Intraoperative Ultrasound in Chiari 1 Decompression: Clarity or Confusion? A Systematic Review

Patients with symptomatic Chiari malformation type 1 (CM-1) usually undergo either bone-only posterior fossa decompression (PFD) or a more invasive procedure involving dural expansion with or without tonsillar resection (PFD+). PFD+ may be more effective but it carries a higher risk of complications. Intraoperative ultrasound (iUS) may help determine whether PFD alone is sufficient, although specific criteria and its role in surgical decision making are not yet defined.

A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines, using search terms related to iUS, intraoperative sonography, and CM-1. Extracted data included demographics, surgical methods, iUS criteria, and outcomes. Conversion rates and the positive predictive values (PPVs) were calculated to quantify iUS effectiveness. Conversion rate was defined as the proportion of cases requiring secondary PFD+ after initial PFD. PPV was based on the number of successful PFDs relative to all initial PFDs. Risk of bias was evaluated using the Newcastle-Ottawa scale.

From 202 initial articles, 1 prospective and 8 retrospective studies were included, covering 844 pediatric and adult patients. According to the Newcastle-Ottawa scale, 1 study had a low, 3 moderate, and 5 high risk of bias. To assess decompression sufficiency, 8 studies used qualitative iUS criteria, whereas 1 used quantitative thresholds. Follow-up time ranged from 1 to 48 months, with varied outcome measures. Conversion rates ranged from 0% to 16% and PPV from 0.857 to 1.000, depending on the study. Conversion surgery rates were comparable with reoperation rates reported from studies without iUS.

The available evidence does not yet support iUS as a robust testing method to inform intraoperative decision making regarding the extent of decompression, due to the heterogeneity of its application, and the absence of standardized assessment criteria. We propose a reporting framework incorporating all currently reported criteria to induce standardization and guide further research.