Intracranial Compliance, Resistance to CSF-Outflow, and Pressure-Volume Index in Hydrocephalus Patients: A Systematic Review and Meta-Analysis

Objectives

How changes in intracranial compliance (ICC), resistance to cerebrospinal fluid (CSF)-outflow (R_out), and pressure-volume index (PVI) can play a prominent role in clarifying the complexities in the biomechanism and treatment outcomes of hydrocephalus. This study aims to provide a comprehensive review to find the correlation between ICC, R_out, and PVI with intracranial pressure (ICP) characteristics, as well as morphometric parameters, in hydrocephalus patients.

Material and methods

Electronic searches were conducted using the PubMed/MEDLINE, Scopus, Google Scholar, Ovid, Cochrane, and EMBASE databases from their dates of inception to December 2022 using filters for English-language articles. The article selection and data collection were conducted in accordance with PRISMA guidelines and recommendations. We assigned a quality score for each study to evaluate the information and selection bias. The certainty of the pooled data for all articles was assessed based on GRADE criteria. The Funnel plot asymmetry study was used to evaluate publication bias.

Results

The overall pre-treatment ICC, R_out, and PVI were 0.45 ml/mmHg (95% CI, 0.33-0.57; I²=99.7%; P<0.001), 14.93 mmHg/(ml/min) (95% CI, 13.65-16.21; I²= 99.7%; P<0.001) and 19.26 ml (95% CI, 15.63-22.89; I²=98.7%; P<0.001), respectively. The pooled R_out was observed to be higher in adult hydrocephalus compared to pediatric hydrocephalus, whereas the opposite trend was found for PVI. Patients with normal pressure hydrocephalus (NPH) exhibited a higher pooled R_out compared to communicating hydrocephalus. Patients with unimproved outcomes demonstrated a decrease in the effect size of the pooled R_out. The results also showed significant correlations were observed between all ICP characteristics and both the ICC and R_out. The correlation between ICC and the ventricular score was significant. R_out had a significant correlation with the third ventricle index. PVI had significant correlations with Evan's ratio, inverse cella media, and ventricular score.

Conclusion

The results indicate the possible reason for publication bias in some subgroups may be related to methodological heterogeneity in the measurement of pressure-volume parameters. This finding motivates researchers to investigate the effects of different invasive and non-invasive methods on the measurement results of ICC, R_out, and PVI.