# Chest X-Ray as a Screening Tool for Aortic Arch Dilation: CT-Based Evaluation of Reliability

## TL;DR

This study shows that chest X-rays can reliably help rule out aortic arch dilation when combined with age and sex, potentially reducing the need for more expensive imaging.

## Contribution

The study introduces a regression model using CXR measurements, age, and sex to detect aortic dilation with high sensitivity.

## Key findings

- Horizontal aortic knob width on CXR most closely correlates with CTA measurements of aortic dilation.
- A regression model achieved an AUC of 0.884 for detecting aortic dilation greater than 40 mm.
- Using a conservative threshold provided 100% sensitivity and a negative predictive value of 1.00.

## Abstract

Background: Chest radiography (CXR) remains the most common first-line imaging for thoracic abnormalities. While aortic knob width can reflect aortic dilation, no standardized, widely recognized thresholds of clinical utility exist. Methods: This pilot retrospective study analyzed 240 emergency department patients (median age 67 years, 61% male) who underwent both PA CXR and chest computed tomography angiography (CTA) within 7 days. Three aortic knob dimensions (horizontal, oblique, vertical) were measured on CXR and compared with CTA measurements at two anatomical levels: proximal to the brachiocephalic trunk (P-BCT) and distal to the left subclavian artery (D-LSA). Results: The horizontal aortic knob width was most closely related to CTA measurements of P-BCT and D-LSA. A regression model incorporating horizontal knob diameter, age, and sex was characterized with an AUC of 0.884 (95% CI 0.825–0.944) for detecting aortic dilation (>40 mm). Using a conservative threshold with the upper 95% prediction bound exceeding 40 mm led to 100% sensitivity and 54% specificity, with a negative predictive value of 1.00. Conclusions: Simple quantitative CXR measurements of aortic knob width (horizontal), combined with age and sex, can provide additional confidence for excluding aortic arch dilation. Given further validation in diverse populations, if the high negative predictive value of this approach will be confirmed, it may represent a valuable screening tool to guide decisions for advanced imaging, especially due to low cost and wide availability.