Data for this study were obtained from the National Spina Bifida Patient Registry (NSBPR) funded by the Centers for Disease Control and Prevention (CDC). NSBPR began in 2009 with data collected by multidisciplinary spina bifida clinics across the United States. Data are collected annually and sent to a centralized data collection center at the CDC for quality control and analysis. All required NSBPR data elements are collected through a combination of patient interviews and review of medical records.⁵ This process has been described in greater detail in previous reports.¹ Each site participating in NSBPR obtained local IRB approval for patient enrollment and data sharing with CDC.

Patients with a myelomeningocele diagnosis and a history of shunted hydrocephalus were included in this analysis. Any child with a missing date for 1 or more shunt operations was excluded to ensure that the lifetime record of all shunt surgical procedures was known as needed to perform time-to-event analysis for shunt failure. In addition, children who were not enrolled in NSBPR within the first 5 years of life were excluded, as enrollment later than that may lead to inaccurate reporting of surgical procedures that occurred early in life. All surgical procedures used to treat shunt infection were counted as 1 episode of shunt failure, i.e., a shunt infection episode was considered the same as a shunt failure. The enrollment diagram in Fig. 1 shows the inclusion and exclusion criteria that led to the final study cohort.

The specific variables collected for this study included month/year of initial shunt placement, month/year of all subsequent shunt surgical procedures, sex, race/ethnicity, functional level of lesion (FLOL) (as defined by NSBPR), and health insurance status at time of enrollment.⁵

Of 10,253 patients in NSBPR, 1691 met the inclusion criteria for this study (Fig. 1). About half of the included patients were male (875 [51.7%]) and a majority were non- Hispanic White (1080 [64.1%]) (Table 1). Non-Hispanic Black and Hispanic patients represented 7.6% and 21.4% of the cohort, respectively. Nonprivate insurance was reported for 942 (55.7%) patients. FLOL was most commonly mid- and low-lumbar (28.4% and 28.6%, respectively). The excluded patients were more commonly female (52.4%) and had a higher proportion of thoracic-level FLOL (23.5%).

The median (interquartile range) length of follow-up for all included patients was 4.92 (2.66–8.00) years. Nine hundred thirty-eight (55.5%) patients experienced at least 1 shunt failure, 439 (26.0%) patients had at least 2 shunt failures, and 231 (13.7%) had at least 3 shunt failures. The median (95% CI) time from initial shunt placement to the first failure was 2.34 (1.91–3.08) years. Figure 2 shows the Kaplan-Meier survival curve for initial shunt failure. Post hoc analysis was performed using the Kaplan-Meier method to determine the median time from first shunt failure to second shunt failure. Considering only the 938 children who had a first shunt failure, we estimated that the median (95% CI) time to second shunt failure was 5.08 (4.00–6.42) years. Similarly, the estimated median (95% CI) time from second shunt failure to third shunt failure was 2.59 (1.92–4.42) years, with only 439 patients who had a second shunt failure. In the subset of 235 patients with 10 years of follow-up or longer, 61 (26.0%) had no shunt failures, 75 (31.9%) had exactly 1 shunt failure, 41 (17.4%) had exactly 2 failures, 27 (11.5%) had exactly 3 failures, and 31 (13.2%) had 4 or more failures.

Table 2 shows the HRs for experiencing 1 or more shunt failures, with the associations of sex, race/ethnicity, FLOL, and insurance status with shunt failure. Male children had a higher HR (95% CI) for shunt failures of 1.25 (1.09–1.44). In addition, compared with non-Hispanic White children, children of minority race/ethnicity had a lower HR for shunt failures (non-Hispanic Black children HR 0.74, 95% CI 0.55–0.99; Hispanic children HR 0.74, 95% CI 0.62–0.88). FLOL was not associated with shunt failure in any analysis.

Analysis of lifetime shunt revisions by age showed fewer total lifetime shunt revisions in younger patients, with increases in each year of life, as expected. Children younger than 1 year underwent a mean ± SD of 1.14 ± 0.81 shunt revisions. Children aged 13 years underwent a mean ± SD of 2.77 shunt revisions. Visual inspection of the averages, plotted by age, revealed a linear relationship (Fig. 3). Therefore, post hoc linear regression analysis was performed (Fig. 3), which found an increase of 0.133 shunt revisions per year of life (R² = 0.96).

We have conducted a longitudinal analysis of time to shunt failure in children with myelomeningocele by using a national data set. This is the first study of this large population to analyze shunt failures after the first failure. As such, it has the potential to inform counseling of families of children with myelomeningocele and hydrocephalus about what to expect as their children age.

Analysis of time from initial shunt placement to the first shunt failure showed an estimated median time to failure of 2.34 years. This result is consistent with the results reported in prior published studies, including the randomized Shunt Design Trial and Endoscopic Shunt Insertion Study.^2,3,7-9 Similarly, our analysis of time to subsequent shunt failures after the first and second shunt failures is similar to previously published data.⁴ Overall, relatively few patients had more than 2 shunt failures (only 13.7% of the overall sample). These data support the notion that although shunt failure is relatively common among children with myelomeningocele, multiple shunt failures do not occur in the first several years of life for most children.

Previous studies have shown that there is an increased risk of recurrent shunt failure after shunt revision.^4,10 We used a proportional means model in an attempt to identify other factors that may affect the likelihood of multiple shunt failures. Male sex showed an association with all shunt failures (HR 1.25) (Table 2). In general, hydrocephalus is thought to be slightly more common in male infants.^10,11 Previous studies of risk factors for shunt failure have either not included sex as a variable or have shown no significant difference between male and female children.^2-4,10,12-14 However, in the large series that do report sex as an associated variable, the relationship between male sex and shunt failure was similar in magnitude (HR 1.1–1.5), but with 95% CIs that were not statistically signilicant.^4,12-14 The sample size of the present study is larger than the samples of most previous studies, thus increasing the power of the present study to show statistically significant associations. It is possible that male children manifest shunt failure with more obvious symptoms than female children. Other possibilities may be that male children are overdiagnosed with possible shunt malfunction or that female children are underdiagnosed. Because it is unclear why sex is a risk factor for shunt failure, more studies of this phenomenon are warranted.

Children of minority race/ethnicity also showed significantly lower probability of shunt failure compared with non-Hispanic White children. One possible explanation of this finding is that these children are underdiagnosed. Hispanic families are known to be at higher risk for socioeconomic disadvantage, may have low English proficiency, and may have challenges accessing healthcare.^15,16 These factors may have had a role in the present observations as well. Because untreated shunt failure has the potential for adverse developmental outcomes, this is an important potential disparity that requires further study. Non-Hispanic Black children also had a lower HR for shunt failure than White children. The same logic of disparity may apply, in that it is possible that social or structural factors may lead to fewer shunt evaluations in minority children, or that there are unconscious biases that affect the likelihood of considering a diagnosis of shunt failure in a non-White child.¹⁷ These observations warrant future study.

Our finding of a nearly linear increase in shunt revisions with each year of life provides another method for estimating the number of shunt operations in the 1st decade of life, an estimate that may also be useful for counseling families. These results are similar to the findings of a Monte Carlo simulation based on several large data sets of shunt failure.¹⁸

This analysis demonstrated that the estimated median time to shunt failure after initial placement was 2.34 years in a large nationwide sample of children with myelomeningocele. Even though half of shunts failed after about 2.5 years, only about 26% experienced 2 or more failures and only about 14% experienced 3 or more failures. This information may be helpful when counseling patients and families about the risk of subsequent failure. Important potential disparities based on sex and race/ethnicity were identified. Future research may assist in explaining these disparities.