Ultrasound and CT Agreement for Non-Invasive ONSD Measurement: A Systematic Review and Meta-Analysis

The measurement of the optic nerve sheath diameter (ONSD) is an established non-invasive technique for diagnosing and monitoring elevated intracranial pressure (ICP) across various imaging modalities. However, the agreement between ONSD measurements obtained using ultrasonography (US) and computed tomography (CT) remains unclear. This systematic review and meta-analysis aimed to evaluate the concordance between these modalities for ONSD measurement in the diagnosis of elevated ICP, exploring whether they yield equivalent results and can be used interchangeably in clinical practice.

We systematically searched PubMed, Cochrane Library and Lilacs databases for randomized and non-randomized studies that simultaneously compared US and CT measurements of the ONSD in patients diagnosed with elevated ICP. Only studies reporting mean ONSD measurements for both modalities were included. Heterogeneity among studies was assessed using the I² statistic, and a random-effects model was applied to synthesize pooled estimates for outcomes. The primary outcome was the mean difference between ONSD measurements obtained by US and CT and the inter-class correlation coefficient (ICC). Due to the high heterogeneity observed, we conducted subgroup and sensitivity analysis.

We included 8 non-randomized studies with 273 patients. The pooled mean difference between US and CT measurements of the ONSD was MD -0.07 mm; 95% confidence interval [CI] -0.75 to 0.61; p = 0.85, indicating no statistically significant difference between the two modalities. Substantial heterogeneity was observed across studies. Bland-Altman analysis demonstrated limits of agreement ranging from -1.52 to 1.38 mm., with most data points falling within these limits. The ICC was 0.80 (95% CI: 0.26-0.96), indicating substantial agreement between the two imaging modalities.

In conclusion, US and CT show general agreement in ONSD measurements for patients with elevated ICP. While heterogeneity was high, both modalities appear comparable, with US offering advantages in portability and radiation avoidance, and CT serving as a reliable alternative in emergencies.