Abstract

BackgroundAs the population continues to age, the number of adults receiving care for hydrocephalus is expected to increase. Here, we assess trends in the utilization and physician reimbursement for ventriculoperitoneal shunts (VPS), lumboperitoneal shunting (LPS), and endoscopic third ventriculostomy (ETV) for adult hydrocephalus.

MethodsThe Medicare Part B National Summary Data files from 2000 to 2021 were collected, and information was extracted on procedures performed per year, total charges billed, and actual payments. Linear mixed-model regression analyses were conducted to assess the significance of changes in procedural volume and physician reimbursement over time while adjusting for inflation.

ResultsOver the period studied, there was a 26% increase in VPS placement (P = 0.11), 11.34% increase in ETV utilization (P P P = 0.04). In both inflation-unadjusted and inflation-adjusted analyses, all procedures experienced an annual decline in reimbursement with inflation-adjusted changes of −11.54%/year for ETV, −4.13% for LPS, and −13.12% for VPS. There was a statistically significant difference in the change of rate of reimbursement between LPS procedures and both ETV (P P

ConclusionMedicare reimbursement data shows that a commensurate decline in physician reimbursement has accompanied the ongoing rise in adult hydrocephalus procedures.

Keywords: Cerebrospinal fluid diversion, Hydrocephalus, Medicare, Neurosurgery, Physician reimbursement

INTRODUCTION

Hydrocephalus affects approximately 179/100,000 individuals over the age of 60, with approximately half of cases reported to be idiopathic normal pressure hydrocephalus (iNPH).[ 1 , 13 ] Definitive management for symptomatic patients consists of cerebrospinal fluid (CSF) diversion by three main modalities: ventriculoperitoneal shunting (VPS), lumboperitoneal shunting (LPS), or endoscopic third ventriculostomy (ETV).[ 21 ] VPS is traditionally the most commonly performed procedure in adult hydrocephalus patients and has been shown to improve gait biomechanics in iNPH patients.[ 14 ] Others have argued for the use of LPS, citing similar complication rates while minimizing the risk of brain injury.[ 20 ] Nonetheless, LPS can be disadvantageous due to their tendency to migrate, procedural challenges, particularly in obese patients, and difficulty in accessing the reservoir relative to VPS. In addition, like VPS, they can be associated with subdural hematomas/hygromas, device infections, and device failure (e.g., obstruction and disconnection), which occur in up to 22% of patients.[ 20 ]

As the relative clinical efficacy of these different strategies continues to be assessed, there is growing interest on the part of payors to understand the rates at which these procedures are utilized. Heterogeneity within patient data accounts for the variance noted in terms of economic costs, length of stay (LOS), and patient outcomes for patients with hydrocephalus. Chief among these payors are the Centers for Medicare and Medicaid Services (CMS), the single largest payer for persons over 65.[ 5 , 6 ] The elderly age range is the population segment in which adult hydrocephalus is most common, and additionally, this age range is expected to increase to an estimated 78 million by 2030.[ 3 , 19 ] In this patient population, hydrocephalus is increasingly recognized as a cause of long-term disability, as a study by Marmarou et al. noted up to 14% of US nursing home residents suffer from symptomatic iNPH.[ 19 ]

As CSF-diversion procedures are the gold standard of care for these patients, a thorough understanding of the size of this clinical population and the costs of caring for them is merited. Therefore, our objective of this study was to evaluate trends in utilization and physician reimbursement for VPS, LPS, and ETV procedures for Medicare patients undergoing treatment of adult hydrocephalus and help guide clinical decision making appropriately.

MATERIALS AND METHODS

Data source and extraction

The Medicare Part B National Summary Data files are publicly available from the years 2000 to 2021.[ 4 ] This database was queried to identify patients who underwent VPS, LPS, or ETV for adult hydrocephalus. Relevant procedures were identified using Current Procedural Terminology (CPT) coding. To identify eligible patients, the following CPT codes were used: VPS (62223), LPS (63740–with laminectomy; 63741–without laminectomy), and ETV (62200–without guidance; 62201–with guidance). To calculate procedure-level reimbursement, the total charges for each CPT code in a given fiscal year were divided by the total procedures identified by that CPT code.

Inflation adjustment

The United States Consumer Price Index (U.S. Bureau of Labor Statistics, Washington DC, USA) was used to adjust reported reimbursements into 2021 dollars for each fiscal year.[ 26 ] Percentage change over the years examined was calculated. Descriptive statistics on the mean reimbursement for each year included in the study were tabulated for inflation-unadjusted and inflation-adjusted metrics.

Statistical analysis

Payment data and the average annual procedure volume over the 22 years were presented as mean ± standard deviation. In addition, the mean Medicare reimbursements to physicians per claim were calculated to derive a percent change in reimbursement difference between 2000 and 2021.

Changes in procedural volume and physician reimbursement over time were tested for significant trends using linear mixed-model regression analyses. The year was utilized as the predictive variable and natural logarithm transformation of physician reimbursement or annual procedural volume was used as the outcome variable. Linear mixed models were used to account for the potential effects of clustering and correlation within the data. One-way analysis of variance (ANOVA) was used to look for significant differences between procedure types with regard to the trends in procedure volume and inflation-adjusted reimbursement. Individual between-group differences were performed using Tukey’s post hoc test. Wilcox test was used to compare the volume of LPS and VPS before and after 2015. The year 2015 was chosen to analyze the effect of the SINPHONI clinical trial on the utilization rate of LPS and VPS.[ 16 ] All analysis was done using R (R Core Development Team, Vienna, Austria). Statistical significance was defined by P < 0.05.

RESULTS

ETV

Procedural volume analysis

Total ETV volume increased significantly from 194 procedures in 2000 to 216 procedures in 2021 (P < 0.01), reaching a maximum of 281 procedures in 2016 [ Table 1 ]. Sub-analysis based on the use of image guidance showed a 76.5% decrease in non-image guided procedures (P < 0.01) and a concurrent 1472% increase in the volume of image-guided procedures (P < 0.01). The majority of the change occurred between 2002 and 2010 [ Figure 1 ].

Table 1:

Change in the inflation-adjusted and inflation-unadjusted mean Medicare reimbursement to physicians per ETV procedure and procedure volume from 2000 to 2021.

Figure 1:

Comparison of the annual volume of procedures billed to Medicare Type B each year for endoscopic third ventriculostomy, lumboperitoneal, and ventriculoperitoneal (VP) shunt. For VP, the Y-axis value is the number of procedures performed/10. LP: Lumboperitoneal, ETV: Endoscopic third ventriculostomy.

Reimbursement analysis

Non-inflation adjusted procedural reimbursement showed a 21.98% increase from $717.23 in 2000 to $874.90 in 2021 (P < 0.01). Subanalysis by CPT code showed a non-significant increase of 5.56% ($798.28–$842.68) in the non-image guided group and a significant increase of 42.59% ($636.18–$907.13) in the image-guided group over the study period [ Table 2 ]. After adjusting for inflation, there was a significant decrease from $1,111.46 to $874.90 (−21.28%, P < 0.01; [ Table 1 and Figure 2 ]). Unguided procedures saw a larger decrease in reimbursement, decreasing from $1,237.06 in 2000 to $842.68 in 2021 (−31.88%) than did image-guided procedures (−8.00%, from $985.96 in 2000 to $907.13 in 2021).

Table 2:

Change in the inflation-adjusted and inflation-unadjusted mean Medicare reimbursement to physicians per LPS procedure and procedure volume from 2000 to 2021.

Figure 2:

Comparison of inflation-adjusted Mean Medicare reimbursement to physicians per endoscopic third ventriculostomy, lumboperitoneal, and ventriculoperitoneal shunt. LP: Lumboperitoneal, ETV: Endoscopic third ventriculostomy, VP: Ventriculoperitoneal.

LPS

Procedural volume analysis

Total LPS procedural volume decreased from 576 procedures in 2000 to 328 procedures in 2021 (−43.1%; P < 0.01; [ Table 2 ]). Subanalysis by CPT code showed a 25.53% decrease in LPS without laminectomy (372 vs. 277; P = 0.04) and a 74.51% decrease in LPS with laminectomy (51 vs. 204; P = 0.03).

Reimbursement analysis

Reimbursement [ Table 2 ] before adjusting for inflation showed a mean increase in reimbursement of 32.08% across the study period ($450.04 vs. $482.13; P < 0.01). After adjusting, however, a significant decrease (30.86%) in reimbursement was noted for all procedures ($697.42 vs. $482.14; P < 0.01; [ Figure 2 ]). Subanalysis by CPT code showed a non-significant increase in unadjusted reimbursement for LPS without laminectomy (−9.56%; P = 0.32) and commensurate significant increase in unadjusted reimbursement for LPS with laminectomy (19.74%; P < 0.01). Both procedures showed significant decreases in inflation-adjusted reimbursement: LPS without laminectomy (−41.64%; P < 0.01) and with laminectomy (−22.73%; P < 0.01).

VPS

Procedural volume analysis

The overall number of VPS procedures increased non-significantly across the study period, from 6689 procedures in 2000 to 8434 procedures in 2021 (P = 0.11; [ Table 3 and Figure 1 ]). Specifically, the number of procedures performed increased by 2707 between 2004 and 2005. There were 10,437 VPS procedures performed in 2005, which was the highest procedural volume in the years investigated.

Table 3:

Change in the inflation-adjusted and inflation-unadjusted mean Medicare reimbursement to physicians per VPS procedure and procedure volume from 2000 to 2021.

Reimbursement analysis

Absolute reimbursement showed an 8.11% decrease across the study period (P = 0.17, [ Table 3 ]). However, after adjusting for inflation, there was a statistically significant 40.70% decrease in VPS physician reimbursement between 2000 and 2021 (P < 0.01; [ Figure 2 ]).

Comparison among procedures

Procedure volume

Average annual growth rates (AAGR) for ETV, LPS, and VPS were 4.29%, −8.78%, and 45.83%, respectively [ Table 4 ]. One-way ANOVA showed a significant difference between the AAGR of LPS and VPS (P = 0.04), though there were no significant differences between the AAGR of ETV and LPS or ETV and VPS.

Table 4:

Comparison of annual volume of procedures billed to Medicare Type B each year for placement of ETV, LP, and VP shunt.

Medicare reimbursement

The AAGR for ETV, LPS, and VPS were −11.54%, −4.13%, and −13.12%, respectively [ Table 5 ]. One-way ANOVA showed significant differences between the AAGR of ETV and LPS (P < 0.01) as well as between LPS and VPS (P < 0.01). There was no significant difference between the AAGR of ETV and VPS.

Table 5:

Comparison of inflation-adjusted Mean Medicare reimbursement to physicians per ETV, LP, and VP shunt.

Shunt comparison with 2015

There was a statistically significant decrease in LPS shunts placed without laminectomy (P = 0.05) and with a laminectomy (P < 0.01) when comparing the 2000–2015 and post-2015 study periods [ Table 6 ]. The mean number of annual LP shunts placed without laminectomy was 279.56 ± 48.95 from 2000 to 2015 and 230 ± 44.38 between 2016 and 2021. For LP shunts with laminectomy, the mean annual placement was 162.43 ± 69.80 from 2000 to 2015 and 70.33 ± 24.31 afterward. There was no statistical change in VPS volume between the two time groups (P = 0.18).

Table 6:

Difference in annual procedure volume before and after the 2015 publication of the SINPHONI-2 trial.

DISCUSSION

The costs of providing effective care for the aging U.S. population present an ongoing challenge for CMS, the primary insurer for Americans over 65 years of age.[ 3 , 5 , 8 , 18 , 25 ] In the present study, trends in CSF diversion procedure utilization and physician reimbursement were examined for Medicare patients with adult hydrocephalus. Overall, there was a small increase in ETV procedural volume, along with a larger increase in VPS placement and a commensurate decrease in LPS. Across all three procedures, there was a significant decrease in inflation-adjusted reimbursement, with the greatest overall decreases being in VPS placement and LPS placement without laminectomy. Reimbursement declines have varied significantly between the procedure types, with a notable inverse relationship between annualized reimbursement cuts and the procedure utilized.

Surgical candidate selection and variability in procedure utilization

Among patients in the Medicare population, the most common causes of hydrocephalus are iNPH and communicating hydrocephalus following subarachnoid hemorrhage. In both cases, CSF diversion provides definitive therapy. As with post-hemorrhagic hydrocephalus, iNPH responsiveness to shunting is variable, which may, in part, drive regional variation in VPS placement.[ 18 ] Alvi et al.[ 1 ] reported the presence of such variation within the United States based on their analysis of the National Inpatient Sample. The authors noted that VPS was used less commonly within the Northeast region relative to the other three demographic regions (Midwest, South, and West), while LPS placement was more commonly used in the Midwest and Northeast regions relative to the South and West.

Similar variability in the usage of VPS was noted in a recent population-level analysis by Mansoor et al.[ 18 ] using national registry data from Norway. They found significant regional variation in shunt utilization amongst adult hydrocephalus patients, with rates of shunt placement in the Northern region being over twice that observed in the Central region amongst the 70–79-year-old and ≥80-year-old age groups. In light of the efficacy and apparent cost effectiveness of CSF diversion procedures for iNPH,[ 15 , 28 ] the declining inflation-adjusted reimbursement observed in the present data appears counterintuitive. However, they likely reflect overall attempts to curtail medical expenditures. The Balanced Budget Act of 1997, which governed physician reimbursement until 2015, gave CMS the authority to determine Medicare payments to physicians. One key aspect of this legislation was the sustainable growth rate, implemented to control Medicare spending on physician reimbursements and address budget deficits. As a result, CMS consistently reduced Medicare expenditures to physicians, leading to declining reimbursement for many commonly performed surgical procedures, including placement of VP shunts, as noted by the results of our analysis.[ 24 ] Thus, declining inflation-adjusted reimbursement could conceivably be related to a decline in Medicare reimbursement.

Effects of decreased reimbursement

Medicare is the largest payer for inpatient procedures in the United States and serves as a benchmark for insurance providers nationwide.[ 7 ] Consequently, identifying trends in Medicare reimbursement can provide insight into the future behaviors of other insurance providers.[ 22 ] In the present case, the noted decrease in reimbursement by Medicare for hydrocephalus care may belie future decreased reimbursement across all insurance providers. The present results mirror similar trends for Medicare reimbursement in other surgical specialties.[ 5 , 10 , 11 , 22 ] With further cuts, there may be a decrease in the number of neurosurgeons treating Medicare patients or, at minimum, a decrease in the number of Medicare patients seen by each surgeon. Specifically, a nationwide survey conducted by the American Association of Neurological Surgeons and Congress of Neurological Surgeons in 2010 revealed that neurosurgeons were beginning to limit their availability to Medicare patients.[ 2 ] The follow-up publication by Rosenow and Orrico noted administrative burden and poor reimbursement as the two biggest drivers of neurosurgeons not accepting Medicare patients.[ 23 ] In addition, among the survey respondents who reported treating a lower number of Medicare patients over the survey period, nearly 60% reported that declining reimbursements were the motivation for this shift. Although this thinking was far from uniform among the survey recipients, these attitudes suggest that declining Medicare reimbursement may result in a decrease in the availability of neurosurgical care for Medicare patients.

Changes in procedure volume

Our analysis noted an increase in the number of VPS placed across the study period, though the trend was not significant. By comparison, using the National Inpatient Sample, Alvi et al. found a significant increase in the number of open and laparoscopic VPS placed between 2007 and 2017. Of note though, these authors focused only on VPS for iNPH.[ 1 ] In addition to showing a global increase in procedures, the authors noted significant geographic variability in the procedure performed for hydrocephalus treatment. VPS placement was used less commonly within the Northeast region relative to the other three demographic regions (Midwest, South, and West), while LP shunt placement was more commonly used in the Midwest and Northeast regions relative to the South and West. Data granularity was insufficient to explain the observed differences, but the authors suggested that it could stem from differences in the hospital facilities within the region. Similar variability in the usage of VP shunting was noted in a recent population-level analysis by Isaacs et al. using national registry data from Norway.[ 12 ] They found significant regional variation in shunt utilization among adult hydrocephalus patients, with rates of shunt placement in the Northern region being over twice that observed in the Central region amongst the 70–79-year-old and ≥80-year-old age groups. Like Alvi et al., [ 1 ] Mansoor et al. acknowledged that it was unclear why such practice variation existed but speculated that it could derive from a lack of consensus on what diagnostic criteria defined normal pressure hydrocephalus.[ 18 ] Imperatively, the underutilization of LPSs could be accounted for by the reduced indication of this procedure per the literature.

Our results also showed an increase in ETV procedures across the examined time frame. Although less commonly employed in adult patients, an increasing body of literature has begun to suggest obstructive adult hydrocephalus may be treated with upfront ETV.[ 9 , 12 , 26 , 27 ] For example, Grand et al. described 243 adult patients treated with ETV, of whom 72.8% were successfully treated; 36 patients required a primary or revision VPS, and 30 failed to improve following ETV but refused further CSF diversion. All failures appeared within the 1^st 49 months of treatment. Notably, there were only 9 complications in the cohort (3.6%), of which 5 required significant medical attention (2%).[ 9 ] Contemporaneously, Isaacs et al. described a 20-year series of 163 patients treated with an ETV for symptomatic hydrocephalus, of whom 51 had already failed VPS and were undergoing secondary ETV (31.3%).[ 12 ] The authors reported clinical improvement in 130 patients (80%) and found that most complications were minor. Complications were more common in the secondary versus primary ETV group (16% vs. 2%, P = 0.010), which was also less likely to experience improvement in their symptoms (65% vs. 87%; P = 0.002).[ 12 ] Waqar et al. similarly investigated 190 adults receiving an ETV over 18 years. They noted success in 139 patients (73%) and, in a time-to-event analysis, found that only a prior history of shunting predicted subsequent ETV failure (HR = 1.946, P = 0.021).[ 27 ]

Shunt procedure prevalence after SINPHONI-2

Based on a 2015 study by Kazui et al., LP shunts were suggested as a possible first-line treatment for iNHP.[ 16 ] Interestingly, we found that there was a statistically significant decrease in the number of LP shunts placed, both with and without a laminectomy, when the data were analyzed as pre- and post-2015 cohorts. However, a more recent cohort study by Liu et al. with a 3-year minimum follow-up found that improvements in cognition following LP shunting were short-term, with only 57% reporting long-term improvement.[ 17 ]

Limitations

This study has several limitations that should be acknowledged. First, the data used for analysis were obtained solely from Medicare Part B claims, which focus solely on physician fees and outpatient care. The largest portion of reimbursement stems from hospitalization cost/facility fees, which are covered under Part A. There may be contrasting trends in Part A reimbursement that help to explain the observed changes in procedural volume. In addition, Medicare is only one insurer for the aged population. Although it is often the trend-setter for private insurance, the correlation is unlikely to be perfect and so the present findings may not be directly generalizable to the broader private insurance market. An additional limitation is that the study is retrospective, which precludes us from identifying any causal linkage between procedure volume and reimbursement. Furthermore, as the present study employed a large administrative database, it is subject to potential coding errors or inaccuracies. In addition, the analysis focused solely on Medicare Part B claims and did not include reimbursement data from Medicare Part C (Medicare Advantage), despite its growing significance in medical reimbursement. Unfortunately, data on Medicare Part C were not obtainable from alternative sources. Furthermore, specific medical diagnoses for individual patients were not available for inclusion in this cost-analysis study, so it is not clear if the relative breakdown of VPS, LPS, and ETV utilization is changing for any specific diagnostic group within the adult hydrocephalus population. Despite these limitations, the present study represents the first to assess and compare relative utilization and Medicare reimbursement data for the placement of VP shunts, LP shunts, and ETVs.

CONCLUSION

The present data demonstrate that there has been a significant decline in inflation-adjusted physician Medicare reimbursement for CSF diversion procedures for patients with adult hydrocephalus, reflective of global declines in reimbursement for neurosurgical procedures. Across the period examined, there was a decline in LPS utilization and commensurate increases in VPS and ETV procedures, though these did not correlate with changes in reimbursement. We believe publication of these results will help promote future policy changes with respect to CSF diversion procedure reimbursement.

Ethical approval

The Institutional Review Board approval is not required as it is a retrospective study.

Declaration of patient consent

Patient’s consent not required as there are no patients in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

References

1. Alvi MA, Brown D, Yolcu Y, Zreik J, Javeed S, Bydon M. Prevalence and trends in management of idiopathic normal pressure hydrocephalus in the United States: Insights from the national inpatient sample. World Neurosurg. 2021. 145: e38-52

2. American Association of Neurological Surgeons Congress of Neurological Surgeo, editors. Survey of Medicare participation among neurosurgeons. 2010. p. Available from: https://www.cns.org/assets/ddd328e0/95e8/4b3d/8113/9a8471e7aa68/636947316226100000/medicaresurveyreport2010final-pdf [Last accessed on 2025 Feb 20]

3. Center for Medicare and Medicaid Services. Medicare beneficiary demographics. Available from: https://www.medpac.gov/wp/content/uploads/2021/10/july2021_medpac_databook_sec2_sec.pdf [Last accessed on 2023 Jun 07].

4. Center for Medicare and Medicaid Services. Part B national summary data file (previously known as BESS). Available from: https://www.cms.gov/data/research/statistics/trends/and/reports/part/b/national/summary-data-file [Last accessed on 2024 Sep 10].

5. De Nardi M, French E, Jones JB, McCauley J. Medical spending of the US elderly. Fisc Stud. 2016. 37: 717-47

6. Edmonds VS, Haglin JM, Tyson MD. Declining medicare reimbursement for urologists: An opportunity for informed advocacy. J Urol. 2021. 206: 10-2

7. El-Nahal W. An overview of Medicare for clinicians. J Gen Intern Med. 2020. 35: 3702-6

8. Gaudette É, Tysinger B, Cassil A, Goldman DP. Health and health care of Medicare beneficiaries in 2030. Forum Health Econ Policy. 2015. 18: 75-96

9. Grand W, Leonardo J, Chamczuk AJ, Korus AJ. Endoscopic third ventriculostomy in 250 adults with hydrocephalus: Patient selection, outcomes, and complications. Neurosurgery. 2016. 78: 109-19

10. Gupta N, Haglin JM, Marostica CW, Thornburg DA, Casey WJ. Trends in Medicare reimbursement for reconstructive plastic surgery procedures: 2000 to 2019. Plast Reconstr Surg. 2020. 146: 1541-51

11. Haglin JM, Lott A, Kugelman DN, Konda SR, Egol KA. Declining medicare reimbursement in orthopaedic trauma surgery: 2000-2020. J Orthop Trauma. 2021. 35: 79-85

12. Isaacs AM, Bezchlibnyk YB, Yong H, Koshy D, Urbaneja G, Hader WJ. Endoscopic third ventriculostomy for treatment of adult hydrocephalus: Long-term follow-up of 163 patients. Neurosurg Focus. 2016. 41: E3

13. Isaacs AM, Riva-Cambrin J, Yavin D, Hockley A, Pringsheim TM, Jette N. Age-specific global epidemiology of hydrocephalus: Systematic review, metanalysis and global birth surveillance. PLoS One. 2019. 14: e0210851

14. Jusue-Torres I, Brown DA, Pennington Z, Cogswell PM, Ali F, Graff-Radford N. Objective assessment of patients with idiopathic normal pressure hydrocephalus following ventriculoperitoneal shunt placement using activity-monitoring data: Pilot study. Neurosurg Focus. 2023. 54: E6

15. Kameda M, Yamada S, Atsuchi M, Kimura T, Kazui H, Miyajima M. Cost-effectiveness analysis of shunt surgery for idiopathic normal pressure hydrocephalus based on the SINPHONI and SINPHONI-2 trials. Acta Neurochir (Wien). 2017. 159: 995-1003

16. Kazui H, Miyajima M, Mori E, Ishikawa M, SINPHONI-2 Investigators. Lumboperitoneal shunt surgery for idiopathic normal pressure hydrocephalus (SINPHONI-2): An open-label randomised trial. Lancet Neurol. 2015. 14: 585-94

17. Liu JT, Su PH. The efficacy and limitation of lumboperitoneal shunt in normal pressure hydrocephalus. Clin Neurol Neurosurg. 2020. 193: 105748

18. Mansoor N, Gulati S, Fredriksli OA, Salvesen Ø Solheim O. Epidemiology and practice variations of shunt surgery for hydrocephalus: A nationwide registry-based study. J Neurosurg. 2023. 139: 892-900

19. Marmarou A, Young HF, Aygok GA. Estimated incidence of normal pressure hydrocephalus and shunt outcome in patients residing in assisted-living and extended-care facilities. Neurosurg Focus. 2007. 22: E1

20. Miyajima M, Kazui H, Mori E, Ishikawa M. One-year outcome in patients with idiopathic normal-pressure hydrocephalus: Comparison of lumboperitoneal shunt to ventriculoperitoneal shunt. J Neurosurg. 2016. 125: 1483-92

21. Poca MA, Sahuquillo J. Short-term medical management of hydrocephalus. Expert Opin Pharmacother. 2005. 6: 1525-38

22. Pollock JR, Chen JY, Dorius DA, Haglin JM, Swanson DL, Williams K. Decreasing physician Medicare reimbursement for dermatology services. J Am Acad Dermatol. 2022. 86: 1154-6

23. Rosenow JM, Orrico KO. Neurosurgeons’ responses to changing Medicare reimbursement. Neurosurg Focus. 2014. 37: E12

24. Sibia US, Millen JC, Klune JR, Bilchik A, Foshag LJ. Analysis of 10-year trends in Medicare physician fee schedule payments in surgery. Surgery. 2024. 175: 920-6

25. Singh R, Parikh PP, De La Peña NM, Bhandarkar AR, Doan MK, Patel NP. Trends in the neurosurgical workforce and implications in providing for an aging population. World Neurosurg. 2022. 160: e261-6

26. U.S. Bureau of Labor Statistics. Measuring price change in the CPI: Medical care. Available from: https://www.bls.gov/cpi/factsheets/medical-care.html [Last accessed on 2024 Nov 26].

27. Waqar M, Ellenbogen JR, Stovell MG, Al-Mahfoudh R, Mallucci C, Jenkinson MD. Long-term outcomes of endoscopic third ventriculostomy in adults. World Neurosurg. 2016. 94: 386-93

28. Williams MA, Sharkey P, Van Doren D, Thomas G, Rigamonti D. Influence of shunt surgery on healthcare expenditures of elderly fee-for-service Medicare beneficiaries with hydrocephalus. J Neurosurg. 2007. 107: 21-8