 95% CI 0.56-1.49, p = 0.7) compared to standard care.

CONCLUSION

In a large, observational multicenter cohort, IT antibiotics and AICs do not confer a statistically significant risk reduction compared to standard care for pediatric patients undergoing low-risk (i.e., initial or revision) shunt surgeries.

Techniques to Reduce the Rate of Infection in Surgeries for Cerebrospinal Fluid Shunting in Adults

OBJECTIVE

Cerebrospinal fluid shunt placement is associated with high rates of infection. Multiple standardized protocols, particularly in pediatric populations, have been proposed to mitigate this infection rate. We sought to determine the effectiveness of a standardized shunt infection protocol in a large adult population.

METHODS

A retrospective cohort study of adults presenting for primary cerebrospinal fluid shunt placement from 2012 to 2022. The primary outcome of interest was shunt infection. The primary exposure of interest was implementation of the shunt protocol (began October 2015). Secondary exposures of interest included use and type of perioperative antibiotics and total operating room time.

RESULTS

In total, 820 patients were included, 140 before protocol implementation and 680 after protocol implementation. The overall number of infections over the study period was 15 (1.8% infection rate), with 8 infections preprotocol (5.7%) and 7 infections during the protocol period (1.0%). The infection protocol was associated with a decreased infection rate (odds rato [OR] 0.18, 95% confidence interval [CI] 0.05-0.58, P = 0.002). Total operating room time (OR 1.38 per 30-minute increase, 95% CI 1.05-1.81, P = 0.021) was associated with increased infection rate. Patients who received antibiotics with primarily gram-positive coverage (cefazolin or equivalent) did not have significantly different odds of shunt infection as patients who received broad-spectrum coverage (OR 2.10, 95% CI 0.56-7.88, P = 0.274).

CONCLUSIONS

The implementation of an evidence-based perioperative shunt infection protocol is an effective method to decrease shunt infections. Broad-spectrum perioperative antibiotics may not have greater efficacy than gram-positive only coverage, but more research is required.

The Top 100 Most Cited Journal Articles on Hydrocephalus

Hydrocephalus represents a significant burden of disease, with more than 383,000 new cases annually worldwide. When the magnitude of this condition is considered, a centralized archive of pertinent literature is of great clinical value. From a neurosurgical standpoint, hydrocephalus is one of the most frequently treated conditions in the field. The focus of this study was to identify the top 100 journal articles specific to hydrocephalus using bibliometric analysis. Using the Journal of Citation Report database, 10 journals were identified. The Web of Science Core Collection was then searched using each journal name and the search term "hydrocephalus." The results were ordered by "Times Cited" and searched by the number of citations. The database contained journal articles from 1976 to 2021, and the following variables were collected for analysis: journal, article type, year of publication, and the number of citations. Journal articles were excluded if they had no relation to hydrocephalus, mostly involved basic science research, or included animal studies. Ten journals were identified using the above criteria, and a catalog of the 100 most cited publications in the hydrocephalus literature was created. Articles were arranged from highest to lowest citation number, with further classification by journal, article type, and publication year. Of the 100 articles referenced, 38 were review articles, 24 were original articles, 15 were comparative studies, 11 were clinical trials, six were multi-center studies, three were cross-sectional, and three were case reports with reviews. Articles were also sorted by study type and further stratified by etiology. If the etiology was not specified, studies were instead subcategorized by treatment type. Etiologies such as aqueductal stenosis, tumors, and other obstructive causes of hydrocephalus were classified as obstructive (n=6). Communicating (n=15) included idiopathic, normal pressure hydrocephalus, and other non-obstructive etiologies. The category "other" (n=3) was assigned to studies that included etiologies, populations, and/or treatments that did not fit into the classifications previously outlined. Through our analysis of highly cited journal articles focusing on different etiologies and the surgical or medical management of hydrocephalus, we hope to elucidate important trends. By establishing the 100 most cited hydrocephalus articles, we contribute one source, stratified for efficient referencing, to facilitate clinical care and future research on hydrocephalus.

Dual catheter and double-lumen cerebrospinal fluid shunt systems with backflow mechanisms

PURPOSE

We previously developed a novel functional benchtop apparatus to simulate catheter occlusion in vitro utilizing avian vitelline membrane and chalaza to test catheter designs and de-obstruction techniques. Here, we study the integration of double-lumen catheter-mediated backflow in the shunt system assembly and its potential for an in-line de-obstruction of an obstructed ventricular catheter.

METHODS

A double-lumen catheter was connected to a standard proximal shunt catheter for all trials. One limb of the double-lumen catheter was connected to the backflow mechanisms and allowed to loop back for fluid access. A micropump and a bi-corporal electromagnetic pump were utilized to provide various degrees of backflow at predetermined intervals. Flow rates were measured after initial occlusion and after implementation of the backflow mechanisms, and degrees of catheter blockage was calculated as a percentage of the unoccluded flow rate. Flow visualization was also used.

RESULTS

In baseline blockage of less than 50%, the average occluding agent weighed 0.3-0.6 g with baseline flow rates of 8.5-11.9 mL/min. After 5 min of backflow using a micropump, the degree of blockage was reduced in 50% of trials. Additional backflow for 5 min did not provide further improvements in flow rate. In baseline blockage of greater than 50%, the average occluding agent weighed 0.8-1.3 g with baseline flow rates of 1.1-4.2 mL/min. After 5 min of backflow, the system demonstrated a decreased blockage in 20% of trials; additional backflow for 5 min further improved the flow rate in 40% of the total trials. Only magnetic plates provided enough force to provide pulsatile backflow in the bi-corporal electromagnetic system.

CONCLUSIONS

The preliminary results of connecting a standard proximal catheter in series with a double-lumen catheter show a slight change in the percent occlusion from the baseline status several times when the retrograde flow occurred via one limb of the catheter. Additionally, the de-obstruction seems related to the length of the interval of the backflow and the initial percentage occlusion of the proximal catheter. The statistical analysis does not reveal a statistically significant reduction in occlusion in the proximal catheter with either backflow interval.

A novel, benchtop model for quantitative analysis of resistance in ventricular catheters

INTRODUCTION

The mechanisms of catheter obstruction are still poorly understood, but the literature suggests that resistance to fluid flow plays a significant role. We developed and assessed a gravity-driven device that measures flow through ventricular catheters. We used this device to quantitatively analyze the resistances of unused ventricular catheters used in the treatment of hydrocephalus; failed hydrocephalus catheters from our catheter biorepository were also evaluated quantitatively.

METHODS

Catheters of three manufacturing companies were inserted into the benchtop model, which records time, flow rate, and pressure data using sensors. The relative resistances of catheters across six design models were evaluated. Experiments were performed to evaluate changes in the relative resistance of a catheter when the catheter's holes were progressively closed. The relative resistance of explanted catheters from our catheter biorepository was also measured.

RESULTS

Experimental results showed significant differences (P<0.05) between the relative resistances of different catheter models just after being removed from their packaging. A non-linear trend of increasing resistance was observed in experiments on catheters with artificially obstructed holes. Data from five individual benchtop models were compared, and the differences in measured data between the models were found to be negligible. A significant increase (P < 0.05) in relative resistance was observed in explanted catheters.

CONCLUSION

The current study sought to propose a novel in-vitro model and use it to examine data on differences in relative resistance among catheter models. From these experiments, we can rapidly correlate clinical patient cohorts to identify mechanisms of luminal shunt obstruction.

Cerebrospinal fluid shunt malfunctions: A reflective review

PURPOSE

Pediatric hydrocephalus is a common and challenging condition. To date, the ventriculoperitoneal shunt (VPS) is still the main lifesaving treatment option. Nonetheless, it remains imperfect and is associated with multiple short- and long-term complications. This paper is a reflective review of the current state of the VPS, our knowledge gaps, and the future state of shunts in neurosurgical practice.

METHODS AND RESULTS

The authors' reflections are based on a review of shunts and shunt-related literature.

CONCLUSION

Overall, there is still an urgent need for the neurosurgical community to actively improve current strategies for shunt failures and shunt-related morbidity. The authors emphasize the role of collaborative efforts amongst like-minded clinicians to establish pragmatic approaches to avoid shunt complications.

Retrospective comparison of long-term functionality and revision rate of two different shunt valves in pediatric and adult patients

PURPOSE

The most frequent therapy of hydrocephalus is implantation of ventriculoperitoneal shunts for diverting cerebrospinal into the peritoneal cavity. We compared two adjustable valves, proGAV and proGAV 2.0, for complications resulting in revision surgery.

METHODS

Four hundred patients undergoing primary shunt implantation between 2014 and 2020 were analyzed for overall revision rate, 1-year revision rate, and revision-free survival observing patient age, sex, etiology of hydrocephalus, implantation site, prior diversion of cerebrospinal fluid, and cause of revision.

RESULTS

All data were available of all 400 patients (female/male 208/192). Overall, 99 patients underwent revision surgery after primary implantation. proGAV valve was implanted in 283 patients, and proGAV 2.0 valves were implanted in 117 patients. There was no significant difference between the two shunt valves concerning revision rate (p = 0.8069), 1-year revision rate (p = 0.9077), revision-free survival (p = 0.6921), and overall survival (p = 0.3232). Regarding 1-year revision rate, we observed no significant difference between the two shunt valves in pediatric patients (40.7% vs 27.6%; p = 0.2247). Revision operation had to be performed more frequently in pediatric patients (46.6% vs 24.8%; p = 0.0093) with a significant higher number of total revisions with proGAV than proGAV 2.0 (33 of 59 implanted shunts [55.9%] vs. 8 of 29 implanted shunts [27.6%]; p = 0.0110) most likely due to longer follow-up in the proGAV-group. For this reason, we clearly put emphasis on analyzing results regarding 1-year revision rate.

CONCLUSION

According to the target variables we analyzed, aside from lifetime revision rate in pediatric patients, there is no significant difference between the two shunt valves.

Endoscopic Third Ventriculostomy versus Ventriculoperitoneal Shunt in Patients with Obstructive Hydrocephalus: An Updated Systematic Review and Meta-Analysis

Endoscopic third ventriculostomy (ETV) and ventriculoperitoneal shunt (VPS) are surgical methods for treating obstructive hydrocephalus. However, there is still disagreement regarding the most effective technique, in terms of both operative success and postoperative complications. Therefore, we performed a systematic review and meta-analysis to compare the efficacy and safety of these two methods in patients with obstructive hydrocephalus. We performed a systematic search of the PubMed, Scopus, and Cochrane Library databases. Randomized clinical trials (RCTs) comparing ETV and VPS in pediatric or adult patients with obstructive hydrocephalus were included. The outcomes included were operative success, postoperative cerebrospinal fluid leak, postoperative infection, postoperative or intraoperative bleeding, blockage rate, and mortality. The risk ratio (RR) was calculated with a 95% confidence interval (CI). Heterogeneity was evaluated with I 2 statistics. We used a fixed-effects model for outcomes with I 2  < 25% and DerSimonian and Laird random-effects model for other conditions. The Cochrane collaboration tool for assessing the risk of bias in randomized trials was used for risk-of-bias assessment. R, version 4.2.1, was used for statistical analyses. Of the 2,353 identified studies, 5 RCTs were included, involving 310 patients with obstructive hydrocephalus, of which 163 underwent ETV. There was a significant difference in favor of ETV for postoperative infection (risk ratio [RR]: 0.11; 95% confidence interval [CI]: 0.04-0.33; p  < 0.0001; I 2  = 0%) and blockage rate (RR: 0.15; 95% CI: 0.03-0.75; p  = 0.02; I 2  = 53%). Meanwhile, there was no significant difference between groups for the postoperative or intraoperative bleeding (RR: 0.44; 95% CI: 0.17-1.15; p  = 0.09; I 2  = 0%), postoperative cerebrospinal fluid leak (RR: 0.65; 95% CI: 0.22-1.92; p  = 0.44; I 2  = 18%), operative success (RR: 1.18; 95% CI: 0.77-1.82; p  = 0.44; I 2  = 84%), and mortality (RR: 0.19; 95% CI: 0.03-1.09; p  = 0.06; I 2  = 0%). Three RCTs had some concerns about the risk of bias and one RCT had a high risk of bias due to the process of randomization and selection of reported results. Thus, this meta-analysis of RCTs evaluating ETV compared with VPS demonstrated that although there is no superiority of ETV in terms of operative success, the incidence of complications was significantly higher in patients who underwent VPS. Our results suggest that the use of ETV provides greater benefits for the treatment of obstructive hydrocephalus. However, more RCTs are needed to corroborate the superiority of ETV.

Inhibition of serum- and glucocorticoid-induced kinase 1 ameliorates hydrocephalus in preclinical models

BACKGROUND

Hydrocephalus is a pathological accumulation of cerebrospinal fluid (CSF), leading to ventriculomegaly. Hydrocephalus may be primary or secondary to traumatic brain injury, infection, or intracranial hemorrhage. Regardless of cause, current treatment involves surgery to drain the excess CSF. Importantly, there are no long-term, effective pharmaceutical treatments and this represents a clinically unmet need. Many forms of hydrocephalus involve dysregulation in water and electrolyte homeostasis, making this an attractive, druggable target.

METHODS

In vitro, a combination of electrophysiological and fluid flux assays was used to elucidate secretory transepithelial electrolyte and fluid flux in a human cell culture model of the choroid plexus epithelium and to determine the involvement of serum-, glucocorticoid-induced kinase 1 (SGK1). In vivo, MRI studies were performed in a genetic rat model of hydrocephalus to determine effects of inhibition of SGK1 with a novel inhibitor, SI113.

RESULTS

In the cultured cell line, SI113 reduced secretory transepithelial electrolyte and fluid flux. In vivo, SI113 blocks the development of hydrocephalus with no effect on ventricular size of wild-type animals and no overt toxic effects. Mechanistically, the development of hydrocephalus in the rat model involves an increase in activated, phosphorylated SGK1 with no change in the total amount of SGK1. SI113 inhibits phosphorylation with no changes in total SGK1 levels in the choroid plexus epithelium.

CONCLUSION

These data provide a strong preclinical basis for the use of SGK1 inhibitors in the treatment of hydrocephalus.

Inpatient healthcare burden and variables influencing hydrocephalus-related admissions across the lifespan

OBJECTIVE

The aims of this study were to quantify inpatient healthcare costs, describe patient demographics, and analyze variables influencing costs for pediatric and adult hydrocephalus shunt-related admissions in the US.

METHODS

A cross-sectional study was performed using the 2019 Healthcare Cost and Utilization Project Kids' Inpatient Database (KID) and National Inpatient Sample (NIS), nationally representative weighted data sets of hospital discharges for pediatric and adult patients, respectively. International Classification of Diseases, 10th Revision, Clinical Modification and Procedure Coding System (ICD-10-CM/PCS) code filters for data extraction were queried for admission information. Age at admission was categorized into five groups (≤ 28 days, 29 days to < 1 year, 1-18 years, 19-64 years, and ≥ 65 years).

RESULTS

In 2019, there were 36,898 shunt-related hospital admissions accounting for 495,138 hospital days and a total cost of more than $2.06 billion. Initial shunt placements accounted for 53.5% of all admissions and nearly 60% of the total cost. The median cost per admission was $22,700 and the median length of stay was 5 days. Admissions for shunt infection requiring revision had the highest median cost at $71,300 (p < 0.001) and the longest median length of stay at 25 days (p < 0.001) compared with initial shunt placements. By age, admissions that occurred in the first 28 days of life cost almost 5 times more than the median, $110,500 versus $22,700, respectively, and resulted in hospital stays that were 8 times longer than the median, 41 versus 5 days, respectively. Individuals aged ≥ 65 years accounted for 28% of the total shunt-related admissions. Almost two-thirds (65.3%) of shunt-related admissions were classified as nonelective. The median cost of nonelective procedures was double that of elective admissions, $33,900 versus $15,100, respectively (p < 0.001), and resulted in almost 5 times longer hospital stays, 9 versus 2 days, respectively (p < 0.001). Shunt-related admissions were predominantly male across all age groups (54.7%-57.4% male) except the 19- to 64-year age group. In the 19- to 64-year age group, females accounted for 51.1% of admissions. Insurance status was largely age dependent. Of all admissions, 33.1% used private insurance, 32.9% Medicare, and 27.7% Medicaid.

CONCLUSIONS

This is the first study to quantify the patient demographics and cost of hydrocephalus shunt-related admissions across the entire age spectrum. Shunt-related admissions cost the US more than $2.06 billion dollars per year and represent only a fraction of the total cost of hydrocephalus care.

Surgical instruments and catheter damage during ventriculoperitoneal shunt assembly

OBJECTIVE

Current surgical techniques use common surgical instruments for sterile shunt assembly. This study investigated the impact of using these techniques and surgical instruments on the mechanical integrity of the ventriculoperitoneal shunt system, specifically shunt catheters.

METHODS

The authors conducted failure testing on 85 rifampin-coated catheters and 85 barium-impregnated catheters using 5 different surgical instruments and 2 different surgical techniques. In technique A, the distal end of the catheter was pushed onto the shunt valve inlet connector with the surgical instrument. In technique B, the catheter was pulled over the inlet connector. One hundred sixty catheters underwent 10-repetition-maximum testing, in which the catheter either failed before completion of 10 consecutive assembly/disassembly repetitions or the catheter completed 10 consecutive repetitions. The authors also conducted 100-repetition-maximum tests on 5 barium-impregnated and 5 rifampin-coated catheters using technique A.

RESULTS

Catheter failure rates were significantly different among the different instruments used in assembly (p ≤ 0.001). Post hoc analysis showed that using mosquito forceps with shods resulted in a significantly lower catheter failure rate than the other instruments (p < 0.0005). The catheter failure rate of technique A was significantly lower than that of technique B (5% vs 81%, p < 0.001). There was no statistical difference between the failure rates of the barium and rifampin catheters (42% vs 44%, p = 0.9), but the barium catheters outperformed the rifampin catheters in the 100-repetition-maximum trials (p = 0.02). Instrument type (p = 0.0232) and catheter type (p = 0.0096) were both significant factors in determining the number of assembly/disassembly repetitions needed to cause catheter failure. It took an average of 2.79 repetitions of assembly/disassembly to cause catheter failure. DeBakey forceps had significantly lower mean repetitions to failure (mean 1.38) than the Gerald forceps without teeth (mean 2.73, p = 0.05) and bayonet (mean 3.25, p = 0.02).

CONCLUSIONS

This study was the first of its kind to analyze how physical manipulation affects the mechanical integrity of ventriculoperitoneal shunt components. The authors demonstrated a significantly lower shunt catheter failure rate when mosquito forceps with shods and technique A were used in assembly. Moreover, the authors established that use of DeBakey forceps resulted in failure with fewer assembly/disassembly repetitions than use of the Gerald and bayonet forceps, suggesting that DeBakey forceps are the most damaging instrument.

Use of a Prophylactic Retrograde-Flushing Device in High-Risk Pediatric Patients with Ventriculoperitoneal Shunts: A Technical Note

INTRODUCTION

Ventriculoperitoneal shunt (VPS) malfunction rates are as high as 40% in the first year with posthemorrhagic hydrocephalus (PHH) patients having the highest proximal occlusion risk. Debris, protein, and cellular ingrowth most commonly obstruct the proximal ventricular catheter and/or valve. Historically, no preventative methods have demonstrated efficacy. We present a technical note and case series describing the use of a retrograde proximal flushing device and prophylactic flushing protocol to maintain ventricular catheter patency and reduce proximal shunt occlusions.

METHODS

We present our 2.8-4-year follow-up data on the first 9 pediatric cases of ReFlow (Anuncia Inc, Scottsdale, AZ) device implantation combined with routine prophylactic flushing. Rationale for device implantation, patient selection, surgical procedure details, postoperative follow-up, and prophylactic flushing protocol are discussed as well as pre- and postimplantation ventricular catheter obstruction rates. We include a technical note on the device setup and prophylactic flushing protocol.

RESULTS

Patient average age was 5.6 years and all patients had PHH. Minimal follow-up was 2.8 years (range 2.8-4 years). Prophylactic flushing was initiated between 2 and 14 days after ReFlow implantation and has continued as of the last follow-up. In 7 patients, ReFlow implantation occurred during the revision of an existing shunt and in two, implantation was coincident with initial VPS placement. In the 2 years preceding ReFlow and prophylactic flushing, 14 proximal shunt failures occurred in the 7 patients with existing VPS. This was reduced to only one proximal shunt failure in all 9 patients during the full follow-up period after ReFlow and prophylactic flushing.

CONCLUSION

Pediatric VPS placement carries high rates of proximal catheter occlusion, often leading to emergency surgery, morbidity, or even death. The ReFlow device along with routine prophylactic flushing may reduce proximal obstruction and need for revision surgery. Higher patient numbers and longer follow-up periods are necessary to further elucidate the safety and effect of such a device on longer term shunt failures and revision surgery.

Consideration of Kinase Inhibitors for the Treatment of Hydrocephalus

Hydrocephalus is a devastating condition characterized by excess cerebrospinal fluid (CSF) in the brain. Currently, the only effective treatment is surgical intervention, usually involving shunt placement, a procedure prone to malfunction, blockage, and infection that requires additional, often repetitive, surgeries. There are no long-term pharmaceutical treatments for hydrocephalus. To initiate an intelligent drug design, it is necessary to understand the biochemical changes underlying the pathology of this chronic condition. One potential commonality in the various forms of hydrocephalus is an imbalance in fluid–electrolyte homeostasis. The choroid plexus, a complex tissue found in the brain ventricles, is one of the most secretory tissues in the body, producing approximately 500 mL of CSF per day in an adult human. In this manuscript, two key transport proteins of the choroid plexus epithelial cells, transient receptor potential vanilloid 4 and sodium, potassium, 2 chloride co-transporter 1, will be considered. Both appear to play key roles in CSF production, and their inhibition or genetic manipulation has been shown to affect CSF volume. As with most transporters, these proteins are regulated by kinases. Therefore, specific kinase inhibitors are also potential targets for the development of pharmaceuticals to treat hydrocephalus.

Chronic Pleural Effusion in Ventriculoperitoneal Shunt due to Diaphragmatic CSF Fistula: Report of a Case Treated by Endoscopic Choroid Plexus Coagulation and Literature Review

INTRODUCTION

Chronic pleural cerebrospinal fluid (CSF) effusion is a rare complication after ventriculoperitoneal (VP) shunt insertion and only 18 cases in children and adults have been described so far without catheter dislocation to the intrathoracic cavity.

CASE PRESENTATION

We report on a 4-year-old girl with a complex history of underlying neurogenetic disorder, a hypoxic-ischemic encephalopathy after influenza A infection with septic shock and severe acute respiratory distress syndrome, followed by meningitis at the age of 10 months. In consequence, she developed a severe cerebral atrophy and post-meningitic hydrocephalus requiring placement of a VP shunt. At age 4, she was admitted with community-acquired mycoplasma pneumonia and developed increasing pleural effusions leading to severe respiratory distress and requiring continuous chest tube drainage (up to 1,000-1,400 mL/day) that could not be weaned. β trace protein, in CSF present at concentrations >6 mg/L, was found in the pleural fluid at low concentrations of 2.7 mg/L. An abdomino-thoracic CSF fistula was finally proven by single photon emission computerized tomography combined with low-dose computer tomography. After shunt externalization, the pleural effusion stopped and the chest tube was removed. CSF production rate remains high above 500 mL/24 h. An atrial CSF shunt could not be placed, since a hemodynamically relevant atrial septum defect with frail circulatory balance would not have tolerated the large CSF volumes. Therefore, she underwent a total bilateral endoscopic choroid plexus laser coagulation (CPC) within the lateral ventricles via bi-occipital burr holes. Postoperatively CSF production rate went close to 0 mL and after external ventricular drain removal no signs and symptoms of hydrocephalus developed during a follow-up of now 2.5 years.

CONCLUSION

In summary, pleural effusions in patients with VP shunt can rarely be caused by an abdomino-thoracic fistula, with non-elevated β-trace protein in the pleural fluid. The majority of reported cases in literature were treated by ventriculoatrial shunt. This is the 2nd reported case, which has been successfully treated by radical CPC alone including the temporal horn choroid plexus, making the child shunt independent.

Image quality and related outcomes of the ShuntScope for catheter implantation in pediatric hydrocephalus-experience of 65 procedures

PURPOSE

Ventricular catheter implantation in pediatric hydrocephalus can become a highly challenging task due to abnormal anatomical configuration or the need for trans-aqueductal stent placement. Transluminal endoscopy with the ShuntScope has been invented to increase the rate of successful catheter placements. This study aims to evaluate ShuntScope's image qualities and related surgical outcomes in the pediatric population.

METHODS

A retrospective analysis of all pediatric patients undergoing ventricular catheter placement using the ShuntScope from 01/2012 to 01/2022 in the author's department was performed. Demographic, clinical, and radiological data were evaluated. The visualization quality of the intraoperative endoscopy was stratified into the categories of excellent, medium, and poor and compared to the postoperative catheter tip placement. Follow-up evaluation included the surgical revision rate due to proximal catheter occlusion.

RESULTS

A total of 65 ShuntScope-assisted surgeries have been performed on 51 children. The mean age was 5.1 years. The most common underlying pathology was a tumor- or cyst-related hydrocephalus in 51%. Achieved image quality was excellent in 41.5%, medium in 43%, and poor in 15.5%. Ideal catheter placement was achieved in 77%. There were no intraoperative complications and no technique-related morbidity associated with the ShuntScope. The revision rate due to proximal occlusion was 4.61% during a mean follow-up period of 39.7 years. No statistical correlation between image grade and accuracy of catheter position was observed (p-value was 0.290).

CONCLUSION

The ShuntScope can be considered a valuable addition to standard surgical tools in treating pediatric hydrocephalus. Even suboptimal visualization contributes to high rates of correct catheter placement and, thereby, to a favorable clinical outcome.

Distal shunt placement in pediatric ventriculoperitoneal shunt surgery: an international survey of practice

OBJECTIVE

Ventriculoperitoneal shunt (VPS) surgery is a common treatment for hydrocephalus in children and adults, making it one of the most common procedures in neurosurgery. Children being treated with a VPS often require several revisions during their lifetime with a lifetime revision rate of up to 80%. Several different techniques exist for inserting the distal catheter, while mini-laparotomy, trocar, or laparoscopy is traditionally used. As opposed to adults, only few studies exist, comparing the outcome of the different distal catheter placement techniques in children. This international survey aims to investigate the current daily practice concerning distal shunt placement techniques in children.

MATERIAL AND METHODS

An online questionnaire investigating the different techniques used to place the distal catheter in pediatric VPS surgery was distributed internationally. All results were analyzed using descriptive and comparative statistics.

RESULTS

A total of 139 responses were obtained. Mini-laparotomy was reported to be the most frequently used technique (n = 104, 74.8%) for distal shunt placement in children, while laparoscopic or trocar-assisted placements were only used by 3.6% (n = 5) and 21.6% (n = 30) of all respondents, respectively. Over half (n = 75, 54.0%) of all respondents do not believe that laparoscopic placement improves the outcome.

CONCLUSION

This international survey shows that mini-laparotomy is the most frequently used technique for distal VPS placement in children all over the world. Further randomized trials are needed to elucidate this matter.

Factors affecting ventriculoperitoneal shunt revision: a post hoc analysis of the British Antibiotic and Silver Impregnated Catheter Shunt multicenter randomized controlled trial

OBJECTIVE

The British Antibiotic and Silver Impregnated Catheter Shunt (BASICS) trial established level I evidence of the superiority of antibiotic-impregnated catheters in the prevention of infection of newly implanted ventriculoperitoneal shunts (VPSs). A wealth of patient, shunt, and surgery-specific data were collected from trial participants beyond that of the prespecified trial objectives.

METHODS

This post hoc analysis of the BASICS survival data explores the impact of patient age, hydrocephalus etiology, catheter type, valve type, and previous external ventricular drain on the risk of infection or mechanical failure. Time to failure was analyzed using Fine and Gray survival regression models for competing risk.

RESULTS

Among 1594 participants, 75 patients underwent revision for infection and 323 for mechanical failure. Multivariable analysis demonstrated an increased risk of shunt infection associated with patient ages < 1 month (subdistribution hazard ratio [sHR] 4.48, 95% CI 2.06-9.72; p < 0.001) and 1 month to < 1 year (sHR 2.67, 95% CI 1.27-5.59; p = 0.009), as well as for adults with posthemorrhagic hydrocephalus (sHR 2.75, 95% CI 1.21-6.26; p = 0.016). Age ≥ 65 years was found to be independently associated with reduced infection risk (sHR 0.26, 95% CI 0.10-0.69; p = 0.007). Antibiotic-impregnated catheter use was also associated with reduced infection risk (sHR 0.43, 95% CI 0.22-0.84; p = 0.014). Independent risk factors predisposing to mechanical failure were age < 1 month (sHR 1.51, 95% CI 1.03-2.21; p = 0.032) and 1 month to < 1 year (sHR 1.31, 95% CI 0.95-1.81; p = 0.046). Age ≥ 65 years was demonstrated to be the only independent protective factor against mechanical failure risk (sHR 0.64, 95% CI 0.40-0.94; p = 0.024).

CONCLUSIONS

Age is the predominant risk for VPS revision for infection and/or mechanical failure, with neonates and infants being the most vulnerable.

Ventriculoperitoneal Shunt Malfunction in a Pediatric Patient Due to Compression by Skull Growth: A Case Report

There are various causes of ventriculoperitoneal shunt (VPS) failures. Patients who receive shunt placement during childhood need follow-up for decades as they grow, especially in the early periods of life. Herein, we report a rare case of mechanical shunt obstruction in a pediatric patient in whom a cramped burr hole and skull growth compressed the tube and obstructed cerebrospinal fluid flow. A 6-year-old girl presented to our hospital with nausea and headache. She was born preterm and developed intraventricular hemorrhage followed by VPS placement for hydrocephalus; thereafter, she had no need for shunt revision until this admission. After careful evaluation of the patency of the shunt system, the presence of tube stenosis was suspected at the site of the shunt tube penetrating the burr hole of the skull. During the operation to revise the shunt tube, a compressed tube was observed at the exit from the skull. After enlarging the narrowed burr hole and reconstructing the proximal catheter, her symptoms immediately improved. Previously, only one case of shunt malfunction due to tube compression from bone growth has been reported in a pediatric patient with osteopetrosis. To the best of our knowledge, such a condition has never been described in pediatric patients with no metabolic bone disease. Although it is rare, obstruction at the exit from the skull due to bone growth should be included in differential diagnoses for young patients during a long follow-up after VPS.

Time to shunt failure in children with myelomeningocele: an analysis of the National Spina Bifida Patient Registry

OBJECTIVE

Hydrocephalus is common among children with myelomeningocele and is most frequently treated with a ventriculoperitoneal shunt (VPS). Although much is known about factors related to first shunt failure, relatively less data are available about shunt failures after the first one. The purpose of this study was to use a large data set to explore time from initial VPS placement to first shunt failure in children with myelomeningocele and to explore factors related to multiple shunt failures.

METHODS

Data were obtained from the National Spina Bifida Patient Registry. Children with myelomeningocele who were enrolled within the first 5 years of life and had all lifetime shunt operations recorded in the registry were included. Kaplan-Meier survival curves were constructed to evaluate time from initial shunt placement to first shunt failure. The total number of children who experienced at least 2 shunt failures was calculated. A proportional means model was performed to calculate adjusted hazard ratios (HRs) for shunt failure on the basis of sex, race/ethnicity, lesion level, and insurance status.

RESULTS

In total, 1691 children met the inclusion criteria. The median length of follow-up was 5.0 years. Fifty-five percent of patients (938 of 1691) experienced at least 1 shunt failure. The estimated median time from initial shunt placement to first failure was 2.34 years (95% confidence interval [CI] 1.91-3.08 years). Twenty-six percent of patients had at least 2 shunt failures, and 14% of patients had at least 3. Male children had higher likelihood of shunt revision (HR 1.25, 95% CI 1.09-1.44). Children of minority race/ethnicity had a lower likelihood of all shunt revisions (non-Hispanic Black children HR 0.74, 95% CI 0.55-0.98; Hispanic children HR 0.74, 95% CI 0.62-0.88; children of other ethnicities HR 0.80, 95% CI 0.62-1.03).

CONCLUSIONS

Among the children with myelomeningocele, the estimated median time to shunt failure was 2.34 years. Forty-five percent of children never had shunt failure. The observed higher likelihood of shunt revisions among males and lower likelihood among children of minority race/ethnicity illustrate a possible disparity in hydrocephalus care that warrants additional study. Overall, these results provide important information that can be used to counsel parents of children with myelomeningocele about the expected course of shunted hydrocephalus.

The effect of A1 and A2 reactive astrocyte expression on hydrocephalus shunt failure

Background

The composition of tissue obstructing neuroprosthetic devices is largely composed of inflammatory cells with a significant astrocyte component. In a first-of-its-kind study, we profile the astrocyte phenotypes present on hydrocephalus shunts.

Methods

qPCR and RNA in-situ hybridization were used to quantify pro-inflammatory (A1) and anti-inflammatory (A2) reactive astrocyte phenotypes by analyzing C3 and EMP1 genes, respectively. Additionally, CSF cytokine levels were quantified using ELISA. In an in vitro model of astrocyte growth on shunts, different cytokines were used to prevent the activation of resting astrocytes into the A1 and A2 phenotypes. Obstructed and non-obstructed shunts were characterized based on the degree of actual tissue blockage on the shunt surface instead of clinical diagnosis.

Results

The results showed a heterogeneous population of A1 and A2 reactive astrocytes on the shunts with obstructed shunts having a significantly higher proportion of A2 astrocytes compared to non-obstructed shunts. In addition, the pro-A2 cytokine IL-6 inducing proliferation of astrocytes was found at higher concentrations among CSF from obstructed samples. Consequently, in the in vitro model of astrocyte growth on shunts, cytokine neutralizing antibodies were used to prevent activation of resting astrocytes into the A1 and A2 phenotypes which resulted in a significant reduction in both A1 and A2 growth.

Conclusions

Therefore, targeting cytokines involved with astrocyte A1 and A2 activation is a promising intervention aimed to prevent shunt obstruction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00367-3.

Hydrocephalus: historical analysis and considerations for treatment

Hydrocephalus is a serious condition that affects patients of all ages, resulting from a multitude of causes. While the etiologies of hydrocephalus are numerous, many of the acute and chronic symptoms of the condition are shared. These symptoms include disorientation and pain (headaches), cognitive and developmental changes, vision and sleep disturbances, and gait abnormalities. This collective group of symptoms combined with the effectiveness of CSF diversion as a surgical intervention for many types of the condition suggest that the various etiologies may share common cellular and molecular dysfunctions. The incidence rate of pediatric hydrocephalus is approximately 0.1-0.6% of live births, making it as common as Down syndrome in infants. Diagnosis and treatment of various forms of adult hydrocephalus remain understudied and underreported. Surgical interventions to treat hydrocephalus, though lifesaving, have a high incidence of failure. Previously tested pharmacotherapies for the treatment of hydrocephalus have resulted in net zero or negative outcomes for patients potentially due to the lack of understanding of the cellular and molecular mechanisms that contribute to the development of hydrocephalus. Very few well-validated drug targets have been proposed for therapy; most of these have been within the last 5 years. Within the last 50 years, there have been only incremental improvements in surgical treatments for hydrocephalus, and there has been little progress made towards prevention or cure. This demonstrates the need to develop nonsurgical interventions for the treatment of hydrocephalus regardless of etiology. The development of new treatment paradigms relies heavily on investment in researching the common molecular mechanisms that contribute to all of the forms of hydrocephalus, and requires the concerted support of patient advocacy organizations, government- and private-funded research, biotechnology and pharmaceutical companies, the medical device industry, and the vast network of healthcare professionals.

Reduction in the cerebrospinal fluid protein level after bevacizumab treatment in patients with optic pathway low-grade gliomas

Optic pathway gliomas (OPG) can cause elevated cerebrospinal fluid (CSF) protein concentrations. We report on two patients with suprasellar low-grade gliomas and high CSF protein levels (590 and 551 mg/dl) that precluded shunt implantation. After two and three doses of bevacizumab, respectively, the levels dropped dramatically to 191 and 178 mg/dl, respectively. Bevacizumab treatment was associated with a decrease in CSF protein level, allowing successful shunt placement. Our results are consistent with the pharmacological mechanism of bevacizumab, which decreases protein leakage from blood vessels to the ventricles.

The Sheep as a Comprehensive Animal Model to Investigate Interdependent Physiological Pressure Propagation and Multiparameter Influence on Cerebrospinal Fluid Dynamics

The present study aims to develop a suitable animal model for evaluating the physiological interactions between cerebrospinal fluid (CSF) dynamics, hemodynamics, and abdominal compartment pressures. We seek to contribute to the enhanced recognition of the pathophysiology of CSF-dependent neurological disorders like hydrocephalus and the improvement of available treatment options. To date, no comprehensive animal model of CSF dynamics exists, and establishing an accurate model will advance our understanding of complex CSF physiology. Persisting knowledge gaps surrounding the communication and pressure propagation between the cerebrospinal space and adjacent anatomical compartments exacerbate the development of novel therapies for neurological diseases. Hence, the need for further investigation of the interactions of vascular, craniospinal, and abdominal pressures remains beyond dispute. Moreover, the results of this animal study support the optimization of in vitro test benches for medical device development, e.g., ventriculoperitoneal shunts. Six female white alpine sheep were surgically equipped with pressure sensors to investigate the physiological values of intracranial, intrathecal, arterial, central venous, jugular venous, vesical pressure, and four differently located abdominal pressures. These values were measured simultaneously during the acute animal trial with sheep under general anesthesia. Both carotid and femoral arterial blood pressure indicate a reliable and comparable representation of the systematic blood pressure. However, the jugular venous pressure and the central venous pressure in sheep in dorsal recumbency do not correlate well under general anesthesia. Furthermore, there is a trend for possible comparability of lateral intraventricular and lumbar intrathecal pressure. Nevertheless, animal body position during measurements must be considered since different body constitutions can alter the horizontal line between the cerebral ventricles and the lumbar subarachnoid space. While intra-abdominal pressure measurement in the four different abdominal quadrants yielded greater inter-individual variability, intra-vesical pressure measurements in our setting delivered comparable values for all sheep. We established a novel and comprehensive ovine animal model to investigate interdependent physiologic pressure propagation and multiparameter influences on CSF dynamics. The results of this study will contribute to further in vitro bench testing, the derivation of novel quantitative models, and the development of a pathologic ovine hydrocephalus model.

Computational Modeling and Simulation to Quantify the Effects of Obstructions on the Performance of Ventricular Catheters Used in Hydrocephalus Treatment

Pediatric hydrocephalus is a debilitating condition that affects an estimated 1-2 in 1000 newborns, and there is no cure. A traditional treatment is surgical insertion of a shunt system which was designed 50 years ago, and minimal ensuing progress has been made in improving the failure rate of these devices resulting in the need for multiple brain surgeries during an affected child's lifetime for shunt replacement. A first step toward decreasing the failure rate is to optimize the ventricular catheter component of the shunt to minimize its propensity for obstruction. Given the many geometric properties and patient specific in vivo conditions needed to characterize the fluid dynamics affecting ventricular catheter performance, validated computational simulation is an efficient method to rapidly explore and evaluate the effects of this large parameter space to inform improved design and to investigate patient specific shunt performance. This chapter provides the details on how to build a computational model of a ventricle and implanted catheter, analyze the fluid dynamics through an obstructed catheter, and postprocess the results to predict catheter performance for varying geometry and in vivo conditions.

Programmable Shunt Valves for Pediatric Hydrocephalus: 22-Year Experience from a Singapore Children's Hospital

(1) Background: pediatric hydrocephalus is a challenging condition. Programmable shunt valves (PSV) have been increasingly used. This study is undertaken to firstly, to objectively evaluate the efficacy of PSV as a treatment modality for pediatric hydrocephalus; and next, review its associated patient outcomes at our institution. Secondary objectives include the assessment of our indications for PSV, and corroboration of our results with published literature. (2) Methods: this is an ethics-approved, retrospective study. Variables of interest include age, gender, hydrocephalus etiology, shunt failure rates and incidence of adjustments made per PSV. Data including shunt failure, implant survival, and utility comparisons between PSV types are subjected to statistical analyses. (3) Results: in this case, 51 patients with PSV are identified for this study, with 32 index and 19 revision shunts. There are 3 cases of shunt failure (6%). The mean number of adjustments per PSV is 1.82 times and the mean number of adjustments made per PSV is significantly lower for MEDTRONIC™ Strata PSVs compared with others (p = 0.031). Next, PSV patients that are adjusted more frequently include cases of shunt revisions, PSVs inserted due to CSF over-drainage and tumor-related hydrocephalus. (4) Conclusion: we describe our institutional experience of PSV use in pediatric hydrocephalus and its advantages in a subset of patients whose opening pressures are uncertain and evolving.

Shunt technology for infants and a lifetime

The use of cerebrospinal fluid (CSF) shunts remains a fundamental therapeutic modality in the management of hydrocephalus. Nowadays, neurosurgeons have an arsenal of different shunt technologies on their hands, with several companies producing many different configurations of them. The greatest difficulty of treating a child with hydrocephalus is to deal with a brain that will enormously change its size and hydrodynamic conditions and a body that will multiply its height and weight in a short time. Detailed knowledge of the hydrodynamic properties of shunts is mandatory for any neurosurgeon and much more for those taking care of pediatric patients. It is necessary to know that these properties of the valve may influence the evolution of the patient after shunting and it is recognized that a patient physiology-specific valve selection may yield better outcomes and decrease complications. This article provides a summary of the most common available CSF valves and overdrainage control devices, their technology, and possible combinations. The objective is to offer a quick overview of the armamentarium to facilitate the recognition of the implanted device and improve the selection of the most suitable valve for each patient.

Hydrocephalus in Low and Middle-Income Countries - Progress and Challenges

Hydrocephalus remains one of the most commonly treated neurosurgical conditions worldwide. Caring for patients with hydrocephalus requires infrastructure and political support and initiative; these are often difficult to obtain in low- and middle-income countries (LMICs). Some innovations that have arisen in LMICs have traveled up the financial gradient to high-income countries, such as the combination of endoscopic third ventriculostomy with choroid plexus coagulation to manage hydrocephalus. The development of neuro-endoscopy has played a major role in managing hydrocephalus worldwide; however, LMICs still face specific challenges, such as limited access to shunt hardware, a disproportionately high incidence of post-infectious hydrocephalus, unique microbiological spectra, and often poor access to follow-up care and neuroimaging. This has received increased attention since the Lancet Commission on Global Surgery. The goal of improving access to quality neurosurgical care through various initiatives in LMICs will be discussed in this manuscript. The need for neurosurgeons continues to grow in LMICs, where better access to neurosurgical care, adequate neurosurgical training and political support, and patient education are needed to improve the quality of life for patients with common neurosurgical conditions. Despite these challenges, treating hydrocephalus remains a worthwhile endeavor for many patients.

Readmissions after ventricular shunting in pediatric patients with hydrocephalus: a Nationwide Readmissions Database analysis

OBJECTIVE

Cerebrospinal fluid diversion via ventricular shunting is a common surgical treatment for hydrocephalus in the pediatric population. No longitudinal follow-up data for a multistate population-based cohort of pediatric patients undergoing ventricular shunting in the United States have been published. In the current review of a nationwide population-based data set, the authors aimed to assess rates of shunt failure and hospital readmission in pediatric patients undergoing new ventricular shunt placement. They also review patient- and hospital-level factors associated with shunt failure and readmission.

METHODS

Included in this study was a population-based sample of pediatric patients with hydrocephalus who, in 2010-2014, had undergone new ventricular shunt placement and had sufficient follow-up, as recorded in the Nationwide Readmissions Database. The authors analyzed the rate of revision within 6 months, readmission rates at 30 and 90 days, and potential factors associated with shunt failure including patient- and hospital-level variables and type of hydrocephalus.

RESULTS

A total of 3520 pediatric patients had undergone initial ventriculoperitoneal shunt placement for hydrocephalus at an index admission. Twenty percent of these patients underwent shunt revision within 6 months. The median time to revision was 44.5 days. Eighteen percent of the patients were readmitted within 30 days and 31% were readmitted within 90 days. Different-hospital readmissions were rare, occurring in ≤ 6% of readmissions. Increased hospital volume was not protective against readmission or shunt revision. Patients with grade 3 or 4 intraventricular hemorrhage were more likely to have shunt malfunctions. Patients who had private insurance and who were treated at a large hospital were less likely to be readmitted.

CONCLUSIONS

In a nationwide, population-based database with longitudinal follow-up, shunt failure and readmission were common. Although patient and hospital factors were associated with readmission and shunt failure, system-wide phenomena such as insufficient centralization of care and fragmentation of care were not observed. Efforts to reduce readmissions in pediatric patients undergoing ventricular shunt procedures should focus on coordinating care in patients with complex neurological diseases and on reducing healthcare disparities associated with readmission.

Thoracic abscess due to unusual migration of a ventriculoperitoneal shunt and literature review

Background:

Thoracic complications of ventriculoperitoneal (VP) cerebrospinal fluid shunting are rare and the diagnosis is difficult without neurological impairment.

Case Description:

We report a case of a 36-year-old woman who had a VP shunt in the right side when she was 13 years for a posterior fossa ependymoma and hydrocephalus. 23 years after surgery, she developed acute yellowfish cough and sputum, and the computed tomography scan found an intrathoracic cyst. She had a thoracotomy for the cyst and during surgery, we found the peritoneal catheter of the VP shunt, with a collected abscess in the left side. The patient was treated for the abscess and the VP shunt was removed. We also review the literature cases of thoracic complications after VP shunts.

Conclusion:

Thoracic abscess due to VP shunt migration is extremely rare and could happen after a long time delay VP shunt surgery.

Laparoscopy in a Patient With a Ventriculoperitoneal Shunt: A Case Report and Literature Review

Objective

This case emphasizes the safety of laparoscopy in patients with ventriculoperitoneal shunts.

Summary of background data

Previously published reports have suggested possible risks associated with laparoscopy in patients with ventriculoperitoneal shunt.

Methods

We report a case of a 17-year-old male with a ventriculoperitoneal shunt inserted 6 years ago to manage hydrocephalus that developed after surgery for medulloblastoma. The patient presented with a 5-day history of abdominal pain. He was diagnosed as having acute biliary pancreatitis. We performed laparoscopic cholecystectomy with the ventriculoperitoneal shunt in place.

Conclusion

The patient had an uneventful recovery with no shunt-related complications.

Ventriculopleural shunts in a pediatric population: a review of 170 consecutive patients

OBJECTIVE

The authors sought to determine the outcome of using the pleural space as the terminus for ventricular CSF-diverting shunts in a pediatric population.

METHODS

All ventriculopleural (VPl) shunt insertions or revisions done between 1978 and 2018 in patients at Children's Hospital Los Angeles were identified. Data recorded for analysis were age, sex, weight, etiology of hydrocephalus, previous shunt history, reason for VPl shunt insertion or conversion from a ventriculoperitoneal (VP) or ventriculoatrial (VA) shunt, valve type, nature of malfunction, presence of shunt infection or pleural effusion, and conversion to a different distal site.

RESULTS

A total of 170 patients (mean age 14 ± 4 years) with a VPl shunt who were followed up for a mean of 57 ± 53 months were identified. The reasons for conversion to a VPl shunt for 167 patients were previous shunt infection in 57 (34%), multiple abdominal procedures in 44 (26%), inadequate absorption of CSF in 34 (20%), abdominal pseudocyst in 25 (15%), and obesity in 7 (4%). No VPl revisions were required in 97 (57%) patients. Of the 73 (43%) patients who did require revision, the most common reason was proximal obstruction in 32 (44%). The next most frequent complication was pleural effusion in 22 (30%) and included 3 patients with shunt infection. All 22 patients with a clinically significant pleural effusion required changing the distal end of the shunt from the pleural space. Pleural effusion was more likely to occur in VPl shunts without an antisiphon valve. Of the 29 children < 10 years old, 7 (24%) developed a pleural effusion requiring a revision of the distal catheter to outside the pleural space compared with 15 (11%) who were older (p = 0.049). There were 14 shunt infections with a rate of 4.2% per procedure and 8.2% per patient.

CONCLUSIONS

VPl shunts in children younger than 10 years of age have a significantly higher rate of symptomatic pleural effusion, requiring revision of the shunt's terminus to a different location. VPl shunt complication rates are similar to those of VP shunts. The technical difficulty of inserting a VPl shunt is comparable to that of a VP shunt. In a patient older than 10 years, all else being equal, the authors recommend that the distal end of a shunt be placed into the pleural space rather than the right atrium if the peritoneal cavity is not suitable.

Accurate placement of parieto-occipital shunt ventricular catheter: use of craniometrics and technical note

PURPOSE

Ventriculoperitoneal shunt insertion is one of the most commonly performed procedures in neurosurgery but has a relatively high complication rate. One important source of complications is shunt malposition from erroneous placement of the parieto-occipital burr hole or poor shunt trajectory. There are significant variations in the freehand parieto-occipital approach amongst neurosurgeons that are derived from variations in technique or experience. The patient's skull shape or size is also often not taken into consideration if fixed measurements are used to define the burr hole entry point. The authors suggest a variation to the technique of ventricular catheter placement by relying on the patient's own craniometrics and skull landmarks.

METHODS

The technique is illustrated and supported by analysis of a case series of 25 patients undergoing shunt placement.

RESULTS

By this method, all shunts were positioned in the lateral ventricle. Using a 3-point scale, the catheter position was evaluated: grade 1, free floating in cerebrospinal fluid; grade 2, touching the choroid plexus or ventricular wall; and grade 3, tip within the parenchyma. The catheter position was grade 1 in sixteen (64%) cases and grade 2 in nine (36%) cases; none was grade 3. Only one shunt malfunction occurred from proximal shunt obstruction in the series.

CONCLUSION

The use of this technique aims to reduce operator and patient variability as contributors to shunt malposition, to increase user reproducibility and decrease the learning curve for trainees. Further prospective study could be designed to validate the technique.

Just Stick a Scope in: Laparoscopic Ventriculoperitoneal Shunt Placement in the Pediatric Reoperative Abdomen

BACKGROUND

Ventriculoperitoneal shunt (VPS) placement into the reoperative abdomen can be challenging due to intraperitoneal adhesions. Laparoscopic guidance may provide safe abdominal access and identify an area for optimal cerebrospinal fluid drainage. The study aim was to compare laparoscopic-assisted VPS placement to an "open" approach in patients with prior abdominal surgery.

MATERIALS AND METHODS

A retrospective review was performed of children undergoing VPS placement into a reoperative abdomen from 2009-2019. Clinical data were collected, and patients undergoing laparoscopy (LAP) were compared to those undergoing an open approach (OPEN).

RESULTS

A total of 120 children underwent 169 VPS placements at a median age of 8 y (IQR 2-15 y), and a mean number of two prior abdominal operations (IQR 1-2). Laparoscopy was used in 24% of cases. Shunt-related complications within 30 d were lower in the LAP group (0% versus 19%, P = 0.001), as were VPS-related postoperative emergency department visits (0% versus 13%, P = 0.003) and readmissions (0% versus 13%, P = 0.013). Shunt malfunction rates were higher (42% OPEN versus 25% LAP, P = 0.03) and occurred sooner in the OPEN group (median 26 versus 78 wk, P = 0.01). The LAP group demonstrated shorter operative times (63 versus 100 min, P < 0.0001), and the only bowel injury. Time to feeds, length of stay, and mortality were similar between groups.

CONCLUSIONS

Laparoscopic guidance during VPS placement into the reoperative abdomen is associated with a decrease in shunt-related complications, longer shunt patency, and shorter operative times. Prospective study may clarify the potential benefits of laparoscopy in this setting.

Pediatric shunt revision analysis within the first year of shunt placement: A single center experience

Background

Hydrocephalus is a common problem in neurosurgery with shunt placement remains the mainstay of the management. However, shunt placement generally requires following surgical procedures, including shunt revision. Despite the recent developments, the incidence of shunt failure remains high, approximately 30-51% in the 1^st year following the shunt placement.

Methods

An observational retrospective study of pediatric neurosurgery patients whom underwent CSF shunting procedure, both primary and repeated VPS, VAS, CPS, and subdural-peritoneal shunt procedures between January 2018 and May 2019. The patients were observed for 12 months for potential complication requiring shunt revision following the shunt placement.

Results

A total of 142 patients underwent shunt placement. The shunt revision within 12 months was found in 26 patients (18.3%), 25 cases were VPS (96.2%) and one case was CPS (3.8%). The mean period of time between shunt placement to shunt revision was 3.96 months. Age of under 6 months old during the shunt placement showed significantly higher risk for shunt revision (RR 2.32 CI 1.13-4.74, P = 0.018). The most common diagnosis requiring shunt revision was congenital anomaly (16 cases, 61.5%). The most common cause of revision was shunt malfunction, with 21 cases (80.8%) followed by infected shunt with 5 cases (19.2%).

Conclusion

The 1^st year observation showed relatively high rate for shunt revision. The patient underwent shunt procedure should be regularly followed up in long period for better evaluation of the outcome. The application of shunt registry in some countries appears to be efficient and beneficial for sustainable follow-up in patients underwent shunt placement.

Antisiphon device: a review of existing mechanisms and clinical applications to prevent overdrainage in shunted hydrocephalic patients

Overdrainage of cerebrospinal fluid is one of the most notorious complications after ventriculoperitoneal shunt implantation. Siphon effect plays a major role in the development of overdrainage. Various overdrainage-preventing devices have been invented to counteract the siphon effect. Though some of the devices are designed to reduce the flow instead of providing antisiphoning effect, they are generally called antisiphon devices (ASDs). The basics of siphoning, the mechanisms and physical properties of currently available devices are described in this article. The clinical efficacy, shunt survival, and considerations on patient factors are also discussed. There are three kinds of ASD design, diaphragm, gravitational, and flow reducing devices. Flow reducing ASD is always open and the flow it controls is relatively stable. On the other hand, it may not provide sufficient flow in nocturnal intracranial pressure elevations. Diaphragm and gravitational devices are sensitive to the position of the patients. Diaphragm device is sensitive to the external pressure and the relative position of the device to the mastoid process. The gravitational device is sensitive to the angle between the axis of the device and the head. Many studies showed encouraging results with gravitational devices. Studies regarding diaphragm devices either showed better or similar outcomes comparing to differential pressure valves. Clinical studies regarding flow-reducing devices and head-to-head comparison between different mechanisms are warranted. This review aims to provide a useful reference for clinical practice of hydrocephalus.

CSF shunt valve occlusion-does CSF protein and cell count matter?

BACKGROUND

Shunt obstruction is a common cause of shunt failure in the treatment of hydrocephalus. Valve occlusion is traditionally believed to originate from elevated CSF protein or cellular components, although detailed evidence is scarce and contradictory. Therefore, this study aimed to examine CSF protein and cell count as risk factors for valve obstruction.

METHODS

We retrospectively examined 274 patients who underwent shunt placement for hydrocephalus between 2009 and 2018 and had at least 1 year follow-up. Age, aetiology of hydrocephalus, valve type, occurrence of revision, reason for revision and CSF protein and cell count at the time of shunt insertion and revision surgery were analysed.

RESULTS

Thirty-two of 274 patients (11.7%) required revision surgery due to valve occlusion. Mean time to revision was 143 days. CSF white blood cell (WBC) count but not protein was associated with valve occlusion overall. Of all obstructed valve patients, 25% showed CSF protein level within the normal range, whereas 13.6% of the patients overall showed greatly elevated CSF protein level without evidence of valve obstruction. Persistently elevated CSF protein level at the time of shunt revision was significantly associated with valve obstruction within 90 days of initial insertion (early occlusion). Children with congenital malformations and post-haemorrhagic patients were significantly overrepresented in the occlusion group, particularly in the early occlusion group.

CONCLUSION

Pathological CSF values such as WBC count and persistently elevated protein level serves as a risk factor for early valve obstruction. Late obstruction occurs independent of normal CSF values. Infants are particularly prone to early and late valve obstructions. CSF protein level at shunt insertion is not predictive of valve occlusion.

Mechanical complications of cerebrospinal fluid shunt. Differences between adult and pediatric populations: myths or reality?

OBJECTIVE

Shunt malfunctions seem more frequent in children (44 to 81%) than in adults (18 to 29%). Because of discrepancies between studies, it is not possible to affirm this disparity. The objective was to verify whether the incidence of cerebrospinal fluid (CSF) shunt malfunctions is higher in children than adults.

METHODS

We present a retrospective series of child and adult patients who underwent CSF shunt placement between 2000 and 2013 with a Sophysa SM8® valve.

RESULTS

599 adults and 98 children (sex ratio 1.28) underwent CSF shunt placement. Age at first surgery ranged between 1 day of life and 90 years (mean of 55.8 years, SD 25.8, median 64.8 years). The mean follow-up was 4 years (SD 4.264, 0-16; median 3 years). The cumulative complication rate was 25.5% (178/697). Mechanical complications were disconnection (25.1%), migration (11.8%), intracranial catheter obstruction (8.9%) and malposition (8.4%). The mean delay for the first revision was 1.90 years (0-13.9), (SD 2.73, median 0.5). The probability of shunt failure was 65% at 10 years in the child group and 36% at 10 years in the adult group. Moreover, in the child group, 33% of revisions occurred during the first year after shunt placement versus 17% in the adult group. Thus, the probability of shunt failure was higher in children than in adults (log-rank test, p < 0.001).

CONCLUSIONS

This is the first retrospective study, comparing children and adults undergoing CSF shunt using the same valve, able to confirm the higher rate of complications in children.

Image quality of EOS low-dose radiography in comparison with conventional radiography for assessment of ventriculoperitoneal shunt integrity

OBJECTIVE

Patients with shunted hydrocephalus often accumulate high levels of radiation over their lifetimes during evaluation of hardware integrity. Current practice involves the use of a series of conventional radiographs for this purpose. Newer low-dose EOS radiography is currently used to evaluate scoliosis but has not been explored to evaluate shunt integrity on a large scale. The goal of this study was to compare the quality of imaging using EOS low-dose radiography to conventional radiography to evaluate shunt tubing.

METHODS

A retrospective chart review was performed on 57 patients who previously had both conventional radiographs and low-dose EOS images of their cerebral shunt tubing from 2000 to 2018. Patient demographics (age, sex, type of shunt tubing, primary diagnosis) were collected. Conventional radiographic images and low-dose EOS images were independently analyzed by a neurosurgeon and neuroradiologist in three categories: image quality, delineation of shunt, and distinction of shunt compared to adjacent anatomy.

RESULTS

All patients had shunted hydrocephalus due to spina bifida and Chiari type II malformation. Ratings of EOS and conventional radiographic images by both raters did not differ significantly in terms of image quality (rater 1, p = 0.499; rater 2, p = 0.578) or delineation of shunt (p = 0.107 and p = 0.256). Conventional radiographic images received significantly higher ratings than EOS on the ability to distinguish the shunt versus adjacent anatomy by rater 1 (p = 0.039), but not by rater 2 (p = 0.149). The overall score of the three categories combined was not significantly different between EOS and conventional radiography (rater 1, p = 0.818; rater 2, p = 0.186). In terms of cost, an EOS image was less costly than a conventional radiography shunt series ($236-$366 and $1300-$1547, respectively). The radiation dose was also lower for EOS images, with an effective dose of 0.086-0.140 mSv compared to approximately 1.6 mSv for a similar field of view with conventional radiography.

CONCLUSIONS

The image quality of low-dose EOS radiography does not significantly differ from conventional radiography for the evaluation of cerebral shunts. In addition, EOS affords a much lower radiation dose and a lower cost.

Standardization of cerebrospinal fluid shunt valves in pediatric hydrocephalus: an analysis of cost, operative time, length of stay, and shunt failure

OBJECTIVE

CSF shunts are the most common procedures performed in the pediatric neurosurgical population. Despite attempts in multiple studies, a superior shunt valve has never been shown. Because of this, the authors aim was to examine the impact of shunt valve standardization at their institution to determine if there is a difference in surgical cost, operative time, or short-term postoperative shunt failure.

METHODS

A retrospective analysis at the authors' institution was performed for all new CSF diversion shunts, as well as shunt revisions requiring a new valve, or a new valve and at least a new proximal or distal catheter over a 1-year period (January 1, 2016, to December 31, 2016). After a period of transition, neurosurgeons were encouraged to use only one type of fixed-differential-pressure valve and one type of programmable valve when performing shunt surgeries. These patients who underwent "standardized" shunt surgery over a 1-year period (January 1, 2018, to December 31, 2018) were then compared to patients in the prestandardization epoch. All patients were followed for a 12-month period after surgery. Demographic information, surgical cost, operative time, and postoperative shunt failure data were collected in all patients in the study.

RESULTS

The authors analyzed 87 shunt surgeries in patients prior to standardization and 94 shunt surgeries in patients after standardization. The rate of violation of the standardized shunt valve policy after implementation was 5.3% (5 of 94 procedures). When comparing the prestandardization group to those who received the standardized valve, operative costs were less ($1821.04 vs $1333.75, p = 0.0034). There was no difference in operative times between groups (78 minutes vs 81 minutes, p = 0.5501). There was no difference in total number of shunt failures between the two groups at 12 months after surgery (p = 0.0859). The rate of postoperative infection was consistent with the literature at 8%.

CONCLUSIONS

In accordance with quality improvement principles, the reduction of unexplained clinical variance invariably leads to a decrease in cost and, more importantly, increased value. In this study, the implementation of a standardized shunt valve decreased operative cost. There were no differences in postoperative shunt failures at 12 months after surgery and no differences in length of surgery. Standardizing shunt valves in the treatment of pediatric hydrocephalus seems to be cost-effective and safe.

OS reboot

Cerebrospinal fluid (CSF) diversion or shunting procedures are the most commonly performed surgery for the treatment of hydrocephalus and are often employed in the management of elevated intracranial pressure due to a variety of diseases. Despite their popularity however, approximately 50% of shunts fail within the first two years, and several revisions are required within the first decade after placement. Ophthalmologists may encounter patients with a CSF shunt to evaluate for concerns of vision loss or diplopia and to determine if papilledema is present. We discuss the neuro-ophthalmic manifestations and evaluation of possible CSF shunt malfunction.

A high-resolution real-time quantification of astrocyte cytokine secretion under shear stress for investigating hydrocephalus shunt failure

It has been hypothesized that physiological shear forces acting on medical devices implanted in the brain significantly accelerate the rate to device failure in patients with chronically indwelling neuroprosthetics. In hydrocephalus shunt devices, shear forces arise from cerebrospinal fluid flow. The shunt's unacceptably high failure rate is mostly due to obstruction with adherent inflammatory cells. Astrocytes are the dominant cell type bound directly to obstructing shunts, rapidly manipulating their activation via shear stress-dependent cytokine secretion. Here we developed a total internal reflection fluorescence microscopy combined with a microfluidic shear device chip (MSDC) for quantitative analysis and direct spatial-temporal mapping of secreted cytokines at the single-cell level under physiological shear stress to identify the root cause for shunt failure. Real-time secretion imaging at 1-min time intervals enabled successful detection of a significant increase of astrocyte IL-6 cytokine secretion under shear stress greater than 0.5 dyne/cm2, validating our hypothesis and highlighting the importance of reducing shear stress activation of cells.

Evaluating the Effects of Cerebrospinal Fluid Protein Content on the Performance of Differential Pressure Valves and Antisiphon Devices Using a Novel Benchtop Shunting Model

BACKGROUND

Hydrocephalus is managed by surgically implanting flow-diversion technologies such as differential pressure valves and antisiphoning devices; however, such hardware is prone to failure. Extensive research has tested them in flow-controlled settings using saline or de-aerated water, yet little has been done to validate their performance in a setting recreating physiologically relevant parameters, including intracranial pressures, cerebrospinal fluid (CSF) protein content, and body position.

OBJECTIVE

To more accurately chart the episodic drainage characteristics of flow-diversion technology. A gravity-driven benchtop model of flow was designed and tested continuously during weeks-long trials.

METHODS

Using a hydrostatic pressure gradient as the sole driving force, interval flow rates of 6 valves were examined in parallel with various fluids. Daily trials in the upright and supine positions were run with fluid output collected from distal catheters placed at alternating heights for extended intervals.

RESULTS

Significant variability in flow rates was observed, both within specific individual valves across different trials and among multiple valves of the same type. These intervalve and intravalve variabilities were greatest during supine trials and with increased protein. None of the valves showed evidence of overt obstruction during 30 d of exposure to CSF containing 5 g/L protein.

CONCLUSION

Day-to-day variability of ball-in-cone differential pressure shunt valves may increase overdrainage risk. Narrow-lumen high-resistance flow control devices as tested here under similar conditions appear to achieve more consistent flow rates, suggesting their use may be advantageous, and did not demonstrate any blockage or trend of decreasing flow over the 3 wk of chronic use.