Anterior clear space: how clear? How often? How come?

Area of Science:

• Radiology
• Thoracic imaging

Background:

• The retrosternal clear space (RSCS) and retrocardiac region are key areas on lateral chest radiographs.
• Understanding normal variations in opacity is crucial for accurate interpretation.

Purpose of the Study:

• To compare the opacity of the RSCS and retrocardiac region on normal lateral chest radiographs.
• To measure the RSCS and identify factors influencing its appearance.
• To evaluate the clinical significance of these radiographic findings.

Main Methods:

• Evaluation of lateral chest radiographs and computed tomographic (CT) scans from 38 patients with normal studies.
• Correlation of radiographic findings with CT scan data.

Main Results:

• Retrosternal and retrocardiac opacity were equal in 50% of patients.
• The retrosternal region was more opaque in 42%, notably in women (10/12) compared to men (6/26).
• The anterior margin of the ascending aorta was visualized in only 24% of cases, with a mean sternum-to-aorta distance of 29 mm.

Conclusions:

• Greater retrosternal opacity than retrocardiac opacity is a frequent normal finding on lateral chest radiographs, especially in women.
• Measurement of sternum-to-aorta distance can be challenging; distances over 2.5 cm may be within normal limits.