To our knowledge this is the largest pediatric analysis of VPS failure related to CSF biochemistry. Our rate of VPS failure is consistent with the literature and confirms that a significant cohort of patients require at least one VPS revision procedure [5, 7, 9] (Table 1). Our data also indicates that, for every doubling in peri-operative CSFp: (1) the odds of early VPS failure within 90-days increase by 19% (Table 2), and (2) the odds of delayed VPS failure within 1-year increases by 15% (Table 3). Older patient age is protective for VPS failure. Despite the high incidence of VPS failure and development in our understanding of hydrocephalus, predicting device failure in clinical practice remains a challenge [3, 5], and the value of CSFp in this respect has been debated [9, 13–16]. The results herein are a valuable addition to the literature describing the potential of CSFp in predicting VPS failure.
These results suggest CFSp has a role in early and late device failure, and therefore a possible sustained pathological process. Across early and late device failure, predictive value was retained on multivariate analysis for variables such as CSF RBC count, patient age, underlying aetiology, and procedure urgency. Our findings are supported by a large clinical study investigating valve-specific obstruction, finding significantly higher CSFp concentrations in early valve obstructions [9]. Similarly, a review of obstructed VPS devices for tuberculous meningitis patients described a strong relationship between CSFp and VPS obstruction [7]. Furthermore, a recent clinical study described marked elevation of inflammatory proteins IL-6, IL-8, IL-10, MMP-7, and MMP-9 in patients with higher historical incidence of VPS obstruction [20]. Other clinical cohort studies have failed to demonstrate this relationship [13, 14, 17]. One explanation for the difference in findings may be the impact of natural variability in CSFp on smaller cohort sizes used in these studies (33–95 patients).. In-vitro flow-studies have similarly assessed the effect of CSFp on shunt flow, using high concentration CSF-albumin [16, 18, 19]. They observe no difference in CSF flow and device failure with raised albumin concentrations, however albumin has no inflammatory capacity and these models do not account for the predominance of inflammatory proteins in acquired hydrocephalus [22–26]. Under homestatic conditions, albumin is the predominant CSF protein by approximately eight fold [19]. However, inflammatory proteins such as cytokines, immunoglobulins and complement are markeldy elevated in communicating hydrocephalus [18, 19, 22–25]. Evidence for dysregulate inflammation and glial cell activation in VPS failure is growing [11, 28–31]. Multiple immunohistochemical analyses on obstructed VPS devices [11, 28–31]. A recent immunohistochemical analysis described a marked local astrocyte, macrophage, and microglia presence in obstructed VPS catheters [11]. Microglia and astrocytes are intimately approximated to the proximal VPS catheter, and reactive gliosis in this pro-inflammatory environment may underly VPS fouling.
Hydrocephalus aetiology is thought to affect VPS failure risk, with a higher incidence of failure in vascular aetiologies [32]. Our results demonstrate vascular aetiology held significance on univariate analysis in predicting late shunt failure, however this was not significant on multivariate analysis (Table 3). CSF-RCC which holds close relation to underlying aetiology held a trend toward signifance in predicting late VPS failure (OR 1.07, 1.00-1.15, p = 0.052, Table 3). Vascular aetiologies may cause chronic communicating hydrocephalus by extravasation of red blood cells, followed by erythrolysis with a reactive inflammatory fibrosis at sites of CSF reabsorption such as arachnoid granulations [30, 32]. Lysis protein products, such as haem, are pro-inflammatory and likely mediate both hydrocephalus and VPS obstruction, rather than whole erythrocytes. This may explain our finding that on multivariate analysis CSFp retains significant predictive value when adjusted for underlying aetiology.
Older patient age was independently protective for odds of early and late VPS failure on multivariate analysis (Table 2, 3). This is consistent with other pediatric populations [33, 34], in which patients less than 1-year old are significantly more likely to suffer failure. This may be accounted for by the inclusion of preterm infants, or differences in immune capacity [33].
These results define a phenomen observed in clinical practice, increased incidence in VPS failure in the setting of raised CSFp levels [7]. Factoring CSFp levels into clinical decision-making for timing of VPS insertion, may reduce the significant burden of morbidity experienced by these patients and their families. Similarly, patient follow-up and risk-stratification may be informed by our findings for patients in which CSFp is known to be elevated.
Strengths and Limitations
We have collected data from a large cohort of pediatric patients. We have also analysed values of CSFp collected over a sequence of days to mitigate variable CSFp levels evident across a series of single collections. While there exists cause-effect limitations inherent to our retrospective design, our results have demonstrated strong associations that catalyse the need for further investigation. Excluding cases of culture positive CSF infections was important because we were interested primarily in the failure of VPS devices for causes not-related to infection. However, 30% of VPS infections are culture negative [4], so we cannot rule out infection-related CSFp elevation in a subset of our cohort. Finally, variability in hydrocephalus aetiology by geographic and socio-economic separation is well-documented [22], This cohort represents the Australian pediatric population and external validity to other cohorts may be limited.